Question

I have this PHP function (using PHP 5.3) that I use to decrypt files, it used to work just fine, but now that I moved to Amazon EC2 (based on Amazon Linux Image 2012.3), it seems that mcrypt install is either corrupted or not available at all.

Initial tests suggests that file decryption does work on smaller files, but not on 20MB+ files (which is not a particularly large size).

I tracked the problem down to this line, which is causing an Error 500 (I’m not getting mcrypt_module_open is undefined, just 500 server error)

$td = mcrypt_module_open ('rijndael-128', '', 'cbc', '');

What’s strange, I checked /etc/php.ini, I can’t see mcrypt at all (assuming I’m looking at the correct php.ini/path of course!)

The PHP code/function is:

function decrypt_file ($inputfile, $outputfile)
{
    $key        = FILE_KEY;  // <-- assign private key
    $buffersize = 16384;

    // Open $inputfile for reading binary
    $input      = fopen ($inputfile, 'rb');

    // Error opening $inputfile, return false
    if (!$input)
        return false;

    // Open $outputfile for writing binary
    $output     = fopen ($outputfile, 'wb');

    // Error opening $outputfile, return false
    if (!$output)
        return false;

    // Open the cipher module
    $td = mcrypt_module_open ('rijndael-128', '', 'cbc', '');

    // Read the IV from $inputfile
    $iv = fread ($input, 16);

    // Compute the SHA512 of the IV (salt) and Key and use 32 bytes (256 bit) of the result as the encryption key
    $keyhash = substr (hash ('sha512', $iv . $key, true), 0, 32);

    // Intialize encryption
    mcrypt_generic_init ($td, $keyhash, $iv);

    while (!feof ($input))
    {
        $buffer = fread ($input, $buffersize);

        // Encrypt the data
        $buffer = mdecrypt_generic ($td, $buffer);

        // Remove padding for last block
        if (feof ($input))
        {
            $padsize = ord ($buffer[strlen ($buffer) - 1]);
            $buffer  = substr ($buffer, 0, strlen ($buffer) - $padsize);
        }

        // Write the encrypted data to $output
        fwrite ($output, $buffer, strlen ($buffer));
    }

    fclose ($input);
    fclose ($output);

    // Deinitialize encryption module
    mcrypt_generic_deinit ($td);

    // Close encryption module
    mcrypt_module_close ($td);

    return true;
}

Anyone knows how to fix that? I’m using PHP 5.3 with CodeIgniter 2.1 (thought this is most likely not related to CodeIgniter)

Answer 1

It looks like you don’t have mcrypt installed. Try running:

sudo yum install php-mcrypt

…from the command line on your instance.