BlockGenerator.java

/*
 * Curecoin 2.0.0a Source Code
 * Copyright (c) 2015 Curecoin Developers
 * Distributed under MIT License
 * Requires Apache Commons Library
 * Supports Java 1.7+
 */

import java.util.*;
import java.security.*;
import javax.xml.bind.DatatypeConverter;

/**
 * This class provides all functionality required to pack and sign blocks. 
 * In order for a block to be valid on the network, it must include a valid timestamp, blockNum, previousBlockHash, difficulty, winningNonce, ledgerHash (not in 2.0.0a1), certificate, and be signed by the miner.
 * 
 * When Curecoin 2.0 receives a certificate over RPC, it will gather the pool of pending transactions, test each transaction for available balances and such, and attempt to create a block, and send it to the network. 
 * Block Format:
 *  {timestamp:blockNum:previousBlockHash:difficulty:winningNonce},{ledgerHash},{transactions},{redeemAddress:arbitraryData:maxNonce:authorityName:blockNum:prevBlockHash},{certificateSignatureData},{certificateSigantureIndex},{blockHash},{minerSignature},{minerSignatureIndex} 
 */
public class BlockGenerator
{
    /**
     * The parameters are a mouthful. This method takes all of the building blocks (heh....) of a Curecoin block, and compiles them together into a format that the network will accept.
     * Compiling a block consists of lining up all of the block elements until the block hash, hashing the partial block, appending the blockHash, and signing the entire String. 
     * Peers on the network will be able to deconstruct the block in the same process to verify the signature's validity, blockHash, and signature.
     * 
     * @param timestamp Timestamp of block
     * @param blockNum Number of block to create
     * @param difficulty Difficulty to place into new block
     * @param winningNonce The nonce that mines the certificate under the difficulty of the previous block
     * @param ledgerHash Hash of the current ledger BEFORE transactions held in this block are applied
     * @param transactions ArrayList<String> containing all transactions in order to be included in the block
     * @param certificate Certificate used to create the block
     * @param signingAddress Address to sign with, this should be the same as the redeemAddress of certificate
     * @param privateKey Private key of signingAddress, used to create the signature
     * @param minerSignatureIndex Index to use for signing the block
     * 
     */
    public static String compileBlock(long timestamp, int blockNum, String previousBlockHash, long difficulty, int winningNonce, String ledgerHash, ArrayList<String> transactions, Certificate certificate, String signingAddress, String privateKey, long minerSignatureIndex)
    {
        System.out.println("Creating block...");
        System.out.println("timestamp: " + timestamp);
        System.out.println("blockNum: " + blockNum);
        System.out.println("previousBlockHash: " + previousBlockHash);
        System.out.println("difficulty: " + difficulty);
        System.out.println("winningNonce: " + winningNonce);
        System.out.println("ledgerHash: " + ledgerHash);
        System.out.println("signingAddress: " + signingAddress);
        System.out.println("Certificate: " + certificate.getFullCertificate());
        if (minerSignatureIndex < 0)
        {
            minerSignatureIndex = 0;
        }
        System.out.println("minerSignatureIndex: " + minerSignatureIndex);
        System.out.println("privateKey: " + privateKey);
        //This String will be added to a lot.
        String block = "";
        block += "{" + timestamp + ":" + blockNum + ":" + previousBlockHash + ":" + difficulty + ":" + winningNonce + "},{" + ledgerHash + "},{";
        String transactionString = "";
        for (int i = 0; i < transactions.size(); i++)
        {
            if (transactions.get(i).length() > 10)
            {
                transactionString += transactions.get(i) + "*";
            }
        }
        if (transactionString.length() > 1) //Otherwise this will throw an indexOutOfBoundsError for blocks with no explicit transactions!
        {
            transactionString = transactionString.substring(0, transactionString.length() - 1);
        }
        block += transactionString + "}," + certificate.getFullCertificate();
        try
        {
            MessageDigest md = MessageDigest.getInstance("SHA-256");
            String blockHash =  DatatypeConverter.printHexBinary(md.digest(block.getBytes("UTF-8")));
            block += ",{" + blockHash + "}";
            System.out.println("pre-block: " + block);
            String signature = new MerkleAddressUtility().getMerkleSignature(block, privateKey, minerSignatureIndex, signingAddress);
            System.out.println("signature: " + signature);
            block += ",{" + signature + "},{" + minerSignatureIndex + "}";
            return block;
        } catch (Exception e)
        {
            System.out.println("[CRITICAL ERROR] UNABLE TO SIGN A BLOCK!");
            e.printStackTrace();
            return null;
        }
    }
}