<?php

/**
 * DokuWiki Plugin passpolicy (Helper Component)
 *
 * Check password policies and generate random passwords accordingly
 *
 * @license GPL 2 http://www.gnu.org/licenses/gpl-2.0.html
 * @author  Andreas Gohr <andi@splitbrain.org>
 */
class helper_plugin_passpolicy extends DokuWiki_Plugin
{

    /** @var int number of character pools that have to be used at least */
    public $min_pools = 1;

    /** @var int minimum length of the password (bytes) */
    public $min_length = 6;

    /** @var string what type of password generation to use? */
    public $autotype = 'random';

    /** @var int minimum bit strength auto generated passwords should have */
    public $autobits = 64;

    /** @var bool disallow common passwords */
    public $nocommon = true;

    /** @var bool disallow leaked passwords */
    public $noleaked = true;

    /** @var array allowed character pools */
    public $usepools = array(
        'lower' => true,
        'upper' => false,
        'numeric' => true,
        'special' => false,
    );

    /** @var int number of consecutive letters that may not be in the username, 0 to disable */
    public $usernamecheck = 0;

    /** @var int policy violation error */
    public $error = 0;

    /** @var array the different pools to use when generating passwords */
    public $pools = array(
        'lower' => 'abcdefghijklmnopqrstuvwxyz',
        'upper' => 'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
        'numeric' => '0123456789',
        'special' => '!"$%&/()=?{[]}\\*+~\'#,;.:-_<>|@',
    );

    protected $wordlist = array();
    protected $wordlistlength = 0;
    protected $msgshown = false;

    const LENGTH_VIOLATION = 1;
    const POOL_VIOLATION = 2;
    const USERNAME_VIOLATION = 4;
    const COMMON_VIOLATION = 8;
    const LEAK_VIOLATION = 16;

    /**
     * Constructor
     *
     * Sets the policy from the DokuWiki config
     */
    public function __construct()
    {
        $this->min_length = $this->getConf('minlen');
        $this->min_pools = $this->getConf('minpools');
        $this->usernamecheck = $this->getConf('user');
        $this->autotype = $this->getConf('autotype');
        $this->autobits = $this->getConf('autobits');
        $this->nocommon = $this->getConf('nocommon');
        $this->noleaked = $this->getConf('noleaked');

        $opts = explode(',', $this->getConf('pools'));
        if (count($opts)) { // ignore empty pool setups
            $this->usepools = array();
            foreach ($opts as $pool) {
                $this->usepools[$pool] = true;
            }
        }
        if ($this->min_pools > count($this->usepools)) $this->min_pools = $this->usepools;
    }

    /**
     * Generates a random password according to the backend settings
     *
     * @param string $username
     * @param int $try internal variable, do not set!
     * @return bool|string
     * @throws Exception when the generator fails to create a policy compliant password
     */
    public function generatePassword($username, $try = 0)
    {
        if ($this->autotype == 'pronouncable') {
            $pw = $this->pronouncablePassword();
            if ($pw && $this->checkPolicy($pw, $username)) return $pw;
        }

        if ($this->autotype == 'phrase') {
            $pw = $this->randomPassphrase();
            if ($pw && $this->checkPolicy($pw, $username)) return $pw;
        }

        $pw = $this->randomPassword();
        if ($pw && $this->checkPolicy($pw, $username)) return $pw;

        // still here? we might have clashed with the user name by accident
        if ($try < 3) return $this->generatePassword($username, $try + 1);

        // still here? now we have a real problem
        throw new Exception('can\'t create a random password matching the password policy');
    }

    /**
     * Gives a human readable explanation of the current policy as plain text.
     *
     * @return string
     */
    public function explainPolicy()
    {
        // we need access to the settings.php translations for the pool names
        // FIXME core should provide a way to access them
        global $conf;
        $lang = array();
        $path = dirname(__FILE__);
        @include($path . '/lang/en/settings.php');
        if ($conf['lang'] != 'en') @include($path . '/lang/' . $conf['lang'] . '/settings.php');

        // load pool names
        $pools = array();
        foreach ($this->usepools as $pool => $on) {
            if ($on) $pools[] = $lang['pools_' . $pool];
        }

        $text = '';
        if ($this->min_length) {
            $text .= sprintf($this->getLang('length'), $this->min_length) . "\n";
        }
        if ($this->min_pools) {
            $text .= sprintf($this->getLang('pools'), $this->min_pools, join(', ', $pools)) . "\n";
        }
        if ($this->usernamecheck == 1) {
            $text .= $this->getLang('user1') . "\n";
        }
        if ($this->usernamecheck > 1) {
            $text .= sprintf($this->getLang('user2'), $this->usernamecheck) . "\n";
        }
        if ($this->nocommon) {
            $text .= $this->getLang('nocommon');
        }
        if ($this->noleaked) {
            $text .= $this->getLang('noleaked');
        }

        return trim($text);
    }

    /**
     * Checks a given password for policy violation
     *
     * @param string $pass true if the password validates against the policy
     * @param string $username
     * @return bool
     */
    public function checkPolicy($pass, $username)
    {
        $this->error = 0;

        // check length first:
        if (strlen($pass) < $this->min_length) {
            $this->error = helper_plugin_passpolicy::LENGTH_VIOLATION;
            return false;
        }

        $matched_pools = 0;
        if (!empty($this->usepools['lower'])) $matched_pools += (int)preg_match('/[a-z]/', $pass);
        if (!empty($this->usepools['upper'])) $matched_pools += (int)preg_match('/[A-Z]/', $pass);
        if (!empty($this->usepools['numeric'])) $matched_pools += (int)preg_match('/[0-9]/', $pass);
        if (!empty($this->usepools['special'])) {
            $matched_pools += (int)preg_match('/[^A-Za-z0-9]/',
                $pass);
        } // we consider everything else special
        if ($matched_pools < $this->min_pools) {
            $this->error = helper_plugin_passpolicy::POOL_VIOLATION;
            return false;
        }

        $pass = utf8_strtolower($pass);
        $username = utf8_strtolower($username);

        if ($this->usernamecheck && $username) {
            // simplest case first
            if (utf8_stripspecials($pass, '', '\._\-:\*') == utf8_stripspecials($username, '', '\._\-:\*')) {
                $this->error = helper_plugin_passpolicy::USERNAME_VIOLATION;
                return false;
            }

            // find possible chunks in the lenght defined in policy
            if ($this->usernamecheck > 1) {
                $chunks = array();
                for ($i = 0; $i < utf8_strlen($pass) - $this->usernamecheck + 1; $i++) {
                    $chunk = utf8_substr($pass, $i, $this->usernamecheck + 1);
                    if ($chunk == utf8_stripspecials($chunk, '', '\._\-:\*')) {
                        $chunks[] = $chunk; // only word chars are checked
                    }
                }

                // check chunks against user name
                $chunks = array_map('preg_quote_cb', $chunks);
                $re = join('|', $chunks);

                if (preg_match("/($re)/", $username)) {
                    $this->error = helper_plugin_passpolicy::USERNAME_VIOLATION;
                    return false;
                }
            }
        }

        if ($this->nocommon) {
            $commons = file(__DIR__ . '/10k-common-passwords.txt');
            if (in_array("$pass\n", $commons)) {
                $this->error = helper_plugin_passpolicy::COMMON_VIOLATION;
                return false;
            }
        }

        if ($this->noleaked && $this->isLeaked($pass)) {
            $this->error = helper_plugin_passpolicy::LEAK_VIOLATION;
            return false;
        }

        return true;
    }

    /**
     * Creates a completely random password
     *
     * @return string
     */
    protected function randomPassword()
    {
        $num_bits = $this->autobits;
        $output = '';
        $characters = '';

        // always use these pools
        foreach (array('lower', 'upper', 'numeric') as $pool) {
            $pool_len = strlen($this->pools[$pool]);
            $output .= $this->pools[$pool][$this->rand(0, $pool_len - 1)]; // add one char already
            $characters .= $this->pools[$pool]; // add to full pool
            $num_bits -= $this->bits($pool_len);
        }

        // if specials are wanted, limit them to a sane amount of 3
        if (!empty($this->usepools['special'])) {
            $pool_len = strlen($this->pools['special']);
            $poolbits = $this->bits($pool_len);

            $sane = ceil($this->autobits / 25);
            for ($i = 0; $i < $sane; $i++) {
                $output .= $this->pools['special'][$this->rand(0, $pool_len - 1)];
                $num_bits -= $poolbits;
            }
        }

        // now prepare the full pool
        $pool_len = strlen($characters);
        $poolbits = $this->bits($pool_len);

        // add random chars
        do {
            $output .= $characters[$this->rand(0, $pool_len - 1)];
            $num_bits -= $poolbits;
        } while ($num_bits > 0 || strlen($output) < $this->min_length);

        // shuffle to make sure our intial chars are not necessarily at the start
        return str_shuffle($output);
    }

    /**
     * Creates a pronouncable password
     *
     * @return bool|string  the new password, false on error
     */
    protected function pronouncablePassword()
    {
        $num_bits = $this->autobits;

        // prepare speakable char classes
        $consonants = 'bcdfghjklmnprstvwz'; //consonants except hard to speak ones
        $vowels = 'aeiou';
        $all = $consonants . $vowels;

        // prepare lengths
        $c_len = strlen($consonants);
        $v_len = strlen($vowels);
        $a_len = $c_len + $v_len;

        // prepare bitcounts
        $c_bits = $this->bits($c_len);
        $v_bits = $this->bits($v_len);
        $a_bits = $this->bits($a_len);

        // prepare policy compliant postfix
        $postfix = '';
        if ($this->usepools['numeric']) {
            $postfix .= $this->rand(10, 99);
            $num_bits -= $this->bits(99 - 10);
        }
        if ($this->usepools['special']) {
            $spec_len = strlen($this->pools['special']);
            $postfix .= $this->pools['special'][rand(0, $spec_len - 1)];
            $num_bits -= $this->bits($spec_len);
        }

        // create words
        $output = '';
        do {
            $output .= $consonants[$this->rand(0, $c_len - 1)];
            $output .= $vowels[$this->rand(0, $v_len - 1)];
            $output .= $all[$this->rand(0, $a_len - 1)];

            $num_bits -= $c_bits;
            $num_bits -= $v_bits;
            $num_bits -= $a_bits;
        } while ($num_bits > 0 || strlen($output) < $this->min_length);

        // now ensure policy compliance by uppercasing and postfixing
        if ($this->usepools['upper']) $output = ucfirst($output);
        if ($postfix) $output .= $postfix;

        return $output;
    }

    /**
     * Creates a passphrase from random words
     *
     * @return string
     * @author Solar Designer
     * @author Michael Samuel
     */
    protected function randomPassphrase()
    {
        $num_bits = $this->autobits;

        // prepare policy compliant prefix
        $prefix = '';
        if ($this->usepools['numeric']) {
            $prefix .= $this->rand(0, 999);
            $num_bits -= $this->bits(999);
        }
        if ($this->usepools['special']) {
            $spec_len = strlen($this->pools['special']);
            $prefix .= $this->pools['special'][rand(0, $spec_len - 1)];
            $num_bits -= $this->bits($spec_len);
        }

        // load the words to use
        $this->loadwordlist();
        $wordbits = $this->bits($this->wordlistlength);

        // generate simple all lowercase word phrase
        $output = '';
        do {
            $output .= $this->wordlist[$this->rand(0, $this->wordlistlength - 1)] . ' ';
            $num_bits -= $wordbits;
        } while ($num_bits > 0 || strlen($output) < $this->min_length);

        // now ensure policy compliance by uppercasing and prefixing
        if ($this->usepools['upper']) $output = ucwords($output);
        if ($prefix) $output = $prefix . ' ' . $output;

        return trim($output);
    }

    /**
     * Return the number of bits in an integer
     *
     * @param int $number
     * @return int
     * @author Michael Samuel
     */
    protected function bits($number)
    {
        $bits = 0;

        while ($number > 0) {
            $number >>= 1;
            $bits += 1;
        }

        return $bits;
    }

    /**
     * Random number generator using the best available source
     *
     * @param int $min
     * @param int $max
     * @return int
     * @author Michael Samuel
     */
    public function rand($min, $max)
    {
        $real_max = $max - $min;
        $mask = (1 << $this->bits($real_max)) - 1;

        try {
            do {
                $bytes = $this->trueRandomBytes(4);
                $unpack = unpack("lnum", $bytes);
                $integer = $unpack["num"] & $mask;
            } while ($integer > $real_max);
        } catch (Exception $e) {
            if (!$this->msgshown) {
                msg('No secure random generator available, falling back to less secure mt_rand()', -1);
                $this->msgshown = true;
            }
            return mt_rand($min, $max);
        }

        return $integer + $min;
    }

    /**
     * Return truly (pseudo) random bytes
     *
     * @param int $bytes number of bytes to get
     * @return string binary random strings
     * @throws Exception when no usable random generator is found
     * @link   http://www.php.net/manual/de/function.mt-rand.php#83655
     * @author Mark Seecof
     */
    protected function trueRandomBytes($bytes)
    {
        $strong = false;
        $rbytes = false;

        if (function_exists('openssl_random_pseudo_bytes')) {
            $rbytes = openssl_random_pseudo_bytes($bytes, $strong);
        }

        // If no strong SSL randoms available, try OS the specific ways
        if (!$strong) {
            // Unix/Linux platform
            $fp = @fopen('/dev/urandom', 'rb');
            if ($fp !== false) {
                $rbytes = fread($fp, $bytes);
                fclose($fp);
            }

            // MS-Windows platform
            if (class_exists('COM')) {
                // http://msdn.microsoft.com/en-us/library/aa388176(VS.85).aspx
                try {
                    $CAPI_Util = new COM('CAPICOM.Utilities.1');
                    $rbytes = $CAPI_Util->GetRandom($bytes, 0);

                    // if we ask for binary data PHP munges it, so we
                    // request base64 return value.  We squeeze out the
                    // redundancy and useless ==CRLF by hashing...
                    if ($rbytes) $rbytes = md5($rbytes, true);
                } catch (Exception $ex) {
                    // fail
                }
            }
        }
        if (strlen($rbytes) < $bytes) $rbytes = false;

        if ($rbytes === false) throw new Exception('No true random generator available');

        return $rbytes;
    }

    /**
     * loads the word list for phrase generation
     *
     * Words are taken from the wiki's own search index and are complemented with a
     * list of 4096 English words. This list comes from a passphrase generator
     * mentioned on sci.crypt, religious and possibly offensive words have been
     * replaced with less conflict laden words
     */
    protected function loadwordlist()
    {
        if ($this->wordlistlength) return; //list already loaded

        // load one of the local word index files
        $indexer = new helper_plugin_passpolicy__index();
        $this->wordlist = $indexer->getIndex('w', $this->rand(4, 6));
        $this->wordlist = array_filter($this->wordlist,
            'utf8_isASCII'); //only ASCII, users might have trouble typing other things

        // add our own word list to fill up
        $this->wordlist += file(dirname(__FILE__) . '/words.txt', FILE_IGNORE_NEW_LINES);
        $this->wordlistlength = count($this->wordlist);
    }

    /**
     * Check if the given password has been leaked
     *
     * Uses k-anonymity
     *
     * @param string $password
     * @return bool
     */
    protected function isLeaked($password)
    {
        $sha1 = sha1($password);
        $prefix = substr($sha1, 0, 5);
        $url = "https://api.pwnedpasswords.com/range/$prefix";
        $http = new DokuHTTPClient();
        $http->timeout = 5;
        $list = $http->get($url);
        if (!$list) return false; // we didn't get a proper response, assume the password is okay

        $results = explode("\n", $list);
        foreach ($results as $result) {
            list($result,) = explode(':', $result); // strip off the number
            $result = $prefix . strtolower($result);
            if ($sha1 == $result) return true; // leak found
        }

        return false;
    }
}

/**
 * Class helper_plugin_passpolicy__index
 *
 * just to access a protected function
 */
class helper_plugin_passpolicy__index extends Doku_Indexer
{
    /** @inheritDoc */
    public function getIndex($idx, $suffix)
    {
        return parent::getIndex($idx, $suffix);
    }
}