Sample Java class to decrypt AES128 encryption

Question

Looking for some sample Java code that decrypts AES encrypted string. I'm trying to encrypt using Apex's Crypto class and decrypt using Java.

Answer 1

The easiest way is to use the Managed IV methods in crypto which will place the Initialization Vector on the front of your cipherText

So, for this Apex:

String clearText = 'the quick brown fox jumps over the lazy dog';
Blob key = EncodingUtil.base64Decode('mRMjHmlC1C+1L/Dkz8EJuw==');
Blob cipherText = Crypto.encryptWithManagedIV('AES128', key, Blob.valueOf(clearText));
String encodedCipherText = EncodingUtil.base64Encode(cipherText); 
System.debug(encodedCipherText);

Here's the corresponding Java

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Base64;
import java.util.Arrays;

public class AESDecrypt {

    private static final String characterEncoding = "UTF-8";
    private static final String cipherTransformation = "AES/CBC/PKCS5Padding";
    private static final String aesEncryptionAlgorithm = "AES";

    public static byte[] decryptBase64EncodedWithManagedIV(String encryptedText, String key) throws Exception {
        byte[] cipherText = Base64.decodeBase64(encryptedText.getBytes());
        byte[] keyBytes = Base64.decodeBase64(key.getBytes());
        return decryptWithManagedIV(cipherText, keyBytes);
    }

    public static byte[] decryptWithManagedIV(byte[] cipherText, byte[] key) throws Exception{
        byte[] initialVector = Arrays.copyOfRange(cipherText,0,16);
        byte[] trimmedCipherText = Arrays.copyOfRange(cipherText,16,cipherText.length); 
        return decrypt(trimmedCipherText, key, initialVector);
    }

    public static byte[] decrypt(byte[] cipherText, byte[] key, byte[] initialVector) throws Exception{
        Cipher cipher = Cipher.getInstance(cipherTransformation);
        SecretKeySpec secretKeySpecy = new SecretKeySpec(key, aesEncryptionAlgorithm);
        IvParameterSpec ivParameterSpec = new IvParameterSpec(initialVector);
        cipher.init(Cipher.DECRYPT_MODE, secretKeySpecy, ivParameterSpec);
        cipherText = cipher.doFinal(cipherText);
        return cipherText;
    }

    public static void main(String args[]) throws Exception{
        byte[] clearText = decryptBase64EncodedWithManagedIV("CERcUfcNbCAkVxklXVpMqko2FqhE12iU6eldQ9jpFPUl+uVQXKDCXxtfPQ1hwt9A5fIbt60kdVgyFhb2V40z7w==", "mRMjHmlC1C+1L/Dkz8EJuw==");
        System.out.println("ClearText:" + new String(clearText,characterEncoding));
    }


}

Answer 2

apex crypto uses AES(128/192/256)/CBC/PCKS5Padding. Any standard Cipher example from a java tutorial should do the job. Create the Cipher with the IV, create the SecretKey from your key and the AES strength and doFinal() on the encryption. Thats it.

Sorry abt the formatting. total n00b on these forums...

byte [] encBytes = ...; /* your enc string */
SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
byte[] iv = ...; /* your IV */;
IvParameterSpec ivSpec = new IvParameterSpec(iv);
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);
byte[] decBytes = cipher.doFinal(encBytes);
String decStr = new String(decBytes);