--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pkcs_1_pss_decode.c	Mon May 31 18:21:40 2004 +0000
@@ -0,0 +1,121 @@
+/* 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 "mycrypt.h"
+
+/* PKCS #1 PSS Signature Padding -- Tom St Denis */
+
+#ifdef PKCS_1
+
+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[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))) != 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];
+   }
+
+   /* 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 */