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
|
/* $OpenBSD: deattack.c,v 1.14 2001/06/23 15:12:18 itojun Exp $ */
/*
* Cryptographic attack detector for ssh - source code
*
* Copyright (c) 1998 CORE SDI S.A., Buenos Aires, Argentina.
*
* All rights reserved. Redistribution and use in source and binary
* forms, with or without modification, are permitted provided that
* this copyright notice is retained.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
* WARRANTIES ARE DISCLAIMED. IN NO EVENT SHALL CORE SDI S.A. BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY OR
* CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR MISUSE OF THIS
* SOFTWARE.
*
* Ariel Futoransky <futo@core-sdi.com>
* <http://www.core-sdi.com>
*
* Modified for use in PuTTY by Simon Tatham
*/
#include <assert.h>
#include "misc.h"
#include "ssh.h"
typedef unsigned char uchar;
typedef unsigned short uint16;
/* SSH Constants */
#define SSH_MAXBLOCKS (32 * 1024)
#define SSH_BLOCKSIZE (8)
/* Hashing constants */
#define HASH_MINSIZE (8 * 1024)
#define HASH_ENTRYSIZE (sizeof(uint16))
#define HASH_FACTOR(x) ((x)*3/2)
#define HASH_UNUSEDCHAR (0xff)
#define HASH_UNUSED (0xffff)
#define HASH_IV (0xfffe)
#define HASH_MINBLOCKS (7*SSH_BLOCKSIZE)
/* Hash function (Input keys are cipher results) */
#define HASH(x) GET_32BIT_MSB_FIRST(x)
#define CMP(a, b) (memcmp(a, b, SSH_BLOCKSIZE))
uchar ONE[4] = { 1, 0, 0, 0 };
uchar ZERO[4] = { 0, 0, 0, 0 };
struct crcda_ctx {
uint16 *h;
uint32 n;
};
void *crcda_make_context(void)
{
struct crcda_ctx *ret = snew(struct crcda_ctx);
ret->h = NULL;
ret->n = HASH_MINSIZE / HASH_ENTRYSIZE;
return ret;
}
void crcda_free_context(void *handle)
{
struct crcda_ctx *ctx = (struct crcda_ctx *)handle;
if (ctx) {
sfree(ctx->h);
ctx->h = NULL;
sfree(ctx);
}
}
static void crc_update(uint32 *a, void *b)
{
*a = crc32_update(*a, b, 4);
}
/* detect if a block is used in a particular pattern */
static int check_crc(uchar *S, uchar *buf, uint32 len, uchar *IV)
{
uint32 crc;
uchar *c;
crc = 0;
if (IV && !CMP(S, IV)) {
crc_update(&crc, ONE);
crc_update(&crc, ZERO);
}
for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
if (!CMP(S, c)) {
crc_update(&crc, ONE);
crc_update(&crc, ZERO);
} else {
crc_update(&crc, ZERO);
crc_update(&crc, ZERO);
}
}
return (crc == 0);
}
/* Detect a crc32 compensation attack on a packet */
int detect_attack(void *handle, uchar *buf, uint32 len, uchar *IV)
{
struct crcda_ctx *ctx = (struct crcda_ctx *)handle;
register uint32 i, j;
uint32 l;
register uchar *c;
uchar *d;
assert(!(len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
len % SSH_BLOCKSIZE != 0));
for (l = ctx->n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
;
if (ctx->h == NULL) {
ctx->n = l;
ctx->h = snewn(ctx->n, uint16);
} else {
if (l > ctx->n) {
ctx->n = l;
ctx->h = sresize(ctx->h, ctx->n, uint16);
}
}
if (len <= HASH_MINBLOCKS) {
for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
if (IV && (!CMP(c, IV))) {
if ((check_crc(c, buf, len, IV)))
return 1; /* attack detected */
else
break;
}
for (d = buf; d < c; d += SSH_BLOCKSIZE) {
if (!CMP(c, d)) {
if ((check_crc(c, buf, len, IV)))
return 1; /* attack detected */
else
break;
}
}
}
return 0; /* ok */
}
memset(ctx->h, HASH_UNUSEDCHAR, ctx->n * HASH_ENTRYSIZE);
if (IV)
ctx->h[HASH(IV) & (ctx->n - 1)] = HASH_IV;
for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
for (i = HASH(c) & (ctx->n - 1); ctx->h[i] != HASH_UNUSED;
i = (i + 1) & (ctx->n - 1)) {
if (ctx->h[i] == HASH_IV) {
if (!CMP(c, IV)) {
if (check_crc(c, buf, len, IV))
return 1; /* attack detected */
else
break;
}
} else if (!CMP(c, buf + ctx->h[i] * SSH_BLOCKSIZE)) {
if (check_crc(c, buf, len, IV))
return 1; /* attack detected */
else
break;
}
}
ctx->h[i] = j;
}
return 0; /* ok */
}
|
