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, tomstdenis (at) gmail.com, http://libtomcrypt.com 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(hLen); 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 x = 1; 96 XMEMCPY(seed, msg + x, hLen); 97 x += hLen; 98 99 /* now read the masked DB */ 100 XMEMCPY(DB, msg + x, modulus_len - hLen - 1); 101 x += modulus_len - hLen - 1; 102 103 /* compute MGF1 of maskedDB (hLen) */ 104 if ((err = pkcs_1_mgf1(hash_idx, DB, modulus_len - hLen - 1, mask, hLen)) != CRYPT_OK) { 105 goto LBL_ERR; 106 } 107 108 /* XOR against seed */ 109 for (y = 0; y < hLen; y++) { 110 seed[y] ^= mask[y]; 111 } 112 113 /* compute MGF1 of seed (k - hlen - 1) */ 114 if ((err = pkcs_1_mgf1(hash_idx, seed, hLen, mask, modulus_len - hLen - 1)) != CRYPT_OK) { 115 goto LBL_ERR; 116 } 117 118 /* xor against DB */ 119 for (y = 0; y < (modulus_len - hLen - 1); y++) { 120 DB[y] ^= mask[y]; 121 } 122 123 /* now DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */ 124 125 /* compute lhash and store it in seed [reuse temps!] */ 126 x = modulus_len; 127 if (lparam != NULL) { 128 if ((err = hash_memory(hash_idx, lparam, lparamlen, seed, &x)) != CRYPT_OK) { 129 goto LBL_ERR; 130 } 131 } else { 132 /* can't pass hash_memory a NULL so use DB with zero length */ 133 if ((err = hash_memory(hash_idx, DB, 0, seed, &x)) != CRYPT_OK) { 134 goto LBL_ERR; 135 } 136 } 137 138 /* compare the lhash'es */ 139 if (XMEMCMP(seed, DB, hLen) != 0) { 140 err = CRYPT_OK; 141 goto LBL_ERR; 142 } 143 144 /* now zeroes before a 0x01 */ 145 for (x = hLen; x < (modulus_len - hLen - 1) && DB[x] == 0x00; x++) { 146 /* step... */ 147 } 148 149 /* error out if wasn't 0x01 */ 150 if (x == (modulus_len - hLen - 1) || DB[x] != 0x01) { 151 err = CRYPT_INVALID_PACKET; 152 goto LBL_ERR; 153 } 154 155 /* rest is the message (and skip 0x01) */ 156 if ((modulus_len - hLen - 1 - ++x) > *outlen) { 157 *outlen = modulus_len - hLen - 1 - x; 158 err = CRYPT_BUFFER_OVERFLOW; 159 goto LBL_ERR; 160 } 161 162 /* copy message */ 163 *outlen = modulus_len - hLen - 1 - x; 164 XMEMCPY(out, DB + x, modulus_len - hLen - 1 - x); 165 x += modulus_len - hLen - 1; 166 167 /* valid packet */ 168 *res = 1; 169 170 err = CRYPT_OK; 171 LBL_ERR: 172 #ifdef LTC_CLEAN_STACK 173 zeromem(DB, modulus_len); 174 zeromem(seed, hLen); 175 zeromem(mask, modulus_len); 176 #endif 177 178 XFREE(seed); 179 XFREE(mask); 180 XFREE(DB); 181 182 return err; 183 } 184 185 #endif /* PKCS_1 */ 186 187 /* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_oaep_decode.c,v $ */ 188 /* $Revision: 1.11 $ */ 189 /* $Date: 2006/11/01 09:28:17 $ */ 190
