HDUtils.java

/**
 * Copyright 2013 Matija Mazi.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.devcoin.crypto;

import com.google.common.collect.ImmutableList;
import org.spongycastle.asn1.sec.SECNamedCurves;
import org.spongycastle.asn1.x9.X9ECParameters;
import org.spongycastle.crypto.digests.SHA512Digest;
import org.spongycastle.crypto.macs.HMac;
import org.spongycastle.crypto.params.ECDomainParameters;
import org.spongycastle.crypto.params.KeyParameter;
import org.spongycastle.math.ec.ECCurve;
import org.spongycastle.math.ec.ECPoint;

import java.math.BigInteger;
import java.nio.ByteBuffer;
import java.util.Arrays;

/**
 * Static utilities used in BIP 32 Hierarchical Deterministic Wallets (HDW).
 */
public final class HDUtils {

    private HDUtils() { }

    private static final ECDomainParameters ecParams;

    static {
        // All clients must agree on the curve to use by agreement. Bitcoin uses secp256k1.
        X9ECParameters params = SECNamedCurves.getByName("secp256k1");
        ecParams = new ECDomainParameters(params.getCurve(), params.getG(), params.getN(), params.getH());
    }

    static HMac createHmacSha256Digest(byte[] key) {
        SHA512Digest digest = new SHA512Digest();
        HMac hMac = new HMac(digest);
        hMac.init(new KeyParameter(key));
        return hMac;
    }

    static byte[] hmacSha256(HMac hmacSha256, byte[] input) {
        hmacSha256.reset();
        hmacSha256.update(input, 0, input.length);
        byte[] out = new byte[64];
        hmacSha256.doFinal(out, 0);
        return out;
    }

    public static byte[] hmacSha256(byte[] key, byte[] data) {
        return hmacSha256(createHmacSha256Digest(key), data);
    }

    static BigInteger toBigInteger(byte[] bytes) {
        return new BigInteger(1, bytes);
    }

    static ECPoint compressedCopy(ECPoint pubKPoint) {
        return getCurve().createPoint(pubKPoint.getX().toBigInteger(), pubKPoint.getY().toBigInteger(), true);
    }

    static ECCurve getCurve() {
        return getEcParams().getCurve();
    }

    static ECPoint toUncompressed(ECPoint pubKPoint) {
        return getCurve().createPoint(pubKPoint.getX().toBigInteger(), pubKPoint.getY().toBigInteger(), false);
    }

    static byte[] toCompressed(byte[] uncompressedPoint) {
        return compressedCopy(getCurve().decodePoint(uncompressedPoint)).getEncoded();
    }

    static byte[] longTo4ByteArray(long n) {
        byte[] bytes = Arrays.copyOfRange(ByteBuffer.allocate(8).putLong(n).array(), 4, 8);
        assert bytes.length == 4 : bytes.length;
        return bytes;
    }

    static ECDomainParameters getEcParams() {
        return ecParams;
    }

    static byte[] getBytes(ECPoint pubKPoint) {
        return compressedCopy(pubKPoint).getEncoded();
    }

    static ImmutableList<ChildNumber> append(ImmutableList<ChildNumber> path, ChildNumber childNumber) {
        return ImmutableList.<ChildNumber>builder().addAll(path).add(childNumber).build();
    }
}