mcrypt doesn't work in PHP 5.6 on windows/IIS

Question

I have been making heavy use of mcrypt in my php app for years, both on win/IIS and on linux. Although I'm running PHP 5.4.28 on my linux server, I just upgraded to PHP 5.6.11 on my windows 8.1 IIS box. And mcrypt no longer works. It doesn't throw any errors that I can see; it just doesn't work. Here is my encryption function:

function Encrypt($text){ 
    global $salt;
    if($text != "")
        return trim(base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $salt, $text, MCRYPT_MODE_ECB, mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND))));  
    else
        return "";
}   

This works fine on my linux server, but returns blank on my local windows box. From what I have read, mcrypt is built into php 5.6 for windows, so there should be no fiddling with extensions or ini file.

What am I missing?

Answer 1

PHP 5.6 has stronger encryption requirements than 5.4. In 5.6 you'll get this warning, which is really an error because it actually causes encryptions and decryptions to fail:

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

...where "xx" is the length of your salt value. So the salt value has to be exactly 16, 24, or 32 characters in length.