PHP sending encrypted data via the URL - php

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

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.

Answer 2

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 3

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 4

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);
}
}