Question

I am using AES encryption and decryption using java. And I use Appache commons library for conversion from string to byte and vice versa. But when I decrypt data then it is different from the input data that was encrypted using same key? why is so

Here is my code:

public static void main(String[] args) throws Exception {



        String key="this is key";

        String message="This is just an example";

           KeyGenerator kgen = KeyGenerator.getInstance("AES");

           kgen.init(128, new SecureRandom(Base64.decodeBase64(key)));

           // Generate the secret key specs.
           SecretKey skey = kgen.generateKey();

           byte[] raw = skey.getEncoded();

           SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");

           Cipher cipher = Cipher.getInstance("AES");

           cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

           byte[] encrypted= cipher.doFinal(Base64.decodeBase64(message));

           String encryptedString=Base64.encodeBase64String(encrypted);

           cipher.init(Cipher.DECRYPT_MODE, skeySpec);

           byte[] original =
             cipher.doFinal(Base64.decodeBase64(encryptedString));

           System.out.println(Base64.encodeBase64String(original));


    }

I get the output “Thisisjustanexamplc=” where it should have been “This is just an example”. what I need to change in my code. Thanks in advance

Answer 1

You are base-64–decoding your plain text message. You should use message.getBytes(StandardCharsets.UTF_8) (or some other encoding) to convert to bytes instead. Base-64 encode the result of the encryption operation, then base-64 decode it before decrypting. Use new String(original, StandardCharsets.UTF_8) to convert the result of the decryption operation back to text.

In other words, use a character encoding to convert between text and bytes. Use base-64 encoding and decoding to encode binary data in a text form.