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/* 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@gmail.com, http://libtomcrypt.org
*/
#include "tomcrypt.h"
/**
@file pkcs_1_pss_decode.c
PKCS #1 PSS Signature Padding, Tom St Denis
*/
#ifdef PKCS_1
/**
PKCS #1 v2.00 PSS decode
@param msghash The hash to verify
@param msghashlen The length of the hash (octets)
@param sig The signature data (encoded data)
@param siglen The length of the signature data (octets)
@param saltlen The length of the salt used (octets)
@param hash_idx The index of the hash desired
@param modulus_bitlen The bit length of the RSA modulus
@param res [out] The result of the comparison, 1==valid, 0==invalid
@return CRYPT_OK if successful (even if the comparison failed)
*/
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;
LTC_ARGCHK(msghash != NULL);
LTC_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);
/* check sizes */
if ((saltlen > modulus_len) ||
(modulus_len < hLen + saltlen + 2) || (siglen != modulus_len)) {
return CRYPT_PK_INVALID_SIZE;
}
/* 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;
}
/* ensure the 0xBC byte */
if (sig[siglen-1] != 0xBC) {
err = CRYPT_OK;
goto LBL_ERR;
}
/* copy out the DB */
x = 0;
XMEMCPY(DB, sig + x, modulus_len - hLen - 1);
x += modulus_len - hLen - 1;
/* copy out the hash */
XMEMCPY(hash, sig + x, hLen);
x += hLen;
/* check the MSB */
if ((sig[0] & ~(0xFF >> ((modulus_len<<3) - (modulus_bitlen-1)))) != 0) {
err = CRYPT_OK;
goto LBL_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 LBL_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 LBL_ERR;
}
}
/* check for the 0x01 */
if (DB[x++] != 0x01) {
err = CRYPT_OK;
goto LBL_ERR;
}
/* M = (eight) 0x00 || msghash || salt, mask = H(M) */
if ((err = hash_descriptor[hash_idx].init(&md)) != CRYPT_OK) {
goto LBL_ERR;
}
zeromem(mask, 8);
if ((err = hash_descriptor[hash_idx].process(&md, mask, 8)) != CRYPT_OK) {
goto LBL_ERR;
}
if ((err = hash_descriptor[hash_idx].process(&md, msghash, msghashlen)) != CRYPT_OK) {
goto LBL_ERR;
}
if ((err = hash_descriptor[hash_idx].process(&md, DB+x, saltlen)) != CRYPT_OK) {
goto LBL_ERR;
}
if ((err = hash_descriptor[hash_idx].done(&md, mask)) != CRYPT_OK) {
goto LBL_ERR;
}
/* mask == hash means valid signature */
if (memcmp(mask, hash, hLen) == 0) {
*res = 1;
}
err = CRYPT_OK;
LBL_ERR:
#ifdef LTC_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 */
/* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_pss_decode.c,v $ */
/* $Revision: 1.4 $ */
/* $Date: 2005/05/05 14:35:59 $ */
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