1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
6 * The library is free for all purposes without any express
9 * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
14 @file pkcs_1_pss_encode.c
15 PKCS #1 PSS Signature Padding, Tom St Denis
21 PKCS #1 v2.00 Signature Encoding
22 @param msghash The hash to encode
23 @param msghashlen The length of the hash (octets)
24 @param saltlen The length of the salt desired (octets)
25 @param prng An active PRNG context
26 @param prng_idx The index of the PRNG desired
27 @param hash_idx The index of the hash desired
28 @param modulus_bitlen The bit length of the RSA modulus
29 @param out [out] The destination of the encoding
30 @param outlen [in/out] The max size and resulting size of the encoded data
31 @return CRYPT_OK if successful
33 int pkcs_1_pss_encode(const unsigned char *msghash, unsigned long msghashlen,
34 unsigned long saltlen, prng_state *prng,
35 int prng_idx, int hash_idx,
36 unsigned long modulus_bitlen,
37 unsigned char *out, unsigned long *outlen)
39 unsigned char *DB, *mask, *salt, *hash;
40 unsigned long x, y, hLen, modulus_len;
44 LTC_ARGCHK(msghash != NULL);
45 LTC_ARGCHK(out != NULL);
46 LTC_ARGCHK(outlen != NULL);
48 /* ensure hash and PRNG are valid */
49 if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
52 if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {
56 hLen = hash_descriptor[hash_idx].hashsize;
57 modulus_len = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0);
60 if ((saltlen > modulus_len) || (modulus_len < hLen + saltlen + 2)) {
61 return CRYPT_PK_INVALID_SIZE;
64 /* allocate ram for DB/mask/salt/hash of size modulus_len */
65 DB = XMALLOC(modulus_len);
66 mask = XMALLOC(modulus_len);
67 salt = XMALLOC(modulus_len);
68 hash = XMALLOC(modulus_len);
69 if (DB == NULL || mask == NULL || salt == NULL || hash == NULL) {
86 /* generate random salt */
88 if (prng_descriptor[prng_idx].read(salt, saltlen, prng) != saltlen) {
89 err = CRYPT_ERROR_READPRNG;
94 /* M = (eight) 0x00 || msghash || salt, hash = H(M) */
95 if ((err = hash_descriptor[hash_idx].init(&md)) != CRYPT_OK) {
99 if ((err = hash_descriptor[hash_idx].process(&md, DB, 8)) != CRYPT_OK) {
102 if ((err = hash_descriptor[hash_idx].process(&md, msghash, msghashlen)) != CRYPT_OK) {
105 if ((err = hash_descriptor[hash_idx].process(&md, salt, saltlen)) != CRYPT_OK) {
108 if ((err = hash_descriptor[hash_idx].done(&md, hash)) != CRYPT_OK) {
112 /* generate DB = PS || 0x01 || salt, PS == modulus_len - saltlen - hLen - 2 zero bytes */
114 XMEMSET(DB + x, 0, modulus_len - saltlen - hLen - 2);
115 x += modulus_len - saltlen - hLen - 2;
117 XMEMCPY(DB + x, salt, saltlen);
120 /* generate mask of length modulus_len - hLen - 1 from hash */
121 if ((err = pkcs_1_mgf1(hash_idx, hash, hLen, mask, modulus_len - hLen - 1)) != CRYPT_OK) {
126 for (y = 0; y < (modulus_len - hLen - 1); y++) {
130 /* output is DB || hash || 0xBC */
131 if (*outlen < modulus_len) {
132 *outlen = modulus_len;
133 err = CRYPT_BUFFER_OVERFLOW;
137 /* DB len = modulus_len - hLen - 1 */
139 XMEMCPY(out + y, DB, modulus_len - hLen - 1);
140 y += modulus_len - hLen - 1;
143 XMEMCPY(out + y, hash, hLen);
149 /* now clear the 8*modulus_len - modulus_bitlen most significant bits */
150 out[0] &= 0xFF >> ((modulus_len<<3) - (modulus_bitlen-1));
152 /* store output size */
153 *outlen = modulus_len;
156 #ifdef LTC_CLEAN_STACK
157 zeromem(DB, modulus_len);
158 zeromem(mask, modulus_len);
159 zeromem(salt, modulus_len);
160 zeromem(hash, modulus_len);
173 /* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_pss_encode.c,v $ */
174 /* $Revision: 1.7 $ */
175 /* $Date: 2006/06/16 21:53:41 $ */