| 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} |
| 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 |
| static BigInteger selectGenerator( |
| BigInteger p, |
| BigInteger q, |
| SecureRandom random) |
| { |
| BigInteger pMinusTwo = p.subtract(TWO); |
| BigInteger g; |
| |
| // Handbook of Applied Cryptography 4.86 |
| do |
| { |
| g = BigIntegers.createRandomInRange(TWO, pMinusTwo, random); |
| } |
| while (g.modPow(TWO, p).equals(ONE) |
| || g.modPow(q, p).equals(ONE)); |
| |
| /* |
| // RFC 2631 2.1.1 (and see Handbook of Applied Cryptography 4.81) |
| do |
| { |
| BigInteger h = createInRange(TWO, pMinusTwo, random); |
| |
| g = h.modPow(TWO, p); |
| } |
| while (g.equals(ONE)); |
| */ |
| |
| return g; |
| } |
| } |