JAVA: AES Decryption

Question

I'm currently running into problems decrypting my data. The base64 of the encoded string is being stored in the database. So, I'm printing out the encoded string and then trying to run it back through with "DECRYPT" instead of "ENCRYPT". However, I never get a value that the Decrypter method likes, it always gives me an error about parameters or the value not being 16 bytes.

public class crypto {
    public static void main(String [] args) {
        String s = args[0];
        String s1 = args[1];
        String ivkey = "thisisasecretkey";
        byte[] ivraw = ivkey.getBytes();
        SecretKeySpec skeySpec = new SecretKeySpec(ivraw, "AES");

        if (s.equalsIgnoreCase("ENCRYPT")) {
            try {
                Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
                cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
                byte[] encrypted = cipher.doFinal(s1.getBytes());
                System.out.println(new String(Base64.encodeBase64(encrypted)));

            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        } else {
            try {
                Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
                cipher.init(Cipher.DECRYPT_MODE, skeySpec);
                byte[] encrypted = cipher.doFinal(s1.getBytes());
                System.out.println(new String(Base64.decodeBase64(encrypted)));

            } catch (Exception e) {
                e.printStackTrace();
            }

        }
        return;
    };
}

command:crypto "ENCRYPT" "password"
output: 5eQvSzPG1TE2AybgCmeV6A==

command:crytpo "DECRYPT" "5eQvSzPG1TE2AybgCmeV6A=="
output: java.security.InvalidKeyException: Parameters missing

I'm aware of the security flaws, that's not what I'm asking about and I would prefer answers/comments not get cluttered with best practices.

Maarten Bodewes · Accepted Answer · 2014-06-24 22:05:30Z

2

You should do base 64 decoding, and you should do that before decrypting.

answered Jun 24, 2014 at 22:05

Maarten Bodewes

94.6k15 gold badges169 silver badges289 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Uku Loskit · Accepted Answer · 2014-06-24 22:24:47Z

1

You are not including the initialization vector (IV). AES in CBC mode has both a 16 byte IV and the 16 byte symmetric key.

String IV = "AAAAAAAAAAAAAAAA"; // generate this randomly
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, skeySpec, new IvParameterSpec(IV.getBytes()));
byte[] encrypted = cipher.doFinal(s.getBytes());

Edit: as it turns out, encryption does not require a IV to be provided (as owlstead pointed out), but decryption does. The best bet would be to be explicit and use IV in both encryption and decryption. Change your decryption function to include the IV, and you will run into the other error in your code that owlstead pointed out.

edited Jun 24, 2014 at 22:24

answered Jun 24, 2014 at 22:04

Uku Loskit

42.2k9 gold badges97 silver badges98 bronze badges

3 Comments

Maarten Bodewes Over a year ago

You should use an IV, but Java - or at least the default Oracle provider in Java - uses a zero-valued IV if it is not specified explicitly.

Uku Loskit Over a year ago

I am using OpenJDK and if I do not specify the IV i get the same error as OP.

Maarten Bodewes Over a year ago

My bad too, it seems both issues could lead to exceptions, voted up.

Collectives™ on Stack Overflow

JAVA: AES Decryption

2 Answers 2

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related