PHP sending encrypted data via the URL

Question

I'm trying to send encrypted data over the url to another site (using file_get_contents("anotherUrl.php?hash=$encryptedString"). The problem is, sometimes, the encryption contains some special characters, like +, and this causes the decryption to fail.

Here are my encryption / decryption methods:

public function encrypt($string, $key)
{
    return base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, md5($key), $string, MCRYPT_MODE_CBC, md5(md5($key))));
}

public function decrypt($encrypted, $key)
{
    return rtrim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, md5($key), base64_decode($encrypted), MCRYPT_MODE_CBC, md5(md5($key))), "\0");
}

Here's an example encrypted string which contains a +, and I'm guessing that this causes the decryption to fail.

oWCrVPaS+5GbxcQFc0fulUk/zRAkDD60av4zlPiWskE=

Any ideas how I should solve this? I've tried to do urlencode() and urldecode() on the hash, however that also seems to cause the encryption to break. Is there a way to change the encryption algorithm to get it to only return url safe characters?

Answer 1

In order to solve this problem I now use the following (after 3 hours of pain), and it works great.

Feel free to copy and paste

function encrypt($pure_string) {
    $dirty = array("+", "/", "=");
    $clean = array("_PLUS_", "_SLASH_", "_EQUALS_");
    $iv_size = mcrypt_get_iv_size(MCRYPT_BLOWFISH, MCRYPT_MODE_ECB);
    $_SESSION['iv'] = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $encrypted_string = mcrypt_encrypt(MCRYPT_BLOWFISH, $_SESSION['encryption-key'], utf8_encode($pure_string), MCRYPT_MODE_ECB, $_SESSION['iv']);
    $encrypted_string = base64_encode($encrypted_string);
    return str_replace($dirty, $clean, $encrypted_string);
}

function decrypt($encrypted_string) { 
    $dirty = array("+", "/", "=");
    $clean = array("_PLUS_", "_SLASH_", "_EQUALS_");

    $string = base64_decode(str_replace($clean, $dirty, $encrypted_string));

    $decrypted_string = mcrypt_decrypt(MCRYPT_BLOWFISH, $_SESSION['encryption-key'],$string, MCRYPT_MODE_ECB, $_SESSION['iv']);
    return $decrypted_string;
}

Answer 2

Instead of using Base64 for encoding your data you can also use Base32 (RFC 4648) which is URL-safe because it only uses letters A–Z (case-insensitive) and the digits 2–7. There is already a PHP library for encoding/decoding. Note that Base32 takes ~20% more space than Base64.

You can also use URLcrypt which is a handy library helping you with encryption and Base32 encoding.

Answer 3

class Encryption {
    var $skey   = "SuPerEncKey2010"; // you can change it

    public  function safe_b64encode($string) {

        $data = base64_encode($string);
        $data = str_replace(array('+','/','='),array('-','_',''),$data);
        return $data;
    }

    public function safe_b64decode($string) {
        $data = str_replace(array('-','_'),array('+','/'),$string);
        $mod4 = strlen($data) % 4;
        if ($mod4) {
            $data .= substr('====', $mod4);
        }
        return base64_decode($data);
    }

    public  function encode($value){ 

        if(!$value){return false;}
        $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, $this->skey, $text, MCRYPT_MODE_ECB, $iv);
        return trim($this->safe_b64encode($crypttext)); 
    }

    public function decode($value){

        if(!$value){return false;}
        $crypttext = $this->safe_b64decode($value); 
        $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, $this->skey, $crypttext, MCRYPT_MODE_ECB, $iv);
        return trim($decrypttext);
    }
}

Answer 4

Take a look at this thread:

Passing base64 encoded strings in URL

Essentially you DO want to urlencode() before sending the string, however you do NOT want to urldecode() at the other end.