ZelCash address validation helper

import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
 
public class BitcoinAddressValidator {
 
    private static final String ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
 
    public static boolean validateBitcoinAddress(String addr) {
        if (addr.length() < 27 || addr.length() > 36)
            return false;
        byte[] decoded = decodeBase58To25Bytes(addr);
        if (decoded == null)
            return false;
 
        byte[] hash1 = sha256(Arrays.copyOfRange(decoded, 0, 22));
        byte[] hash2 = sha256(hash1);
 
        return Arrays.equals(Arrays.copyOfRange(hash2, 0, 4), Arrays.copyOfRange(decoded, 22, 26));
    }
 
    private static byte[] decodeBase58To25Bytes(String input) {
        BigInteger num = BigInteger.ZERO;
        if (input.charAt(0) != 't')
        	return null;
        if (input.charAt(1) != '1' && input.charAt(1) != '3')
        	return null;
        for (char t : input.toCharArray()) {
            int p = ALPHABET.indexOf(t);
            if (p == -1)
                return null;
            num = num.multiply(BigInteger.valueOf(58)).add(BigInteger.valueOf(p));
        }
 
        byte[] result = new byte[26];
        byte[] numBytes = num.toByteArray();
        System.arraycopy(numBytes, 0, result, result.length - numBytes.length, numBytes.length);
        return result;
    }
 
    private static byte[] sha256(byte[] data) {
        try {
            MessageDigest md = MessageDigest.getInstance("SHA-256");
            md.update(data);
            return md.digest();
        } catch (NoSuchAlgorithmException e) {
            throw new IllegalStateException(e);
        }
    }
 
    public static void main(String[] args) {
        assertBitcoin("t1dmNSMGoUXHaoKd48A8qudXhQPK5ughDv5", true);
        assertBitcoin("t1Zb6bbGLqrGWr9tVZ22k8SnxKC7TEXWWrW", true);
        assertBitcoin("t1Zb6bbGLqrGWr9tVZ22k8SnxKC7TEaWWrW", false);
        assertBitcoin("t3LQtHUDoe7ZhhvddRv4vnaoNAhCr2f4oFN", true);
        assertBitcoin("t2LQtHUDoe7ZhhvddRv4vnaoNAhCr2f4oFN", false);
        assertBitcoin("1M1Xw2rczxkF3p3wiNHaTmxvbpZZ7M6vaa", false);
        assertBitcoin("t3LQtHUDoe7ZhhvddRv4vnaoNAhCraf4oFN", false);
        assertBitcoin("asdad", false);
    }
 
    private static void assertBitcoin(String address, boolean expected) {
        boolean actual = validateBitcoinAddress(address);
        if (actual != expected)
            throw new AssertionError(String.format("Expected %s for %s, but got %s.", expected, address, actual));
    }
}