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comparison src/pk/pkcs1/pkcs_1_oaep_decode.c @ 192:9cc34777b479 libtomcrypt

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propagate from branch 'au.asn.ucc.matt.ltc-orig' (head 9ba8f01f44320e9cb9f19881105ae84f84a43ea9) to branch 'au.asn.ucc.matt.dropbear.ltc' (head dbf51c569bc34956ad948e4cc87a0eeb2170b768)
author Matt Johnston <matt@ucc.asn.au>
date Sun, 08 May 2005 06:36:47 +0000
parents 1c15b283127b
children 39d5d58461d6
comparison
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164:cd1143579f00 192:9cc34777b479
1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 *
9 * Tom St Denis, [email protected], http://libtomcrypt.org
10 */
11 #include "tomcrypt.h"
12
13 /**
14 @file pkcs_1_oaep_decode.c
15 OAEP Padding for PKCS #1, Tom St Denis
16 */
17
18 #ifdef PKCS_1
19
20 /**
21 PKCS #1 v2.00 OAEP decode
22 @param msg The encoded data to decode
23 @param msglen The length of the encoded data (octets)
24 @param lparam The session or system data (can be NULL)
25 @param lparamlen The length of the lparam
26 @param modulus_bitlen The bit length of the RSA modulus
27 @param hash_idx The index of the hash desired
28 @param out [out] Destination of decoding
29 @param outlen [in/out] The max size and resulting size of the decoding
30 @param res [out] Result of decoding, 1==valid, 0==invalid
31 @return CRYPT_OK if successful (even if invalid)
32 */
33 int pkcs_1_oaep_decode(const unsigned char *msg, unsigned long msglen,
34 const unsigned char *lparam, unsigned long lparamlen,
35 unsigned long modulus_bitlen, int hash_idx,
36 unsigned char *out, unsigned long *outlen,
37 int *res)
38 {
39 unsigned char *DB, *seed, *mask;
40 unsigned long hLen, x, y, modulus_len;
41 int err;
42
43 LTC_ARGCHK(msg != NULL);
44 LTC_ARGCHK(out != NULL);
45 LTC_ARGCHK(outlen != NULL);
46 LTC_ARGCHK(res != NULL);
47
48 /* default to invalid packet */
49 *res = 0;
50
51 /* test valid hash */
52 if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
53 return err;
54 }
55 hLen = hash_descriptor[hash_idx].hashsize;
56 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
57
58 /* test hash/message size */
59 if ((2*hLen >= (modulus_len - 2)) || (msglen != modulus_len)) {
60 return CRYPT_PK_INVALID_SIZE;
61 }
62
63 /* allocate ram for DB/mask/salt of size modulus_len */
64 DB = XMALLOC(modulus_len);
65 mask = XMALLOC(modulus_len);
66 seed = XMALLOC(modulus_len);
67 if (DB == NULL || mask == NULL || seed == NULL) {
68 if (DB != NULL) {
69 XFREE(DB);
70 }
71 if (mask != NULL) {
72 XFREE(mask);
73 }
74 if (seed != NULL) {
75 XFREE(seed);
76 }
77 return CRYPT_MEM;
78 }
79
80 /* ok so it's now in the form
81
82 0x00 || maskedseed || maskedDB
83
84 1 || hLen || modulus_len - hLen - 1
85
86 */
87
88 /* must have leading 0x00 byte */
89 if (msg[0] != 0x00) {
90 err = CRYPT_OK;
91 goto LBL_ERR;
92 }
93
94 /* now read the masked seed */
95 for (x = 1, y = 0; y < hLen; y++) {
96 seed[y] = msg[x++];
97 }
98
99 /* now read the masked DB */
100 for (y = 0; y < modulus_len - hLen - 1; y++) {
101 DB[y] = msg[x++];
102 }
103
104 /* compute MGF1 of maskedDB (hLen) */
105 if ((err = pkcs_1_mgf1(DB, modulus_len - hLen - 1, hash_idx, mask, hLen)) != CRYPT_OK) {
106 goto LBL_ERR;
107 }
108
109 /* XOR against seed */
110 for (y = 0; y < hLen; y++) {
111 seed[y] ^= mask[y];
112 }
113
114 /* compute MGF1 of seed (k - hlen - 1) */
115 if ((err = pkcs_1_mgf1(seed, hLen, hash_idx, mask, modulus_len - hLen - 1)) != CRYPT_OK) {
116 goto LBL_ERR;
117 }
118
119 /* xor against DB */
120 for (y = 0; y < (modulus_len - hLen - 1); y++) {
121 DB[y] ^= mask[y];
122 }
123
124 /* now DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */
125
126 /* compute lhash and store it in seed [reuse temps!] */
127 x = modulus_len;
128 if (lparam != NULL) {
129 if ((err = hash_memory(hash_idx, lparam, lparamlen, seed, &x)) != CRYPT_OK) {
130 goto LBL_ERR;
131 }
132 } else {
133 /* can't pass hash_memory a NULL so use DB with zero length */
134 if ((err = hash_memory(hash_idx, DB, 0, seed, &x)) != CRYPT_OK) {
135 goto LBL_ERR;
136 }
137 }
138
139 /* compare the lhash'es */
140 if (memcmp(seed, DB, hLen) != 0) {
141 err = CRYPT_OK;
142 goto LBL_ERR;
143 }
144
145 /* now zeroes before a 0x01 */
146 for (x = hLen; x < (modulus_len - hLen - 1) && DB[x] == 0x00; x++) {
147 /* step... */
148 }
149
150 /* error out if wasn't 0x01 */
151 if (x == (modulus_len - hLen - 1) || DB[x] != 0x01) {
152 err = CRYPT_OK;
153 goto LBL_ERR;
154 }
155
156 /* rest is the message (and skip 0x01) */
157 if ((modulus_len - hLen - 1) - ++x > *outlen) {
158 err = CRYPT_BUFFER_OVERFLOW;
159 goto LBL_ERR;
160 }
161
162 /* copy message */
163 *outlen = (modulus_len - hLen - 1) - x;
164 for (y = 0; x != (modulus_len - hLen - 1); ) {
165 out[y++] = DB[x++];
166 }
167
168 /* valid packet */
169 *res = 1;
170
171 err = CRYPT_OK;
172 LBL_ERR:
173 #ifdef LTC_CLEAN_STACK
174 zeromem(DB, modulus_len);
175 zeromem(seed, modulus_len);
176 zeromem(mask, modulus_len);
177 #endif
178
179 XFREE(seed);
180 XFREE(mask);
181 XFREE(DB);
182
183 return err;
184 }
185
186 #endif /* PKCS_1 */