btc_validate.java

package org.whatnick.btc;

import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;

public class btc_validate {
	
	private final static String template = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
	
	public static boolean check_bc(String BTC_address)
	{
		byte[] decoded = decode_base58(BTC_address);
		byte[] sig = Arrays.copyOfRange(decoded, 21, 25);
		
		try {
			MessageDigest digest = MessageDigest.getInstance("SHA-256");
			byte[] digest1 = digest.digest(Arrays.copyOf(decoded,21));
			byte[] digest2 = Arrays.copyOfRange(digest.digest(digest1),0,4);
			
			
			System.out.println(bytesToHex(digest2));
			System.out.println(bytesToHex(sig));
			
			return Arrays.equals(digest2, sig );
			
		} catch (NoSuchAlgorithmException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			return false;
		}
	}
	
	private static byte[] decode_base58(String BTC_address)
	{
		BigInteger n = BigInteger.ZERO;
		char[] chars = BTC_address.toCharArray();
		for (char c : chars) {
			//check for valid chars
			long index = template.indexOf(c);
			if (index<0) return null;
			n = (n.multiply(BigInteger.valueOf(58))).add(BigInteger.valueOf(index));
		}
		
		byte[] out = new byte[25];
		byte[] unpadded = n.toByteArray();
		
		for(int i=1;i<=unpadded.length;i++)
		{
			out[25-i] = unpadded[unpadded.length-i];
		}
	
		return out;
	}
	
	
	final protected static char[] hexArray = "0123456789ABCDEF".toCharArray();
	public static String bytesToHex(byte[] bytes) {
	    char[] hexChars = new char[bytes.length * 2];
	    for ( int j = 0; j < bytes.length; j++ ) {
	        int v = bytes[j] & 0xFF;
	        hexChars[j * 2] = hexArray[v >>> 4];
	        hexChars[j * 2 + 1] = hexArray[v & 0x0F];
	    }
	    return new String(hexChars);
	}
	
	public static void main(String[] args)
	{
		String bc = "1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i";
		System.out.println(check_bc(bc));
		System.out.println(check_bc(bc.replace('N', 'P')));
		System.out.println(check_bc("1111111111111111111114oLvT2"));
		System.out.println(check_bc("17NdbrSGoUotzeGCcMMCqnFkEvLymoou9j"));
	}
}