/* 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_1int 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[1024], mask[sizeof(DB)], salt[sizeof(DB)], hash[sizeof(DB)];   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);   /* check sizes */   if ((saltlen > sizeof(salt)) || (modulus_len > sizeof(DB)) ||        (modulus_len < hLen + saltlen + 2) || (siglen != modulus_len)) {      return CRYPT_INVALID_ARG;   }   /* ensure the 0xBC byte */   if (sig[siglen-1] != 0xBC) {      return CRYPT_OK;   }   /* 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) {      return CRYPT_OK;   }   /* 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) {      return 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) {          return CRYPT_OK;       }   }   if (DB[x++] != 0x01) {      return CRYPT_OK;   }   /* M = (eight) 0x00 || msghash || salt, mask = H(M) */   hash_descriptor[hash_idx].init(&md);   zeromem(mask, 8);   if ((err = hash_descriptor[hash_idx].process(&md, mask, 8)) != CRYPT_OK) {      return err;   }   if ((err = hash_descriptor[hash_idx].process(&md, msghash, msghashlen)) != CRYPT_OK) {      return err;   }   if ((err = hash_descriptor[hash_idx].process(&md, DB+x, saltlen)) != CRYPT_OK) {      return err;   }   if ((err = hash_descriptor[hash_idx].done(&md, mask)) != CRYPT_OK) {      return err;   }   /* mask == hash means valid signature */   if (memcmp(mask, hash, hLen) == 0) {      *res = 1;   }#ifdef CLEAN_STACK   zeromem(DB,   sizeof(DB));      zeromem(mask, sizeof(mask));      zeromem(salt, sizeof(salt));      zeromem(hash, sizeof(hash));   #endif   return CRYPT_OK;}#endif /* PKCS_1 */