crypt/decrypt over 2 pages

mberman

i've done searching in the PHPBuilder Snippit Library, and on other sites. I've found a google search unsuccessfully, also.

I'm sure there's a way to do this... I want to take a string, i.e. an IP, make it un human-readable, but not necessarially encrypted, so I can pass it via the url via get. The point here is to make it so that when the IP is passed via the URL, people can't just change what the script knows as their IP by simply changing it in the URL.

I know there are functions that do that - my problem arises in the fact that I encrypt it in one page load and decrypt it on another.

So, a page is loaded which gets and encrypts the IP. It prints a form for additional information. It then sends the form on to another page which decrypts the IP. All of the encrypt/decrypt functions I've found work like a charm within the page, but seed themselves differently when it encrypts/decrypts not within the same page load. And this means that I just get garbage...

Any ideas?

TIA

Sgarissta

Take a look at php's [man]mcrypt[/mant] support for the ability to encrypt/decrypt consistently.

mberman

I looked into mcrypt (thanks, Sgarissta) - but I haven't been able to get anywhere with it. This is what I have so far, derived from the PHP man pages:

<?PHP
/* A lot of this stuff I got from the example on PHP.net, for mcrypt_encrypt... */
$key = "fookey is good";
if($proc) {
	$data = $_GET["data"];
	$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB);
	$iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
	$foo = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $data, MCRYPT_MODE_ECB, $iv);
	echo $foo;	//should print "This is a test..."
} else {
	$text = "This is a test...";
	$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, $key, $text, MCRYPT_MODE_ECB, $iv);
	echo "<a href='test2.php?proc=yes&data=$crypttext'>here</a>";
}
?>

It just prints jibberish, so my guess is that the decrypt part is broken...