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 key is set - can not change it. It has to be a local change, I think my local PHP version is too advanced for the project I loaded. How can I fix this?

Answer 1

I went ahead and created a function based on Hanky 웃 Panky's answer.

This can be used with any key length to make sure it's the correct size.

function pad_key($key){
    // key is too large
    if(strlen($key) > 32) return false;

    // set sizes
    $sizes = array(16,24,32);

    // loop through sizes and pad key
    foreach($sizes as $s){
        while(strlen($key) < $s) $key = $key."\0";
        if(strlen($key) == $s) break; // finish if the key matches a size
    }

    // return
    return $key;
}

Answer 2

For Laravel 5

Just run php artisan key:generate:

Application key [EaaJgaD0uFDEg7tpvMOqKfAQ46Bqi8Va] set successfully.

If you don't see your key updated, just paste it in your .env file.

APP_KEY=EaaJgaD0uFDEg7tpvMOqKfAQ46Bqi8Va

Refresh your page

Answer 3

You don't need to pad the key with "\0".

I had the same issue when migrating to a new PHP 7 server and I got the message :

mcrypt_decrypt(): Key of size 19 not supported by this algorithm. Only keys of sizes 16, 24 or 32 supported.

The key I had in the code was a string of 19 characters, I simply changed it to a string of 32 characters and everything was fine again.

So as the error message suggests, use a valid size key.

Answer 4

If your encryption code looks like this:

<?php
  function encryptCookie($value){
    if(!$value){return false;}
    $key = 'aNdRgUkXp2s5v8y/B?E(H+MbQeShVmYq';
    $text = $value;
    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $crypttext = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $text, MCRYPT_MODE_ECB, $iv);
    return trim(base64_encode($crypttext)); //encode for cookie
   }
 function decryptCookie($value){
    if(!$value){return false;}
    $key = 'aNdRgUkXp2s5v8y/B?E(H+MbQeShVmYq';
    $crypttext = base64_decode($value); //decode cookie
    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $decrypttext = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $crypttext, MCRYPT_MODE_ECB, $iv);
    return trim($decrypttext);
   }
?>

You will want to change the $key to a 128 or 256 bit encrypted code. I simply copied a code that I generated from here: Generate Code

I created a 256 bit code for mine which consists of 32 characters and thus fixes the issue of the invalid key size of 15 or whatever number is causing the error. So whatever is set for $key you need to change that to a valid code and then it should work fine.

Answer 5

Did you update to 5.6? It says

Invalid key and iv sizes are no longer accepted. mcrypt_decrypt() will now throw a warning and return FALSE if the inputs are invalid. Previously keys and IVs were padded with '\0' bytes to the next valid size.

Reference

Read the last line of that quote, and there you will find your solution :)

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

That means you need to pad your key with \0 (that's what previous versions were doing for you)

$key=$key."\0";

Answer 6

I had the same problem, but fixed it with this

public function setKey($key) {
    $len = strlen($key);
    if($len < 24 && $len != 16){
        $key = str_pad($key, 24, "\0", STR_PAD_RIGHT); 
    } elseif ($len > 24 && $len < 32) {
        $key = str_pad($key, 32, "\0", STR_PAD_RIGHT);       
    }elseif ($len > 32){
        $key = substr($key, 0, 32);
    }
    $this->key = $key;
 }