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A Java Bitcoin library

There is a newer version: 0.17-beta1

/*
 * Copyright 2013 Matija Mazi.
 * Copyright 2014 Giannis Dzegoutanis.
 *
 * 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 org.bitcoinj.crypto;

import org.bouncycastle.crypto.digests.SHA512Digest;
import org.bouncycastle.crypto.macs.HMac;
import org.bouncycastle.crypto.params.KeyParameter;

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

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

    static HMac createHmacSha512Digest(byte[] key) {
        SHA512Digest digest = new SHA512Digest();
        HMac hMac = new HMac(digest);
        hMac.init(new KeyParameter(key));
        return hMac;
    }

    static byte[] hmacSha512(HMac hmacSha512, byte[] input) {
        hmacSha512.reset();
        hmacSha512.update(input, 0, input.length);
        byte[] out = new byte[64];
        hmacSha512.doFinal(out, 0);
        return out;
    }

    public static byte[] hmacSha512(byte[] key, byte[] data) {
        return hmacSha512(createHmacSha512Digest(key), data);
    }

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

    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;
    }
}