iOS/PHP kCCDecodeError - php

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

From the FBEncryptor Github page (emphasis mine):
Supported encryption algorithm is AES 256 bit only.
But in your code snippet above, you're doing:
mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $ciphertext, MCRYPT_MODE_CBC, $iv);
i.e. decrypting with AES 128 bit as your cipher.
You'll need to correct your code accordingly. Other common mistakes include using mismatched padding and block cipher operation modes.

Answer 2

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;
}