159 lines
4.0 KiB
C
159 lines
4.0 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://libtomcrypt.org
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*/
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#include "mycrypt.h"
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/* PKCS #1 PSS Signature Padding -- Tom St Denis */
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#ifdef PKCS_1
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int pkcs_1_pss_decode(const unsigned char *msghash, unsigned long msghashlen,
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const unsigned char *sig, unsigned long siglen,
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unsigned long saltlen, int hash_idx,
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unsigned long modulus_bitlen, int *res)
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{
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unsigned char *DB, *mask, *salt, *hash;
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unsigned long x, y, hLen, modulus_len;
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int err;
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hash_state md;
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_ARGCHK(msghash != NULL);
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_ARGCHK(res != NULL);
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/* default to invalid */
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*res = 0;
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/* ensure hash is valid */
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if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
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return err;
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}
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hLen = hash_descriptor[hash_idx].hashsize;
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modulus_len = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0);
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/* allocate ram for DB/mask/salt/hash of size modulus_len */
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DB = XMALLOC(modulus_len);
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mask = XMALLOC(modulus_len);
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salt = XMALLOC(modulus_len);
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hash = XMALLOC(modulus_len);
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if (DB == NULL || mask == NULL || salt == NULL || hash == NULL) {
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if (DB != NULL) {
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XFREE(DB);
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}
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if (mask != NULL) {
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XFREE(mask);
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}
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if (salt != NULL) {
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XFREE(salt);
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}
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if (hash != NULL) {
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XFREE(hash);
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}
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return CRYPT_MEM;
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}
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/* check sizes */
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if ((saltlen > modulus_len) ||
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(modulus_len < hLen + saltlen + 2) || (siglen != modulus_len)) {
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err = CRYPT_INVALID_ARG;
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goto __ERR;
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}
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/* ensure the 0xBC byte */
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if (sig[siglen-1] != 0xBC) {
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err = CRYPT_OK;
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goto __ERR;
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}
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/* copy out the DB */
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for (x = 0; x < modulus_len - hLen - 1; x++) {
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DB[x] = sig[x];
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}
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/* copy out the hash */
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for (y = 0; y < hLen; y++) {
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hash[y] = sig[x++];
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}
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/* check the MSB */
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if ((sig[0] & ~(0xFF >> ((modulus_len<<3) - (modulus_bitlen-1)))) != 0) {
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err = CRYPT_OK;
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goto __ERR;
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}
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/* generate mask of length modulus_len - hLen - 1 from hash */
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if ((err = pkcs_1_mgf1(hash, hLen, hash_idx, mask, modulus_len - hLen - 1)) != CRYPT_OK) {
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goto __ERR;
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}
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/* xor against DB */
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for (y = 0; y < (modulus_len - hLen - 1); y++) {
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DB[y] ^= mask[y];
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}
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/* now clear the first byte [make sure smaller than modulus] */
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DB[0] &= 0xFF >> ((modulus_len<<3) - (modulus_bitlen-1));
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/* DB = PS || 0x01 || salt, PS == modulus_len - saltlen - hLen - 2 zero bytes */
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/* check for zeroes and 0x01 */
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for (x = 0; x < modulus_len - saltlen - hLen - 2; x++) {
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if (DB[x] != 0x00) {
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err = CRYPT_OK;
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goto __ERR;
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}
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}
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/* check for the 0x01 */
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if (DB[x++] != 0x01) {
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err = CRYPT_OK;
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goto __ERR;
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}
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/* M = (eight) 0x00 || msghash || salt, mask = H(M) */
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hash_descriptor[hash_idx].init(&md);
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zeromem(mask, 8);
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if ((err = hash_descriptor[hash_idx].process(&md, mask, 8)) != CRYPT_OK) {
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goto __ERR;
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}
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if ((err = hash_descriptor[hash_idx].process(&md, msghash, msghashlen)) != CRYPT_OK) {
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goto __ERR;
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}
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if ((err = hash_descriptor[hash_idx].process(&md, DB+x, saltlen)) != CRYPT_OK) {
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goto __ERR;
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}
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if ((err = hash_descriptor[hash_idx].done(&md, mask)) != CRYPT_OK) {
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goto __ERR;
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}
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/* mask == hash means valid signature */
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if (memcmp(mask, hash, hLen) == 0) {
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*res = 1;
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}
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err = CRYPT_OK;
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__ERR:
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#ifdef CLEAN_STACK
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zeromem(DB, modulus_len);
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zeromem(mask, modulus_len);
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zeromem(salt, modulus_len);
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zeromem(hash, modulus_len);
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#endif
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XFREE(hash);
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XFREE(salt);
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XFREE(mask);
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XFREE(DB);
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return err;
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}
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#endif /* PKCS_1 */
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