File: rfc1446.txt

package info (click to toggle)
doc-rfc 20170121-1
  • links: PTS, VCS
  • area: non-free
  • in suites: stretch
  • size: 541,932 kB
  • ctags: 32
  • sloc: xml: 267,963; sh: 101; python: 90; perl: 42; makefile: 13
file content (3068 lines) | stat: -rw-r--r-- 108,733 bytes parent folder | download | duplicates (6)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068



          Network Working Group                                J. Galvin
          Request for Comments: 1446         Trusted Information Systems
                                                           K. McCloghrie
                                                      Hughes LAN Systems
                                                              April 1993


                                Security Protocols
                               for version 2 of the
                   Simple Network Management Protocol (SNMPv2)


          Status of this Memo

          This RFC specifes an IAB standards track protocol for the
          Internet community, and requests discussion and suggestions
          for improvements.  Please refer to the current edition of the
          "IAB Official Protocol Standards" for the standardization
          state and status of this protocol.  Distribution of this memo
          is unlimited.


          Table of Contents


          1 Introduction ..........................................    2
          1.1 A Note on Terminology ...............................    3
          1.2 Threats .............................................    4
          1.3 Goals and Constraints ...............................    5
          1.4 Security Services ...................................    6
          1.5 Mechanisms ..........................................    7
          1.5.1 Message Digest Algorithm ..........................    8
          1.5.2 Symmetric Encryption Algorithm ....................    9
          2 SNMPv2 Party ..........................................   11
          3 Digest Authentication Protocol ........................   14
          3.1 Generating a Message ................................   16
          3.2 Receiving a Message .................................   18
          4 Symmetric Privacy Protocol ............................   21
          4.1 Generating a Message ................................   21
          4.2 Receiving a Message .................................   22
          5 Clock and Secret Distribution .........................   24
          5.1 Initial Configuration ...............................   25
          5.2 Clock Distribution ..................................   28
          5.3 Clock Synchronization ...............................   29
          5.4 Secret Distribution .................................   31
          5.5 Crash Recovery ......................................   34
          6 Security Considerations ...............................   37
          6.1 Recommended Practices ...............................   37
          6.2 Conformance .........................................   39
          6.3 Protocol Correctness ................................   42




          Galvin & McCloghrie                                   [Page i]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          6.3.1 Clock Monotonicity Mechanism ......................   43
          6.3.2 Data Integrity Mechanism ..........................   43
          6.3.3 Data Origin Authentication Mechanism ..............   44
          6.3.4 Restricted Administration Mechanism ...............   44
          6.3.5 Message Timeliness Mechanism ......................   45
          6.3.6 Selective Clock Acceleration Mechanism ............   46
          6.3.7 Confidentiality Mechanism .........................   47
          7 Acknowledgements ......................................   48
          8 References ............................................   49
          9 Authors' Addresses ....................................   51








































          Galvin & McCloghrie                                   [Page 1]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          1.  Introduction

          A network management system contains: several (potentially
          many) nodes, each with a processing entity, termed an agent,
          which has access to management instrumentation; at least one
          management station; and, a management protocol, used to convey
          management information between the agents and management
          stations.  Operations of the protocol are carried out under an
          administrative framework which defines both authentication and
          authorization policies.

          Network management stations execute management applications
          which monitor and control network elements.  Network elements
          are devices such as hosts, routers, terminal servers, etc.,
          which are monitored and controlled through access to their
          management information.

          In the Administrative Model for SNMPv2 document [1], each
          SNMPv2 party is, by definition, associated with a single
          authentication protocol and a single privacy protocol.  It is
          the purpose of this document, Security Protocols for SNMPv2,
          to define one such authentication and one such privacy
          protocol.

          The authentication protocol provides a mechanism by which
          SNMPv2 management communications transmitted by the party may
          be reliably identified as having originated from that party.
          The authentication protocol defined in this memo also reliably
          determines that the message received is the message that was
          sent.

          The privacy protocol provides a mechanism by which SNMPv2
          management communications transmitted to said party are
          protected from disclosure.  The privacy protocol in this memo
          specifies that only authenticated messages may be protected
          from disclosure.

          These protocols are secure alternatives to the so-called
          "trivial" protocol defined in [2].

               USE OF THE TRIVIAL PROTOCOL ALONE DOES NOT CONSTITUTE
               SECURE NETWORK MANAGEMENT.  THEREFORE, A NETWORK
               MANAGEMENT SYSTEM THAT IMPLEMENTS ONLY THE TRIVIAL
               PROTOCOL IS NOT CONFORMANT TO THIS SPECIFICATION.






          Galvin & McCloghrie                                   [Page 2]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          The Digest Authentication Protocol is described in Section 3.
          It provides a data integrity service by transmitting a message
          digest - computed by the originator and verified by the
          recipient - with each SNMPv2 message.  The data origin
          authentication service is provided by prefixing the message
          with a secret value known only to the originator and
          recipient, prior to computing the digest.  Thus, data
          integrity is supported explicitly while data origin
          authentication is supported implicitly in the verification of
          the digest.

          The Symmetric Privacy Protocol is described in Section 4.  It
          protects messages from disclosure by encrypting their contents
          according to a secret cryptographic key known only to the
          originator and recipient.  The additional functionality
          afforded by this protocol is assumed to justify its additional
          computational cost.

          The Digest Authentication Protocol depends on the existence of
          loosely synchronized clocks between the originator and
          recipient of a message.  The protocol specification makes no
          assumptions about the strategy by which such clocks are
          synchronized.  Section 5.3 presents one strategy that is
          particularly suited to the demands of SNMP network management.

          Both protocols described here require the sharing of secret
          information between the originator of a message and its
          recipient.  The protocol specifications assume the existence
          of the necessary secrets.  The selection of such secrets and
          their secure distribution to appropriate parties may be
          accomplished by a variety of strategies.  Section 5.4 presents
          one such strategy that is particularly suited to the demands
          of SNMP network management.


          1.1.  A Note on Terminology

          For the purpose of exposition, the original Internet-standard
          Network Management Framework, as described in RFCs 1155, 1157,
          and 1212, is termed the SNMP version 1 framework (SNMPv1).
          The current framework is termed the SNMP version 2 framework
          (SNMPv2).








          Galvin & McCloghrie                                   [Page 3]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          1.2.  Threats

          Several of the classical threats to network protocols are
          applicable to the network management problem and therefore
          would be applicable to any SNMPv2 security protocol.  Other
          threats are not applicable to the network management problem.
          This section discusses principal threats, secondary threats,
          and threats which are of lesser importance.

          The principal threats against which any SNMPv2 security
          protocol should provide protection are:


          Modification of Information
               The SNMPv2 protocol provides the means for management
               stations to interrogate and to manipulate the value of
               objects in a managed agent.  The modification threat is
               the danger that some party may alter in-transit messages
               generated by an authorized party in such a way as to
               effect unauthorized management operations, including
               falsifying the value of an object.

          Masquerade
               The SNMPv2 administrative model includes an access
               control model.  Access control necessarily depends on
               knowledge of the origin of a message.  The masquerade
               threat is the danger that management operations not
               authorized for some party may be attempted by that party
               by assuming the identity of another party that has the
               appropriate authorizations.

          Two secondary threats are also identified.  The security
          protocols defined in this memo do provide protection against:

          Message Stream Modification
               The SNMPv2 protocol is based upon a connectionless
               transport service which may operate over any subnetwork
               service.  The re-ordering, delay or replay of messages
               can and does occur through the natural operation of many
               such subnetwork services.  The message stream
               modification threat is the danger that messages may be
               maliciously re-ordered, delayed or replayed to an extent
               which is greater than can occur through the natural
               operation of a subnetwork service, in order to effect
               unauthorized management operations.





          Galvin & McCloghrie                                   [Page 4]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          Disclosure
               The disclosure threat is the danger of eavesdropping on
               the exchanges between managed agents and a management
               station.  Protecting against this threat is mandatory
               when the SNMPv2 is used to create new SNMPv2 parties [1]
               on which subsequent secure operation might be based.
               Protecting against the disclosure threat may also be
               required as a matter of local policy.

          There are at least two threats that a SNMPv2 security protocol
          need not protect against.  The security protocols defined in
          this memo do not provide protection against:

          Denial of Service
               A SNMPv2 security protocol need not attempt to address
               the broad range of attacks by which service to authorized
               parties is denied.  Indeed, such denial-of-service
               attacks are in many cases indistinguishable from the type
               of network failures with which any viable network
               management protocol must cope as a matter of course.

          Traffic Analysis
               In addition, a SNMPv2 security protocol need not attempt
               to address traffic analysis attacks.  Indeed, many
               traffic patterns are predictable - agents may be managed
               on a regular basis by a relatively small number of
               management stations - and therefore there is no
               significant advantage afforded by protecting against
               traffic analysis.


          1.3.  Goals and Constraints

          Based on the foregoing account of threats in the SNMP network
          management environment, the goals of a SNMPv2 security
          protocol are enumerated below.

          (1)  The protocol should provide for verification that each
               received SNMPv2 message has not been modified during its
               transmission through the network in such a way that an
               unauthorized management operation might result.

          (2)  The protocol should provide for verification of the
               identity of the originator of each received SNMPv2
               message.





          Galvin & McCloghrie                                   [Page 5]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          (3)  The protocol should provide that the apparent time of
               generation for each received SNMPv2 message is recent.

          (4)  The protocol should provide, when necessary, that the
               contents of each received SNMPv2 message are protected
               from disclosure.

          In addition to the principal goal of supporting secure network
          management, the design of any SNMPv2 security protocol is also
          influenced by the following constraints:

          (1)  When the requirements of effective management in times of
               network stress are inconsistent with those of security,
               the former are preferred.

          (2)  Neither the security protocol nor its underlying security
               mechanisms should depend upon the ready availability of
               other network services (e.g., Network Time Protocol (NTP)
               or secret/key management protocols).

          (3)  A security mechanism should entail no changes to the
               basic SNMP network management philosophy.


          1.4.  Security Services

          The security services necessary to support the goals of a
          SNMPv2 security protocol are as follows.

          Data Integrity
               is the provision of the property that data has not been
               altered or destroyed in an unauthorized manner, nor have
               data sequences been altered to an extent greater than can
               occur non-maliciously.

          Data Origin Authentication
               is the provision of the property that the claimed origin
               of received data is corroborated.

          Data Confidentiality
               is the provision of the property that information is not
               made available or disclosed to unauthorized individuals,
               entities, or processes.







          Galvin & McCloghrie                                   [Page 6]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          The protocols specified in this memo require both data
          integrity and data origin authentication to be used at all
          times.  For these protocols, it is not possible to realize
          data integrity without data origin authentication, nor is it
          possible to realize data origin authentication without data
          integrity.

          Further, there is no provision for data confidentiality
          without both data integrity and data origin authentication.


          1.5.  Mechanisms

          The security protocols defined in this memo employ several
          types of mechanisms in order to realize the goals and security
          services described above:

          o    In support of data integrity, a message digest algorithm
               is required.  A digest is calculated over an appropriate
               portion of a SNMPv2 message and included as part of the
               message sent to the recipient.

          o    In support of data origin authentication and data
               integrity, the portion of a SNMPv2 message that is
               digested is first prefixed with a secret value shared by
               the originator of that message and its intended
               recipient.

          o    To protect against the threat of message delay or replay,
               (to an extent greater than can occur through normal
               operation), a timestamp value is included in each message
               generated.  A recipient evaluates the timestamp to
               determine if the message is recent.  This protection
               against the threat of message delay or replay does not
               imply nor provide any protection against unauthorized
               deletion or suppression of messages.  Other mechanisms
               defined independently of the security protocol can also
               be used to detect message replay (e.g., the request-id
               [2]), or for set operations, the re-ordering, replay,
               deletion, or suppression of messages (e.g., the MIB
               variable snmpSetSerialNo [14]).

          o    In support of data confidentiality, a symmetric
               encryption algorithm is required.  An appropriate portion
               of the message is encrypted prior to being transmitted to





          Galvin & McCloghrie                                   [Page 7]





          RFC 1446        Security Protocols for SNMPv2       April 1993


               its recipient.

          The security protocols in this memo are defined independently
          of the particular choice of a message digest and encryption
          algorithm - owing principally to the lack of a suitable metric
          by which to evaluate the security of particular algorithm
          choices.  However, in the interests of completeness and in
          order to guarantee interoperability, Sections 1.5.1 and 1.5.2
          specify particular choices, which are considered acceptably
          secure as of this writing.  In the future, this memo may be
          updated by the publication of a memo specifying substitute or
          alternate choices of algorithms, i.e., a replacement for or
          addition to the sections below.


          1.5.1.  Message Digest Algorithm

          In support of data integrity, the use of the MD5 [3] message
          digest algorithm is chosen.  A 128-bit digest is calculated
          over the designated portion of a SNMPv2 message and included
          as part of the message sent to the recipient.

          An appendix of [3] contains a C Programming Language
          implementation of the algorithm.  This code was written with
          portability being the principal objective.  Implementors may
          wish to optimize the implementation with respect to the
          characteristics of their hardware and software platforms.

          The use of this algorithm in conjunction with the Digest
          Authentication Protocol (see Section 3) is identified by the
          ASN.1 object identifier value v2md5AuthProtocol, defined in
          [4].  (Note that this protocol is a modified version of the
          md5AuthProtocol protocol defined in RFC 1352.)

          For any SNMPv2 party for which the authentication protocol is
          v2md5AuthProtocol, the size of its private authentication key
          is 16 octets.

          Within an authenticated management communication generated by
          such a party, the size of the authDigest component of that
          communication (see Section 3) is 16 octets.









          Galvin & McCloghrie                                   [Page 8]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          1.5.2.  Symmetric Encryption Algorithm

          In support of data confidentiality, the use of the Data
          Encryption Standard (DES) in the Cipher Block Chaining mode of
          operation is chosen.  The designated portion of a SNMPv2
          message is encrypted and included as part of the message sent
          to the recipient.

          Two organizations have published specifications defining the
          DES: the National Institute of Standards and Technology (NIST)
          [5] and the American National Standards Institute [6].  There
          is a companion Modes of Operation specification for each
          definition (see [7] and [8], respectively).

          The NIST has published three additional documents that
          implementors may find useful.

          o    There is a document with guidelines for implementing and
               using the DES, including functional specifications for
               the DES and its modes of operation [9].

          o    There is a specification of a validation test suite for
               the DES [10].  The suite is designed to test all aspects
               of the DES and is useful for pinpointing specific
               problems.

          o    There is a specification of a maintenance test for the
               DES [11].  The test utilizes a minimal amount of data and
               processing to test all components of the DES.  It
               provides a simple yes-or-no indication of correct
               operation and is useful to run as part of an
               initialization step, e.g., when a computer reboots.

          The use of this algorithm in conjunction with the Symmetric
          Privacy Protocol (see Section 4) is identified by the ASN.1
          object identifier value desPrivProtocol, defined in [4].

          For any SNMPv2 party for which the privacy protocol is
          desPrivProtocol, the size of the private privacy key is 16
          octets, of which the first 8 octets are a DES key and the
          second 8 octets are a DES Initialization Vector.  The 64-bit
          DES key in the first 8 octets of the private key is a 56 bit
          quantity used directly by the algorithm plus 8 parity bits -
          arranged so that one parity bit is the least significant bit
          of each octet.  The setting of the parity bits is ignored.





          Galvin & McCloghrie                                   [Page 9]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          The length of the octet sequence to be encrypted by the DES
          must be an integral multiple of 8.  When encrypting, the data
          should be padded at the end as necessary; the actual pad value
          is insignificant.

          If the length of the octet sequence to be decrypted is not an
          integral multiple of 8 octets, the processing of the octet
          sequence should be halted and an appropriate exception noted.
          Upon decrypting, the padding should be ignored.









































          Galvin & McCloghrie                                  [Page 10]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          2.  SNMPv2 Party

          Recall from [1] that a SNMPv2 party is a conceptual, virtual
          execution context whose operation is restricted (for security
          or other purposes) to an administratively defined subset of
          all possible operations of a particular SNMPv2 entity.  A
          SNMPv2 entity is an actual process which performs network
          management operations by generating and/or responding to
          SNMPv2 protocol messages in the manner specified in [12].
          Architecturally, every SNMPv2 entity maintains a local
          database that represents all SNMPv2 parties known to it.







































          Galvin & McCloghrie                                  [Page 11]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          A SNMPv2 party may be represented by an ASN.1 value with the
          following syntax:

               SnmpParty ::= SEQUENCE {
                 partyIdentity
                    OBJECT IDENTIFIER,
                 partyTDomain
                    OBJECT IDENTIFIER,
                 partyTAddress
                    OCTET STRING,
                 partyMaxMessageSize
                    INTEGER,
                 partyAuthProtocol
                    OBJECT IDENTIFIER,
                 partyAuthClock
                    INTEGER,
                 partyAuthPrivate
                    OCTET STRING,
                 partyAuthPublic
                    OCTET STRING,
                 partyAuthLifetime
                    INTEGER,
                 partyPrivProtocol
                    OBJECT IDENTIFIER,
                 partyPrivPrivate
                    OCTET STRING,
                 partyPrivPublic
                    OCTET STRING
               }

          For each SnmpParty value that represents a SNMPv2 party, the
          generic significance of each of its components is defined in
          [1].  For each SNMPv2 party that supports the generation of
          messages using the Digest Authentication Protocol, additional,
          special significance is attributed to certain components of
          that party's representation:

          o    Its partyAuthProtocol component is called the
               authentication protocol and identifies a combination of
               the Digest Authentication Protocol with a particular
               digest algorithm (such as that defined in Section 1.5.1).
               This combined mechanism is used to authenticate the
               origin and integrity of all messages generated by the
               party.






          Galvin & McCloghrie                                  [Page 12]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          o    Its partyAuthClock component is called the authentication
               clock and represents a notion of the current time that is
               specific to the party.

          o    Its partyAuthPrivate component is called the private
               authentication key and represents any secret value needed
               to support the Digest Authentication Protocol and
               associated digest algorithm.

          o    Its partyAuthPublic component is called the public
               authentication key and represents any public value that
               may be needed to support the authentication protocol.
               This component is not significant except as suggested in
               Section 5.4.

          o    Its partyAuthLifetime component is called the lifetime
               and represents an administrative upper bound on
               acceptable delivery delay for protocol messages generated
               by the party.

          For each SNMPv2 party that supports the receipt of messages
          via the Symmetric Privacy Protocol, additional, special
          significance is attributed to certain components of that
          party's representation:

          o    Its partyPrivProtocol component is called the privacy
               protocol and identifies a combination of the Symmetric
               Privacy Protocol with a particular encryption algorithm
               (such as that defined in Section 1.5.2).  This combined
               mechanism is used to protect from disclosure all protocol
               messages received by the party.

          o    Its partyPrivPrivate component is called the private
               privacy key and represents any secret value needed to
               support the Symmetric Privacy Protocol and associated
               encryption algorithm.

          o    Its partyPrivPublic component is called the public
               privacy key and represents any public value that may be
               needed to support the privacy protocol.  This component
               is not significant except as suggested in Section 5.4.









          Galvin & McCloghrie                                  [Page 13]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          3.  Digest Authentication Protocol

          This section describes the Digest Authentication Protocol.  It
          provides both for verifying the integrity of a received
          message (i.e., the message received is the message sent) and
          for verifying the origin of a message (i.e., the reliable
          identification of the originator).  The integrity of the
          message is protected by computing a digest over an appropriate
          portion of a message.  The digest is computed by the
          originator of the message, transmitted with the message, and
          verified by the recipient of the message.

          A secret value known only to the originator and recipient of
          the message is prefixed to the message prior to the digest
          computation.  Thus, the origin of the message is known
          implicitly with the verification of the digest.

          A requirement on parties using this Digest Authentication
          Protocol is that they shall not originate messages for
          transmission to any destination party which does not also use
          this Digest Authentication Protocol.  This restriction
          excludes undesirable side effects of communication between a
          party which uses these security protocols and a party which
          does not.

          Recall from [1] that a SNMPv2 management communication is
          represented by an ASN.1 value with the following syntax:

               SnmpMgmtCom ::= [2] IMPLICIT SEQUENCE {
                 dstParty
                    OBJECT IDENTIFIER,
                 srcParty
                    OBJECT IDENTIFIER,
                 context
                    OBJECT IDENTIFIER,
                 pdu
                    PDUs
               }

          For each SnmpMgmtCom value that represents a SNMPv2 management
          communication, the following statements are true:

          o    Its dstParty component is called the destination and
               identifies the SNMPv2 party to which the communication is
               directed.





          Galvin & McCloghrie                                  [Page 14]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          o    Its srcParty component is called the source and
               identifies the SNMPv2 party from which the communication
               is originated.

          o    Its context component identifies the SNMPv2 context
               containing the management information referenced by the
               communication.

          o    Its pdu component has the form and significance
               attributed to it in [12].

          Recall from [1] that a SNMPv2 authenticated management
          communication is represented by an ASN.1 value with the
          following syntax:

               SnmpAuthMsg ::= [1] IMPLICIT SEQUENCE {
                 authInfo
                    ANY, - defined by authentication protocol
                 authData
                    SnmpMgmtCom
               }

          For each SnmpAuthMsg value that represents a SNMPv2
          authenticated management communication, the following
          statements are true:

          o    Its authInfo component is called the authentication
               information and represents information required in
               support of the authentication protocol used by both the
               SNMPv2 party originating the message, and the SNMPv2
               party receiving the message.  The detailed significance
               of the authentication information is specific to the
               authentication protocol in use; it has no effect on the
               application semantics of the communication other than its
               use by the authentication protocol in determining whether
               the communication is authentic or not.

          o    Its authData component is called the authentication data












          Galvin & McCloghrie                                  [Page 15]





          RFC 1446        Security Protocols for SNMPv2       April 1993


               and represents a SNMPv2 management communication.

          In support of the Digest Authentication Protocol, an authInfo
          component is of type AuthInformation:

               AuthInformation ::= [2] IMPLICIT SEQUENCE {
                 authDigest
                    OCTET STRING,
                 authDstTimestamp
                    UInteger32,
                 authSrcTimestamp
                    UInteger32
               }

          For each AuthInformation value that represents authentication
          information, the following statements are true:

          o    Its authDigest component is called the authentication
               digest and represents the digest computed over an
               appropriate portion of the message, where the message is
               temporarily prefixed with a secret value for the purposes
               of computing the digest.

          o    Its authSrcTimestamp component is called the
               authentication timestamp and represents the time of the
               generation of the message according to the partyAuthClock
               of the SNMPv2 party that originated it.  Note that the
               granularity of the authentication timestamp is 1 second.

          o    Its authDstTimestamp component is called the
               authentication timestamp and represents the time of the
               generation of the message according to the partyAuthClock
               of the SNMPv2 party that is to receive it.  Note that the
               granularity of the authentication timestamp is 1 second.


          3.1.  Generating a Message

          This section describes the behavior of a SNMPv2 entity when it
          acts as a SNMPv2 party for which the authentication protocol
          is administratively specified as the Digest Authentication
          Protocol.  Insofar as the behavior of a SNMPv2 entity when
          transmitting protocol messages is defined generically in [1],
          only those aspects of that behavior that are specific to the
          Digest Authentication Protocol are described below.  In





          Galvin & McCloghrie                                  [Page 16]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          particular, this section describes the encapsulation of a
          SNMPv2 management communication into a SNMPv2 authenticated
          management communication.

          According to Section 3.1 of [1], a SnmpAuthMsg value is
          constructed during Step 3 of generic processing.  In
          particular, it states the authInfo component is constructed
          according to the authentication protocol identified for the
          SNMPv2 party originating the message.  When the relevant
          authentication protocol is the Digest Authentication Protocol,
          the procedure performed by a SNMPv2 entity whenever a
          management communication is to be transmitted by a SNMPv2
          party is as follows.

          (1)  The local database is consulted to determine the
               authentication clock and private authentication key
               (extracted, for example, according to the conventions
               defined in Section 1.5.1) of the SNMPv2 party originating
               the message.  The local database is also consulted to
               determine the authentication clock of the receiving
               SNMPv2 party.

          (2)  The authSrcTimestamp component is set to the retrieved
               authentication clock value of the message's source.  The
               authDstTimestamp component is set to the retrieved
               authentication clock value of the message's intended
               recipient.

          (3)  The authentication digest is temporarily set to the
               private authentication key of the SNMPv2 party
               originating the message.  The SnmpAuthMsg value is
               serialized according to the conventions of [13] and [12].
               A digest is computed over the octet sequence representing
               that serialized value using, for example, the algorithm
               specified in Section 1.5.1.  The authDigest component is
               set to the computed digest value.

          As set forth in [1], the SnmpAuthMsg value is then
          encapsulated according to the appropriate privacy protocol
          into a SnmpPrivMsg value.  This latter value is then
          serialized and transmitted to the receiving SNMPv2 party.









          Galvin & McCloghrie                                  [Page 17]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          3.2.  Receiving a Message

          This section describes the behavior of a SNMPv2 entity upon
          receipt of a protocol message from a SNMPv2 party for which
          the authentication protocol is administratively specified as
          the Digest Authentication Protocol.  Insofar as the behavior
          of a SNMPv2 entity when receiving protocol messages is defined
          generically in [1], only those aspects of that behavior that
          are specific to the Digest Authentication Protocol are
          described below.

          According to Section 3.2 of [1], a SnmpAuthMsg value is
          evaluated during Step 9 of generic processing.  In particular,
          it states the SnmpAuthMsg value is evaluated according to the
          authentication protocol identified for the SNMPv2 party that
          originated the message.  When the relevant authentication
          protocol is the Digest Authentication Protocol, the procedure
          performed by a SNMPv2 entity whenever a management
          communication is received by a SNMPv2 party is as follows.

          (1)  If the ASN.1 type of the authInfo component is not
               AuthInformation, the message is evaluated as unauthentic,
               and the snmpStatsBadAuths counter [14] is incremented.
               Otherwise, the authSrcTimestamp, authDstTimestamp, and
               authDigest components are extracted from the SnmpAuthMsg
               value.

          (2)  The local database is consulted to determine the
               authentication clock, private authentication key
               (extracted, for example, according to the conventions
               defined in Section 1.5.1), and lifetime of the SNMPv2
               party that originated the message.

          (3)  If the authSrcTimestamp component plus the lifetime is
               less than the authentication clock, the message is
               evaluated as unauthentic, and the snmpStatsNotInLifetimes
               counter [14] is incremented.

          (4)  The authDigest component is extracted and temporarily
               recorded.

          (5)  A new SnmpAuthMsg value is constructed such that its
               authDigest component is set to the private authentication
               key and its other components are set to the value of the
               corresponding components in the received SnmpAuthMsg





          Galvin & McCloghrie                                  [Page 18]





          RFC 1446        Security Protocols for SNMPv2       April 1993


               value.  This new SnmpAuthMsg value is serialized
               according to the conventions of [13] and [12].  A digest
               is computed over the octet sequence representing that
               serialized value using, for example, the algorithm
               specified in Section 1.5.1.

                                            NOTE
                    Because serialization rules are unambiguous but may
                    not be unique, great care must be taken in
                    reconstructing the serialized value prior to
                    computing the digest.  Implementations may find it
                    useful to keep a copy of the original serialized
                    value and then simply modify the octets which
                    directly correspond to the placement of the
                    authDigest component, rather than re-applying the
                    serialization algorithm to the new SnmpAuthMsg
                    value.

          (6)  If the computed digest value is not equal to the digest
               value temporarily recorded in step 4 above, the message
               is evaluated as unauthentic, and the
               snmpStatsWrongDigestValues counter [14] is incremented.

          (7)  The message is evaluated as authentic.

          (8)  The local database is consulted for access privileges
               permitted by the local access policy to the originating
               SNMPv2 party with respect to the receiving SNMPv2 party.
               If any level of access is permitted, then:

                 the authentication clock value locally recorded for the
                 originating SNMPv2 party is advanced to the
                 authSrcTimestamp value if this latter exceeds the
                 recorded value; and,

                 the authentication clock value locally recorded for the
                 receiving SNMPv2 party is advanced to the
                 authDstTimestamp value if this latter exceeds the
                 recorded value.

              (Note that this step is conceptually independent from
              Steps 15-17 of Section 3.2 in [1]).

          If the SnmpAuthMsg value is evaluated as unauthentic, an
          authentication failure is noted and the received message is





          Galvin & McCloghrie                                  [Page 19]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          discarded without further processing.  Otherwise, processing
          of the received message continues as specified in [1].
















































          Galvin & McCloghrie                                  [Page 20]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          4.  Symmetric Privacy Protocol

          This section describes the Symmetric Privacy Protocol.  It
          provides for protection from disclosure of a received message.
          An appropriate portion of the message is encrypted according
          to a secret key known only to the originator and recipient of
          the message.

          This protocol assumes the underlying mechanism is a symmetric
          encryption algorithm.  In addition, the message to be
          encrypted must be protected according to the conventions of
          the Digest Authentication Protocol.

          Recall from [1] that a SNMPv2 private management communication
          is represented by an ASN.1 value with the following syntax:

               SnmpPrivMsg ::= [1] IMPLICIT SEQUENCE {
                 privDst
                    OBJECT IDENTIFIER,
                 privData
                    [1] IMPLICIT OCTET STRING
               }

          For each SnmpPrivMsg value that represents a SNMPv2 private
          management communication, the following statements are true:

          o    Its privDst component is called the privacy destination
               and identifies the SNMPv2 party to which the
               communication is directed.

          o    Its privData component is called the privacy data and
               represents the (possibly encrypted) serialization
               (according to the conventions of [13] and [12]) of a
               SNMPv2 authenticated management communication.


          4.1.  Generating a Message

          This section describes the behavior of a SNMPv2 entity when it
          communicates with a SNMPv2 party for which the privacy
          protocol is administratively specified as the Symmetric
          Privacy Protocol.  Insofar as the behavior of a SNMPv2 entity
          when transmitting a protocol message is defined generically in
          [1], only those aspects of that behavior that are specific to
          the Symmetric Privacy Protocol are described below.  In





          Galvin & McCloghrie                                  [Page 21]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          particular, this section describes the encapsulation of a
          SNMPv2 authenticated management communication into a SNMPv2
          private management communication.

          According to Section 3.1 of [1], a SnmpPrivMsg value is
          constructed during Step 5 of generic processing.  In
          particular, it states the privData component is constructed
          according to the privacy protocol identified for the SNMPv2
          party receiving the message.  When the relevant privacy
          protocol is the Symmetric Privacy Protocol, the procedure
          performed by a SNMPv2 entity whenever a management
          communication is to be transmitted by a SNMPv2 party is as
          follows.

          (1)  If the SnmpAuthMsg value is not authenticated according
               to the conventions of the Digest Authentication Protocol,
               the generation of the private management communication
               fails according to a local procedure, without further
               processing.

          (2)  The local database is consulted to determine the private
               privacy key of the SNMPv2 party receiving the message
               (represented, for example, according to the conventions
               defined in Section 1.5.2).

          (3)  The SnmpAuthMsg value is serialized according to the
               conventions of [13] and [12].

          (4)  The octet sequence representing the serialized
               SnmpAuthMsg value is encrypted using, for example, the
               algorithm specified in Section 1.5.2 and the extracted
               private privacy key.

          (5)  The privData component is set to the encrypted value.

          As set forth in [1], the SnmpPrivMsg value is then serialized
          and transmitted to the receiving SNMPv2 party.


          4.2.  Receiving a Message

          This section describes the behavior of a SNMPv2 entity when it
          acts as a SNMPv2 party for which the privacy protocol is
          administratively specified as the Symmetric Privacy Protocol.
          Insofar as the behavior of a SNMPv2 entity when receiving a





          Galvin & McCloghrie                                  [Page 22]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          protocol message is defined generically in [1], only those
          aspects of that behavior that are specific to the Symmetric
          Privacy Protocol are described below.

          According to Section 3.2 of [1], the privData component of a
          received SnmpPrivMsg value is evaluated during Step 4 of
          generic processing.  In particular, it states the privData
          component is evaluated according to the privacy protocol
          identified for the SNMPv2 party receiving the message.  When
          the relevant privacy protocol is the Symmetric Privacy
          Protocol, the procedure performed by a SNMPv2 entity whenever
          a management communication is received by a SNMPv2 party is as
          follows.

          (1)  The local database is consulted to determine the private
               privacy key of the SNMPv2 party receiving the message
               (represented, for example, according to the conventions
               defined in Section 1.5.2).

          (2)  The contents octets of the privData component are
               decrypted using, for example, the algorithm specified in
               Section 1.5.2 and the extracted private privacy key.

          Processing of the received message continues as specified in
          [1].

























          Galvin & McCloghrie                                  [Page 23]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          5.  Clock and Secret Distribution

          The protocols described in Sections 3 and 4 assume the
          existence of loosely synchronized clocks and shared secret
          values.  Three requirements constrain the strategy by which
          clock values and secrets are distributed.

          o    If the value of an authentication clock is decreased, the
               private authentication key must be changed concurrently.

               When the value of an authentication clock is decreased,
               messages that have been sent with a timestamp value
               between the value of the authentication clock and its new
               value may be replayed.  Changing the private
               authentication key obviates this threat.

          o    The private authentication key and private privacy key
               must be known only to the parties requiring knowledge of
               them.

               Protecting the secrets from disclosure is critical to the
               security of the protocols.  Knowledge of the secrets must
               be as restricted as possible within an implementation.
               In particular, although the secrets may be known to one
               or more persons during the initial configuration of a
               device, the secrets should be changed immediately after
               configuration such that their actual value is known only
               to the software.  A management station has the additional
               responsibility of recovering the state of all parties
               whenever it boots, and it may address this responsibility
               by recording the secrets on a long-term storage device.
               Access to information on this device must be as
               restricted as is practically possible.

          o    There must exist at least one SNMPv2 entity that assumes
               the role of a responsible management station.

               This management station is responsible for ensuring that
               all authentication clocks are synchronized and for
               changing the secret values when necessary.  Although more
               than one management station may share this
               responsibility, their coordination is essential to the
               secure management of the network.  The mechanism by which
               multiple management stations ensure that no more than one
               of them attempts to synchronize the clocks or update the





          Galvin & McCloghrie                                  [Page 24]





          RFC 1446        Security Protocols for SNMPv2       April 1993


               secrets at any one time is a local implementation issue.

               A responsible management station may either support clock
               synchronization and secret distribution as separate
               functions, or combine them into a single functional unit.

          The first section below specifies the procedures by which a
          SNMPv2 entity is initially configured.  The next two sections
          describe one strategy for distributing clock values and one
          for determining a synchronized clock value among SNMPv2
          parties supporting the Digest Authentication Protocol.  For
          SNMPv2 parties supporting the Symmetric Privacy Protocol, the
          next section describes a strategy for distributing secret
          values.  The last section specifies the procedures by which a
          SNMPv2 entity recovers from a "crash."


          5.1.  Initial Configuration

          This section describes the initial configuration of a SNMPv2
          entity that supports the Digest Authentication Protocol or
          both the Digest Authentication Protocol and the Symmetric
          Privacy Protocol.

          When a network device is first installed, its initial, secure
          configuration must be done manually, i.e., a person must
          physically visit the device and enter the initial secret
          values for at least its first secure SNMPv2 party.  This
          requirement suggests that the person will have knowledge of
          the initial secret values.

          In general, the security of a system is enhanced as the number
          of entities that know a secret is reduced.  Requiring a person
          to physically visit a device every time a SNMPv2 party is
          configured not only exposes the secrets unnecessarily but is
          administratively prohibitive.  In particular, when MD5 is
          used, the initial authentication secret is 128 bits long and
          when DES is used an additional 128 bits are needed - 64 bits
          each for the key and initialization vector.  Clearly, these
          values will need to be recorded on a medium in order to be
          transported between a responsible management station and a
          managed agent.  The recommended procedure is to configure a
          small set of initial SNMPv2 parties for each SNMPv2 entity,
          one pair of which may be used initially to configure all other
          SNMPv2 parties.





          Galvin & McCloghrie                                  [Page 25]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          In fact, there is a minimal, useful set of SNMPv2 parties that
          could be configured between each responsible management
          station and managed agent.  This minimal set includes one of
          each of the following for both the responsible management
          station and the managed agent:

          o    a SNMPv2 party for which the authentication protocol and
               privacy protocol are the values noAuth and noPriv,
               respectively,

          o    a SNMPv2 party for which the authentication protocol
               identifies the mechanism defined in Section 1.5.1 and its
               privacy protocol is the value noPriv, and

          o    a SNMPv2 party for which the authentication protocol and
               privacy protocol identify the mechanisms defined in
               Section 1.5.1 and Section 1.5.2, respectively.

          The last of these SNMPv2 parties in both the responsible
          management station and the managed agent could be used to
          create all other SNMPv2 parties.

          Configuring one pair of SNMPv2 parties to be used to configure
          all other parties has the advantage of exposing only one pair
          of secrets - the secrets used to configure the minimal, useful
          set identified above.  To limit this exposure, the responsible
          management station should change these values as its first
          operation upon completion of the initial configuration.  In
          this way, secrets are known only to the peers requiring
          knowledge of them in order to communicate.

          The Management Information Base (MIB) document [4] supporting
          these security protocols specifies 6 initial party identities
          and initial values, which, by convention, are assigned to the
          parties and their associated parameters.

          These 6 initial parties are required to exist as part of the
          configuration of implementations when first installed, with
          the exception that implementations not providing support for a
          privacy protocol only need the 4 initial parties for which the
          privacy protocol is noPriv.  When installing a managed agent,
          these parties need to be configured with their initial
          secrets, etc., both in the responsible management station and
          in the new agent.






          Galvin & McCloghrie                                  [Page 26]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          If the responsible management station is configured first, it
          can be used to generate the initial secrets and provide them
          to a person, on a suitable medium, for distribution to the
          managed agent.  The following sequence of steps describes the
          initial configuration of a managed agent and its responsible
          management station.

          (1)  Determine the initial values for each of the attributes
               of the SNMPv2 party to be configured.  Some of these
               values may be computed by the responsible management
               station, some may be specified in the MIB document, and
               some may be administratively determined.

          (2)  Configure the parties in the responsible management
               station, according to the set of initial values.  If the
               management station is computing some initial values to be
               entered into the agent, an appropriate medium must be
               present to record the values.

          (3)  Configure the parties in the managed agent, according to
               the set of initial values.

          (4)  The responsible management station must synchronize the
               authentication clock values for each party it shares with
               each managed agent.  Section 5.3 specifies one strategy
               by which this could be accomplished.

          (5)  The responsible management station should change the
               secret values manually configured to ensure the actual
               values are known only to the peers requiring knowledge of
               them in order to communicate.  To do this, the management
               station generates new secrets for each party to be
               reconfigured and distributes the updates using any
               strategy which protects the new values from disclosure;
               use of a SNMPv2 set operation acting on the managed
               objects defined in [4] is such a strategy.  Upon
               receiving positive acknowledgement that the new values
               have been distributed, the management station should
               update its local database with the new values.

          If the managed agent does not support a protocol that protects
          messages from disclosure, e.g., the Symmetric Privacy Protocol
          (see section 5.4), then the distribution of new secrets, after
          the compromise of existing secrets, is not possible.  In this
          case, the new secrets can only be distributed by a physical





          Galvin & McCloghrie                                  [Page 27]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          visit to the device.

          If there are other SNMPv2 protocol entities requiring
          knowledge of the secrets, the responsible management station
          must distribute the information upon completion of the initial
          configuration.  The considerations, mentioned above,
          concerning the protection of secrets from disclosure, also
          apply in this case.


          5.2.  Clock Distribution

          A responsible management station must ensure that the
          authentication clock value for each SNMPv2 party for which it
          is responsible

          o    is loosely synchronized among all the local databases in
               which it appears,

          o    is reset, as indicated below, upon reaching its maximal
               value, and

          o    is non-decreasing, except as indicated below.

          The skew among the clock values must be accounted for in the
          lifetime value, in addition to the expected communication
          delivery delay.

          A skewed authentication clock may be detected by a number of
          strategies, including knowledge of the accuracy of the system
          clock, unauthenticated queries of the party database, and
          recognition of authentication failures originated by the
          party.

          Whenever clock skew is detected, and whenever the SNMPv2
          entities at both the responsible management station and the
          relevant managed agent support an appropriate privacy protocol
          (e.g., the Symmetric Privacy Protocol), a straightforward
          strategy for the correction of clock skew is simultaneous
          alteration of authentication clock and private key for the
          relevant SNMPv2 party.  If the request to alter the key and
          clock for a particular party originates from that same party,
          then, prior to transmitting that request, the local notion of
          the authentication clock is artificially advanced to assure
          acceptance of the request as authentic.





          Galvin & McCloghrie                                  [Page 28]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          More generally, however, since an authentication clock value
          need not be protected from disclosure, it is not necessary
          that a managed agent support a privacy protocol in order for a
          responsible management station to correct skewed clock values.
          The procedure for correcting clock skew in the general case is
          presented in Section 5.3.

          In addition to correcting skewed notions of authentication
          clocks, every SNMPv2 entity must react correctly as an
          authentication clock approaches its maximal value.  If the
          authentication clock for a particular SNMPv2 party ever
          reaches the maximal time value, the clock must halt at that
          value.  (The value of interest may be the maximum less
          lifetime.  When authenticating a message, its authentication
          timestamp is added to lifetime and compared to the
          authentication clock.  A SNMPv2 entity must guarantee that the
          sum is never greater than the maximal time value.) In this
          state, the only authenticated request a management station
          should generate for this party is one that alters the value of
          at least its authentication clock and private authentication
          key.  In order to reset these values, the responsible
          management station may set the authentication timestamp in the
          message to the maximal time value.

          The value of the authentication clock for a particular SNMPv2
          party must never be altered such that its new value is less
          than its old value, unless its private authentication key is
          also altered at the same time.


          5.3.  Clock Synchronization

          Unless the secrets are changed at the same time, the correct
          way to synchronize clocks is to advance the slower clock to be
          equal to the faster clock.  Suppose that party agentParty is
          realized by the SNMPv2 entity in a managed agent; suppose that
          party mgrParty is realized by the SNMPv2 entity in the
          corresponding responsible management station.  For any pair of
          parties, there are four possible conditions of the
          authentication clocks that could require correction:

          (1)  The management station's notion of the value of the
               authentication clock for agentParty exceeds the agent's
               notion.






          Galvin & McCloghrie                                  [Page 29]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          (2)  The management station's notion of the value of the
               authentication clock for mgrParty exceeds the agent's
               notion.

          (3)  The agent's notion of the value of the authentication
               clock for agentParty exceeds the management station's
               notion.

          (4)  The agent's notion of the value of the authentication
               clock for mgrParty exceeds the management station's
               notion.

          The selective clock acceleration mechanism intrinsic to the
          protocol corrects conditions 1, 2 and 3 as part of the normal
          processing of an authentic message.  Therefore, the clock
          adjustment procedure below does not provide for any
          adjustments in those cases.  Rather, the following sequence of
          steps specifies how the clocks may be synchronized when
          condition 4 is manifest.

          (1)  The responsible management station saves its existing
               notion of the authentication clock for the party
               mgrParty.

          (2)  The responsible management station retrieves the
               authentication clock value for mgrParty from the agent.
               This retrieval must be an unauthenticated request, since
               the management station does not know if the clocks are
               synchronized.  If the request fails, the clocks cannot be
               synchronized, and the clock adjustment procedure is
               aborted without further processing.

          (3)  If the notion of the authentication clock for mgrParty
               just retrieved from the agent exceeds the management
               station's notion, then condition 4 is manifest, and the
               responsible management station advances its notion of the
               authentication clock for mgrParty to match the agent's
               notion.

          (4)  The responsible management station retrieves the
               authentication clock value for mgrParty from the agent.
               This retrieval must be an authenticated request, in order
               that the management station may verify that the clock
               value is properly synchronized.  If this authenticated
               query fails, then the management station restores its





          Galvin & McCloghrie                                  [Page 30]





          RFC 1446        Security Protocols for SNMPv2       April 1993


               previously saved notion of the clock value, and the clock
               adjustment procedure is aborted without further
               processing.  Otherwise, clock synchronization has been
               successfully realized.

          Administrative advancement of a clock as described above does
          not introduce any new vulnerabilities, since the value of the
          clock is intended to increase with the passage of time.  A
          potential operational problem is the rejection of authentic
          management operations that were authenticated using a previous
          value of the relevant party clock.  This possibility may be
          avoided if a management station suppresses generation of
          management traffic between relevant parties while this clock
          adjustment procedure is in progress.


          5.4.  Secret Distribution

          This section describes one strategy by which a SNMPv2 entity
          that supports both the Digest Authentication Protocol and the
          Symmetric Privacy Protocol can change the secrets for a
          particular SNMPv2 party.

          The frequency with which the secrets of a SNMPv2 party should
          be changed is a local administrative issue.  However, the more
          frequently a secret is used, the more frequently it should be
          changed.  At a minimum, the secrets must be changed whenever
          the associated authentication clock approaches its maximal
          value (see Section 6).  Note that, owing to both
          administrative and automatic advances of the authentication
          clock described in this memo, the authentication clock for a
          SNMPv2 party may well approach its maximal value sooner than
          might otherwise be expected.

          The following sequence of steps specifies how a responsible
          management station alters a secret value (i.e., the private
          authentication key or the private privacy key) for a
          particular SNMPv2 party.  There are two cases.

          First, setting the initial secret for a new party:

          (1)  The responsible management station generates a new secret
               value.







          Galvin & McCloghrie                                  [Page 31]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          (2)  The responsible management station encapsulates a SNMPv2
               setRequest in a SNMPv2 private management communication
               with at least the following properties.

                    Its source supports the Digest Authentication
                    Protocol and the Symmetric Privacy Protocol.

                    Its destination supports the Symmetric Privacy
                    Protocol and the Digest Authentication Protocol.

          (3)  The SNMPv2 private management communication is
               transmitted to its destination.

          (4)  Upon receiving the request, the recipient processes the
               message according to [12] and [1].

          (5)  The recipient encapsulates a SNMPv2 response in a SNMPv2
               private management communication with at least the
               following properties.

                    Its source supports the Digest Authentication
                    Protocol and the Symmetric Privacy Protocol.

                    Its destination supports the Symmetric Privacy
                    Protocol and the Digest Authentication Protocol.

          (6)  The SNMPv2 private management communication is
               transmitted to its destination.

          (7)  Upon receiving the response, the responsible management
               station updates its local database with the new value.

          Second, modifying the current secret of an existing party:

          (1)  The responsible management station generates a new secret
               value.

          (2)  The responsible management station encapsulates a SNMPv2
               setRequest in a SNMPv2 management communication with at
               least the following properties.

                    Its source and destination supports the Digest
                    Authentication Protocol.







          Galvin & McCloghrie                                  [Page 32]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          (3)  The SNMPv2 private management communication is
               transmitted to its destination.

          (4)  Upon receiving the request, the recipient processes the
               message according to [12] and [1].

          (5)  The recipient encapsulates a SNMPv2 response in a SNMPv2
               management communication with at least the following
               properties.

                    Its source and destination supports the Digest
                    Authentication Protocol.

          (6)  The SNMPv2 management communication is transmitted to its
               destination.

          (7)  Upon receiving the response, the responsible management
               station updates its local database with the new value.

          If the responsible management station does not receive a
          response to its request, there are two possible causes.

          o    The request may not have been delivered to the
               destination.

          o    The response may not have been delivered to the
               originator of the request.

          In order to distinguish the two possible error conditions, a
          responsible management station could check the destination to
          see if the change has occurred.  Unfortunately, since the
          secret values are unreadable, this is not directly possible.

          The recommended strategy for verifying key changes is to set
          the public value corresponding to the secret being changed to
          a recognizable, novel value: that is, alter the public
          authentication key value for the relevant party when changing
          its private authentication key, or alter its public privacy
          key value when changing its private privacy key.  In this way,
          the responsible management station may retrieve the public
          value when a response is not received, and verify whether or
          not the change has taken place.  (This strategy is available
          since the public values are not used by the protocols defined
          in this memo.  If this strategy is employed, then the public
          values are significant in this context.  Of course, protocols





          Galvin & McCloghrie                                  [Page 33]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          using the public values may make use of this strategy
          directly.)

          One other scenario worthy of mention is using a SNMPv2 party
          to change its own secrets.  In this case, the destination will
          change its local database prior to generating a response.
          Thus, the response will be constructed according to the new
          value.  However, the responsible management station will not
          update its local database until after the response is
          received.  This suggests the responsible management station
          may receive a response which will be evaluated as unauthentic,
          unless the correct secret is used.  The responsible management
          station may either account for this scenario as a special
          case, or use an alteration of the relevant public values (as
          described above) to verify the key change.

          Note, during the period of time after the request has been
          sent and before the response is received, the management
          station must keep track of both the old and new secret values.
          Since the delay may be the result of a network failure, the
          management station must be prepared to retain both values for
          an extended period of time, including across reboots.


          5.5.  Crash Recovery

          This section describes the requirements for SNMPv2 protocol
          entities in connection with recovery from system crashes or
          other service interruptions.

          For each SNMPv2 party in the local database for a particular
          SNMPv2 entity, its identity, authentication clock, private
          authentication key, and private privacy key must enjoy non-
          volatile, incorruptible representations.  If possible,
          lifetime should also enjoy a non-volatile, incorruptible
          representation.  If said SNMPv2 entity supports other security
          protocols or algorithms in addition to the two defined in this
          memo, then the authentication protocol and the privacy
          protocol for each party also require non-volatile,
          incorruptible representation.

          The authentication clock of a SNMPv2 party is a critical
          component of the overall security of the protocols.  The
          inclusion of a reliable representation of a clock in a SNMPv2
          entity is required for overall security.  A reliable clock





          Galvin & McCloghrie                                  [Page 34]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          representation ensures that a clock's value is monotonically
          increasing, even across a power loss or other system failure
          of the local SNMPv2 entity.  One example of a reliable clock
          representation is that provided by battery-powered clock-
          calendar devices incorporated into some contemporary systems.
          Another example is storing and updating a clock value in non-
          volatile storage at a frequency of once per U (e.g., 24)
          hours, and re-initialising that clock value on every reboot as
          the stored value plus U+1 hours.  It is assumed that
          management stations always support reliable clock
          representations, where clock adjustment by a human operator
          during crash recovery may contribute to that reliability.

          If a managed agent crashes and does not reboot in time for its
          responsible management station to prevent its authentication
          clock from reaching its maximal value, upon reboot the clock
          must be halted at its maximal value.  The procedures specified
          in Section 5.3 would then apply.

          Upon recovery, those attributes of each SNMPv2 party that do
          not enjoy non-volatile or reliable representation are
          initialized as follows.

          o    If the private authentication key is not the OCTET STRING
               of zero length, the authentication protocol is set to
               identify use of the Digest Authentication Protocol in
               conjunction with the algorithm specified in Section
               1.5.1.

          o    If the lifetime is not retained, it should be initialized
               to zero.

          o    If the private privacy key is not the OCTET STRING of
               zero length, the privacy protocol is set to identify use
               of the Symmetric Privacy Protocol in conjunction with the
               algorithm specified in Section 1.5.2.

          Upon detecting that a managed agent has rebooted, a
          responsible management station must reset all other party
          attributes, including the lifetime if it was not retained.  In
          order to reset the lifetime, the responsible management
          station should set the authentication timestamp in the message
          to the sum of the authentication clock and desired lifetime.
          This is an artificial advancement of the authentication
          timestamp in order to guarantee the message will be authentic





          Galvin & McCloghrie                                  [Page 35]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          when received by the recipient.

















































          Galvin & McCloghrie                                  [Page 36]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          6.  Security Considerations

          This section highlights security considerations relevant to
          the protocols and procedures defined in this memo.  Practices
          that contribute to secure, effective operation of the
          mechanisms defined here are described first.  Constraints on
          implementation behavior that are necessary to the security of
          the system are presented next.  Finally, an informal account
          of the contribution of each mechanism of the protocols to the
          required goals is presented.


          6.1.  Recommended Practices

          This section describes practices that contribute to the
          secure, effective operation of the mechanisms defined in this
          memo.

          o    A management station should discard SNMPv2 responses for
               which neither the request-id component nor the
               represented management information corresponds to any
               currently outstanding request.

               Although it would be typical for a management station to
               do this as a matter of course, in the context of these
               security protocols it is significant owing to the
               possibility of message duplication (malicious or
               otherwise).

          o    A management station should not interpret an agent's lack
               of response to an authenticated SNMPv2 management
               communication as a conclusive indication of agent or
               network failure.

               It is possible for authentication failure traps to be
               lost or suppressed as a result of authentication clock
               skew or inconsistent notions of shared secrets.  In order
               either to facilitate administration of such SNMPv2
               parties or to provide for continued management in times
               of network stress, a management station implementation
               may provide for arbitrary, artificial advancement of the
               timestamp or selection of shared secrets on locally
               generated messages.







          Galvin & McCloghrie                                  [Page 37]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          o    The lifetime value for a SNMPv2 party should be chosen
               (by the local administration) to be as small as possible,
               given the accuracy of clock devices available, relevant
               round-trip communications delays, and the frequency with
               which a responsible management station will be able to
               verify all clock values.

               A large lifetime increases the vulnerability to malicious
               delays of SNMPv2 messages.  The implementation of a
               management station may accommodate changing network
               conditions during periods of network stress by
               effectively increasing the lifetimes of the source and
               destination parties.  The management station accomplishes
               this by artificially advancing its notion of the source
               party's clock on messages it sends, and by artificially
               increasing its notion of the source party`s lifetime on
               messages it receives.

          o    When sending state altering messages to a managed agent,
               a management station should delay sending successive
               messages to the managed agent until a positive
               acknowledgement is received for the previous message or
               until the previous message expires.

               No message ordering is imposed by the SNMPv2.  Messages
               may be received in any order relative to their time of
               generation and each will be processed in the ordered
               received.  Note that when an authenticated message is
               sent to a managed agent, it will be valid for a period of
               time that does not exceed lifetime under normal
               circumstances, and is subject to replay during this
               period.

               Indeed, a management station must cope with the loss and
               re-ordering of messages resulting from anomalies in the
               network as a matter of course.

               However, a managed object, snmpSetSerialNo [14], is
               specifically defined for use with SNMPv2 set operations
               in order to provide a mechanism to ensure the processing
               of SNMPv2 messages occurs in a specific order.

          o    The frequency with which the secrets of a SNMPv2 party
               should be changed is indirectly related to the frequency
               of their use.





          Galvin & McCloghrie                                  [Page 38]





          RFC 1446        Security Protocols for SNMPv2       April 1993


               Protecting the secrets from disclosure is critical to the
               overall security of the protocols.  Frequent use of a
               secret provides a continued source of data that may be
               useful to a cryptanalyst in exploiting known or perceived
               weaknesses in an algorithm.  Frequent changes to the
               secret avoid this vulnerability.

               Changing a secret after each use is generally regarded as
               the most secure practice, but a significant amount of
               overhead may be associated with that approach.

               Note, too, in a local environment the threat of
               disclosure may be insignificant, and as such the changing
               of secrets may be less frequent.  However, when public
               data networks are the communication paths, more caution
               is prudent.

          o    In order to foster the greatest degree of security, a
               management station implementation must support
               constrained, pairwise sharing of secrets among SNMPv2
               entities as its default mode of operation.

               Owing to the use of symmetric cryptography in the
               protocols defined here, the secrets associated with a
               particular SNMPv2 party must be known to all other SNMPv2
               parties with which that party may wish to communicate.
               As the number of locations at which secrets are known and
               used increases, the likelihood of their disclosure also
               increases, as does the potential impact of that
               disclosure.  Moreover, if the set of SNMPv2 protocol
               entities with knowledge of a particular secret numbers
               more than two, data origin cannot be reliably
               authenticated because it is impossible to determine with
               any assurance which entity of that set may be the
               originator of a particular SNMPv2 message.  Thus, the
               greatest degree of security is afforded by configurations
               in which the secrets for each SNMPv2 party are known to
               at most two protocol entities.


          6.2.  Conformance

          A SNMPv2 entity implementation that claims conformance to this
          memo must satisfy the following requirements:






          Galvin & McCloghrie                                  [Page 39]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          (1)  It must implement the noAuth and noPriv protocols whose
               object identifiers are defined in [4].

                    noAuth  This protocol signifies that messages
                    generated by a party using it are not protected as
                    to origin or integrity.  It is required to ensure
                    that a party's authentication clock is always
                    accessible.

                    noPriv  This protocol signifies that messages
                    received by a party using it are not protected from
                    disclosure.  It is required to ensure that a party's
                    authentication clock is always accessible.

          (2)  It must implement the Digest Authentication Protocol in
               conjunction with the algorithm defined in Section 1.5.1.

          (3)  It must include in its local database at least one SNMPv2
               party with the following parameters set as follows:

                    partyAuthProtocol is set to noAuth and

                    partyPrivProtocol is set to noPriv.

               This party must have a MIB view [1] specified that
               includes at least the authentication clock of all other
               parties.  Alternatively, the authentication clocks of the
               other parties may be partitioned among several similarly
               configured parties according to a local implementation
               convention.

          (4)  For each SNMPv2 party about which it maintains
               information in a local database, an implementation must
               satisfy the following requirements:

                    (a) It must not allow a party's parameters to be set
                    to a value inconsistent with its expected syntax.
                    In particular, Section 1.4 specifies constraints for
                    the chosen mechanisms.

                    (b) It must, to the maximal extent possible,
                    prohibit read-access to the private authentication
                    key and private encryption key under all
                    circumstances except as required to generate and/or
                    validate SNMPv2 messages with respect to that party.





          Galvin & McCloghrie                                  [Page 40]





          RFC 1446        Security Protocols for SNMPv2       April 1993


                    This prohibition includes prevention of read-access
                    by the entity's human operators.

                    (c) It must allow the party's authentication clock
                    to be publicly accessible.  The correct operation of
                    the Digest Authentication Protocol requires that it
                    be possible to determine this value at all times in
                    order to guarantee that skewed authentication clocks
                    can be resynchronized.

                    (d) It must prohibit alterations to its record of
                    the authentication clock for that party
                    independently of alterations to its record of the
                    private authentication key (unless the clock
                    alteration is an advancement).

                    (e) It must never allow its record of the
                    authentication clock for that party to be
                    incremented beyond the maximal time value and so
                    "roll-over" to zero.

                    (f) It must never increase its record of the
                    lifetime for that party except as may be explicitly
                    authorized (via imperative command or securely
                    represented configuration information) by the
                    responsible network administrator.

                    (g) In the event that the non-volatile,
                    incorruptible representations of a party's
                    parameters (in particular, either the private
                    authentication key or private encryption key) are
                    lost or destroyed, it must alter its record of these
                    quantities to random values so subsequent
                    interaction with that party requires manual
                    redistribution of new secrets and other parameters.

          (5)  If it selects new value(s) for a party's secret(s), it
               must avoid bad or obvious choices for said secret(s).
               Choices to be avoided are boundary values (such as all-
               zeros) and predictable values (such as the same value as
               previously or selecting from a predetermined set).

          (6)  It must ensure that a received message for which the
               originating party uses the Digest Authentication Protocol
               but the receiving party does not, is always declared to





          Galvin & McCloghrie                                  [Page 41]





          RFC 1446        Security Protocols for SNMPv2       April 1993


               be unauthentic.  This may be achieved explicitly via an
               additional step in the procedure for processing a
               received message, or implicitly by verifying that all
               local access control policies enforce this requirement.


          6.3.  Protocol Correctness

          The correctness of these SNMPv2 security protocols with
          respect to the stated goals depends on the following
          assumptions:

          (1)  The chosen message digest algorithm satisfies its design
               criteria.  In particular, it must be computationally
               infeasible to discover two messages that share the same
               digest value.

          (2)  It is computationally infeasible to determine the secret
               used in calculating a digest on the concatenation of the
               secret and a message when both the digest and the message
               are known.

          (3)  The chosen symmetric encryption algorithm satisfies its
               design criteria.  In particular, it must be
               computationally infeasible to determine the cleartext
               message from the ciphertext message without knowledge of
               the key used in the transformation.

          (4)  Local notions of a party's authentication clock while it
               is associated with a specific private key value are
               monotonically non-decreasing (i.e., they never run
               backwards) in the absence of administrative
               manipulations.

          (5)  The secrets for a particular SNMPv2 party are known only
               to authorized SNMPv2 protocol entities.

          (6)  Local notions of the authentication clock for a
               particular SNMPv2 party are never altered such that the
               authentication clock's new value is less than the current
               value without also altering the private authentication
               key.

          For each mechanism of the protocol, an informal account of its
          contribution to the required goals is presented below.





          Galvin & McCloghrie                                  [Page 42]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          Pseudocode fragments are provided where appropriate to
          exemplify possible implementations; they are intended to be
          self-explanatory.


          6.3.1.  Clock Monotonicity Mechanism

          By pairing each sequence of a clock's values with a unique
          key, the protocols partially realize goal 3, and the
          conjunction of this property with assumption 6 above is
          sufficient for the claim that, with respect to a specific
          private key value, all local notions of a party's
          authentication clock are, in general, non-decreasing with
          time.


          6.3.2.  Data Integrity Mechanism

          The protocols require computation of a message digest computed
          over the SNMPv2 message prepended by the secret for the
          relevant party.  By virtue of this mechanism and assumptions 1
          and 2, the protocols realize goal 1.

          Normally, the inclusion of the message digest value with the
          digested message would not be sufficient to guarantee data
          integrity, since the digest value can be modified in addition
          to the message while it is enroute.  However, since not all of
          the digested message is included in the transmission to the
          destination, it is not possible to substitute both a message
          and a digest value while enroute to a destination.

          Strictly speaking, the specified strategy for data integrity
          does not detect a SNMPv2 message modification which appends
          extraneous material to the end of such messages.  However,
          owing to the representation of SNMPv2 messages as ASN.1
          values, such modifications cannot - consistent with goal 1 -
          result in unauthorized management operations.

          The data integrity mechanism specified in this memo protects
          only against unauthorized modification of individual SNMPv2
          messages.  A more general data integrity service that affords
          protection against the threat of message stream modification
          is not realized by this mechanism, although limited protection
          against reordering, delay, and duplication of messages within
          a message stream are provided by other mechanisms of the





          Galvin & McCloghrie                                  [Page 43]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          protocol.


          6.3.3.  Data Origin Authentication Mechanism

          The data integrity mechanism requires the use of a secret
          value known only to communicating parties.  By virtue of this
          mechanism and assumptions 1 and 2, the protocols explicitly
          prevent unauthorized modification of messages.  Data origin
          authentication is implicit if the message digest value can be
          verified.  That is, the protocols realize goal 2.


          6.3.4.  Restricted Administration Mechanism

          This memo requires that implementations preclude
          administrative alterations of the authentication clock for a
          particular party independently from its private authentication
          key (unless that clock alteration is an advancement).  An
          example of an efficient implementation of this restriction is
          provided in a pseudocode fragment below.  This pseudocode
          fragment meets the requirements of assumption 6.  Observe that
          the requirement is not for simultaneous alteration but to
          preclude independent alteration.  This latter requirement is
          fairly easily realized in a way that is consistent with the
          defined semantics of the SNMPv2 set operation.
























          Galvin & McCloghrie                                  [Page 44]





          RFC 1446        Security Protocols for SNMPv2       April 1993


               Void partySetKey (party, newKeyValue)
               {
                   if (party->clockAltered) {
                      party->clockAltered = FALSE;
                      party->keyAltered = FALSE;
                      party->keyInUse = newKeyValue;
                      party->clockInUse = party->clockCache;
                   }
                   else {
                      party->keyAltered = TRUE;
                      party->keyCache = newKeyValue;
                   }
               }

               Void partySetClock (party, newClockValue)
               {
                   if (party->keyAltered) {
                      party->keyAltered = FALSE;
                      party->clockAltered = FALSE;
                      party->clockInUse = newClockValue;
                      party->keyInUse = party->keyCache;
                   }
                   else {
                      party->clockAltered = TRUE;
                      party->clockCache = newClockValue;
                   }
               }


          6.3.5.  Message Timeliness Mechanism

          The definition of the SNMPv2 security protocols requires that,
          if the authentication timestamp value on a received message -
          augmented by an administratively chosen lifetime value - is
          less than the local notion of the clock for the originating
          SNMPv2 party, the message is not delivered.


               if (timestampOfReceivedMsg +
                      party->administrativeLifetime <=
                      party->localNotionOfClock) {
                      msgIsValidated = FALSE;
               }







          Galvin & McCloghrie                                  [Page 45]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          By virtue of this mechanism, the protocols realize goal 3.  In
          cases in which the local notions of a particular SNMPv2 party
          clock are moderately well-synchronized, the timeliness
          mechanism effectively limits the age of validly delivered
          messages.  Thus, if an attacker diverts all validated messages
          for replay much later, the delay introduced by this attack is
          limited to a period that is proportional to the skew among
          local notions of the party clock.


          6.3.6.  Selective Clock Acceleration Mechanism

          The definition of the SNMPv2 security protocols requires that,
          if either of the timestamp values for the originating or
          receiving parties on a received, validated message exceeds the
          corresponding local notion of the clock for that party, then
          the local notion of the clock for that party is adjusted
          forward to correspond to said timestamp value.  This mechanism
          is neither strictly necessary nor sufficient to the security
          of the protocol; rather, it fosters the clock synchronization
          on which valid message delivery depends - thereby enhancing
          the effectiveness of the protocol in a management context.


               if (msgIsValidated) {
                      if (timestampOfReceivedMsg >
                            party->localNotionOfClock) {
                            party->localNotionOfClock =
                                  timestampOfReceivedMsg;
                      }
               }


          The effect of this mechanism is to synchronize local notions
          of a party clock more closely in the case where a sender's
          notion is more advanced than a receiver's.  In the opposite
          case, this mechanism has no effect on local notions of a party
          clock and either the received message is validly delivered or
          not according to other mechanisms of the protocol.

          Operation of this mechanism does not, in general, improve the
          probability of validated delivery for messages generated by
          party participants whose local notion of the party clock is
          relatively less advanced.  In this case, queries from a
          management station may not be validly delivered and the





          Galvin & McCloghrie                                  [Page 46]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          management station needs to react appropriately (e.g., by use
          of the strategy described in section 5.3).  In contrast, the
          delivery of SNMPv2 trap messages generated by an agent that
          suffers from a less advanced notion of a party clock is more
          problematic, for an agent may lack the capacity to recognize
          and react to security failures that prevent delivery of its
          messages.  Thus, the inherently unreliable character of trap
          messages is likely to be compounded by attempts to provide for
          their validated delivery.


          6.3.7.  Confidentiality Mechanism

          The protocols require the use of a symmetric encryption
          algorithm when the data confidentiality service is required.
          By virtue of this mechanism and assumption 3, the protocols
          realize goal 4.

































          Galvin & McCloghrie                                  [Page 47]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          7.  Acknowledgements

          This document is based, almost entirely, on RFC 1352.















































          Galvin & McCloghrie                                  [Page 48]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          8.  References

          [1]  Galvin, J., and McCloghrie, K., "Administrative Model for
               version 2 of the Simple Network Management Protocol
               (SNMPv2)", RFC 1445, Trusted Information Systems, Hughes
               LAN Systems, April 1993.

          [2]  Case, J., Fedor, M., Schoffstall, M., Davin, J., "Simple
               Network Management Protocol", STD 15, RFC 1157, SNMP
               Research, Performance Systems International, MIT
               Laboratory for Computer Science, May 1990.

          [3]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
               MIT Laboratory for Computer Science, April 1992.

          [4]  McCloghrie, K., and Galvin, J., "Party MIB for version 2
               of the Simple Network Management Protocol (SNMPv2)", RFC
               1447, Hughes LAN Systems, Trusted Information Systems,
               April 1993.

          [5]  Data Encryption Standard, National Institute of Standards
               and Technology.  Federal Information Processing Standard
               (FIPS) Publication 46-1.  Supersedes FIPS Publication 46,
               (January, 1977; reaffirmed January, 1988).

          [6]  Data Encryption Algorithm, American National Standards
               Institute.  ANSI X3.92-1981, (December, 1980).

          [7]  DES Modes of Operation, National Institute of Standards
               and Technology.  Federal Information Processing Standard
               (FIPS) Publication 81, (December, 1980).

          [8]  Data Encryption Algorithm - Modes of Operation, American
               National Standards Institute.  ANSI X3.106-1983, (May
               1983).

          [9]  Guidelines for Implementing and Using the NBS Data
               Encryption Standard, National Institute of Standards and
               Technology.  Federal Information Processing Standard
               (FIPS) Publication 74, (April, 1981).

          [10] Validating the Correctness of Hardware Implementations of
               the NBS Data Encryption Standard, National Institute of
               Standards and Technology.  Special Publication 500-20.






          Galvin & McCloghrie                                  [Page 49]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          [11] Maintenance Testing for the Data Encryption Standard,
               National Institute of Standards and Technology.  Special
               Publication 500-61, (August, 1980).

          [12] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Protocol Operations for version 2 of the Simple Network
               Management Protocol (SNMPv2)", RFC 1448, SNMP Research,
               Inc., Hughes LAN Systems, Dover Beach Consulting, Inc.,
               Carnegie Mellon University, April 1993.

          [13] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Transport Mappings for version 2 of the Simple Network
               Management Protocol (SNMPv2)", RFC 1449, SNMP Research,
               Inc., Hughes LAN Systems, Dover Beach Consulting, Inc.,
               Carnegie Mellon University, April 1993.

          [14] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Management Information Base for version 2 of the Simple
               Network Management Protocol (SNMPv2)", RFC 1450, SNMP
               Research, Inc., Hughes LAN Systems, Dover Beach
               Consulting, Inc., Carnegie Mellon University, April 1993.





























          Galvin & McCloghrie                                  [Page 50]





          RFC 1446        Security Protocols for SNMPv2       April 1993


          9.  Authors' Addresses

               James M. Galvin
               Trusted Information Systems, Inc.
               3060 Washington Road, Route 97
               Glenwood, MD 21738

               Phone:  +1 301 854-6889
               EMail:  galvin@tis.com


               Keith McCloghrie
               Hughes LAN Systems
               1225 Charleston Road
               Mountain View, CA  94043
               US

               Phone: +1 415 966 7934
               Email: kzm@hls.com































          Galvin & McCloghrie                                  [Page 51]