AES encryption using Java and PHP

Question

I have recently used the AES algorithm in Java in order to cipher a text. Now I need to rebuild that algorithm in PHP, but I have no idea how, because PHP algorithms on the internet return different results. Maybe you can help me.

This is the Java-code to encrypt:

private static final String KEY = "57238004e784498bbc2f8bf984565090";

public static String encrypt(final String plaintext) throws GeneralSecurityException {
    SecretKeySpec sks = new SecretKeySpec(hexStringToByteArray(KEY), "AES");
    Cipher cipher = Cipher.getInstance("AES");
    cipher.init(Cipher.ENCRYPT_MODE, sks, cipher.getParameters());
    byte[] encrypted = cipher.doFinal(plaintext.getBytes());
    return byteArrayToHexString(encrypted);
}

public static byte[] hexStringToByteArray(String s) {
    byte[] b = new byte[s.length() / 2];
    for (int i = 0; i < b.length; i++) {
        int index = i * 2;
        int v = Integer.parseInt(s.substring(index, index + 2), 16);
        b[i] = (byte) v;
    }
    return b;
}

public static String byteArrayToHexString(byte[] b) {
    StringBuilder sb = new StringBuilder(b.length * 2);
    for (int i = 0; i < b.length; i++) {
        int v = b[i] & 0xff;
        if (v < 16) {
            sb.append('0');
        }
        sb.append(Integer.toHexString(v));
    }
    return sb.toString().toUpperCase();
}

Can you guys possibly help me with building a PHP script, that returns the same results?

Example: The plaintext "STACKOVERFLOW" is encrypted to "FA652ECCDC39A11A93D2458AA2A0793C".

Thanks in advance!

ECB is not secure. You need to use CBC, and pass an IV. Depending on your security boundaries, you probably also need authenticated encryption, such as GCM. — SLaks
– SLaks, Commented Jul 24, 2013 at 13:41

Community · Accepted Answer · 2023-11-17 20:42:18Z

3

This should do it:

function encrypt($plaintext, $key) {
    $plaintext = pkcs5_pad($plaintext, 16);
    return bin2hex(mcrypt_encrypt(MCRYPT_RIJNDAEL_128, hex2bin($key), $plaintext, MCRYPT_MODE_ECB));
}

function decrypt($encrypted, $key) {
    $decrypted = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, hex2bin($key), hex2bin($encrypted), MCRYPT_MODE_ECB);
    $padSize = ord(substr($decrypted, -1));
    return substr($decrypted, 0, $padSize*-1);
}

function pkcs5_pad ($text, $blocksize)
{
    $pad = $blocksize - (strlen($text) % $blocksize);
    return $text . str_repeat(chr($pad), $pad);
}

The reason that other PHP algorithms you found were returning different results is likely because of the padding. The default for AES in Java is PKCS5, but PHP doesn't have native support for this (hence the pkcs5_pad function).

As SLacks has said, you really should not be using ECB though. Either get the Java code changed or re-encrypt your existing data if need be. As long as you continue using ECB, you're putting your data at risk.

Credit: Padding function taken from here.

edited Nov 17, 2023 at 20:42

CommunityBot

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answered Jul 24, 2013 at 15:13

Syon

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3 Comments

Rico Herwig Over a year ago

Could you give me the decrypt-php-function, too? And thanks so much! It works.

Syon Over a year ago

Added per your request.

Pavel Vlasov Over a year ago

Awesome work, Syon! Both cryptic functions gave me the same result.

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