Is it safe to use encryption before urlencode /urldecode. encrypted GET url does not return same value, replacing all + with spaces occasionally

Question

Hi I am using an encryption function to encrypt my URI before getting it urlencoded and function to finally decrypt it back after I urldecoded in receiving page. Its working fine often but occasionally urldecode replacing all the + with spaces thus making my decrypt function fail.

Here are my encrypt and decrypt functions:

function encryptIt( $q ) {
    $cryptKey  = 'aJB0rGtIn5UB1xG40efydp';
    $qEncoded      = base64_encode( mcrypt_encrypt( MCRYPT_RIJNDAEL_256, md5( $cryptKey ), $q, MCRYPT_MODE_CBC, md5( md5( $cryptKey ) ) ) );
    return( $qEncoded );
}

function decryptIt( $q ) {
    $cryptKey  = 'aJB0rGtIn5UB1xG40efydp';
    $qDecoded      = rtrim( mcrypt_decrypt( MCRYPT_RIJNDAEL_256, md5( $cryptKey ), base64_decode( $q ), MCRYPT_MODE_CBC, md5( md5( $cryptKey ) ) ), "\0");
    return( $qDecoded );
}

And here is how I am preparing my GET Url :

                $encrypted_id = encryptIt( $id );

                $uri=urlencode($encrypted_id);
                $uri="http://example.com/xyz.php?id=".$uri; 

And then my receiving script:

               $id=urldecode($_GET['id']);
               $id=decryptIt($id);

Is it safe to use encryption/decryption and URlencode / urldecode at same time? or I am doing it wrong way somewhere .

Answer 1

Don't call urldecode() in the receiver. PHP automatically decodes all the URL parameters before it puts them into $_GET. So you're decoding twice; the automatic decode translates %2B to +, and then your call to urldecode() translates + to space.