Bleichenbacher's DSA attack

CHANGES

@@ -3,6 +3,10 @@
 
  Changes between 0.9.6 and 0.9.7  [xx XXX 2000]
 
+  *) Add new function BN_rand_range(), and fix DSA_sign_setup() to prevent
+     Bleichenbacher's DSA attack.
+     [Ulf Moeller]
+
   *) Update Rijndael code to version 3.0 and change EVP AES ciphers to
      handle the new API. Currently only ECB, CBC modes supported. Add new
      AES OIDs. Add TLS AES ciphersuites as described in the "AES Ciphersuites

crypto/bn/bn.h

@@ -329,6 +329,7 @@ BIGNUM *BN_CTX_get(BN_CTX *ctx);
 void	BN_CTX_end(BN_CTX *ctx);
 int     BN_rand(BIGNUM *rnd, int bits, int top,int bottom);
 int     BN_pseudo_rand(BIGNUM *rnd, int bits, int top,int bottom);
+int	BN_rand_range(BIGNUM *rnd, BIGNUM *min, BIGNUM *max);
 int	BN_num_bits(const BIGNUM *a);
 int	BN_num_bits_word(BN_ULONG);
 BIGNUM *BN_new(void);

crypto/bn/bn_rand.c

@@ -168,3 +168,14 @@ int     BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom)
 	return bnrand(2, rnd, bits, top, bottom);
 	}
 #endif
+
+/* random number r: min <= r < max */
+int	BN_rand_range(BIGNUM *r, BIGNUM *min, BIGNUM *max)
+	{
+	int n = BN_num_bits(max);
+	do
+		{
+		if (!BN_rand(r, n, 0, 0)) return 0;
+		} while ((min && BN_cmp(r, min) < 0) || BN_cmp(r, max) >= 0);
+	return 1;
+	}

crypto/dsa/dsa_ossl.c

@@ -180,13 +180,7 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp)
 	kinv=NULL;
 
 	/* Get random k */
-	for (;;)
+	if (!BN_rand_range(&k, BN_value_one(), dsa->q)) goto err;
-		{
-		if (!BN_rand(&k, BN_num_bits(dsa->q), 0, 0)) goto err;
-		if (BN_cmp(&k,dsa->q) >= 0)
-			BN_sub(&k,&k,dsa->q);
-		if (!BN_is_zero(&k)) break;
-		}
 
 	if ((dsa->method_mont_p == NULL) && (dsa->flags & DSA_FLAG_CACHE_MONT_P))
 		{

doc/crypto/BN_rand.pod

@@ -12,6 +12,8 @@ BN_rand, BN_pseudo_rand - generate pseudo-random number
 
  int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom);
 
+ int BN_rand_range(BIGNUM *rnd, BIGNUM *min, BIGNUM *max);
+
 =head1 DESCRIPTION
 
 BN_rand() generates a cryptographically strong pseudo-random number of
@@ -25,11 +27,15 @@ this function are not necessarily unpredictable. They can be used for
 non-cryptographic purposes and for certain purposes in cryptographic
 protocols, but usually not for key generation etc.
 
-The PRNG must be seeded prior to calling BN_rand().
+BN_rand_range() generates a cryptographically strong pseudo-random
+number B<rnd> in the range B<min> E<lt>= B<rnd> E<lt> B<max>. B<min>
+may be NULL, in that case 0 E<lt>= B<rnd> E<lt> B<max>.
+
+The PRNG must be seeded prior to calling BN_rand() or BN_rand_range().
 
 =head1 RETURN VALUES
 
-BN_rand() and BN_pseudo_rand() return 1 on success, 0 on error.
+The functions return 1 on success, 0 on error.
 The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
 
 =head1 SEE ALSO
@@ -40,6 +46,7 @@ L<RAND_add(3)|RAND_add(3)>, L<RAND_bytes(3)|RAND_bytes(3)>
 =head1 HISTORY
 
 BN_rand() is available in all versions of SSLeay and OpenSSL.
-BN_pseudo_rand() was added in OpenSSL 0.9.5.
+BN_pseudo_rand() was added in OpenSSL 0.9.5, and BN_rand_range()
+in OpenSSL 0.9.6a.
 
 =cut

doc/crypto/bn.pod

@@ -68,6 +68,7 @@ bn - multiprecision integer arithmetics
 
  int BN_rand(BIGNUM *rnd, int bits, int top, int bottom);
  int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom);
+ int BN_rand_range(BIGNUM *rnd, BIGNUM *min, BIGNUM *max);
 
  BIGNUM *BN_generate_prime(BIGNUM *ret, int bits,int safe, BIGNUM *add,
          BIGNUM *rem, void (*callback)(int, int, void *), void *cb_arg);