[Zerocoin] include 0 in randBignum() range

random-zebra · random-zebra · commit 253c63edad3b · 2019-05-17T12:46:22.000+02:00
diff --git a/src/libzerocoin/bignum_gmp.cpp b/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
diff --git a/src/libzerocoin/bignum_openssl.cpp b/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
 */
diff --git a/src/test/zerocoin_bignum_tests.cpp b/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()));
     }
 }

Original file line number	Diff line number	Diff line change
`@@ -21,9 +21,7 @@ bool testRandKBitBignum(int k_bits)`
`21`	`21`	`bool testRandBignum(CBigNum limit)`
`22`	`22`	`{`
`23`	`23`	`CBigNum x = CBigNum::randBignum(limit);`
`24`		`- if (limit < 2)`
`25`		`- return x == CBigNum(0);`
`26`		`- return 0 < x && x < limit;`
	`24`	`+ return 0 <= x && x < limit;`
`27`	`25`	`}`
`28`	`26`
`29`	`27`	`BOOST_AUTO_TEST_SUITE(zerocoin_bignum_tests)`
`@@ -84,7 +82,7 @@ BOOST_AUTO_TEST_CASE(bignum_random_generation_tests)`
`84`	`82`	`}`
`85`	`83`
`86`	`84`	`for(int i=1; i<3000; i++) {`
`87`		`- CBigNum x = CBigNum::randKBitBignum(i);`
	`85`	`+ CBigNum x = 1 + CBigNum::randKBitBignum(i);`
`88`	`86`	`BOOST_CHECK_MESSAGE(testRandBignum(x), strprintf("CBigNum::randBignum(x) failed with x=%s", x.ToString()));`
`89`	`87`	`}`
`90`	`88`	`}`