static byte[] addChecksum(byte[] input) {
int inputLength = input.length;
byte[] checksummed = new byte[inputLength + 4];
System.arraycopy(input, 0, checksummed, 0, inputLength);
byte[] checksum = Sha256Hash.hashTwice(input);
System.arraycopy(checksum, 0, checksummed, inputLength, 4);
return checksummed;
}
