| /* 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@iahu.ca, http://libtomcrypt.org |
| */ |
| #include "mycrypt.h" |
| |
| /* PKCS #1 PSS Signature Padding -- Tom St Denis */ |
| |
| #ifdef PKCS_1 |
| |
| int pkcs_1_pss_decode(const unsigned char *msghash, unsigned long msghashlen, |
| const unsigned char *sig, unsigned long siglen, |
| unsigned long saltlen, int hash_idx, |
| unsigned long modulus_bitlen, int *res) |
| { |
| unsigned char *DB, *mask, *salt, *hash; |
| unsigned long x, y, hLen, modulus_len; |
| int err; |
| hash_state md; |
| |
| _ARGCHK(msghash != NULL); |
| _ARGCHK(res != NULL); |
| |
| /* default to invalid */ |
| *res = 0; |
| |
| /* ensure hash is valid */ |
| 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); |
| |
| /* allocate ram for DB/mask/salt/hash of size modulus_len */ |
| DB = XMALLOC(modulus_len); |
| mask = XMALLOC(modulus_len); |
| salt = XMALLOC(modulus_len); |
| hash = XMALLOC(modulus_len); |
| if (DB == NULL || mask == NULL || salt == NULL || hash == NULL) { |
| if (DB != NULL) { |
| XFREE(DB); |
| } |
| if (mask != NULL) { |
| XFREE(mask); |
| } |
| if (salt != NULL) { |
| XFREE(salt); |
| } |
| if (hash != NULL) { |
| XFREE(hash); |
| } |
| return CRYPT_MEM; |
| } |
| |
| /* check sizes */ |
| if ((saltlen > modulus_len) || |
| (modulus_len < hLen + saltlen + 2) || (siglen != modulus_len)) { |
| err = CRYPT_INVALID_ARG; |
| goto __ERR; |
| } |
| |
| /* ensure the 0xBC byte */ |
| if (sig[siglen-1] != 0xBC) { |
| err = CRYPT_OK; |
| goto __ERR; |
| } |
| |
| /* copy out the DB */ |
| for (x = 0; x < modulus_len - hLen - 1; x++) { |
| DB[x] = sig[x]; |
| } |
| |
| /* copy out the hash */ |
| for (y = 0; y < hLen; y++) { |
| hash[y] = sig[x++]; |
| } |
| |
| /* check the MSB */ |
| if ((sig[0] & ~(0xFF >> ((modulus_len<<3) - (modulus_bitlen-1)))) != 0) { |
| err = CRYPT_OK; |
| goto __ERR; |
| } |
| |
| /* generate mask of length modulus_len - hLen - 1 from hash */ |
| if ((err = pkcs_1_mgf1(hash, hLen, hash_idx, mask, modulus_len - hLen - 1)) != CRYPT_OK) { |
| goto __ERR; |
| } |
| |
| /* xor against DB */ |
| for (y = 0; y < (modulus_len - hLen - 1); y++) { |
| DB[y] ^= mask[y]; |
| } |
| |
| /* now clear the first byte [make sure smaller than modulus] */ |
| DB[0] &= 0xFF >> ((modulus_len<<3) - (modulus_bitlen-1)); |
| |
| /* DB = PS || 0x01 || salt, PS == modulus_len - saltlen - hLen - 2 zero bytes */ |
| |
| /* check for zeroes and 0x01 */ |
| for (x = 0; x < modulus_len - saltlen - hLen - 2; x++) { |
| if (DB[x] != 0x00) { |
| err = CRYPT_OK; |
| goto __ERR; |
| } |
| } |
| |
| /* check for the 0x01 */ |
| if (DB[x++] != 0x01) { |
| err = CRYPT_OK; |
| goto __ERR; |
| } |
| |
| /* M = (eight) 0x00 || msghash || salt, mask = H(M) */ |
| if ((err = hash_descriptor[hash_idx].init(&md)) != CRYPT_OK) { |
| goto __ERR; |
| } |
| zeromem(mask, 8); |
| if ((err = hash_descriptor[hash_idx].process(&md, mask, 8)) != CRYPT_OK) { |
| goto __ERR; |
| } |
| if ((err = hash_descriptor[hash_idx].process(&md, msghash, msghashlen)) != CRYPT_OK) { |
| goto __ERR; |
| } |
| if ((err = hash_descriptor[hash_idx].process(&md, DB+x, saltlen)) != CRYPT_OK) { |
| goto __ERR; |
| } |
| if ((err = hash_descriptor[hash_idx].done(&md, mask)) != CRYPT_OK) { |
| goto __ERR; |
| } |
| |
| /* mask == hash means valid signature */ |
| if (memcmp(mask, hash, hLen) == 0) { |
| *res = 1; |
| } |
| |
| err = CRYPT_OK; |
| __ERR: |
| #ifdef CLEAN_STACK |
| zeromem(DB, modulus_len); |
| zeromem(mask, modulus_len); |
| zeromem(salt, modulus_len); |
| zeromem(hash, modulus_len); |
| #endif |
| |
| XFREE(hash); |
| XFREE(salt); |
| XFREE(mask); |
| XFREE(DB); |
| |
| return err; |
| } |
| |
| #endif /* PKCS_1 */ |