Test19EncDec.java

package mytest;

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import java.security.Key;

import org.apache.commons.codec.binary.Base64;

public class Test19EncDec {

    private static final String ALGORITHM = "AES/ECB/PKCS5Padding";
    private static final byte[] KEY = "StBet9834#$10BCy".getBytes();

    public static void main(String[] args) {
        String pt = "5123456789012346";
        String ct = encryptCreditCard(pt);

        System.out.println("Recovered Plaintext: " + decryptCreditCard(ct));
        System.out.println("Expected Plaintext: " + pt);
    }

    private static String encryptCreditCard(String ccNumber) {
        Key key = new SecretKeySpec(KEY, "AES");
        try {
            Cipher c = Cipher.getInstance(ALGORITHM);
            c.init(Cipher.ENCRYPT_MODE, key);
            byte[] ccNumberBytes = ccNumber.getBytes();
            byte[] encCCNumber = c.doFinal(ccNumberBytes);

            return new String(Base64.encodeBase64(encCCNumber));
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    private static String decryptCreditCard(String ciphertext) {
        Key key = new SecretKeySpec(KEY, "AES");
        try {
            Cipher c = Cipher.getInstance(ALGORITHM);
            c.init(Cipher.DECRYPT_MODE, key);
            byte[] ccENCBytes = Base64.decodeBase64(ciphertext);
            byte[] ccDECBytes = c.doFinal(ccENCBytes);
            return new String(ccDECBytes);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}