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@sbrl /comment_key.php Secret
Last active Jan 30, 2018

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[Comment Key System] A comment key generation and verification system to prevent spam on low-value targets. #blog #antispam #microlibrary
<?php
/***********************************************
* Comment Key Generation System
***********************************************
* By Starbeamrainbowlabs <feedback@starbeamrainbowlabs.com>
*
* A set of functions to protect low-value comment boxes, contact us
* forms, etc. from spam.
*
* It works by recording the time the page the form is on was loaded,
* and then checking to make sure that it was loaded for at least
* 10 - 15 seconds, and not more than 24 hours.
*
* This is done by taking the current UNIX timestamp, running it through
* a number of (arbitrary) reversible transformations, and then
* embedding it in the form as a hidden field. When the form is
* submitted, the transformations are reversed and the time the page
* was loaded checked.
*
* Note that this is not suitable for high-value targets, as it can very
* easily be bypassed and reverse-engineered by any determined human.
*
***********************************************
* Changelog:
* 30th January 2018:
* Initial Release.
*/
/**
* Generates a new comment key.
* Note that the 'encryption' used is not secure - it's just simple XOR!
* It's mainly to better support verification in complex setups and
* serve as a nother annoying hurdle for spammers.
* TODO: Swap out the XOR for openssl AES symmetric encryption
* @param string $pass The password to transform it with. Should be a pre-selected random string.
* @return string A new comment key stamped at the current time.
*/
function key_generate($pass) {
$new_key = strval(time());
// Repeat the key so that it's long enough to XOR the key with
$pass_enc = str_repeat($pass, (strlen($new_key) / strlen($pass)) + 1);
$new_key = $new_key ^ $pass_enc;
return base64_encode(strrev($new_key));
}
/**
* Decodes the given key.
* @param string $key The key to decode.
* @param string $pass The password to decode it with.
* @return int The time that the key was generated.
*/
function key_decode($key, $pass) {
$key_dec = strrev(base64_decode($key));
// Repeat the key so that it's long enough to XOR the key with
$pass_dec = str_repeat($pass, (strlen($key_dec) / strlen($pass)) + 1);
return intval($key_dec ^ $pass_dec);
}
/**
* Verifies a key.
* @param string $key The key to decode and verify.
* @param string $pass The password to decode the key with.
* @param int $min_age The minimum required age for the key.
* @param int $max_age The maximum allowed age for the key.
* @return bool Whether the key is valid or not.
*/
function key_verify($key, $pass, $min_age, $max_age) {
$age = time() - key_decode($key, $pass);
return $age >= $min_age && $age <= $max_age;
}
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