mcrypt_decrypt() error change key size

Question

mcrypt_decrypt(): Key of size 15 not supported by this algorithm. Only keys of sizes 16, 24 or 32 supported

How Can I fix this issue? my

Answer 1

You can just use str_pad() for this. In its simplest form, this will suffice.

function padKey($key) 
{
    // Get the current key size
    $keySize = strlen($key);

    // Set an array containing the valid sizes
    $validSizes = [16,24,32];

    // Loop through sizes and return correct padded $key
    foreach($validSizes as $validSize) {
        if ($keySize <= $validSize) return str_pad($key, $validSize, "\0");
    }

    // Throw an exception if the key is greater than the max size
    throw new Exception("Key size is too large"); 

}

The other answers will do just fine. I'm just taking advantage of the built in PHP function str_pad here instead of appending "\0" in a loop.