Android encryption

Question

I am working on an android application, and I need to use encryption for one aspect of it. I am really indifferent to which algorithm I use (AES, DES, RSA, etc...). I am aware that Java has a crypto package, but I am not at all familiar with. Can someone post an example on how to do an encrypt/decrypt function?

Thanks

Answer 1

The java AES library has a flaw in it that allows, under the right circumstances, a listener to decrypt the packets sent. See Padding Oracle Exploit Tool vs Apache MyFaces.

That being said check out this SO question Java 256bit AES Encryption.

Bouncy Castle AES EXAMPLE Stolen from: http://www.java2s.com/Code/Java/Security/EncryptionanddecryptionwithAESECBPKCS7Padding.htm

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;

public class MainClass {
  public static void main(String[] args) throws Exception {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());    
    byte[] input = "www.java2s.com".getBytes();
    byte[] keyBytes = new byte[] { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09,
        0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17 };

    SecretKeySpec key = new SecretKeySpec(keyBytes, "AES");

    Cipher cipher = Cipher.getInstance("AES/ECB/PKCS7Padding", "BC");

    System.out.println(new String(input));

    // encryption pass
    cipher.init(Cipher.ENCRYPT_MODE, key);

    byte[] cipherText = new byte[cipher.getOutputSize(input.length)];
    int ctLength = cipher.update(input, 0, input.length, cipherText, 0);
    ctLength += cipher.doFinal(cipherText, ctLength);
    System.out.println(new String(cipherText));
    System.out.println(ctLength);

    // decryption pass
    cipher.init(Cipher.DECRYPT_MODE, key);
    byte[] plainText = new byte[cipher.getOutputSize(ctLength)];
    int ptLength = cipher.update(cipherText, 0, ctLength, plainText, 0);
    ptLength += cipher.doFinal(plainText, ptLength);
    System.out.println(new String(plainText));
    System.out.println(ptLength);
  }
}

Answer 2

The algorithm depends a lot on the usage scenario. What is it you're protecting, from whom, where, why and how do you plan to do it?

AES (symmetric cipher) and RSA (asymmetric) function very differently.