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
|
/* xts.c
XEX-based tweaked-codebook mode with ciphertext stealing (XTS)
Copyright (C) 2018 Red Hat, Inc.
This file is part of GNU Nettle.
GNU Nettle is free software: you can redistribute it and/or
modify it under the terms of either:
* the GNU Lesser General Public License as published by the Free
Software Foundation; either version 3 of the License, or (at your
option) any later version.
or
* the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your
option) any later version.
or both in parallel, as here.
GNU Nettle is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received copies of the GNU General Public License and
the GNU Lesser General Public License along with this program. If
not, see http://www.gnu.org/licenses/.
*/
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include "xts.h"
#include "macros.h"
#include "memxor.h"
#include "nettle-internal.h"
#include "block-internal.h"
static void
check_length(size_t length, uint8_t *dst)
{
assert(length >= XTS_BLOCK_SIZE);
/* asserts may be compiled out, try to save the user by zeroing the dst in
* case the buffer contains sensitive data (like the clear text for inplace
* encryption) */
if (length < XTS_BLOCK_SIZE)
memset(dst, '\0', length);
}
/* works also for inplace encryption/decryption */
void
xts_encrypt_message(const void *enc_ctx, const void *twk_ctx,
nettle_cipher_func *encf,
const uint8_t *tweak, size_t length,
uint8_t *dst, const uint8_t *src)
{
union nettle_block16 T;
union nettle_block16 P;
check_length(length, dst);
encf(twk_ctx, XTS_BLOCK_SIZE, T.b, tweak);
/* the zeroth power of alpha is the initial ciphertext value itself, so we
* skip shifting and do it at the end of each block operation instead */
for (;length >= 2 * XTS_BLOCK_SIZE || length == XTS_BLOCK_SIZE;
length -= XTS_BLOCK_SIZE, src += XTS_BLOCK_SIZE, dst += XTS_BLOCK_SIZE)
{
memxor3(P.b, src, T.b, XTS_BLOCK_SIZE); /* P -> PP */
encf(enc_ctx, XTS_BLOCK_SIZE, dst, P.b); /* CC */
memxor(dst, T.b, XTS_BLOCK_SIZE); /* CC -> C */
/* shift T for next block if any */
if (length > XTS_BLOCK_SIZE)
block16_mulx_le(&T, &T);
}
/* if the last block is partial, handle via stealing */
if (length)
{
/* S Holds the real C(n-1) (Whole last block to steal from) */
union nettle_block16 S;
memxor3(P.b, src, T.b, XTS_BLOCK_SIZE); /* P -> PP */
encf(enc_ctx, XTS_BLOCK_SIZE, S.b, P.b); /* CC */
memxor(S.b, T.b, XTS_BLOCK_SIZE); /* CC -> S */
/* shift T for next block */
block16_mulx_le(&T, &T);
length -= XTS_BLOCK_SIZE;
src += XTS_BLOCK_SIZE;
memxor3(P.b, src, T.b, length); /* P |.. */
/* steal ciphertext to complete block */
memxor3(P.b + length, S.b + length, T.b + length,
XTS_BLOCK_SIZE - length); /* ..| S_2 -> PP */
encf(enc_ctx, XTS_BLOCK_SIZE, dst, P.b); /* CC */
memxor(dst, T.b, XTS_BLOCK_SIZE); /* CC -> C(n-1) */
/* Do this after we read src so inplace operations do not break */
dst += XTS_BLOCK_SIZE;
memcpy(dst, S.b, length); /* S_1 -> C(n) */
}
}
void
xts_decrypt_message(const void *dec_ctx, const void *twk_ctx,
nettle_cipher_func *decf, nettle_cipher_func *encf,
const uint8_t *tweak, size_t length,
uint8_t *dst, const uint8_t *src)
{
union nettle_block16 T;
union nettle_block16 C;
check_length(length, dst);
encf(twk_ctx, XTS_BLOCK_SIZE, T.b, tweak);
for (;length >= 2 * XTS_BLOCK_SIZE || length == XTS_BLOCK_SIZE;
length -= XTS_BLOCK_SIZE, src += XTS_BLOCK_SIZE, dst += XTS_BLOCK_SIZE)
{
memxor3(C.b, src, T.b, XTS_BLOCK_SIZE); /* c -> CC */
decf(dec_ctx, XTS_BLOCK_SIZE, dst, C.b); /* PP */
memxor(dst, T.b, XTS_BLOCK_SIZE); /* PP -> P */
/* shift T for next block if any */
if (length > XTS_BLOCK_SIZE)
block16_mulx_le(&T, &T);
}
/* if the last block is partial, handle via stealing */
if (length)
{
union nettle_block16 T1;
/* S Holds the real P(n) (with part of stolen ciphertext) */
union nettle_block16 S;
/* we need the last T(n) and save the T(n-1) for later */
block16_mulx_le(&T1, &T);
memxor3(C.b, src, T1.b, XTS_BLOCK_SIZE); /* C -> CC */
decf(dec_ctx, XTS_BLOCK_SIZE, S.b, C.b); /* PP */
memxor(S.b, T1.b, XTS_BLOCK_SIZE); /* PP -> S */
/* process next block (Pn-1) */
length -= XTS_BLOCK_SIZE;
src += XTS_BLOCK_SIZE;
/* Prepare C, P holds the real P(n) */
memxor3(C.b, src, T.b, length); /* C_1 |.. */
memxor3(C.b + length, S.b + length, T.b + length,
XTS_BLOCK_SIZE - length); /* ..| S_2 -> CC */
decf(dec_ctx, XTS_BLOCK_SIZE, dst, C.b); /* PP */
memxor(dst, T.b, XTS_BLOCK_SIZE); /* PP -> P(n-1) */
/* Do this after we read src so inplace operations do not break */
dst += XTS_BLOCK_SIZE;
memcpy(dst, S.b, length); /* S_1 -> P(n) */
}
}
|
