github #484 added greatest common divisor test to weed out poor candi…

…dates
bcgit · Apr 4, 2019 · f72dd46 · f72dd46
1 parent 868720f
commit f72dd46
Showing 1 changed file with 12 additions and 0 deletions.
diff --git a/core/src/main/java/org/bouncycastle/util/BigIntegers.java b/core/src/main/java/org/bouncycastle/util/BigIntegers.java
@@ -141,6 +141,13 @@ public static BigInteger createRandomBigInteger(int bitLength, SecureRandom rand
         return new BigInteger(1, createRandom(bitLength, random));
     }
 
+    // Hexadecimal value of the product of the 131 smallest odd primes from 3 to 743
+    private static final BigInteger SMALL_PRIMES_PRODUCT = new BigInteger(
+              "8138e8a0fcf3a4e84a771d40fd305d7f4aa59306d7251de54d98af8fe95729a1f"
+            + "73d893fa424cd2edc8636a6c3285e022b0e3866a565ae8108eed8591cd4fe8d2"
+            + "ce86165a978d719ebf647f362d33fca29cd179fb42401cbaf3df0c614056f9c8"
+            + "f3cfd51e474afb6bc6974f78db8aba8e9e517fded658591ab7502bd41849462f",
+        16);
     /**
      * Return a prime number candidate of the specified bit length.
      *
@@ -174,6 +181,11 @@ public static BigInteger createRandomPrime(int bitLength, int certainty, SecureR
             base[base.length - 1] |= 0x01;
 
             rv = new BigInteger(1, base);
+
+            while (!rv.gcd(SMALL_PRIMES_PRODUCT).equals(ONE))
+            {
+                rv = rv.add(TWO);
+            }
         }
         while (!rv.isProbablePrime(certainty));