3 * A cryptographic random generator class used for generating secret keys
5 * This is based in part on Drupal code as well as what we used in our own code
6 * prior to introduction of this class.
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation; either version 2 of the License, or
11 * (at your option) any later version.
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
18 * You should have received a copy of the GNU General Public License along
19 * with this program; if not, write to the Free Software Foundation, Inc.,
20 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
21 * http://www.gnu.org/copyleft/gpl.html
23 * @author Daniel Friesen
30 * Minimum number of iterations we want to make in our drift calculations.
32 const MIN_ITERATIONS
= 1000;
35 * Number of milliseconds we want to spend generating each separate byte
36 * of the final generated bytes.
37 * This is used in combination with the hash length to determine the duration
38 * we should spend doing drift calculations.
40 const MSEC_PER_BYTE
= 0.5;
43 * Singleton instance for public use
45 protected static $singleton = null;
48 * The hash algorithm being used
50 protected $algo = null;
53 * The number of bytes outputted by the hash algorithm
55 protected $hashLength = null;
58 * A boolean indicating whether the previous random generation was done using
59 * cryptographically strong random number generator or not.
61 protected $strong = null;
64 * Initialize an initial random state based off of whatever we can find
66 protected function initialRandomState() {
67 // $_SERVER contains a variety of unstable user and system specific information
68 // It'll vary a little with each page, and vary even more with separate users
69 // It'll also vary slightly across different machines
70 $state = serialize( $_SERVER );
72 // To try vary the system information of the state a bit more
73 // by including the system's hostname into the state
74 $state .= wfHostname();
76 // Try to gather a little entropy from the different php rand sources
77 $state .= rand() . uniqid( mt_rand(), true );
79 // Include some information about the filesystem's current state in the random state
82 // We know this file is here so grab some info about ourself
85 // We must also have a parent folder, and with the usual file structure, a grandparent
86 $files[] = dirname( __FILE__
);
87 $files[] = dirname( dirname( __FILE__
) );
89 // The config file is likely the most often edited file we know should be around
90 // so include its stat info into the state.
91 // The constant with its location will almost always be defined, as WebStart.php defines
92 // MW_CONFIG_FILE to $IP/LocalSettings.php unless being configured with MW_CONFIG_CALLBACK (eg. the installer)
93 if ( defined( 'MW_CONFIG_FILE' ) ) {
94 $files[] = MW_CONFIG_FILE
;
97 foreach ( $files as $file ) {
99 $stat = stat( $file );
102 // stat() duplicates data into numeric and string keys so kill off all the numeric ones
103 foreach ( $stat as $k => $v ) {
104 if ( is_numeric( $k ) ) {
108 // The absolute filename itself will differ from install to install so don't leave it out
109 $state .= realpath( $file );
110 $state .= implode( '', $stat );
112 // The fact that the file isn't there is worth at least a
113 // minuscule amount of entropy.
118 // Try and make this a little more unstable by including the varying process
119 // id of the php process we are running inside of if we are able to access it
120 if ( function_exists( 'getmypid' ) ) {
121 $state .= getmypid();
124 // If available try to increase the instability of the data by throwing in
125 // the precise amount of memory that we happen to be using at the moment.
126 if ( function_exists( 'memory_get_usage' ) ) {
127 $state .= memory_get_usage( true );
130 // It's mostly worthless but throw the wiki's id into the data for a little more variance
131 $state .= wfWikiID();
133 // If we have a secret key or proxy key set then throw it into the state as well
134 global $wgSecretKey, $wgProxyKey;
135 if ( $wgSecretKey ) {
136 $state .= $wgSecretKey;
137 } elseif ( $wgProxyKey ) {
138 $state .= $wgProxyKey;
145 * Randomly hash data while mixing in clock drift data for randomness
147 * @param $data string The data to randomly hash.
148 * @return String The hashed bytes
149 * @author Tim Starling
151 protected function driftHash( $data ) {
152 // Minimum number of iterations (to avoid slow operations causing the loop to gather little entropy)
153 $minIterations = self
::MIN_ITERATIONS
;
154 // Duration of time to spend doing calculations (in seconds)
155 $duration = ( self
::MSEC_PER_BYTE
/ 1000 ) * $this->hashLength();
156 // Create a buffer to use to trigger memory operations
157 $bufLength = 10000000;
158 $buffer = str_repeat( ' ', $bufLength );
161 // Iterate for $duration seconds or at least $minIerations number of iterations
163 $startTime = microtime( true );
164 $currentTime = $startTime;
165 while ( $iterations < $minIterations ||
$currentTime - $startTime < $duration ) {
166 // Trigger some memory writing to trigger some bus activity
167 // This may create variance in the time between iterations
168 $bufPos = ( $bufPos +
13 ) %
$bufLength;
169 $buffer[$bufPos] = ' ';
170 // Add the drift between this iteration and the last in as entropy
171 $nextTime = microtime( true );
172 $delta = (int)( ( $nextTime - $currentTime ) * 1000000 );
174 // Every 100 iterations hash the data and entropy
175 if ( $iterations %
100 === 0 ) {
176 $data = sha1( $data );
178 $currentTime = $nextTime;
181 $timeTaken = $currentTime - $startTime;
182 $data = $this->hash( $data );
184 wfDebug( __METHOD__
. ": Clock drift calculation " .
185 "(time-taken=" . ( $timeTaken * 1000 ) . "ms, " .
186 "iterations=$iterations, " .
187 "time-per-iteration=" . ( $timeTaken / $iterations * 1e6
) . "us)\n" );
192 * Return a rolling random state initially build using data from unstable sources
193 * @return string A new weak random state
195 protected function randomState() {
196 static $state = null;
197 if ( is_null( $state ) ) {
198 // Initialize the state with whatever unstable data we can find
199 // It's important that this data is hashed right afterwards to prevent
200 // it from being leaked into the output stream
201 $state = $this->hash( $this->initialRandomState() );
203 // Generate a new random state based on the initial random state or previous
204 // random state by combining it with clock drift
205 $state = $this->driftHash( $state );
210 * Decide on the best acceptable hash algorithm we have available for hash()
211 * @throws MWException
212 * @return String A hash algorithm
214 protected function hashAlgo() {
215 if ( !is_null( $this->algo
) ) {
219 $algos = hash_algos();
220 $preference = array( 'whirlpool', 'sha256', 'sha1', 'md5' );
222 foreach ( $preference as $algorithm ) {
223 if ( in_array( $algorithm, $algos ) ) {
224 $this->algo
= $algorithm;
225 wfDebug( __METHOD__
. ": Using the {$this->algo} hash algorithm.\n" );
230 // We only reach here if no acceptable hash is found in the list, this should
231 // be a technical impossibility since most of php's hash list is fixed and
232 // some of the ones we list are available as their own native functions
233 // But since we already require at least 5.2 and hash() was default in
234 // 5.1.2 we don't bother falling back to methods like sha1 and md5.
235 throw new MWException( "Could not find an acceptable hashing function in hash_algos()" );
239 * Return the byte-length output of the hash algorithm we are
240 * using in self::hash and self::hmac.
242 * @return int Number of bytes the hash outputs
244 protected function hashLength() {
245 if ( is_null( $this->hashLength
) ) {
246 $this->hashLength
= strlen( $this->hash( '' ) );
248 return $this->hashLength
;
252 * Generate an acceptably unstable one-way-hash of some text
253 * making use of the best hash algorithm that we have available.
255 * @param $data string
256 * @return String A raw hash of the data
258 protected function hash( $data ) {
259 return hash( $this->hashAlgo(), $data, true );
263 * Generate an acceptably unstable one-way-hmac of some text
264 * making use of the best hash algorithm that we have available.
266 * @param $data string
268 * @return String A raw hash of the data
270 protected function hmac( $data, $key ) {
271 return hash_hmac( $this->hashAlgo(), $data, $key, true );
275 * @see self::wasStrong()
277 public function realWasStrong() {
278 if ( is_null( $this->strong
) ) {
279 throw new MWException( __METHOD__
. ' called before generation of random data' );
281 return $this->strong
;
285 * @see self::generate()
287 public function realGenerate( $bytes, $forceStrong = false ) {
288 wfProfileIn( __METHOD__
);
290 wfDebug( __METHOD__
. ": Generating cryptographic random bytes for " . wfGetAllCallers( 5 ) . "\n" );
292 $bytes = floor( $bytes );
294 if ( is_null( $this->strong
) ) {
295 // Set strength to false initially until we know what source data is coming from
296 $this->strong
= true;
299 if ( strlen( $buffer ) < $bytes ) {
300 // If available make use of mcrypt_create_iv URANDOM source to generate randomness
301 // On unix-like systems this reads from /dev/urandom but does it without any buffering
302 // and bypasses openbasedir restrictions, so it's preferable to reading directly
303 // On Windows starting in PHP 5.3.0 Windows' native CryptGenRandom is used to generate
304 // entropy so this is also preferable to just trying to read urandom because it may work
305 // on Windows systems as well.
306 if ( function_exists( 'mcrypt_create_iv' ) ) {
307 wfProfileIn( __METHOD__
. '-mcrypt' );
308 $rem = $bytes - strlen( $buffer );
309 $iv = mcrypt_create_iv( $rem, MCRYPT_DEV_URANDOM
);
310 if ( $iv === false ) {
311 wfDebug( __METHOD__
. ": mcrypt_create_iv returned false.\n" );
314 wfDebug( __METHOD__
. ": mcrypt_create_iv generated " . strlen( $iv ) . " bytes of randomness.\n" );
316 wfProfileOut( __METHOD__
. '-mcrypt' );
320 if ( strlen( $buffer ) < $bytes ) {
321 // If available make use of openssl's random_pseudo_bytes method to attempt to generate randomness.
322 // However don't do this on Windows with PHP < 5.3.4 due to a bug:
323 // http://stackoverflow.com/questions/1940168/openssl-random-pseudo-bytes-is-slow-php
324 // http://git.php.net/?p=php-src.git;a=commitdiff;h=cd62a70863c261b07f6dadedad9464f7e213cad5
325 if ( function_exists( 'openssl_random_pseudo_bytes' )
326 && ( !wfIsWindows() ||
version_compare( PHP_VERSION
, '5.3.4', '>=' ) )
328 wfProfileIn( __METHOD__
. '-openssl' );
329 $rem = $bytes - strlen( $buffer );
330 $openssl_bytes = openssl_random_pseudo_bytes( $rem, $openssl_strong );
331 if ( $openssl_bytes === false ) {
332 wfDebug( __METHOD__
. ": openssl_random_pseudo_bytes returned false.\n" );
334 $buffer .= $openssl_bytes;
335 wfDebug( __METHOD__
. ": openssl_random_pseudo_bytes generated " . strlen( $openssl_bytes ) . " bytes of " . ( $openssl_strong ?
"strong" : "weak" ) . " randomness.\n" );
337 if ( strlen( $buffer ) >= $bytes ) {
338 // openssl tells us if the random source was strong, if some of our data was generated
339 // using it use it's say on whether the randomness is strong
340 $this->strong
= !!$openssl_strong;
342 wfProfileOut( __METHOD__
. '-openssl' );
346 // Only read from urandom if we can control the buffer size or were passed forceStrong
347 if ( strlen( $buffer ) < $bytes && ( function_exists( 'stream_set_read_buffer' ) ||
$forceStrong ) ) {
348 wfProfileIn( __METHOD__
. '-fopen-urandom' );
349 $rem = $bytes - strlen( $buffer );
350 if ( !function_exists( 'stream_set_read_buffer' ) && $forceStrong ) {
351 wfDebug( __METHOD__
. ": Was forced to read from /dev/urandom without control over the buffer size.\n" );
353 // /dev/urandom is generally considered the best possible commonly
354 // available random source, and is available on most *nix systems.
355 wfSuppressWarnings();
356 $urandom = fopen( "/dev/urandom", "rb" );
359 // Attempt to read all our random data from urandom
360 // php's fread always does buffered reads based on the stream's chunk_size
361 // so in reality it will usually read more than the amount of data we're
362 // asked for and not storing that risks depleting the system's random pool.
363 // If stream_set_read_buffer is available set the chunk_size to the amount
364 // of data we need. Otherwise read 8k, php's default chunk_size.
366 // php's default chunk_size is 8k
367 $chunk_size = 1024 * 8;
368 if ( function_exists( 'stream_set_read_buffer' ) ) {
369 // If possible set the chunk_size to the amount of data we need
370 stream_set_read_buffer( $urandom, $rem );
373 $random_bytes = fread( $urandom, max( $chunk_size, $rem ) );
374 $buffer .= $random_bytes;
376 wfDebug( __METHOD__
. ": /dev/urandom generated " . strlen( $random_bytes ) . " bytes of randomness.\n" );
377 if ( strlen( $buffer ) >= $bytes ) {
378 // urandom is always strong, set to true if all our data was generated using it
379 $this->strong
= true;
382 wfDebug( __METHOD__
. ": /dev/urandom could not be opened.\n" );
384 wfProfileOut( __METHOD__
. '-fopen-urandom' );
387 // If we cannot use or generate enough data from a secure source
388 // use this loop to generate a good set of pseudo random data.
389 // This works by initializing a random state using a pile of unstable data
390 // and continually shoving it through a hash along with a variable salt.
391 // We hash the random state with more salt to avoid the state from leaking
392 // out and being used to predict the /randomness/ that follows.
393 if ( strlen( $buffer ) < $bytes ) {
394 wfDebug( __METHOD__
. ": Falling back to using a pseudo random state to generate randomness.\n" );
396 while ( strlen( $buffer ) < $bytes ) {
397 wfProfileIn( __METHOD__
. '-fallback' );
398 $buffer .= $this->hmac( $this->randomState(), mt_rand() );
399 // This code is never really cryptographically strong, if we use it
400 // at all, then set strong to false.
401 $this->strong
= false;
402 wfProfileOut( __METHOD__
. '-fallback' );
405 // Once the buffer has been filled up with enough random data to fulfill
406 // the request shift off enough data to handle the request and leave the
407 // unused portion left inside the buffer for the next request for random data
408 $generated = substr( $buffer, 0, $bytes );
409 $buffer = substr( $buffer, $bytes );
411 wfDebug( __METHOD__
. ": " . strlen( $buffer ) . " bytes of randomness leftover in the buffer.\n" );
413 wfProfileOut( __METHOD__
);
418 * @see self::generateHex()
420 public function realGenerateHex( $chars, $forceStrong = false ) {
421 // hex strings are 2x the length of raw binary so we divide the length in half
422 // odd numbers will result in a .5 that leads the generate() being 1 character
423 // short, so we use ceil() to ensure that we always have enough bytes
424 $bytes = ceil( $chars / 2 );
425 // Generate the data and then convert it to a hex string
426 $hex = bin2hex( $this->generate( $bytes, $forceStrong ) );
427 // A bit of paranoia here, the caller asked for a specific length of string
428 // here, and it's possible (eg when given an odd number) that we may actually
429 // have at least 1 char more than they asked for. Just in case they made this
430 // call intending to insert it into a database that does truncation we don't
431 // want to give them too much and end up with their database and their live
432 // code having two different values because part of what we gave them is truncated
433 // hence, we strip out any run of characters longer than what we were asked for.
434 return substr( $hex, 0, $chars );
437 /** Publicly exposed static methods **/
440 * Return a singleton instance of MWCryptRand
441 * @return MWCryptRand
443 protected static function singleton() {
444 if ( is_null( self
::$singleton ) ) {
445 self
::$singleton = new self
;
447 return self
::$singleton;
451 * Return a boolean indicating whether or not the source used for cryptographic
452 * random bytes generation in the previously run generate* call
453 * was cryptographically strong.
455 * @return bool Returns true if the source was strong, false if not.
457 public static function wasStrong() {
458 return self
::singleton()->realWasStrong();
462 * Generate a run of (ideally) cryptographically random data and return
463 * it in raw binary form.
464 * You can use MWCryptRand::wasStrong() if you wish to know if the source used
465 * was cryptographically strong.
467 * @param $bytes int the number of bytes of random data to generate
468 * @param $forceStrong bool Pass true if you want generate to prefer cryptographically
469 * strong sources of entropy even if reading from them may steal
470 * more entropy from the system than optimal.
471 * @return String Raw binary random data
473 public static function generate( $bytes, $forceStrong = false ) {
474 return self
::singleton()->realGenerate( $bytes, $forceStrong );
478 * Generate a run of (ideally) cryptographically random data and return
479 * it in hexadecimal string format.
480 * You can use MWCryptRand::wasStrong() if you wish to know if the source used
481 * was cryptographically strong.
483 * @param $chars int the number of hex chars of random data to generate
484 * @param $forceStrong bool Pass true if you want generate to prefer cryptographically
485 * strong sources of entropy even if reading from them may steal
486 * more entropy from the system than optimal.
487 * @return String Hexadecimal random data
489 public static function generateHex( $chars, $forceStrong = false ) {
490 return self
::singleton()->realGenerateHex( $chars, $forceStrong );