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
|
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.org
*/
#include "tomcrypt.h"
/**
@file pkcs_1_oaep_decode.c
OAEP Padding for PKCS #1, Tom St Denis
*/
#ifdef PKCS_1
/**
PKCS #1 v2.00 OAEP decode
@param msg The encoded data to decode
@param msglen The length of the encoded data (octets)
@param lparam The session or system data (can be NULL)
@param lparamlen The length of the lparam
@param modulus_bitlen The bit length of the RSA modulus
@param hash_idx The index of the hash desired
@param out [out] Destination of decoding
@param outlen [in/out] The max size and resulting size of the decoding
@param res [out] Result of decoding, 1==valid, 0==invalid
@return CRYPT_OK if successful (even if invalid)
*/
int pkcs_1_oaep_decode(const unsigned char *msg, unsigned long msglen,
const unsigned char *lparam, unsigned long lparamlen,
unsigned long modulus_bitlen, int hash_idx,
unsigned char *out, unsigned long *outlen,
int *res)
{
unsigned char *DB, *seed, *mask;
unsigned long hLen, x, y, modulus_len;
int err;
LTC_ARGCHK(msg != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
LTC_ARGCHK(res != NULL);
/* default to invalid packet */
*res = 0;
/* test valid hash */
if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
return err;
}
hLen = hash_descriptor[hash_idx].hashsize;
modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
/* test hash/message size */
if ((2*hLen >= (modulus_len - 2)) || (msglen != modulus_len)) {
return CRYPT_PK_INVALID_SIZE;
}
/* allocate ram for DB/mask/salt of size modulus_len */
DB = XMALLOC(modulus_len);
mask = XMALLOC(modulus_len);
seed = XMALLOC(hLen);
if (DB == NULL || mask == NULL || seed == NULL) {
if (DB != NULL) {
XFREE(DB);
}
if (mask != NULL) {
XFREE(mask);
}
if (seed != NULL) {
XFREE(seed);
}
return CRYPT_MEM;
}
/* ok so it's now in the form
0x00 || maskedseed || maskedDB
1 || hLen || modulus_len - hLen - 1
*/
/* must have leading 0x00 byte */
if (msg[0] != 0x00) {
err = CRYPT_OK;
goto LBL_ERR;
}
/* now read the masked seed */
x = 1;
XMEMCPY(seed, msg + x, hLen);
x += hLen;
/* now read the masked DB */
XMEMCPY(DB, msg + x, modulus_len - hLen - 1);
x += modulus_len - hLen - 1;
/* compute MGF1 of maskedDB (hLen) */
if ((err = pkcs_1_mgf1(DB, modulus_len - hLen - 1, hash_idx, mask, hLen)) != CRYPT_OK) {
goto LBL_ERR;
}
/* XOR against seed */
for (y = 0; y < hLen; y++) {
seed[y] ^= mask[y];
}
/* compute MGF1 of seed (k - hlen - 1) */
if ((err = pkcs_1_mgf1(seed, hLen, hash_idx, mask, modulus_len - hLen - 1)) != CRYPT_OK) {
goto LBL_ERR;
}
/* xor against DB */
for (y = 0; y < (modulus_len - hLen - 1); y++) {
DB[y] ^= mask[y];
}
/* now DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */
/* compute lhash and store it in seed [reuse temps!] */
x = modulus_len;
if (lparam != NULL) {
if ((err = hash_memory(hash_idx, lparam, lparamlen, seed, &x)) != CRYPT_OK) {
goto LBL_ERR;
}
} else {
/* can't pass hash_memory a NULL so use DB with zero length */
if ((err = hash_memory(hash_idx, DB, 0, seed, &x)) != CRYPT_OK) {
goto LBL_ERR;
}
}
/* compare the lhash'es */
if (memcmp(seed, DB, hLen) != 0) {
err = CRYPT_OK;
goto LBL_ERR;
}
/* now zeroes before a 0x01 */
for (x = hLen; x < (modulus_len - hLen - 1) && DB[x] == 0x00; x++) {
/* step... */
}
/* error out if wasn't 0x01 */
if (x == (modulus_len - hLen - 1) || DB[x] != 0x01) {
err = CRYPT_OK;
goto LBL_ERR;
}
/* rest is the message (and skip 0x01) */
if ((modulus_len - hLen - 1) - ++x > *outlen) {
err = CRYPT_BUFFER_OVERFLOW;
goto LBL_ERR;
}
/* copy message */
*outlen = (modulus_len - hLen - 1) - x;
XMEMCPY(out, DB + x, modulus_len - hLen - 1 - x);
x += modulus_len - hLen - 1;
/* valid packet */
*res = 1;
err = CRYPT_OK;
LBL_ERR:
#ifdef LTC_CLEAN_STACK
zeromem(DB, modulus_len);
zeromem(seed, hLen);
zeromem(mask, modulus_len);
#endif
XFREE(seed);
XFREE(mask);
XFREE(DB);
return err;
}
#endif /* PKCS_1 */
/* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_oaep_decode.c,v $ */
/* $Revision: 1.5 $ */
/* $Date: 2005/06/18 02:37:06 $ */
|
