use rand_bn_range() where possible

Author: sjaeckel

src/math/rand_bn.c

@@ -51,7 +51,7 @@ int rand_bn_bits(void *N, int bits, prng_state *prng, int wprng)
 }
 
 /**
-  Generate a random number N in a range: 0 <= N < limit
+  Generate a random number N in a range: 1 <= N < limit
 */
 int rand_bn_range(void *N, void *limit, prng_state *prng, int wprng)
 {
@@ -63,7 +63,7 @@ int rand_bn_range(void *N, void *limit, prng_state *prng, int wprng)
    do {
      res = rand_bn_bits(N, mp_count_bits(limit), prng, wprng);
      if (res != CRYPT_OK) return res;
-   } while (mp_cmp(N, limit) != LTC_MP_LT);
+   } while (mp_cmp_d(N, 0) != LTC_MP_GT || mp_cmp(N, limit) != LTC_MP_LT);
 
    return CRYPT_OK;
 }

src/pk/dsa/dsa_encrypt_key.c

@@ -35,7 +35,7 @@ int dsa_encrypt_key(const unsigned char *in,   unsigned long inlen,
     unsigned char *expt, *skey;
     void          *g_pub, *g_priv;
     unsigned long  x, y;
-    int            err, qbits;
+    int            err;
 
     LTC_ARGCHK(in      != NULL);
     LTC_ARGCHK(out     != NULL);
@@ -73,14 +73,12 @@ int dsa_encrypt_key(const unsigned char *in,   unsigned long inlen,
        return CRYPT_MEM;
     }
 
-    /* make a random g_priv, g_pub = g^x pair */
-    qbits = mp_count_bits(key->q);
-    do {
-      if ((err = rand_bn_bits(g_priv, qbits, prng, wprng)) != CRYPT_OK) {
-        goto LBL_ERR;
-      }
-      /* private key x should be from range: 1 <= x <= q-1 (see FIPS 186-4 B.1.2) */
-    } while (mp_cmp_d(g_priv, 0) != LTC_MP_GT || mp_cmp(g_priv, key->q) != LTC_MP_LT);
+    /* make a random g_priv, g_pub = g^x pair
+       private key x should be in range: 1 <= x <= q-1 (see FIPS 186-4 B.1.2)
+     */
+    if ((err = rand_bn_range(g_priv, key->q, prng, wprng)) != CRYPT_OK) {
+      goto LBL_ERR;
+    }
 
     /* compute y */
     if ((err = mp_exptmod(key->g, g_priv, key->p, g_pub)) != CRYPT_OK) {

src/pk/dsa/dsa_make_key.c

@@ -24,7 +24,7 @@
 */
 int dsa_make_key_ex(prng_state *prng, int wprng, dsa_key *key)
 {
-  int err, qbits;
+  int err;
 
   LTC_ARGCHK(key         != NULL);
   LTC_ARGCHK(key->x      != NULL);
@@ -37,12 +37,9 @@ int dsa_make_key_ex(prng_state *prng, int wprng, dsa_key *key)
   /* 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
    */
-  qbits = mp_count_bits(key->q);
-  do {
-     if ((err = rand_bn_bits(key->x, qbits, prng, wprng)) != CRYPT_OK)                  { return err; }
-     /* private key x should be from range: 1 <= x <= q-1 (see FIPS 186-4 B.1.2) */
-  } while (mp_cmp_d(key->x, 0) != LTC_MP_GT || mp_cmp(key->x, key->q) != LTC_MP_LT);
-  if ((err = mp_exptmod(key->g, key->x, key->p, key->y)) != CRYPT_OK)                   { return err; }
+  /* private key x should be from range: 1 <= x <= q-1 (see FIPS 186-4 B.1.2) */
+  if ((err = rand_bn_range(key->x, key->q, prng, wprng)) != CRYPT_OK)            { return err; }
+  if ((err = mp_exptmod(key->g, key->x, key->p, key->y)) != CRYPT_OK)            { return err; }
   key->type = PK_PRIVATE;
 
   return CRYPT_OK;