fix BN_rand_range

diff --git a/CHANGES b/CHANGES
index cc1e6cac48ee13341dba0daf84360bd255741f22..18cb9e7b52b1800e07fdd9f0e7a1d5a47b375dea 100644 (file)
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,12 @@
 
  Changes between 0.9.6b and 0.9.6c  [XX xxx XXXX]
 
+  *) Fix BN_rand_range bug pointed out by Dominikus Scherkl
+     <Dominikus.Scherkl@biodata.com>.  (The previous implementation
+     worked incorrectly for those cases where  range = 10..._2  and
+     3*range  is two bits longer than  range.)
+     [Bodo Moeller]
+
   *) Only add signing time to PKCS7 structures if it is not already
      present.
      [Steve Henson]

diff --git a/crypto/bn/bn_rand.c b/crypto/bn/bn_rand.c
index b368d12f807e8aee40f40ef73d7c7c5dc9d03425..4944ffbf232f3b432312f0aba1fedb3237fe1d32 100644 (file)
--- a/crypto/bn/bn_rand.c
+++ b/crypto/bn/bn_rand.c
@@ -238,22 +238,15 @@ static int bn_rand_range(int pseudo, BIGNUM *r, BIGNUM *range)
 
        n = BN_num_bits(range); /* n > 0 */
 
+       /* BN_is_bit_set(range, n - 1) always holds */
+
        if (n == 1)
                {
                if (!BN_zero(r)) return 0;
                }
-       else if (BN_is_bit_set(range, n - 2))
-               {
-               do
-                       {
-                       /* range = 11..._2, so each iteration succeeds with probability >= .75 */
-                       if (!bn_rand(r, n, -1, 0)) return 0;
-                       }
-               while (BN_cmp(r, range) >= 0);
-               }
-       else
+       else if (!BN_is_bit_set(range, n - 2) && !BN_is_bit_set(range, n - 3))
                {
-               /* range = 10..._2,
+               /* range = 100..._2,
                 * so  3*range (= 11..._2)  is exactly one bit longer than  range */
                do
                        {
@@ -272,6 +265,15 @@ static int bn_rand_range(int pseudo, BIGNUM *r, BIGNUM *range)
                        }
                while (BN_cmp(r, range) >= 0);
                }
+       else
+               {
+               do
+                       {
+                       /* range = 11..._2  or  range = 101..._2 */
+                       if (!bn_rand(r, n, -1, 0)) return 0;
+                       }
+               while (BN_cmp(r, range) >= 0);
+               }
 
        return 1;
        }