--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dsa_make_key.c	Mon May 31 18:21:40 2004 +0000
@@ -0,0 +1,117 @@
+/* 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_make_key(prng_state *prng, int wprng, int group_size, int modulus_size, dsa_key *key)
+{
+   mp_int tmp, tmp2;
+   int err, res;
+   unsigned char buf[512];
+
+   _ARGCHK(key  != NULL);
+
+   /* check prng */
+   if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
+      return err;
+   }
+
+   /* check size */
+   if (group_size >= 1024 || group_size <= 15 || 
+       group_size >= modulus_size || (modulus_size - group_size) >= (int)sizeof(buf)) {
+      return CRYPT_INVALID_ARG;
+   }
+
+   /* init mp_ints  */
+   if ((err = mp_init_multi(&tmp, &tmp2, &key->g, &key->q, &key->p, &key->x, &key->y, NULL)) != MP_OKAY) {
+      return mpi_to_ltc_error(err);
+   }
+
+   /* make our prime q */
+   if ((err = rand_prime(&key->q, group_size*8, prng, wprng)) != CRYPT_OK)             { goto error2; }
+
+   /* double q  */
+   if ((err = mp_mul_2(&key->q, &tmp)) != MP_OKAY)                                   { goto error; }
+
+   /* now make a random string and multply it against q */
+   if (prng_descriptor[wprng].read(buf+1, modulus_size - group_size, prng) != (unsigned long)(modulus_size - group_size)) {
+      err = CRYPT_ERROR_READPRNG;
+      goto error2;
+   }
+
+   /* force magnitude */
+   buf[0] = 1;
+
+   /* force even */
+   buf[modulus_size - group_size] &= ~1;
+
+   if ((err = mp_read_unsigned_bin(&tmp2, buf, modulus_size - group_size+1)) != MP_OKAY) { goto error; }
+   if ((err = mp_mul(&key->q, &tmp2, &key->p)) != MP_OKAY)                             { goto error; }
+   if ((err = mp_add_d(&key->p, 1, &key->p)) != MP_OKAY)                               { goto error; }
+   
+   /* now loop until p is prime */
+   for (;;) {
+       if ((err = is_prime(&key->p, &res)) != CRYPT_OK)                                { goto error2; }
+       if (res == MP_YES) break;
+
+       /* add 2q to p and 2 to tmp2 */
+       if ((err = mp_add(&tmp, &key->p, &key->p)) != MP_OKAY)                          { goto error; }
+       if ((err = mp_add_d(&tmp2, 2, &tmp2)) != MP_OKAY)                               { goto error; }
+   }
+
+   /* now p = (q * tmp2) + 1 is prime, find a value g for which g^tmp2 != 1 */
+   mp_set(&key->g, 1);
+
+   do {
+      if ((err = mp_add_d(&key->g, 1, &key->g)) != MP_OKAY)                            { goto error; }
+      if ((err = mp_exptmod(&key->g, &tmp2, &key->p, &tmp)) != MP_OKAY)                { goto error; }
+   } while (mp_cmp_d(&tmp, 1) == MP_EQ);
+
+   /* at this point tmp generates a group of order q mod p */
+   mp_exch(&tmp, &key->g);
+
+   /* so now we have our DH structure, generator g, order q, modulus p 
+      Now we need a random exponent [mod q] and it's power g^x mod p 
+    */
+   do {
+      if (prng_descriptor[wprng].read(buf, group_size, prng) != (unsigned long)group_size) {
+         err = CRYPT_ERROR_READPRNG;
+         goto error2;
+      }
+      if ((err = mp_read_unsigned_bin(&key->x, buf, group_size)) != MP_OKAY)           { goto error; }
+   } while (mp_cmp_d(&key->x, 1) != MP_GT);
+   if ((err = mp_exptmod(&key->g, &key->x, &key->p, &key->y)) != MP_OKAY)              { goto error; }
+   
+   key->type = PK_PRIVATE;
+   key->qord = group_size;
+
+   /* shrink the ram required */
+   if ((err = mp_shrink(&key->g)) != MP_OKAY)                                          { goto error; }
+   if ((err = mp_shrink(&key->p)) != MP_OKAY)                                          { goto error; }
+   if ((err = mp_shrink(&key->q)) != MP_OKAY)                                          { goto error; }
+   if ((err = mp_shrink(&key->x)) != MP_OKAY)                                          { goto error; }
+   if ((err = mp_shrink(&key->y)) != MP_OKAY)                                          { goto error; }
+
+   err = CRYPT_OK;
+
+#ifdef CLEAN_STACK
+   zeromem(buf, sizeof(buf));
+#endif
+
+   goto done;
+error : err = mpi_to_ltc_error(err);
+error2: mp_clear_multi(&key->g, &key->q, &key->p, &key->x, &key->y, NULL);
+done  : mp_clear_multi(&tmp, &tmp2, NULL);
+   return err;
+}
+
+#endif