package com.google.bitcoin.bouncycastle.crypto.agreement.srp; import java.math.BigInteger; import java.security.SecureRandom; import com.google.bitcoin.bouncycastle.crypto.CryptoException; import com.google.bitcoin.bouncycastle.crypto.Digest; import com.google.bitcoin.bouncycastle.util.BigIntegers; public class SRP6Util { private static BigInteger ZERO = BigInteger.valueOf(0); private static BigInteger ONE = BigInteger.valueOf(1); public static BigInteger calculateK(Digest digest, BigInteger N, BigInteger g) { return hashPaddedPair(digest, N, N, g); } public static BigInteger calculateU(Digest digest, BigInteger N, BigInteger A, BigInteger B) { return hashPaddedPair(digest, N, A, B); } public static BigInteger calculateX(Digest digest, BigInteger N, byte[] salt, byte[] identity, byte[] password) { byte[] output = new byte[digest.getDigestSize()]; digest.update(identity, 0, identity.length); digest.update((byte)':'); digest.update(password, 0, password.length); digest.doFinal(output, 0); digest.update(salt, 0, salt.length); digest.update(output, 0, output.length); digest.doFinal(output, 0); return new BigInteger(1, output).mod(N); } public static BigInteger generatePrivateValue(Digest digest, BigInteger N, BigInteger g, SecureRandom random) { int minBits = Math.min(256, N.bitLength() / 2); BigInteger min = ONE.shiftLeft(minBits - 1); BigInteger max = N.subtract(ONE); return BigIntegers.createRandomInRange(min, max, random); } public static BigInteger validatePublicValue(BigInteger N, BigInteger val) throws CryptoException { val = val.mod(N); // Check that val % N != 0 if (val.equals(ZERO)) { throw new CryptoException("Invalid public value: 0"); } return val; } private static BigInteger hashPaddedPair(Digest digest, BigInteger N, BigInteger n1, BigInteger n2) { int padLength = (N.bitLength() + 7) / 8; byte[] n1_bytes = getPadded(n1, padLength); byte[] n2_bytes = getPadded(n2, padLength); digest.update(n1_bytes, 0, n1_bytes.length); digest.update(n2_bytes, 0, n2_bytes.length); byte[] output = new byte[digest.getDigestSize()]; digest.doFinal(output, 0); return new BigInteger(1, output).mod(N); } private static byte[] getPadded(BigInteger n, int length) { byte[] bs = BigIntegers.asUnsignedByteArray(n); if (bs.length < length) { byte[] tmp = new byte[length]; System.arraycopy(bs, 0, tmp, length - bs.length, bs.length); bs = tmp; } return bs; } }