--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtomcrypt/src/pk/dsa/dsa_verify_key.c	Thu Jan 11 03:14:55 2007 +0000
@@ -0,0 +1,100 @@
+/* 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.com
+ */
+#include "tomcrypt.h"
+
+/**
+   @file dsa_verify_key.c
+   DSA implementation, verify a key, Tom St Denis
+*/
+
+#ifdef MDSA
+
+/**
+   Verify a DSA key for validity
+   @param key   The key to verify
+   @param stat  [out]  Result of test, 1==valid, 0==invalid
+   @return CRYPT_OK if successful
+*/
+int dsa_verify_key(dsa_key *key, int *stat)
+{
+   void   *tmp, *tmp2;
+   int    res, err;
+
+   LTC_ARGCHK(key  != NULL);
+   LTC_ARGCHK(stat != NULL);
+
+   /* default to an invalid key */
+   *stat = 0;
+
+   /* first make sure key->q and key->p are prime */
+   if ((err = mp_prime_is_prime(key->q, 8, &res)) != CRYPT_OK) {
+      return err;
+   }
+   if (res == 0) {
+      return CRYPT_OK;
+   }
+
+   if ((err = mp_prime_is_prime(key->p, 8, &res)) != CRYPT_OK) {
+      return err;
+   }
+   if (res == 0) {
+      return CRYPT_OK;
+   }
+
+   /* now make sure that g is not -1, 0 or 1 and <p */
+   if (mp_cmp_d(key->g, 0) == LTC_MP_EQ || mp_cmp_d(key->g, 1) == LTC_MP_EQ) {
+      return CRYPT_OK;
+   }
+   if ((err = mp_init_multi(&tmp, &tmp2, NULL)) != CRYPT_OK)               { return err; }
+   if ((err = mp_sub_d(key->p, 1, tmp)) != CRYPT_OK)                       { goto error; }
+   if (mp_cmp(tmp, key->g) == LTC_MP_EQ || mp_cmp(key->g, key->p) != LTC_MP_LT) {
+      err = CRYPT_OK;
+      goto error;
+   }
+
+   /* 1 < y < p-1 */
+   if (!(mp_cmp_d(key->y, 1) == LTC_MP_GT && mp_cmp(key->y, tmp) == LTC_MP_LT)) {
+      err = CRYPT_OK;
+      goto error;
+   }
+
+   /* now we have to make sure that g^q = 1, and that p-1/q gives 0 remainder */
+   if ((err = mp_div(tmp, key->q, tmp, tmp2)) != CRYPT_OK)             { goto error; }
+   if (mp_iszero(tmp2) != LTC_MP_YES) {
+      err = CRYPT_OK;
+      goto error;
+   }
+
+   if ((err = mp_exptmod(key->g, key->q, key->p, tmp)) != CRYPT_OK)    { goto error; }
+   if (mp_cmp_d(tmp, 1) != LTC_MP_EQ) {
+      err = CRYPT_OK;
+      goto error;
+   }
+
+   /* now we have to make sure that y^q = 1, this makes sure y \in g^x mod p */
+   if ((err = mp_exptmod(key->y, key->q, key->p, tmp)) != CRYPT_OK)       { goto error; }
+   if (mp_cmp_d(tmp, 1) != LTC_MP_EQ) {
+      err = CRYPT_OK;
+      goto error;
+   }
+
+   /* at this point we are out of tests ;-( */
+   err   = CRYPT_OK;
+   *stat = 1;
+error: 
+   mp_clear_multi(tmp, tmp2, NULL);
+   return err;
+}
+#endif
+
+/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_verify_key.c,v $ */
+/* $Revision: 1.6 $ */
+/* $Date: 2006/12/04 03:18:43 $ */