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A Java Bitcoin library
There is a newer version: 0.15-cm06
/*
 * Copyright 2011 Google Inc.
 *
 * 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.core;

import static com.google.common.base.Preconditions.checkArgument;

import java.io.Serializable;
import java.util.Arrays;

import com.google.common.base.Objects;
import com.google.common.primitives.Ints;
import com.google.common.primitives.UnsignedBytes;

/**
 * In Bitcoin the following format is often used to represent some type of key:
 * 
 * 
[one version byte] [data bytes] [4 checksum bytes]
 * 
 * 
and the result is then Base58 encoded. This format is used for addresses, and private keys exported using the
 * dumpprivkey command.
 */
public class VersionedChecksummedBytes implements Serializable, Cloneable, Comparable {
    protected final int version;
    protected byte[] bytes;

    protected VersionedChecksummedBytes(String encoded) throws AddressFormatException {
        byte[] versionAndDataBytes = Base58.decodeChecked(encoded);
        byte versionByte = versionAndDataBytes[0];
        version = versionByte & 0xFF;
        bytes = new byte[versionAndDataBytes.length - 1];
        System.arraycopy(versionAndDataBytes, 1, bytes, 0, versionAndDataBytes.length - 1);
    }

    protected VersionedChecksummedBytes(int version, byte[] bytes) {
        checkArgument(version >= 0 && version < 256);
        this.version = version;
        this.bytes = bytes;
    }

    /**
     * Returns the base-58 encoded String representation of this
     * object, including version and checksum bytes.
     */
    public final String toBase58() {
        // A stringified buffer is:
        //   1 byte version + data bytes + 4 bytes check code (a truncated hash)
        byte[] addressBytes = new byte[1 + bytes.length + 4];
        addressBytes[0] = (byte) version;
        System.arraycopy(bytes, 0, addressBytes, 1, bytes.length);
        byte[] checksum = Sha256Hash.hashTwice(addressBytes, 0, bytes.length + 1);
        System.arraycopy(checksum, 0, addressBytes, bytes.length + 1, 4);
        return Base58.encode(addressBytes);
    }

    @Override
    public String toString() {
        return toBase58();
    }

    @Override
    public int hashCode() {
        return Objects.hashCode(version, Arrays.hashCode(bytes));
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        VersionedChecksummedBytes other = (VersionedChecksummedBytes) o;
        return this.version == other.version && Arrays.equals(this.bytes, other.bytes);
    }

    /**
     * {@inheritDoc}
     *
     * This implementation narrows the return type to VersionedChecksummedBytes
     * and allows subclasses to throw CloneNotSupportedException even though it
     * is never thrown by this implementation.
     */
    @Override
    public VersionedChecksummedBytes clone() throws CloneNotSupportedException {
        return (VersionedChecksummedBytes) super.clone();
    }

    /**
     * {@inheritDoc}
     *
     * This implementation uses an optimized Google Guava method to compare bytes.
     */
    @Override
    public int compareTo(VersionedChecksummedBytes o) {
        int result = Ints.compare(this.version, o.version);
        return result != 0 ? result : UnsignedBytes.lexicographicalComparator().compare(this.bytes, o.bytes);
    }

    /**
     * Returns the "version" or "header" byte: the first byte of the data. This is used to disambiguate what the
     * contents apply to, for example, which network the key or address is valid on.
     *
     * @return A positive number between 0 and 255.
     */
    public int getVersion() {
        return version;
    }
}