diff options
Diffstat (limited to 'core/src/main/java/org/bouncycastle/crypto/generators/DHParametersHelper.java')
-rw-r--r-- | core/src/main/java/org/bouncycastle/crypto/generators/DHParametersHelper.java | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/core/src/main/java/org/bouncycastle/crypto/generators/DHParametersHelper.java b/core/src/main/java/org/bouncycastle/crypto/generators/DHParametersHelper.java new file mode 100644 index 00000000..118bc9cc --- /dev/null +++ b/core/src/main/java/org/bouncycastle/crypto/generators/DHParametersHelper.java @@ -0,0 +1,73 @@ +package org.bouncycastle.crypto.generators; + +import java.math.BigInteger; +import java.security.SecureRandom; + +import org.bouncycastle.util.BigIntegers; + +class DHParametersHelper +{ + private static final BigInteger ONE = BigInteger.valueOf(1); + private static final BigInteger TWO = BigInteger.valueOf(2); + + /* + * Finds a pair of prime BigInteger's {p, q: p = 2q + 1} + * + * (see: Handbook of Applied Cryptography 4.86) + */ + static BigInteger[] generateSafePrimes(int size, int certainty, SecureRandom random) + { + BigInteger p, q; + int qLength = size - 1; + + for (;;) + { + q = new BigInteger(qLength, 2, random); + + // p <- 2q + 1 + p = q.shiftLeft(1).add(ONE); + + if (p.isProbablePrime(certainty) && (certainty <= 2 || q.isProbablePrime(certainty))) + { + break; + } + } + + return new BigInteger[] { p, q }; + } + + /* + * Select a high order element of the multiplicative group Zp* + * + * p and q must be s.t. p = 2*q + 1, where p and q are prime (see generateSafePrimes) + */ + static BigInteger selectGenerator(BigInteger p, BigInteger q, SecureRandom random) + { + BigInteger pMinusTwo = p.subtract(TWO); + BigInteger g; + + /* + * (see: Handbook of Applied Cryptography 4.80) + */ +// do +// { +// g = BigIntegers.createRandomInRange(TWO, pMinusTwo, random); +// } +// while (g.modPow(TWO, p).equals(ONE) || g.modPow(q, p).equals(ONE)); + + + /* + * RFC 2631 2.2.1.2 (and see: Handbook of Applied Cryptography 4.81) + */ + do + { + BigInteger h = BigIntegers.createRandomInRange(TWO, pMinusTwo, random); + + g = h.modPow(TWO, p); + } + while (g.equals(ONE)); + + + return g; + } +} |