Question

I can’t for the life of me work out why when I encrypt something in PHP I can’t then decrypt it in my iOS app, but PHP can decrypt iOS encrypted strings and decrypt/encrypt between itself.

PHP -> Obj-C FAILS.

Yes, I have looked across the net and the only solution I found was to use CBC in PHP which I’m already doing.

I’m using the FBEncryptor library for iOS and these are the encrypt/decrypt functions in PHP:

function encrypt($decrypted)
{    
    $iv = ''; for($i=0;$i<16;$i++){ $iv .= "\0";}
    $ciphertext = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $passKey, $decrypted, MCRYPT_MODE_CBC, $iv);
    $ciphertext = base64_encode($ciphertext);
    return $ciphertext;
}

function decrypt($encrypted)
{
    $iv = ''; for($i=0;$i<16;$i++){ $iv .= "\0";}        
    $ciphertext = base64_decode($encrypted);
    $plaintext = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $passKey, $ciphertext, MCRYPT_MODE_CBC, $iv);
    return $plaintext;
}

Answer 1

I managed to work out the problem. Was a silly mistake on my part with the pass key variable. Here is my final implementation anyway for anyone else that comes across this problem:

function encrypt($decrypted)
{
    $thePassKey = "12345678901234567890123456789012";

    # Add PKCS7 padding.
    $str = $decrypted;
    $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
    if (($pad = $block - (strlen($str) % $block)) < $block) 
    {
        $str .= str_repeat(chr($pad), $pad);
    }

    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
    $iv = ''; for($i=0;$i<$iv_size;$i++){ $iv .= "\0";}
    return base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $thePassKey, $str, MCRYPT_MODE_CBC, $iv));
}

function decrypt($encrypted)
{
    $thePassKey = "12345678901234567890123456789012";

    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
    $iv = ''; for($i=0;$i<$iv_size;$i++){ $iv .= "\0";}
    $str = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $thePassKey, base64_decode($encrypted), MCRYPT_MODE_CBC, $iv);

    # Strip PKCS7 padding.
    $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
    $pad = ord($str[($len = strlen($str)) - 1]);
    if ($pad && $pad < $block && preg_match(
        '/' . chr($pad) . '{' . $pad . '}$/', $str))
    {
        return substr($str, 0, strlen($str) - $pad);
    }

    return $str;
}