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 #include "tomcrypt.h"
10
11 /**
12 @file pkcs_1_oaep_decode.c
13 OAEP Padding for PKCS #1, Tom St Denis
14 */
15
16 #ifdef LTC_PKCS_1
17
18 /**
19 PKCS #1 v2.00 OAEP decode
20 @param msg The encoded data to decode
21 @param msglen The length of the encoded data (octets)
22 @param lparam The session or system data (can be NULL)
23 @param lparamlen The length of the lparam
24 @param modulus_bitlen The bit length of the RSA modulus
25 @param hash_idx The index of the hash desired
26 @param out [out] Destination of decoding
27 @param outlen [in/out] The max size and resulting size of the decoding
28 @param res [out] Result of decoding, 1==valid, 0==invalid
29 @return CRYPT_OK if successful
30 */
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)31 int pkcs_1_oaep_decode(const unsigned char *msg, unsigned long msglen,
32 const unsigned char *lparam, unsigned long lparamlen,
33 unsigned long modulus_bitlen, int hash_idx,
34 unsigned char *out, unsigned long *outlen,
35 int *res)
36 {
37 unsigned char *DB, *seed, *mask;
38 unsigned long hLen, x, y, modulus_len;
39 int err, ret;
40
41 LTC_ARGCHK(msg != NULL);
42 LTC_ARGCHK(out != NULL);
43 LTC_ARGCHK(outlen != NULL);
44 LTC_ARGCHK(res != NULL);
45
46 /* default to invalid packet */
47 *res = 0;
48
49 /* test valid hash */
50 if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
51 return err;
52 }
53 hLen = hash_descriptor[hash_idx].hashsize;
54 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
55
56 /* test hash/message size */
57 if ((2*hLen >= (modulus_len - 2)) || (msglen != modulus_len)) {
58 return CRYPT_PK_INVALID_SIZE;
59 }
60
61 /* allocate ram for DB/mask/salt of size modulus_len */
62 DB = XMALLOC(modulus_len);
63 mask = XMALLOC(modulus_len);
64 seed = XMALLOC(hLen);
65 if (DB == NULL || mask == NULL || seed == NULL) {
66 if (DB != NULL) {
67 XFREE(DB);
68 }
69 if (mask != NULL) {
70 XFREE(mask);
71 }
72 if (seed != NULL) {
73 XFREE(seed);
74 }
75 return CRYPT_MEM;
76 }
77
78 /* ok so it's now in the form
79
80 0x00 || maskedseed || maskedDB
81
82 1 || hLen || modulus_len - hLen - 1
83
84 */
85
86 ret = CRYPT_OK;
87
88 /* must have leading 0x00 byte */
89 if (msg[0] != 0x00) {
90 ret = CRYPT_INVALID_PACKET;
91 }
92
93 /* now read the masked seed */
94 x = 1;
95 XMEMCPY(seed, msg + x, hLen);
96 x += hLen;
97
98 /* now read the masked DB */
99 XMEMCPY(DB, msg + x, modulus_len - hLen - 1);
100 x += modulus_len - hLen - 1;
101
102 /* compute MGF1 of maskedDB (hLen) */
103 if ((err = pkcs_1_mgf1(hash_idx, DB, modulus_len - hLen - 1, mask, hLen)) != CRYPT_OK) {
104 goto LBL_ERR;
105 }
106
107 /* XOR against seed */
108 for (y = 0; y < hLen; y++) {
109 seed[y] ^= mask[y];
110 }
111
112 /* compute MGF1 of seed (k - hlen - 1) */
113 if ((err = pkcs_1_mgf1(hash_idx, seed, hLen, mask, modulus_len - hLen - 1)) != CRYPT_OK) {
114 goto LBL_ERR;
115 }
116
117 /* xor against DB */
118 for (y = 0; y < (modulus_len - hLen - 1); y++) {
119 DB[y] ^= mask[y];
120 }
121
122 /* now DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */
123
124 /* compute lhash and store it in seed [reuse temps!] */
125 x = modulus_len;
126 if (lparam != NULL) {
127 if ((err = hash_memory(hash_idx, lparam, lparamlen, seed, &x)) != CRYPT_OK) {
128 goto LBL_ERR;
129 }
130 } else {
131 /* can't pass hash_memory a NULL so use DB with zero length */
132 if ((err = hash_memory(hash_idx, DB, 0, seed, &x)) != CRYPT_OK) {
133 goto LBL_ERR;
134 }
135 }
136
137 /* compare the lhash'es */
138 if (XMEM_NEQ(seed, DB, hLen) != 0) {
139 ret = CRYPT_INVALID_PACKET;
140 }
141
142 /* now zeroes before a 0x01 */
143 for (x = hLen; x < (modulus_len - hLen - 1) && DB[x] == 0x00; x++) {
144 /* step... */
145 }
146
147 /* error if wasn't 0x01 */
148 if (x == (modulus_len - hLen - 1) || DB[x] != 0x01) {
149 ret = CRYPT_INVALID_PACKET;
150 }
151
152 /* rest is the message (and skip 0x01) */
153 if ((modulus_len - hLen - 1 - ++x) > *outlen) {
154 ret = CRYPT_INVALID_PACKET;
155 }
156
157 if (ret == CRYPT_OK) {
158 /* copy message */
159 *outlen = modulus_len - hLen - 1 - x;
160 XMEMCPY(out, DB + x, modulus_len - hLen - 1 - x);
161
162 /* valid packet */
163 *res = 1;
164 }
165 err = ret;
166
167 LBL_ERR:
168 #ifdef LTC_CLEAN_STACK
169 zeromem(DB, modulus_len);
170 zeromem(seed, hLen);
171 zeromem(mask, modulus_len);
172 #endif
173
174 XFREE(seed);
175 XFREE(mask);
176 XFREE(DB);
177
178 return err;
179 }
180
181 #endif /* LTC_PKCS_1 */
182
183 /* ref: HEAD -> master, tag: v1.18.2 */
184 /* git commit: 7e7eb695d581782f04b24dc444cbfde86af59853 */
185 /* commit time: 2018-07-01 22:49:01 +0200 */
186