diff options
Diffstat (limited to 'core/src/main/java/org/bouncycastle/crypto/generators/CramerShoupParametersGenerator.java')
| -rw-r--r-- | core/src/main/java/org/bouncycastle/crypto/generators/CramerShoupParametersGenerator.java | 197 |
1 files changed, 104 insertions, 93 deletions
diff --git a/core/src/main/java/org/bouncycastle/crypto/generators/CramerShoupParametersGenerator.java b/core/src/main/java/org/bouncycastle/crypto/generators/CramerShoupParametersGenerator.java index 704b1de4..4788a8ca 100644 --- a/core/src/main/java/org/bouncycastle/crypto/generators/CramerShoupParametersGenerator.java +++ b/core/src/main/java/org/bouncycastle/crypto/generators/CramerShoupParametersGenerator.java @@ -8,105 +8,116 @@ import org.bouncycastle.crypto.params.CramerShoupParameters; import org.bouncycastle.crypto.params.DHParameters; import org.bouncycastle.util.BigIntegers; -public class CramerShoupParametersGenerator { - - private int size; - private int certainty; - private SecureRandom random; - - /** - * Initialise the parameters generator. - * - * @param size - * bit length for the prime p - * @param certainty - * a measure of the uncertainty that the caller is willing to tolerate: - * the probability that the generated modulus is prime exceeds (1 - 1/2^certainty). - * The execution time of this method is proportional to the value of this parameter. - * @param random - * a source of randomness - */ - public void init(int size, int certainty, SecureRandom random) { - this.size = size; - this.certainty = certainty; - this.random = random; - } - - /** - * which generates the p and g values from the given parameters, returning - * the CramerShoupParameters object. - * <p> - * Note: can take a while... - */ - public CramerShoupParameters generateParameters() { - // - // find a safe prime p where p = 2*q + 1, where p and q are prime. - // - BigInteger[] safePrimes = ParametersHelper.generateSafePrimes(size, certainty, random); +public class CramerShoupParametersGenerator +{ + private static final BigInteger ONE = BigInteger.valueOf(1); + + private int size; + private int certainty; + private SecureRandom random; + + /** + * Initialise the parameters generator. + * + * @param size bit length for the prime p + * @param certainty a measure of the uncertainty that the caller is willing to tolerate: + * the probability that the generated modulus is prime exceeds (1 - 1/2^certainty). + * The execution time of this method is proportional to the value of this parameter. + * @param random a source of randomness + */ + public void init(int size, int certainty, SecureRandom random) + { + this.size = size; + this.certainty = certainty; + this.random = random; + } + + /** + * which generates the p and g values from the given parameters, returning + * the CramerShoupParameters object. + * <p/> + * Note: can take a while... + */ + public CramerShoupParameters generateParameters() + { + // + // find a safe prime p where p = 2*q + 1, where p and q are prime. + // + BigInteger[] safePrimes = ParametersHelper.generateSafePrimes(size, certainty, random); // BigInteger p = safePrimes[0]; - BigInteger q = safePrimes[1]; - BigInteger g1 = ParametersHelper.selectGenerator(q, random); - BigInteger g2 = ParametersHelper.selectGenerator(q, random); - while(g1.equals(g2)){ - g2 = ParametersHelper.selectGenerator(q, random); - } - - return new CramerShoupParameters(q, g1, g2, new SHA256Digest()); - } - - public CramerShoupParameters generateParameters(DHParameters dhParams){ - BigInteger p = dhParams.getP(); - BigInteger g1 = dhParams.getG(); - - // now we just need a second generator - BigInteger g2 = ParametersHelper.selectGenerator(p, random); - while(g1.equals(g2)){ - g2 = ParametersHelper.selectGenerator(p, random); - } - - return new CramerShoupParameters(p, g1, g2, new SHA256Digest()); - } - - private static class ParametersHelper { - - 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 = q.shiftLeft(1).add(BigInteger.ONE); - if (p.isProbablePrime(certainty) && (certainty <= 2 || q.isProbablePrime(certainty))) { - break; - } - } - - return new BigInteger[] { p, q }; - } - - static BigInteger selectGenerator(BigInteger p, SecureRandom random) { - BigInteger pMinusTwo = p.subtract(TWO); - BigInteger g; + BigInteger q = safePrimes[1]; + BigInteger g1 = ParametersHelper.selectGenerator(q, random); + BigInteger g2 = ParametersHelper.selectGenerator(q, random); + while (g1.equals(g2)) + { + g2 = ParametersHelper.selectGenerator(q, random); + } + + return new CramerShoupParameters(q, g1, g2, new SHA256Digest()); + } + + public CramerShoupParameters generateParameters(DHParameters dhParams) + { + BigInteger p = dhParams.getP(); + BigInteger g1 = dhParams.getG(); + + // now we just need a second generator + BigInteger g2 = ParametersHelper.selectGenerator(p, random); + while (g1.equals(g2)) + { + g2 = ParametersHelper.selectGenerator(p, random); + } + + return new CramerShoupParameters(p, g1, g2, new SHA256Digest()); + } + + private static class ParametersHelper + { + + 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 = q.shiftLeft(1).add(ONE); + if (p.isProbablePrime(certainty) && (certainty <= 2 || q.isProbablePrime(certainty))) + { + break; + } + } + + return new BigInteger[]{p, q}; + } + + static BigInteger selectGenerator(BigInteger p, SecureRandom random) + { + BigInteger pMinusTwo = p.subtract(TWO); + BigInteger g; /* - * RFC 2631 2.2.1.2 (and see: Handbook of Applied Cryptography 4.81) + * RFC 2631 2.2.1.2 (and see: Handbook of Applied Cryptography 4.81) */ - do { - BigInteger h = BigIntegers.createRandomInRange(TWO, pMinusTwo, random); + do + { + BigInteger h = BigIntegers.createRandomInRange(TWO, pMinusTwo, random); - g = h.modPow(TWO, p); - } while (g.equals(BigInteger.ONE)); + g = h.modPow(TWO, p); + } + while (g.equals(ONE)); - return g; - } - } + return g; + } + } } |