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php encryption / compression for putting data in a URL

Posted on 2008-10-21
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Last Modified: 2011-10-03
We are planning to transmit data between web pages using the url. Sort of the following exmaple:

http://www.mysite.com/?data=data_to_be_transmitted_here

We are looking for the best encrypting algorithm to make "data_to_be_trasmitted_here" obscure to the end user. It doesn't have to be secure, just unreadable. We though of using base64_encode() , but ideally we can also compress, so the end result takes less space than the original input string. Is there any other PHP functions / libraries we can use for this?

Again, the requirements are: find a PHP function or library to create an unreadable string, that don't contain special characters (so we can put it on a url) and it is compact, or even smaller than the input string, and that can be decoded back to its original.
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Question by:cabrera48
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6 Comments
 
LVL 15

Expert Comment

by:MMDeveloper
ID: 22769877
is using a database an option? You can put the raw query string in a database and simply reference a row number

mysite.com?data=23

Maybe use sessions to store the data and you dont need to use a query string at all?

I'm not sure how the URL's will be hit (get, post, etc)
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Author Comment

by:cabrera48
ID: 22770143
Unfortunately we can't use sessions or database due to the nature of our application.

In a nutshell, we'll have hundreds of links per page, we are trying to avoid db access as much as possible, and we have some problems with sessions going off-synch when user right-click links and open new browser tabs, and goes back and forth clicking through the different instances of the browsers (the data we are passing thru is a combination of historical / hierarchical clicktrhoughs).

It's kind of a long story to explain, but we can't use database or sessions. Everything has to be appended to the url as specified above.

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LVL 15

Accepted Solution

by:
MMDeveloper earned 300 total points
ID: 22770277
how about this
function compressCrypt($string) {
	return base64_encode(gzcompress($string, 9));
}
 
function decompressCrypt($string) {
	return gzuncompress(base64_decode($string));
}
 
 
compressed and base64 encoded: compressCrypt("your query string");
 
and to return
 
decompressCrypt("your encoded query string");

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LVL 109

Assisted Solution

by:Ray Paseur
Ray Paseur earned 200 total points
ID: 22770744
This might be useful, depending on the character set you want to use.  HTH, ~Ray
/* ************************************************************************* */
function encode_word($string, $code=0) {
 
	$clear_text	= '$%-.0123456789@ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz';
	$scrambled	= 'fjAEokIOzU2q13_h5w794p@6s8B.gPdFVmDTcSZe%rlGKuCyJxHiQLt-RMa$NvWYnb0X';
 
	$reg_text = "[" . $clear_text . "]";
	if (!ereg("$reg_text", $string)) {
return false; }
 
	$cryptodo	= $scrambled;
 
	$string_l	= strlen($string);
	while ($string_l > 0) { $cryptodo .= $scrambled; $string_l--; }
 
	$scramb_l	= strlen($scrambled);
 	$code		= intval($code);
	if ($code > $scramb_l) { $code = 0; }
	if ($code < 0) { $code = 0; }
 
	$kode = $code;
	while ($kode > 0) { $cryptodo .= $scrambled; $kode--; }
 
	$cryptodo	= substr($cryptodo,$code);
 
	$string_l	= strlen($string);
 
	$encoded_string = '';
	while ($string_l > 0) {
		$byte			= substr($string, 0, 1);
		$index			= strpos($clear_text, $byte); 
		$encoded_string	.= substr($cryptodo,$index,1);
		$string			= substr($string,1);
		$cryptodo		= substr($cryptodo, $index+$code);
		$string_l--;
	}
return ($encoded_string);
}
/* ************************************************************************* */
 
/* ************************************************************************* */
function decode_word($string, $code=0) {
 
	$clear_text	= '$%-.0123456789@ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz';
	$scrambled	= 'fjAEokIOzU2q13_h5w794p@6s8B.gPdFVmDTcSZe%rlGKuCyJxHiQLt-RMa$NvWYnb0X';
 
	$cryptodo	= $scrambled;
 
	$string_l	= strlen($string);
	while ($string_l > 0) { $cryptodo .= $scrambled; $string_l--; }
 
	$scramb_l	= strlen($scrambled);
 	$code		= intval($code);
	if ($code > $scramb_l) { $code = 0; }
	if ($code < 0) { $code = 0; }
 
	$kode = $code;
	while ($kode > 0) { $cryptodo .= $scrambled; $kode--; }
 
	$cryptodo	= substr($cryptodo,$code);
 
	$string_l	= strlen($string);
 
	$decoded_string = '';
	while ($string_l > 0) {
		$byte			= substr($string, 0, 1);
		$index			= strpos($cryptodo, $byte);
		$decoded_string	.= substr($clear_text,$index,1);
		$string			= substr($string,1);
		$cryptodo		= substr($cryptodo, $index+$code);
		$string_l--;
	}
return ($decoded_string);
}
/* ************************************************************************* */

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Author Comment

by:cabrera48
ID: 22772554
Both approaches do work, thanks guys.

Looks like base64 will still produce long strings, even if we gzcompress($str,9)  prior to feeding the base64_encode() function.

I just wish there was a way to produce smaller, more compact strings, but given the odd conditions of this application we are willing to live with that.

Thanks
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LVL 109

Expert Comment

by:Ray Paseur
ID: 22775096
You might be able to produce shorter strings if you use a reduced character set.  For example, if you limit yourself to 32 characters, you can get your "alpahbet" into 5 bits.  This can give you a 3-characters in 2-bytes compression.  Another way might be to use a lookup table that associates certain characters in certain positions with an expanded meaning.  For example, an "A" in position #1 means something unique, etc.  In any case, thanks for the points and good luck with your application.   Best, ~Ray
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