437 lines
15 KiB
PHP
437 lines
15 KiB
PHP
<?php
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/**
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* @file
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*
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* csrf-magic is a PHP library that makes adding CSRF-protection to your
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* web applications a snap. No need to modify every form or create a database
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* of valid nonces; just include this file at the top of every
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* web-accessible page (or even better, your common include file included
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* in every page), and forget about it! (There are, of course, configuration
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* options for advanced users).
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*
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* This library is PHP4 and PHP5 compatible.
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*/
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// CONFIGURATION:
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/**
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* By default, when you include this file csrf-magic will automatically check
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* and exit if the CSRF token is invalid. This will defer executing
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* csrf_check() until you're ready. You can also pass false as a parameter to
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* that function, in which case the function will not exit but instead return
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* a boolean false if the CSRF check failed. This allows for tighter integration
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* with your system.
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*/
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$GLOBALS['csrf']['defer'] = true;
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/**
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* This is the amount of seconds you wish to allow before any token becomes
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* invalid; the default is two hours, which should be more than enough for
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* most websites.
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*/
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$GLOBALS['csrf']['expires'] = 7200;
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/**
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* Callback function to execute when there's the CSRF check fails and
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* $fatal == true (see csrf_check). This will usually output an error message
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* about the failure.
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*/
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$GLOBALS['csrf']['callback'] = 'csrf_callback';
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/**
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* Whether or not to include our JavaScript library which also rewrites
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* AJAX requests on this domain. Set this to the web path. This setting only works
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* with supported JavaScript libraries in Internet Explorer; see README.txt for
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* a list of supported libraries.
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*/
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$GLOBALS['csrf']['rewrite-js'] = false;
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/**
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* A secret key used when hashing items. Please generate a random string and
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* place it here. If you change this value, all previously generated tokens
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* will become invalid.
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*/
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$GLOBALS['csrf']['secret'] = ZM_AUTH_HASH_SECRET;
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// nota bene: library code should use csrf_get_secret() and not access
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// this global directly
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/**
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* Set this to false to disable csrf-magic's output handler, and therefore,
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* its rewriting capabilities. If you're serving non HTML content, you should
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* definitely set this false.
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*/
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$GLOBALS['csrf']['rewrite'] = true;
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/**
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* Whether or not to use IP addresses when binding a user to a token. This is
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* less reliable and less secure than sessions, but is useful when you need
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* to give facilities to anonymous users and do not wish to maintain a database
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* of valid keys.
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*/
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$GLOBALS['csrf']['allow-ip'] = true;
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/**
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* If this information is available, use the cookie by this name to determine
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* whether or not to allow the request. This is a shortcut implementation
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* very similar to 'key', but we randomly set the cookie ourselves.
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*/
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$GLOBALS['csrf']['cookie'] = '__csrf_cookie';
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/**
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* If this information is available, set this to a unique identifier (it
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* can be an integer or a unique username) for the current "user" of this
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* application. The token will then be globally valid for all of that user's
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* operations, but no one else. This requires that 'secret' be set.
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*/
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$GLOBALS['csrf']['user'] = false;
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/**
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* This is an arbitrary secret value associated with the user's session. This
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* will most probably be the contents of a cookie, as an attacker cannot easily
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* determine this information. Warning: If the attacker knows this value, they
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* can easily spoof a token. This is a generic implementation; sessions should
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* work in most cases.
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*
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* Why would you want to use this? Lets suppose you have a squid cache for your
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* website, and the presence of a session cookie bypasses it. Let's also say
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* you allow anonymous users to interact with the website; submitting forms
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* and AJAX. Previously, you didn't have any CSRF protection for anonymous users
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* and so they never got sessions; you don't want to start using sessions either,
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* otherwise you'll bypass the Squid cache. Setup a different cookie for CSRF
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* tokens, and have Squid ignore that cookie for get requests, for anonymous
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* users. (If you haven't guessed, this scheme was(?) used for MediaWiki).
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*/
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$GLOBALS['csrf']['key'] = ZM_AUTH_HASH_SECRET;
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/**
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* The name of the magic CSRF token that will be placed in all forms, i.e.
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* the contents of <input type="hidden" name="$name" value="CSRF-TOKEN" />
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*/
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$GLOBALS['csrf']['input-name'] = '__csrf_magic';
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/**
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* Set this to false if your site must work inside of frame/iframe elements,
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* but do so at your own risk: this configuration protects you against CSS
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* overlay attacks that defeat tokens.
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*/
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$GLOBALS['csrf']['frame-breaker'] = true;
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/**
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* Whether or not CSRF Magic should be allowed to start a new session in order
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* to determine the key.
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*/
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$GLOBALS['csrf']['auto-session'] = true;
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/**
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* Whether or not csrf-magic should produce XHTML style tags.
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*/
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$GLOBALS['csrf']['xhtml'] = true;
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// FUNCTIONS:
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// Don't edit this!
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$GLOBALS['csrf']['version'] = '1.0.4';
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/**
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* Rewrites <form> on the fly to add CSRF tokens to them. This can also
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* inject our JavaScript library.
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*/
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function csrf_ob_handler($buffer, $flags) {
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// Even though the user told us to rewrite, we should do a quick heuristic
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// to check if the page is *actually* HTML. We don't begin rewriting until
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// we hit the first <html tag.
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static $is_html = false;
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if (!$is_html) {
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// not HTML until proven otherwise
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if (stripos($buffer, '<html') !== false) {
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$is_html = true;
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} else {
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return $buffer;
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}
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}
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global $cspNonce;
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$tokens = csrf_get_tokens();
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$name = $GLOBALS['csrf']['input-name'];
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$endslash = $GLOBALS['csrf']['xhtml'] ? ' /' : '';
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$input = "<input type='hidden' name='$name' value=\"$tokens\"$endslash>";
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$buffer = preg_replace('#(<form[^>]*method\s*=\s*["\']post["\'][^>]*>)#i', '$1' . $input, $buffer);
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if ($GLOBALS['csrf']['frame-breaker']) {
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$buffer = str_ireplace('</head>', '<script nonce="'.$cspNonce.'">if (top != self) {top.location.href = self.location.href;}</script></head>', $buffer);
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}
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if ($js = $GLOBALS['csrf']['rewrite-js']) {
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$buffer = str_ireplace(
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'</head>',
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'<script nonce="'.$cspNonce.'">'.
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'var csrfMagicToken = "'.$tokens.'";'.
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'var csrfMagicName = "'.$name.'";</script>'.
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'<script src="'.$js.'"></script></head>',
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$buffer
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);
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$script = '<script nonce="'.$cspNonce.'">CsrfMagic.end();</script>';
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$buffer = str_ireplace('</body>', $script . '</body>', $buffer, $count);
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if (!$count) {
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$buffer .= $script;
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}
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}
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return $buffer;
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}
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/**
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* Checks if this is a post request, and if it is, checks if the nonce is valid.
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* @param bool $fatal Whether or not to fatally error out if there is a problem.
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* @return True if check passes or is not necessary, false if failure.
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*/
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function csrf_check($fatal = true) {
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if ($_SERVER['REQUEST_METHOD'] !== 'POST') return true;
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global $cspNonce;
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csrf_start();
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$name = $GLOBALS['csrf']['input-name'];
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$ok = false;
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$tokens = '';
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do {
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if (!isset($_POST[$name])) {
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#Logger::Debug("POST[$name] is not set");
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break;
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#} else {
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#Logger::Debug("POST[$name] is set as " . $_POST[$name] );
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}
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// we don't regenerate a token and check it because some token creation
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// schemes are volatile.
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$tokens = $_POST[$name];
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if (!csrf_check_tokens($tokens)) {
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#Logger::Debug("Failed checking tokens");
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break;
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#} else {
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#Logger::Debug("Token passed");
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}
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$ok = true;
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} while (false);
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if ($fatal && !$ok) {
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$callback = $GLOBALS['csrf']['callback'];
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if (trim($tokens, 'A..Za..z0..9:;,') !== '') $tokens = 'hidden';
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$callback($tokens);
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exit;
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}
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return $ok;
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}
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/**
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* Retrieves a valid token(s) for a particular context. Tokens are separated
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* by semicolons.
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*/
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function csrf_get_tokens() {
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$has_cookies = !empty($_COOKIE);
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// $ip implements a composite key, which is sent if the user hasn't sent
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// any cookies. It may or may not be used, depending on whether or not
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// the cookies "stick"
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$secret = csrf_get_secret();
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if (!$has_cookies && $secret) {
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// :TODO: Harden this against proxy-spoofing attacks
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$IP_ADDRESS = (isset($_SERVER['IP_ADDRESS']) ? $_SERVER['IP_ADDRESS'] : $_SERVER['REMOTE_ADDR']);
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$ip = ';ip:' . csrf_hash($IP_ADDRESS);
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} else {
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$ip = '';
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}
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csrf_start();
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// These are "strong" algorithms that don't require per se a secret
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if ($GLOBALS['csrf']['key']) return 'key:' . csrf_hash($GLOBALS['csrf']['key']) . $ip;
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if (session_id()) return 'sid:' . csrf_hash(session_id()) . $ip;
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if ($GLOBALS['csrf']['cookie']) {
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$val = csrf_generate_secret();
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setcookie($GLOBALS['csrf']['cookie'], $val);
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return 'cookie:' . csrf_hash($val) . $ip;
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}
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// These further algorithms require a server-side secret
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if (!$secret) return 'invalid';
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if ($GLOBALS['csrf']['user'] !== false) {
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return 'user:' . csrf_hash($GLOBALS['csrf']['user']);
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}
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if ($GLOBALS['csrf']['allow-ip']) {
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return ltrim($ip, ';');
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}
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return 'invalid';
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}
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function csrf_flattenpost($data) {
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$ret = array();
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foreach($data as $n => $v) {
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$ret = array_merge($ret, csrf_flattenpost2(1, $n, $v));
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}
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return $ret;
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}
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function csrf_flattenpost2($level, $key, $data) {
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if(!is_array($data)) return array($key => $data);
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$ret = array();
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foreach($data as $n => $v) {
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$nk = $level >= 1 ? $key."[$n]" : "[$n]";
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$ret = array_merge($ret, csrf_flattenpost2($level+1, $nk, $v));
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}
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return $ret;
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}
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/**
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* @param $tokens is safe for HTML consumption
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*/
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function csrf_callback($tokens) {
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// (yes, $tokens is safe to echo without escaping)
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header($_SERVER['SERVER_PROTOCOL'] . ' 403 Forbidden');
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$data = '';
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foreach (csrf_flattenpost($_POST) as $key => $value) {
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if ($key == $GLOBALS['csrf']['input-name']) continue;
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$data .= '<input type="hidden" name="'.htmlspecialchars($key).'" value="'.htmlspecialchars($value).'" />';
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}
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echo "<html><head><title>CSRF check failed</title></head>
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<body>
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<p>CSRF check failed. Your form session may have expired, or you may not have
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cookies enabled.</p>
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<form method='post' action=''>$data<input type='submit' value='Try again' /></form>
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<p>Debug: $tokens</p></body></html>
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";
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}
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/**
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* Checks if a composite token is valid. Outward facing code should use this
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* instead of csrf_check_token()
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*/
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function csrf_check_tokens($tokens) {
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if (is_string($tokens)) $tokens = explode(';', $tokens);
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foreach ($tokens as $token) {
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if (csrf_check_token($token)) return true;
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}
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return false;
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}
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/**
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* Checks if a token is valid.
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*/
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function csrf_check_token($token) {
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#Logger::Debug("Checking CSRF token $token");
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if (strpos($token, ':') === false) {
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#Logger::Debug("Checking CSRF token $token bad because no :");
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return false;
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}
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list($type, $value) = explode(':', $token, 2);
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if (strpos($value, ',') === false) {
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#Logger::Debug("Checking CSRF token $token bad because no ,");
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return false;
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}
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list($x, $time) = explode(',', $token, 2);
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if ($GLOBALS['csrf']['expires']) {
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if (time() > $time + $GLOBALS['csrf']['expires']) {
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#Logger::Debug("Checking CSRF token $token bad because expired");
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return false;
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}
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}
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switch ($type) {
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case 'sid':
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{
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#Logger::Debug("Checking sid: $value === " . csrf_hash(session_id(), $time) );
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return $value === csrf_hash(session_id(), $time);
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}
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case 'cookie':
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$n = $GLOBALS['csrf']['cookie'];
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if (!$n) return false;
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if (!isset($_COOKIE[$n])) return false;
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return $value === csrf_hash($_COOKIE[$n], $time);
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case 'key':
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if (!$GLOBALS['csrf']['key']) {
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Logger::Debug("Checking key: no key set" );
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return false;
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}
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#Logger::Debug("Checking sid: $value === " . csrf_hash($GLOBALS['csrf']['key'], $time) );
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return $value === csrf_hash($GLOBALS['csrf']['key'], $time);
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// We could disable these 'weaker' checks if 'key' was set, but
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// that doesn't make me feel good then about the cookie-based
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// implementation.
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case 'user':
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if (!csrf_get_secret()) return false;
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if ($GLOBALS['csrf']['user'] === false) return false;
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return $value === csrf_hash($GLOBALS['csrf']['user'], $time);
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case 'ip':
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if (!csrf_get_secret()) return false;
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// do not allow IP-based checks if the username is set, or if
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// the browser sent cookies
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if ($GLOBALS['csrf']['user'] !== false) return false;
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if (!empty($_COOKIE)) return false;
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if (!$GLOBALS['csrf']['allow-ip']) return false;
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$IP_ADDRESS = (isset($_SERVER['IP_ADDRESS']) ? $_SERVER['IP_ADDRESS'] : $_SERVER['REMOTE_ADDR']);
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return $value === csrf_hash($IP_ADDRESS, $time);
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}
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return false;
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}
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/**
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* Sets a configuration value.
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*/
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function csrf_conf($key, $val) {
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if (!isset($GLOBALS['csrf'][$key])) {
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trigger_error('No such configuration ' . $key, E_USER_WARNING);
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return;
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}
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$GLOBALS['csrf'][$key] = $val;
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}
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/**
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* Starts a session if we're allowed to.
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*/
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function csrf_start() {
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if ($GLOBALS['csrf']['auto-session'] && !session_id()) {
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session_start();
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}
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}
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/**
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* Retrieves the secret, and generates one if necessary.
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*/
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function csrf_get_secret() {
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if ($GLOBALS['csrf']['secret']) return $GLOBALS['csrf']['secret'];
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$dir = dirname(__FILE__);
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$file = $dir . '/csrf-secret.php';
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$secret = '';
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if (file_exists($file)) {
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include $file;
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return $secret;
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}
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if (is_writable($dir)) {
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$secret = csrf_generate_secret();
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$fh = fopen($file, 'w');
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fwrite($fh, '<?php $secret = "'.$secret.'";' . PHP_EOL);
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fclose($fh);
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return $secret;
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}
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return '';
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}
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/**
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* Generates a random string as the hash of time, microtime, and mt_rand.
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*/
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function csrf_generate_secret($len = 32) {
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$r = '';
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for ($i = 0; $i < $len; $i++) {
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$r .= chr(mt_rand(0, 255));
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}
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$r .= time() . microtime();
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return sha1($r);
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}
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/**
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* Generates a hash/expiry double. If time isn't set it will be calculated
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* from the current time.
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*/
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function csrf_hash($value, $time = null) {
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if (!$time) $time = time();
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return sha1(csrf_get_secret() . $value . $time) . ',' . $time;
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}
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// Load user configuration
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if (function_exists('csrf_startup')) csrf_startup();
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// Initialize our handler
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if ($GLOBALS['csrf']['rewrite']) ob_start('csrf_ob_handler');
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// Perform check
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if (!$GLOBALS['csrf']['defer']) csrf_check();
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