--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtomcrypt/src/pk/pkcs1/pkcs_1_pss_decode.c	Sat Mar 25 12:59:58 2006 +0000
@@ -0,0 +1,177 @@
+/* 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, [email protected], 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 $ */