Decrypt string in java which was encrypted using AES in php

Question

<?php
    # --- ENCRYPTION ---

    # the key should be random binary, use scrypt, bcrypt or PBKDF2 to
    # convert a string into a key
    # key is specified using hexadecimal

    $length = 16;
    $key = openssl_random_pseudo_bytes($length);
    // echo $key;

    // $key = pack('H*', "bcb04b7e103a0cd8b54763051cef08bc55abe029fdebae5e1d417e2ffb2a00a3");
    echo $key."<br/>";

    echo "<br/>";
    # show key size use either 16, 24 or 32 byte keys for AES-128, 192
    # and 256 respectively
    $key_size =  strlen($key);
    echo "Key size: " . $key_size;
    echo "<br/>";

    $plaintext = "This string was AES-256 / CBC / ZeroBytePadding encrypted.";

    # create a random IV to use with CBC encoding
    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);

    # creates a cipher text compatible with AES (Rijndael block size = 128)
    # to keep the text confidential 
    # only suitable for encoded input that never ends with value 00h
    # (because of default zero padding)
    $ciphertext = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key,
                                 $plaintext, MCRYPT_MODE_CBC, $iv);

    # prepend the IV for it to be available for decryption
    $ciphertext = $iv . $ciphertext;

    # encode the resulting cipher text so it can be represented by a string
    $ciphertext_base64 = base64_encode($ciphertext);

    echo  "ENCRYPTED DATA =". $ciphertext_base64;
    echo "<br/>";

    # === WARNING ===

    # Resulting cipher text has no integrity or authenticity added
    # and is not protected against padding oracle attacks.

    # --- DECRYPTION ---

    $ciphertext_dec = base64_decode($ciphertext_base64);

    # retrieves the IV, iv_size should be created using mcrypt_get_iv_size()
    $iv_dec = substr($ciphertext_dec, 0, $iv_size);

    # retrieves the cipher text (everything except the $iv_size in the front)
    $ciphertext_dec = substr($ciphertext_dec, $iv_size);

    # may remove 00h valued characters from end of plain text
    $plaintext_dec = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key,
                                    $ciphertext_dec, MCRYPT_MODE_CBC, $iv_dec);

    echo  "DECRYPTED TEXT = ".$plaintext_dec;
?>

JAVA :-

public static String decryptWithIV(byte[] key, String encrypted)
        throws GeneralSecurityException {

    if (key.length != 16) {
        throw new IllegalArgumentException("Invalid key size.");
    }
    SecretKeySpec skeySpec = new SecretKeySpec(key, "AES");

    Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
    cipher.init(Cipher.DECRYPT_MODE, skeySpec, new IvParameterSpec(
            new byte[16]));
    byte[] original = cipher.doFinal(Base64.decodeBase64(encrypted
            .getBytes()));

    return new String(original);
}

When I run the PHP code I get below 2 details which I copied to my java code.

public static final String KEY = "œ8[,#BÌüïmÕe-<Æ   1^Ž—½R™t3§¡ÚI";
    public static final String ENCRYPTED_DATA = "ASfLnSMyfp9vHN2UTO4TRilUIRywzVfJfrfkrp4gPsP0+lENwEHJ3/YzstfuIESgVFfpkxHGTxuiO+aWZObG5aPoZfrcoIDQLVXeRiysA4s=";

The issue is my key already in byte (When run on localhost), but in my java code its again trying to convert it into byte. I would like to know How can I initialize byte array as I have the key with me from localhost as of now.

Answer 1

There are some problems with your code.

• Your key in Java is only 31 characters long and not 32. Bytes cannot be always represented as a string, because there are sometimes non-prinable characters. You can print your key as hex with bin2hex() or as base64 with base64_encode() and reverse the process in Java like this (hex) or with Base64.decodeBase64().
• Use the same mode of operation and padding like in PHP. That is use "AES/CBC/NoPadding". Since PHP uses ZeroPadding, you will then need to remove the zero bytes at the end after decryption.
• The IV is prepended to the ciphertext in PHP, but you don't slice the IV off in Java. Also, you provide a zero byte IV.

public static String decryptWithIV(byte[] key, String encrypted)
        throws GeneralSecurityException {
    if (key.length != 16) {
        throw new IllegalArgumentException("Invalid key size.");
    }

    byte[] ciphertextBytes = Base64.decodeBase64(encrypted.getBytes());
    IvParameterSpec iv = new IvParameterSpec(ciphertextBytes, 0, 16);
    ciphertextBytes = Arrays.copyOfRange(ciphertextBytes, 16,
            ciphertextBytes.length);

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

    Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
    cipher.init(Cipher.DECRYPT_MODE, skeySpec, iv);
    byte[] original = cipher.doFinal(ciphertextBytes);

    // remove zero bytes at the end
    int lastLength = original.length;
    for (int i = original.length - 1; i > original.length - 16; i--) {
        if (original[i] == (byte) 0) {
            lastLength--;
        } else {
            break;
        }
    }

    return new String(original, 0, lastLength);
}