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Diffstat (limited to 'includes/MWCryptRand.php')
| -rw-r--r-- | includes/MWCryptRand.php | 497 |
1 files changed, 497 insertions, 0 deletions
diff --git a/includes/MWCryptRand.php b/includes/MWCryptRand.php new file mode 100644 index 00000000..bac018e8 --- /dev/null +++ b/includes/MWCryptRand.php @@ -0,0 +1,497 @@ +<?php +/** + * A cryptographic random generator class used for generating secret keys + * + * This is based in part on Drupal code as well as what we used in our own code + * prior to introduction of this class. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + * http://www.gnu.org/copyleft/gpl.html + * + * @author Daniel Friesen + * @file + */ + +class MWCryptRand { + + /** + * Minimum number of iterations we want to make in our drift calculations. + */ + const MIN_ITERATIONS = 1000; + + /** + * Number of milliseconds we want to spend generating each separate byte + * of the final generated bytes. + * This is used in combination with the hash length to determine the duration + * we should spend doing drift calculations. + */ + const MSEC_PER_BYTE = 0.5; + + /** + * Singleton instance for public use + */ + protected static $singleton = null; + + /** + * The hash algorithm being used + */ + protected $algo = null; + + /** + * The number of bytes outputted by the hash algorithm + */ + protected $hashLength = null; + + /** + * A boolean indicating whether the previous random generation was done using + * cryptographically strong random number generator or not. + */ + protected $strong = null; + + /** + * Initialize an initial random state based off of whatever we can find + */ + protected function initialRandomState() { + // $_SERVER contains a variety of unstable user and system specific information + // It'll vary a little with each page, and vary even more with separate users + // It'll also vary slightly across different machines + $state = serialize( $_SERVER ); + + // To try vary the system information of the state a bit more + // by including the system's hostname into the state + $state .= wfHostname(); + + // Try to gather a little entropy from the different php rand sources + $state .= rand() . uniqid( mt_rand(), true ); + + // Include some information about the filesystem's current state in the random state + $files = array(); + + // We know this file is here so grab some info about ourselves + $files[] = __FILE__; + + // We must also have a parent folder, and with the usual file structure, a grandparent + $files[] = __DIR__; + $files[] = dirname( __DIR__ ); + + // The config file is likely the most often edited file we know should be around + // so include its stat info into the state. + // The constant with its location will almost always be defined, as WebStart.php defines + // MW_CONFIG_FILE to $IP/LocalSettings.php unless being configured with MW_CONFIG_CALLBACK (eg. the installer) + if ( defined( 'MW_CONFIG_FILE' ) ) { + $files[] = MW_CONFIG_FILE; + } + + foreach ( $files as $file ) { + wfSuppressWarnings(); + $stat = stat( $file ); + wfRestoreWarnings(); + if ( $stat ) { + // stat() duplicates data into numeric and string keys so kill off all the numeric ones + foreach ( $stat as $k => $v ) { + if ( is_numeric( $k ) ) { + unset( $k ); + } + } + // The absolute filename itself will differ from install to install so don't leave it out + if ( ( $path = realpath( $file ) ) !== false ) { + $state .= $path; + } else { + $state .= $file; + } + $state .= implode( '', $stat ); + } else { + // The fact that the file isn't there is worth at least a + // minuscule amount of entropy. + $state .= '0'; + } + } + + // Try and make this a little more unstable by including the varying process + // id of the php process we are running inside of if we are able to access it + if ( function_exists( 'getmypid' ) ) { + $state .= getmypid(); + } + + // If available try to increase the instability of the data by throwing in + // the precise amount of memory that we happen to be using at the moment. + if ( function_exists( 'memory_get_usage' ) ) { + $state .= memory_get_usage( true ); + } + + // It's mostly worthless but throw the wiki's id into the data for a little more variance + $state .= wfWikiID(); + + // If we have a secret key or proxy key set then throw it into the state as well + global $wgSecretKey, $wgProxyKey; + if ( $wgSecretKey ) { + $state .= $wgSecretKey; + } elseif ( $wgProxyKey ) { + $state .= $wgProxyKey; + } + + return $state; + } + + /** + * Randomly hash data while mixing in clock drift data for randomness + * + * @param string $data The data to randomly hash. + * @return String The hashed bytes + * @author Tim Starling + */ + protected function driftHash( $data ) { + // Minimum number of iterations (to avoid slow operations causing the loop to gather little entropy) + $minIterations = self::MIN_ITERATIONS; + // Duration of time to spend doing calculations (in seconds) + $duration = ( self::MSEC_PER_BYTE / 1000 ) * $this->hashLength(); + // Create a buffer to use to trigger memory operations + $bufLength = 10000000; + $buffer = str_repeat( ' ', $bufLength ); + $bufPos = 0; + + // Iterate for $duration seconds or at least $minIterations number of iterations + $iterations = 0; + $startTime = microtime( true ); + $currentTime = $startTime; + while ( $iterations < $minIterations || $currentTime - $startTime < $duration ) { + // Trigger some memory writing to trigger some bus activity + // This may create variance in the time between iterations + $bufPos = ( $bufPos + 13 ) % $bufLength; + $buffer[$bufPos] = ' '; + // Add the drift between this iteration and the last in as entropy + $nextTime = microtime( true ); + $delta = (int)( ( $nextTime - $currentTime ) * 1000000 ); + $data .= $delta; + // Every 100 iterations hash the data and entropy + if ( $iterations % 100 === 0 ) { + $data = sha1( $data ); + } + $currentTime = $nextTime; + $iterations++; + } + $timeTaken = $currentTime - $startTime; + $data = $this->hash( $data ); + + wfDebug( __METHOD__ . ": Clock drift calculation " . + "(time-taken=" . ( $timeTaken * 1000 ) . "ms, " . + "iterations=$iterations, " . + "time-per-iteration=" . ( $timeTaken / $iterations * 1e6 ) . "us)\n" ); + return $data; + } + + /** + * Return a rolling random state initially build using data from unstable sources + * @return string A new weak random state + */ + protected function randomState() { + static $state = null; + if ( is_null( $state ) ) { + // Initialize the state with whatever unstable data we can find + // It's important that this data is hashed right afterwards to prevent + // it from being leaked into the output stream + $state = $this->hash( $this->initialRandomState() ); + } + // Generate a new random state based on the initial random state or previous + // random state by combining it with clock drift + $state = $this->driftHash( $state ); + return $state; + } + + /** + * Decide on the best acceptable hash algorithm we have available for hash() + * @throws MWException + * @return String A hash algorithm + */ + protected function hashAlgo() { + if ( !is_null( $this->algo ) ) { + return $this->algo; + } + + $algos = hash_algos(); + $preference = array( 'whirlpool', 'sha256', 'sha1', 'md5' ); + + foreach ( $preference as $algorithm ) { + if ( in_array( $algorithm, $algos ) ) { + $this->algo = $algorithm; + wfDebug( __METHOD__ . ": Using the {$this->algo} hash algorithm.\n" ); + return $this->algo; + } + } + + // We only reach here if no acceptable hash is found in the list, this should + // be a technical impossibility since most of php's hash list is fixed and + // some of the ones we list are available as their own native functions + // But since we already require at least 5.2 and hash() was default in + // 5.1.2 we don't bother falling back to methods like sha1 and md5. + throw new MWException( "Could not find an acceptable hashing function in hash_algos()" ); + } + + /** + * Return the byte-length output of the hash algorithm we are + * using in self::hash and self::hmac. + * + * @return int Number of bytes the hash outputs + */ + protected function hashLength() { + if ( is_null( $this->hashLength ) ) { + $this->hashLength = strlen( $this->hash( '' ) ); + } + return $this->hashLength; + } + + /** + * Generate an acceptably unstable one-way-hash of some text + * making use of the best hash algorithm that we have available. + * + * @param $data string + * @return String A raw hash of the data + */ + protected function hash( $data ) { + return hash( $this->hashAlgo(), $data, true ); + } + + /** + * Generate an acceptably unstable one-way-hmac of some text + * making use of the best hash algorithm that we have available. + * + * @param $data string + * @param $key string + * @return String A raw hash of the data + */ + protected function hmac( $data, $key ) { + return hash_hmac( $this->hashAlgo(), $data, $key, true ); + } + + /** + * @see self::wasStrong() + */ + public function realWasStrong() { + if ( is_null( $this->strong ) ) { + throw new MWException( __METHOD__ . ' called before generation of random data' ); + } + return $this->strong; + } + + /** + * @see self::generate() + */ + public function realGenerate( $bytes, $forceStrong = false ) { + wfProfileIn( __METHOD__ ); + + wfDebug( __METHOD__ . ": Generating cryptographic random bytes for " . wfGetAllCallers( 5 ) . "\n" ); + + $bytes = floor( $bytes ); + static $buffer = ''; + if ( is_null( $this->strong ) ) { + // Set strength to false initially until we know what source data is coming from + $this->strong = true; + } + + if ( strlen( $buffer ) < $bytes ) { + // If available make use of mcrypt_create_iv URANDOM source to generate randomness + // On unix-like systems this reads from /dev/urandom but does it without any buffering + // and bypasses openbasedir restrictions, so it's preferable to reading directly + // On Windows starting in PHP 5.3.0 Windows' native CryptGenRandom is used to generate + // entropy so this is also preferable to just trying to read urandom because it may work + // on Windows systems as well. + if ( function_exists( 'mcrypt_create_iv' ) ) { + wfProfileIn( __METHOD__ . '-mcrypt' ); + $rem = $bytes - strlen( $buffer ); + $iv = mcrypt_create_iv( $rem, MCRYPT_DEV_URANDOM ); + if ( $iv === false ) { + wfDebug( __METHOD__ . ": mcrypt_create_iv returned false.\n" ); + } else { + $buffer .= $iv; + wfDebug( __METHOD__ . ": mcrypt_create_iv generated " . strlen( $iv ) . " bytes of randomness.\n" ); + } + wfProfileOut( __METHOD__ . '-mcrypt' ); + } + } + + if ( strlen( $buffer ) < $bytes ) { + // If available make use of openssl's random_pseudo_bytes method to attempt to generate randomness. + // However don't do this on Windows with PHP < 5.3.4 due to a bug: + // http://stackoverflow.com/questions/1940168/openssl-random-pseudo-bytes-is-slow-php + // http://git.php.net/?p=php-src.git;a=commitdiff;h=cd62a70863c261b07f6dadedad9464f7e213cad5 + if ( function_exists( 'openssl_random_pseudo_bytes' ) + && ( !wfIsWindows() || version_compare( PHP_VERSION, '5.3.4', '>=' ) ) + ) { + wfProfileIn( __METHOD__ . '-openssl' ); + $rem = $bytes - strlen( $buffer ); + $openssl_bytes = openssl_random_pseudo_bytes( $rem, $openssl_strong ); + if ( $openssl_bytes === false ) { + wfDebug( __METHOD__ . ": openssl_random_pseudo_bytes returned false.\n" ); + } else { + $buffer .= $openssl_bytes; + wfDebug( __METHOD__ . ": openssl_random_pseudo_bytes generated " . strlen( $openssl_bytes ) . " bytes of " . ( $openssl_strong ? "strong" : "weak" ) . " randomness.\n" ); + } + if ( strlen( $buffer ) >= $bytes ) { + // openssl tells us if the random source was strong, if some of our data was generated + // using it use it's say on whether the randomness is strong + $this->strong = !!$openssl_strong; + } + wfProfileOut( __METHOD__ . '-openssl' ); + } + } + + // Only read from urandom if we can control the buffer size or were passed forceStrong + if ( strlen( $buffer ) < $bytes && ( function_exists( 'stream_set_read_buffer' ) || $forceStrong ) ) { + wfProfileIn( __METHOD__ . '-fopen-urandom' ); + $rem = $bytes - strlen( $buffer ); + if ( !function_exists( 'stream_set_read_buffer' ) && $forceStrong ) { + wfDebug( __METHOD__ . ": Was forced to read from /dev/urandom without control over the buffer size.\n" ); + } + // /dev/urandom is generally considered the best possible commonly + // available random source, and is available on most *nix systems. + wfSuppressWarnings(); + $urandom = fopen( "/dev/urandom", "rb" ); + wfRestoreWarnings(); + + // Attempt to read all our random data from urandom + // php's fread always does buffered reads based on the stream's chunk_size + // so in reality it will usually read more than the amount of data we're + // asked for and not storing that risks depleting the system's random pool. + // If stream_set_read_buffer is available set the chunk_size to the amount + // of data we need. Otherwise read 8k, php's default chunk_size. + if ( $urandom ) { + // php's default chunk_size is 8k + $chunk_size = 1024 * 8; + if ( function_exists( 'stream_set_read_buffer' ) ) { + // If possible set the chunk_size to the amount of data we need + stream_set_read_buffer( $urandom, $rem ); + $chunk_size = $rem; + } + $random_bytes = fread( $urandom, max( $chunk_size, $rem ) ); + $buffer .= $random_bytes; + fclose( $urandom ); + wfDebug( __METHOD__ . ": /dev/urandom generated " . strlen( $random_bytes ) . " bytes of randomness.\n" ); + if ( strlen( $buffer ) >= $bytes ) { + // urandom is always strong, set to true if all our data was generated using it + $this->strong = true; + } + } else { + wfDebug( __METHOD__ . ": /dev/urandom could not be opened.\n" ); + } + wfProfileOut( __METHOD__ . '-fopen-urandom' ); + } + + // If we cannot use or generate enough data from a secure source + // use this loop to generate a good set of pseudo random data. + // This works by initializing a random state using a pile of unstable data + // and continually shoving it through a hash along with a variable salt. + // We hash the random state with more salt to avoid the state from leaking + // out and being used to predict the /randomness/ that follows. + if ( strlen( $buffer ) < $bytes ) { + wfDebug( __METHOD__ . ": Falling back to using a pseudo random state to generate randomness.\n" ); + } + while ( strlen( $buffer ) < $bytes ) { + wfProfileIn( __METHOD__ . '-fallback' ); + $buffer .= $this->hmac( $this->randomState(), mt_rand() ); + // This code is never really cryptographically strong, if we use it + // at all, then set strong to false. + $this->strong = false; + wfProfileOut( __METHOD__ . '-fallback' ); + } + + // Once the buffer has been filled up with enough random data to fulfill + // the request shift off enough data to handle the request and leave the + // unused portion left inside the buffer for the next request for random data + $generated = substr( $buffer, 0, $bytes ); + $buffer = substr( $buffer, $bytes ); + + wfDebug( __METHOD__ . ": " . strlen( $buffer ) . " bytes of randomness leftover in the buffer.\n" ); + + wfProfileOut( __METHOD__ ); + return $generated; + } + + /** + * @see self::generateHex() + */ + public function realGenerateHex( $chars, $forceStrong = false ) { + // hex strings are 2x the length of raw binary so we divide the length in half + // odd numbers will result in a .5 that leads the generate() being 1 character + // short, so we use ceil() to ensure that we always have enough bytes + $bytes = ceil( $chars / 2 ); + // Generate the data and then convert it to a hex string + $hex = bin2hex( $this->generate( $bytes, $forceStrong ) ); + // A bit of paranoia here, the caller asked for a specific length of string + // here, and it's possible (eg when given an odd number) that we may actually + // have at least 1 char more than they asked for. Just in case they made this + // call intending to insert it into a database that does truncation we don't + // want to give them too much and end up with their database and their live + // code having two different values because part of what we gave them is truncated + // hence, we strip out any run of characters longer than what we were asked for. + return substr( $hex, 0, $chars ); + } + + /** Publicly exposed static methods **/ + + /** + * Return a singleton instance of MWCryptRand + * @return MWCryptRand + */ + protected static function singleton() { + if ( is_null( self::$singleton ) ) { + self::$singleton = new self; + } + return self::$singleton; + } + + /** + * Return a boolean indicating whether or not the source used for cryptographic + * random bytes generation in the previously run generate* call + * was cryptographically strong. + * + * @return bool Returns true if the source was strong, false if not. + */ + public static function wasStrong() { + return self::singleton()->realWasStrong(); + } + + /** + * Generate a run of (ideally) cryptographically random data and return + * it in raw binary form. + * You can use MWCryptRand::wasStrong() if you wish to know if the source used + * was cryptographically strong. + * + * @param int $bytes the number of bytes of random data to generate + * @param bool $forceStrong Pass true if you want generate to prefer cryptographically + * strong sources of entropy even if reading from them may steal + * more entropy from the system than optimal. + * @return String Raw binary random data + */ + public static function generate( $bytes, $forceStrong = false ) { + return self::singleton()->realGenerate( $bytes, $forceStrong ); + } + + /** + * Generate a run of (ideally) cryptographically random data and return + * it in hexadecimal string format. + * You can use MWCryptRand::wasStrong() if you wish to know if the source used + * was cryptographically strong. + * + * @param int $chars the number of hex chars of random data to generate + * @param bool $forceStrong Pass true if you want generate to prefer cryptographically + * strong sources of entropy even if reading from them may steal + * more entropy from the system than optimal. + * @return String Hexadecimal random data + */ + public static function generateHex( $chars, $forceStrong = false ) { + return self::singleton()->realGenerateHex( $chars, $forceStrong ); + } + +} |