[Zerocoin] include 0 in randBignum() range

src/libzerocoin/bignum_gmp.cpp

@@ -50,8 +50,8 @@ CBigNum::CBigNum(const std::vector<unsigned char>& vch)
 
 /** PRNGs use OpenSSL for consistency with seed initialization **/
 
-/** Generates a cryptographically secure random number between zero and range exclusive
-* i.e. 0 < returned number < range
+/** Generates a cryptographically secure random number between zero and range-1 (inclusive)
+* i.e. 0 <= returned number < range
 * @param range The upper bound on the number.
 * @return
 */
@@ -69,7 +69,7 @@ CBigNum CBigNum::randBignum(const CBigNum& range)
     CBigNum ret(buf);
     if (ret < 0)
         mpz_neg(ret.bn, ret.bn);
-    return 1 + (ret % (range-1));
+    return (ret % range);
 }
 
 /** Generates a cryptographically secure random k-bit number

src/libzerocoin/bignum_openssl.cpp

@@ -52,8 +52,8 @@ CBigNum::CBigNum(const std::vector<unsigned char>& vch)
     setvch(vch);
 }
 
-/** Generates a cryptographically secure random number between zero and range exclusive
-* i.e. 0 < returned number < range
+/** Generates a cryptographically secure random number between zero and range-1 (inclusive)
+* i.e. 0 <= returned number < range
 * @param range The upper bound on the number.
 * @return
 */

src/test/zerocoin_bignum_tests.cpp

@@ -21,9 +21,7 @@ bool testRandKBitBignum(int k_bits)
 bool testRandBignum(CBigNum limit)
 {
     CBigNum x = CBigNum::randBignum(limit);
-    if (limit < 2)
-        return x == CBigNum(0);
-    return 0 < x && x < limit;
+    return 0 <= x && x < limit;
 }
 
 BOOST_AUTO_TEST_SUITE(zerocoin_bignum_tests)
@@ -84,7 +82,7 @@ BOOST_AUTO_TEST_CASE(bignum_random_generation_tests)
     }
 
     for(int i=1; i<3000; i++) {
-        CBigNum x = CBigNum::randKBitBignum(i);
+        CBigNum x = 1 + CBigNum::randKBitBignum(i);
         BOOST_CHECK_MESSAGE(testRandBignum(x), strprintf("CBigNum::randBignum(x) failed with x=%s", x.ToString()));
     }
 }