Convert encryption/decryption function from Python to PHP - encryption

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)

Answer 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.