NetworkParameters.java

/**
 * 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 com.google.bitcoin.core;

import com.google.bitcoin.bouncycastle.util.encoders.Hex;

import java.io.ByteArrayOutputStream;
import java.io.Serializable;
import java.math.BigInteger;

/**
 * NetworkParameters contains the data needed for working with an instantiation of a BitCoin chain.
 *
 * Currently there are only two, the production chain and the test chain. But in future as BitCoin
 * evolves there may be more. You can create your own as long as they don't conflict.
 */
public class NetworkParameters implements Serializable {
    /**
     * The protocol version this library implements. A value of 31800 means 0.3.18.00.
     */
    public static final int PROTOCOL_VERSION = 31800;

    private static final long serialVersionUID = 2579833727976661964L;

    // TODO: Seed nodes and checkpoint values should be here as well.

    /**
     * Genesis block for this chain.<p>
     *
     * The first block in every chain is a well known constant shared between all BitCoin implemenetations. For a
     * block to be valid, it must be eventually possible to work backwards to the genesis block by following the
     * prevBlockHash pointers in the block headers.<p>
     *
     * The genesis blocks for both test and prod networks contain the timestamp of when they were created,
     * and a message in the coinbase transaction. It says, <i>"The Times 03/Jan/2009 Chancellor on brink of second
     * bailout for banks"</i>.
     */
    public Block genesisBlock;
    /** What the easiest allowable proof of work should be. */
    public BigInteger proofOfWorkLimit;
    /** Default TCP port on which to connect to nodes. */
    public int port;
    /** The header bytes that identify the start of a packet on this network. */
    public long packetMagic;
    /** First byte of a base58 encoded address. */
    public byte addressHeader;
    /** How many blocks pass between difficulty adjustment periods. BitCoin standardises this to be 2015. */
    public int interval;
    /**
     * How much time in seconds is supposed to pass between "interval" blocks. If the actual elapsed time is
     * significantly different from this value, the network difficulty formula will produce a different value. Both
     * test and production BitCoin networks use 2 weeks (1209600 seconds).
     */
    public int targetTimespan;

    private static Block createGenesis(NetworkParameters n) {
        Block genesisBlock = new Block(n);
        Transaction t = new Transaction(n);
        try {
            // A script containing the difficulty bits and the following message:
            //
            //   "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks"
            byte[] bytes = Hex.decode
                        ("04ffff001d0104455468652054696d65732030332f4a616e2f32303039204368616e63656c6c6f72206f6e206272696e6b206f66207365636f6e64206261696c6f757420666f722062616e6b73");
            t.inputs.add(new TransactionInput(n, bytes));
            ByteArrayOutputStream scriptPubKeyBytes = new ByteArrayOutputStream();
            Script.writeBytes(scriptPubKeyBytes, Hex.decode
                            ("04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f"));
            scriptPubKeyBytes.write(Script.OP_CHECKSIG);
            t.outputs.add(new TransactionOutput(n, scriptPubKeyBytes.toByteArray()));
        } catch (Exception e) {
            // Cannot happen.
        }
        genesisBlock.addTransaction(t);
        return genesisBlock;
    }

    static private final int TARGET_TIMESPAN = 14 * 24 * 60 * 60;  // 2 weeks per difficulty cycle, on average.
    static private final int TARGET_SPACING = 10 * 60;  // 10 minutes per block.
    static private final int INTERVAL = TARGET_TIMESPAN / TARGET_SPACING;

    /** Sets up the given NetworkParameters with testnet values. */
    private static NetworkParameters createTestNet(NetworkParameters n) {
        // Genesis hash is 0000000224b1593e3ff16a0e3b61285bbc393a39f78c8aa48c456142671f7110
        // The proof of work limit has to start with 00, as otherwise the value will be interpreted as negative.
        n.proofOfWorkLimit = new BigInteger("0000000fffffffffffffffffffffffffffffffffffffffffffffffffffffffff", 16);
        n.packetMagic = 0xfabfb5daL;
        n.port = 18333;
        n.addressHeader = 111;
        n.interval = INTERVAL;
        n.targetTimespan = TARGET_TIMESPAN;
        n.genesisBlock = createGenesis(n);
        n.genesisBlock.setTime(1296688602L);
        n.genesisBlock.setDifficultyTarget(0x1d07fff8L);
        n.genesisBlock.setNonce(384568319);
        String genesisHash = n.genesisBlock.getHashAsString();
        assert genesisHash.equals("00000007199508e34a9ff81e6ec0c477a4cccff2a4767a8eee39c11db367b008");
        return n;
    }

    /** The test chain created by Gavin. */
    public static NetworkParameters testNet() {
        NetworkParameters n = new NetworkParameters();
        return createTestNet(n);
    }

    /** The primary BitCoin chain created by Satoshi. */
    public static NetworkParameters prodNet() {
        NetworkParameters n = new NetworkParameters();
        n.proofOfWorkLimit = new BigInteger("00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffff", 16);
        n.port = 8333;
        n.packetMagic = 0xf9beb4d9L;
        n.addressHeader = 0;
        n.interval = INTERVAL;
        n.targetTimespan = TARGET_TIMESPAN;
        n.genesisBlock = createGenesis(n);
        n.genesisBlock.setDifficultyTarget(0x1d00ffffL);
        n.genesisBlock.setTime(1231006505L);
        n.genesisBlock.setNonce(2083236893);
        String genesisHash = n.genesisBlock.getHashAsString();
        assert genesisHash.equals("000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f") : genesisHash;
        return n;
    }

    /** Returns a testnet params modified to allow any difficulty target. */
    static NetworkParameters unitTests() {
        NetworkParameters n = new NetworkParameters();
        n = createTestNet(n);
        n.proofOfWorkLimit = new BigInteger("00ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff", 16);
        n.genesisBlock.setDifficultyTarget(Block.EASIEST_DIFFICULTY_TARGET);
        n.interval = 10;
        n.targetTimespan = 200000000;  // 6 years. Just a very big number.
        return n;
    }
}