Convert encryption/decryption function from Python to PHP

Question

I have this Python script to encrypt/decrypt URLs:

# -*- coding: utf-8 -*-
import base64
from operator import itemgetter


class cryptUrl:
    def __init__(self):
        self.key = 'secret'

    def encode(self, str):
        enc = []
        for i in range(len(str)):
            key_c = self.key[i % len(self.key)]
            enc_c = chr((ord(str[i]) + ord(key_c)) % 256)
            enc.append(enc_c)
        return base64.urlsafe_b64encode("".join(enc))

    def decode(self, str):
        dec = []
        str = base64.urlsafe_b64decode(str)
        for i in range(len(str)):
            key_c = self.key[i % len(self.key)]
            dec_c = chr((256 + ord(str[i]) - ord(key_c)) % 256)
            dec.append(dec_c)
        return "".join(dec)

url = "http://google.com";
print cryptUrl().encode(url.decode('utf-8'))

This works fine. For example the above url is converted to 29nX4p-joszS4czg2JPG4dI= and the decryption brings it back to the URL.

Now i want to convert this to a PHP function. So far encryption is working fine....but decryption is not....and i dont know why.....so far i got this:

function base64_url_encode($input) {
    return strtr(base64_encode($input), '+/=', '-_');
}

function base64_url_decode($input) {
    return strtr(base64_decode($input), '-_', '+/=');
}   

function encode ($str)
{
    $key = 'secret';

    $enc = array();
    for ($i;$i<strlen($str);$i++){
        $key_c = $key[$i % strlen($key)];
        $enc_c = chr((ord($str[$i]) + ord($key_c)) % 256);
        $enc[] = $enc_c;
    }
  return base64_url_encode(implode($enc));
}


function decode ($str)
{
    $key = 'secret';

    $dec = array();
    $str = base64_url_decode($str);
    for ($i;$i<strlen($str);$i++){
        $key_c = $key[$i % strlen($key)];
        $dec_c = chr((256 + ord($str[$i]) + ord($key_c)) % 256);
        $dec[] = $dec_c;
    }
  return implode($dec);
}


$str = '29nX4p-joszS4czg2JPG4dI=';
echo decode($str);

Now the above decoding prints out : N>:Tý\&™åª—Væ which is not http://google.com :p Like i said encoding function works though. Why isnt the decoding working ? What am i missing ?

Btw i cant use any other encoding/decoding function. I have a list of URLs encoded with python and i want to move the whole system to a PHP based site....so i need to decode those URLs with a PHP function instead of python.

(Use this page to execute Python: http://www.compileonline.com/execute_python_online.php)

blue · Accepted Answer · 2014-04-04 12:54:46Z

1

Double check the syntax of strtr().

I'd suggest you using in in the following way:

strtr(
    base64_encode($input),
    array(
        '+' => '-',
        '/' => '_',
        '=' => YOUR_REPLACE_CHARACTER
    )
)

Make sure you have YOUR_REPLACE_CHARACTER!

Also, I'm sure you'll handle the reverse function, where you need to simply flip the values of the replace array.

answered Apr 4, 2014 at 12:54

blue

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3 Comments

user1033882 Over a year ago

My above encode function works fine. Like you said i simply flip the values in my decode function and then do the decoding...like in the python script but thats not working.....THAT is my problem...not the encode function.

blue Over a year ago

Please, read my answer again. You're using strtr() the wrong way. Use it like I've wrote and it'd be fine.

Paul Over a year ago

A shorter way to do the same: strtr(base64_encode($input), "+/=" ,"-_X"), where X is your replace character.

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