Encoding and decoding

Question

I am looking to encode some text that could be 1 charchter long or or 10,000 or infinite and decode (reverse the algorithm).

I am looking something like MD5 on PHP, but reversable, as MD5 is one way.

This could be server side or JavaScript. If both, then it's even better.

Answer 1

For compression

In Javascript, http://rumkin.com/tools/compression/compress_huff.php

Also have a look at http://stackoverflow.com/questions/994667/javascript-text-compression-decompression

For encryption

In PHP, you can use mcrypt:

http://www.php.net/manual/en/function.mcrypt-encrypt.php

http://www.php.net/manual/en/function.mcrypt-decrypt.php

Sample code (from above site):

<?php
class Cipher {
    private $securekey, $iv;
    function __construct($textkey) {
        $this->securekey = hash('sha256',$textkey,TRUE);
        $this->iv = mcrypt_create_iv(32);
    }
    function encrypt($input) {
        return base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $this->securekey, $input, MCRYPT_MODE_ECB, $this->iv));
    }
    function decrypt($input) {
        return trim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $this->securekey, base64_decode($input), MCRYPT_MODE_ECB, $this->iv));
    }
}

$cipher = new Cipher('secret passphrase');

$encryptedtext = $cipher->encrypt("hide me");
echo "->encrypt = $encryptedtext<br />";

$decryptedtext = $cipher->decrypt($encryptedtext);
echo "->decrypt = $decryptedtext<br />";

var_dump($cipher);
?> 

Answer 2

There are implementations of rot13 for PHP and JS, as well as URL encoding (PHP, JS).

Answer 3

If you want to compress string, see this question for info on JavaScript implementation of LZW, Huffman, LZ77 and others. I'm pretty sure that there are similar libraries in PHP.