adding time limited token. useful thing. used in openidp and more

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@1426 44740490-163a-0410-bde0-09ae8108e29a

lib/SimpleSAML/Auth/TimeLimitedToken.php

+<?php
+
+
+class SimpleSAML_Auth_TimeLimitedToken {
+
+	var $secretSalt;
+	var $lifetime;
+	var $skew;
+
+	/**
+	 * @param $secretSalt Must be random and unique per installation
+	 * @param $lifeTime Token lifetime in seconds
+	 * @param $skew  Allowed time skew between server that generates and the one that calculates the token
+	 */
+	public function __construct( $lifetime = 900, $secretSalt = NULL, $skew = 1) {
+		if ($secretSalt === NULL) {
+			$config = SimpleSAML_Configuration::getInstance();
+			$secretSalt = $config->getValue('secretsalt');
+		}
+	
+		$this->secretSalt = $secretSalt;
+		$this->lifetime = $lifetime;
+		$this->skew = $skew;
+	}
+	
+	public function addVerificationData($data) {
+		$this->secretSalt .= '|' . $data;
+	}
+	
+	
+	/**
+	 * Calculate the current time offset to the current time slot.
+	 * With some amount of time skew
+	 */
+	private function get_offset() {
+		return ( (time() - $this->skew) % ($this->lifetime + $this->skew) );
+	}
+	
+	/**
+	 * Calculate the given time slot for a given offset.
+	 */
+	private function calculate_time_slot($offset) {
+	
+		#echo 'lifetime is: ' . $this->lifetime;
+		
+		$timeslot = floor( (time() - $offset) / ($this->lifetime + $this->skew) );
+		return $timeslot;
+	}
+	
+	/**
+	 * Calculates a token value for a given offset
+	 */
+	private function calculate_tokenvalue($offset) {
+		// A secret salt that should be randomly generated for each installation.
+		#echo 'Secret salt is: ' . $this->secretSalt;
+		
+		#echo '<p>Calculating sha1( ' . $this->calculate_time_slot($offset) . ':' . $this->secretSalt . '  )<br />';
+		
+		return sha1( $this->calculate_time_slot($offset) . ':' . $this->secretSalt);
+	}
+	
+	/**
+	 * Generates a token which contains of a offset and a token value. Using current offset
+	 */
+	public function generate_token() {
+		$current_offset = $this->get_offset();
+		return dechex($current_offset) . '-' . $this->calculate_tokenvalue($current_offset);
+	}
+	
+	/**
+	 * Validates a full token, by calculating the token value for the provided 
+	 * offset and compares.
+	 */
+	public function validate_token($token) {
+		$splittedtoken = explode('-', $token);
+		$offset = hexdec($splittedtoken[0]);
+		$value  = $splittedtoken[1];
+		
+		
+		#echo 'compare [' . $this->calculate_tokenvalue($offset). '] with [' . $value . '] offset was [' . $offset. ']';
+		
+		return ($this->calculate_tokenvalue($offset) === $value);
+	}
+	
+}
+
+