--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dsa_verify_hash.c	Mon May 31 18:25:41 2004 +0000
@@ -0,0 +1,97 @@
+/* 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"
+
+#ifdef MDSA
+
+int dsa_verify_hash(const unsigned char *sig, unsigned long siglen,
+                    const unsigned char *hash, unsigned long inlen, 
+                    int *stat, dsa_key *key)
+{
+   mp_int r, s, w, v, u1, u2;
+   unsigned long x, y;
+   int err;
+
+   _ARGCHK(sig  != NULL);
+   _ARGCHK(hash != NULL);
+   _ARGCHK(stat != NULL);
+   _ARGCHK(key  != NULL);
+
+   /* default to invalid signature */
+   *stat = 0;
+
+   if (siglen < PACKET_SIZE+2+2) {
+      return CRYPT_INVALID_PACKET;
+   } 
+
+   /* is the message format correct? */
+   if ((err = packet_valid_header((unsigned char *)sig, PACKET_SECT_DSA, PACKET_SUB_SIGNED)) != CRYPT_OK) {
+      return err;
+   }
+
+   /* skip over header */
+   y = PACKET_SIZE;
+
+   /* init our variables */
+   if ((err = mp_init_multi(&r, &s, &w, &v, &u1, &u2, NULL)) != MP_OKAY) {
+      return mpi_to_ltc_error(err);
+   }
+
+   /* read in r followed by s */
+   x = ((unsigned)sig[y]<<8)|((unsigned)sig[y+1]);
+   y += 2;
+   if (y + x > siglen) { 
+      err = CRYPT_INVALID_PACKET;
+      goto done;
+   }
+   if ((err = mp_read_unsigned_bin(&r, (unsigned char *)sig+y, x)) != MP_OKAY)             { goto error; }
+   y += x;
+
+   /* load s */
+   x = ((unsigned)sig[y]<<8)|((unsigned)sig[y+1]);
+   y += 2;
+   if (y + x > siglen) { 
+      err = CRYPT_INVALID_PACKET;
+      goto done;
+   }
+   if ((err = mp_read_unsigned_bin(&s, (unsigned char *)sig+y, x)) != MP_OKAY)             { goto error; }
+
+   /* w = 1/s mod q */
+   if ((err = mp_invmod(&s, &key->q, &w)) != MP_OKAY)                                      { goto error; }
+
+   /* u1 = m * w mod q */
+   if ((err = mp_read_unsigned_bin(&u1, (unsigned char *)hash, inlen)) != MP_OKAY)         { goto error; }
+   if ((err = mp_mulmod(&u1, &w, &key->q, &u1)) != MP_OKAY)                                { goto error; }
+
+   /* u2 = r*w mod q */
+   if ((err = mp_mulmod(&r, &w, &key->q, &u2)) != MP_OKAY)                                 { goto error; } 
+
+   /* v = g^u1 * y^u2 mod p mod q */
+   if ((err = mp_exptmod(&key->g, &u1, &key->p, &u1)) != MP_OKAY)                          { goto error; }
+   if ((err = mp_exptmod(&key->y, &u2, &key->p, &u2)) != MP_OKAY)                          { goto error; }
+   if ((err = mp_mulmod(&u1, &u2, &key->p, &v)) != MP_OKAY)                                { goto error; }
+   if ((err = mp_mod(&v, &key->q, &v)) != MP_OKAY)                                         { goto error; }
+
+   /* if r = v then we're set */
+   if (mp_cmp(&r, &v) == MP_EQ) {
+      *stat = 1;
+   }
+
+   err = CRYPT_OK;
+   goto done;
+
+error : err = mpi_to_ltc_error(err);
+done  : mp_clear_multi(&r, &s, &w, &v, &u1, &u2, NULL);
+   return err;
+}
+
+#endif
+