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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.com
*/
#include "tomcrypt.h"
/**
@file pkcs_1_pss_encode.c
PKCS #1 PSS Signature Padding, Tom St Denis
*/
#ifdef PKCS_1
/**
PKCS #1 v2.00 Signature Encoding
@param msghash The hash to encode
@param msghashlen The length of the hash (octets)
@param saltlen The length of the salt desired (octets)
@param prng An active PRNG context
@param prng_idx The index of the PRNG desired
@param hash_idx The index of the hash desired
@param modulus_bitlen The bit length of the RSA modulus
@param out [out] The destination of the encoding
@param outlen [in/out] The max size and resulting size of the encoded data
@return CRYPT_OK if successful
*/
int pkcs_1_pss_encode(const unsigned char *msghash, unsigned long msghashlen,
unsigned long saltlen, prng_state *prng,
int prng_idx, int hash_idx,
unsigned long modulus_bitlen,
unsigned char *out, unsigned long *outlen)
{
unsigned char *DB, *mask, *salt, *hash;
unsigned long x, y, hLen, modulus_len;
int err;
hash_state md;
LTC_ARGCHK(msghash != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
/* ensure hash and PRNG are valid */
if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
return err;
}
if ((err = prng_is_valid(prng_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)) {
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;
}
/* generate random salt */
if (saltlen > 0) {
if (prng_descriptor[prng_idx].read(salt, saltlen, prng) != saltlen) {
err = CRYPT_ERROR_READPRNG;
goto LBL_ERR;
}
}
/* M = (eight) 0x00 || msghash || salt, hash = H(M) */
if ((err = hash_descriptor[hash_idx].init(&md)) != CRYPT_OK) {
goto LBL_ERR;
}
zeromem(DB, 8);
if ((err = hash_descriptor[hash_idx].process(&md, DB, 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, salt, saltlen)) != CRYPT_OK) {
goto LBL_ERR;
}
if ((err = hash_descriptor[hash_idx].done(&md, hash)) != CRYPT_OK) {
goto LBL_ERR;
}
/* generate DB = PS || 0x01 || salt, PS == modulus_len - saltlen - hLen - 2 zero bytes */
x = 0;
XMEMSET(DB + x, 0, modulus_len - saltlen - hLen - 2);
x += modulus_len - saltlen - hLen - 2;
DB[x++] = 0x01;
XMEMCPY(DB + x, salt, saltlen);
x += saltlen;
/* generate mask of length modulus_len - hLen - 1 from hash */
if ((err = pkcs_1_mgf1(hash_idx, hash, hLen, 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];
}
/* output is DB || hash || 0xBC */
if (*outlen < modulus_len) {
*outlen = modulus_len;
err = CRYPT_BUFFER_OVERFLOW;
goto LBL_ERR;
}
/* DB len = modulus_len - hLen - 1 */
y = 0;
XMEMCPY(out + y, DB, modulus_len - hLen - 1);
y += modulus_len - hLen - 1;
/* hash */
XMEMCPY(out + y, hash, hLen);
y += hLen;
/* 0xBC */
out[y] = 0xBC;
/* now clear the 8*modulus_len - modulus_bitlen most significant bits */
out[0] &= 0xFF >> ((modulus_len<<3) - (modulus_bitlen-1));
/* store output size */
*outlen = modulus_len;
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_encode.c,v $ */
/* $Revision: 1.7 $ */
/* $Date: 2006/06/16 21:53:41 $ */
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