includes/CryptRand.php

   1 <?php
   2 /**
   3  * A cryptographic random generator class used for generating secret keys
   4  *
   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.
   7  *
   8  * @author Daniel Friesen
   9  * @file
  10  */
  11
  12 class MWCryptRand {
  13
  14         /**
  15          * Minimum number of iterations we want to make in our drift calculations.
  16          */
  17         const MIN_ITERATIONS = 1000;
  18
  19         /**
  20          * Number of milliseconds we want to spend generating each separate byte
  21          * of the final generated bytes.
  22          * This is used in combination with the hash length to determine the duration
  23          * we should spend doing drift calculations.
  24          */
  25         const MSEC_PER_BYTE = 0.5;
  26
  27         /**
  28          * Singleton instance for public use
  29          */
  30         protected static $singleton = null;
  31
  32         /**
  33          * The hash algorithm being used
  34          */
  35         protected $algo = null;
  36
  37         /**
  38          * The number of bytes outputted by the hash algorithm
  39          */
  40         protected $hashLength = null;
  41
  42         /**
  43          * A boolean indicating whether the previous random generation was done using
  44          * cryptographically strong random number generator or not.
  45          */
  46         protected $strong = null;
  47
  48         /**
  49          * Initialize an initial random state based off of whatever we can find
  50          */
  51         protected function initialRandomState() {
  52                 // $_SERVER contains a variety of unstable user and system specific information
  53                 // It'll vary a little with each page, and vary even more with separate users
  54                 // It'll also vary slightly across different machines
  55                 $state = serialize( $_SERVER );
  56
  57                 // To try and vary the system information of the state a bit more
  58                 // by including the system's hostname into the state
  59                 $state .= wfHostname();
  60
  61                 // Try to gather a little entropy from the different php rand sources
  62                 $state .= rand() . uniqid( mt_rand(), true );
  63
  64                 // Include some information about the filesystem's current state in the random state
  65                 $files = array();
  66                 // We know this file is here so grab some info about ourself
  67                 $files[] = __FILE__;
  68                 // The config file is likely the most often edited file we know should be around
  69                 // so if the constant with it's location is defined include it's stat info into the state
  70                 if ( defined( 'MW_CONFIG_FILE' ) ) {
  71                         $files[] = MW_CONFIG_FILE;
  72                 }
  73                 foreach ( $files as $file ) {
  74                         wfSuppressWarnings();
  75                         $stat = stat( $file );
  76                         wfRestoreWarnings();
  77                         if ( $stat ) {
  78                                 // stat() duplicates data into numeric and string keys so kill off all the numeric ones
  79                                 foreach ( $stat as $k => $v ) {
  80                                         if ( is_numeric( $k ) ) {
  81                                                 unset( $k );
  82                                         }
  83                                 }
  84                                 // The absolute filename itself will differ from install to install so don't leave it out
  85                                 $state .= realpath( $file );
  86                                 $state .= implode( '', $stat );
  87                         } else {
  88                                 // The fact that the file isn't there is worth at least a
  89                                 // minuscule amount of entropy.
  90                                 $state .= '0';
  91                         }
  92                 }
  93
  94                 // Try and make this a little more unstable by including the varying process
  95                 // id of the php process we are running inside of if we are able to access it
  96                 if ( function_exists( 'getmypid' ) ) {
  97                         $state .= getmypid();
  98                 }
  99
 100                 // If available try to increase the instability of the data by throwing in
 101                 // the precise amount of memory that we happen to be using at the moment.
 102                 if ( function_exists( 'memory_get_usage' ) ) {
 103                         $state .= memory_get_usage( true );
 104                 }
 105
 106                 // It's mostly worthless but throw the wiki's id into the data for a little more variance
 107                 $state .= wfWikiID();
 108
 109                 // If we have a secret key or proxy key set then throw it into the state as well
 110                 global $wgSecretKey, $wgProxyKey;
 111                 if ( $wgSecretKey ) {
 112                         $state .= $wgSecretKey;
 113                 } elseif ( $wgProxyKey ) {
 114                         $state .= $wgProxyKey;
 115                 }
 116
 117                 return $state;
 118         }
 119
 120         /**
 121          * Randomly hash data while mixing in clock drift data for randomness
 122          *
 123          * @param $data string The data to randomly hash.
 124          * @return String The hashed bytes
 125          * @author Tim Starling
 126          */
 127         protected function driftHash( $data ) {
 128                 // Minimum number of iterations (to avoid slow operations causing the loop to gather little entropy)
 129                 $minIterations = self::MIN_ITERATIONS;
 130                 // Duration of time to spend doing calculations (in seconds)
 131                 $duration = ( self::MSEC_PER_BYTE / 1000 ) * $this->hashLength();
 132                 // Create a buffer to use to trigger memory operations
 133                 $bufLength = 10000000;
 134                 $buffer = str_repeat( ' ', $bufLength );
 135                 $bufPos = 0;
 136
 137                 // Iterate for $duration seconds or at least $minIerations number of iterations
 138                 $iterations = 0;
 139                 $startTime = microtime( true );
 140                 $currentTime = $startTime;
 141                 while ( $iterations < $minIterations || $currentTime - $startTime < $duration ) {
 142                         // Trigger some memory writing to trigger some bus activity
 143                         // This may create variance in the time between iterations
 144                         $bufPos = ( $bufPos + 13 ) % $bufLength;
 145                         $buffer[$bufPos] = ' ';
 146                         // Add the drift between this iteration and the last in as entropy
 147                         $nextTime = microtime( true );
 148                         $delta = (int)( ( $nextTime - $currentTime ) * 1000000 );
 149                         $data .= $delta;
 150                         // Every 100 iterations hash the data and entropy
 151                         if ( $iterations % 100 === 0 ) {
 152                                 $data = sha1( $data );
 153                         }
 154                         $currentTime = $nextTime;
 155                         $iterations++;
 156                 }
 157                 $timeTaken = $currentTime - $startTime;
 158                 $data = $this->hash( $data );
 159
 160                 wfDebug( __METHOD__ . ": Clock drift calculation " .
 161                         "(time-taken=" . ( $timeTaken * 1000 ) . "ms, " .
 162                         "iterations=$iterations, " .
 163                         "time-per-iteration=" . ( $timeTaken / $iterations * 1e6 ) . "us)\n" );
 164                 return $data;
 165         }
 166
 167         /**
 168          * Return a rolling random state initially build using data from unstable sources
 169          * @return string A new weak random state
 170          */
 171         protected function randomState() {
 172                 static $state = null;
 173                 if ( is_null( $state ) ) {
 174                         // Initialize the state with whatever unstable data we can find
 175                         // It's important that this data is hashed right afterwards to prevent
 176                         // it from being leaked into the output stream
 177                         $state = $this->hash( $this->initialRandomState() );
 178                 }
 179                 // Generate a new random state based on the initial random state or previous
 180                 // random state by combining it with clock drift
 181                 $state = $this->driftHash( $state );
 182                 return $state;
 183         }
 184
 185         /**
 186          * Decide on the best acceptable hash algorithm we have available for hash()
 187          * @throws MWException
 188          * @return String A hash algorithm
 189          */
 190         protected function hashAlgo() {
 191                 if ( !is_null( $this->algo ) ) {
 192                         return $this->algo;
 193                 }
 194
 195                 $algos = hash_algos();
 196                 $preference = array( 'whirlpool', 'sha256', 'sha1', 'md5' );
 197
 198                 foreach ( $preference as $algorithm ) {
 199                         if ( in_array( $algorithm, $algos ) ) {
 200                                 $this->algo = $algorithm;
 201                                 wfDebug( __METHOD__ . ": Using the {$this->algo} hash algorithm.\n" );
 202                                 return $this->algo;
 203                         }
 204                 }
 205
 206                 // We only reach here if no acceptable hash is found in the list, this should
 207                 // be a technical impossibility since most of php's hash list is fixed and
 208                 // some of the ones we list are available as their own native functions
 209                 // But since we already require at least 5.2 and hash() was default in
 210                 // 5.1.2 we don't bother falling back to methods like sha1 and md5.
 211                 throw new MWException( "Could not find an acceptable hashing function in hash_algos()" );
 212         }
 213
 214         /**
 215          * Return the byte-length output of the hash algorithm we are
 216          * using in self::hash and self::hmac.
 217          *
 218          * @return int Number of bytes the hash outputs
 219          */
 220         protected function hashLength() {
 221                 if ( is_null( $this->hashLength ) ) {
 222                         $this->hashLength = strlen( $this->hash( '' ) );
 223                 }
 224                 return $this->hashLength;
 225         }
 226
 227         /**
 228          * Generate an acceptably unstable one-way-hash of some text
 229          * making use of the best hash algorithm that we have available.
 230          *
 231          * @param $data string
 232          * @return String A raw hash of the data
 233          */
 234         protected function hash( $data ) {
 235                 return hash( $this->hashAlgo(), $data, true );
 236         }
 237
 238         /**
 239          * Generate an acceptably unstable one-way-hmac of some text
 240          * making use of the best hash algorithm that we have available.
 241          *
 242          * @param $data string
 243          * @param $key string
 244          * @return String A raw hash of the data
 245          */
 246         protected function hmac( $data, $key ) {
 247                 return hash_hmac( $this->hashAlgo(), $data, $key, true );
 248         }
 249
 250         /**
 251          * @see self::wasStrong()
 252          */
 253         public function realWasStrong() {
 254                 if ( is_null( $this->strong ) ) {
 255                         throw new MWException( __METHOD__ . ' called before generation of random data' );
 256                 }
 257                 return $this->strong;
 258         }
 259
 260         /**
 261          * @see self::generate()
 262          */
 263         public function realGenerate( $bytes, $forceStrong = false ) {
 264                 wfProfileIn( __METHOD__ );
 265
 266                 wfDebug( __METHOD__ . ": Generating cryptographic random bytes for " . wfGetAllCallers( 5 ) . "\n" );
 267
 268                 $bytes = floor( $bytes );
 269                 static $buffer = '';
 270                 if ( is_null( $this->strong ) ) {
 271                         // Set strength to false initially until we know what source data is coming from
 272                         $this->strong = true;
 273                 }
 274
 275                 if ( strlen( $buffer ) < $bytes ) {
 276                         // If available make use of mcrypt_create_iv URANDOM source to generate randomness
 277                         // On unix-like systems this reads from /dev/urandom but does it without any buffering
 278                         // and bypasses openbasdir restrictions so it's preferable to reading directly
 279                         // On Windows starting in PHP 5.3.0 Windows' native CryptGenRandom is used to generate
 280                         // entropy so this is also preferable to just trying to read urandom because it may work
 281                         // on Windows systems as well.
 282                         if ( function_exists( 'mcrypt_create_iv' ) ) {
 283                                 wfProfileIn( __METHOD__ . '-mcrypt' );
 284                                 $rem = $bytes - strlen( $buffer );
 285                                 $iv = mcrypt_create_iv( $rem, MCRYPT_DEV_URANDOM );
 286                                 if ( $iv === false ) {
 287                                         wfDebug( __METHOD__ . ": mcrypt_create_iv returned false.\n" );
 288                                 } else {
 289                                         $buffer .= $iv;
 290                                         wfDebug( __METHOD__ . ": mcrypt_create_iv generated " . strlen( $iv ) . " bytes of randomness.\n" );
 291                                 }
 292                                 wfProfileOut( __METHOD__ . '-mcrypt' );
 293                         }
 294                 }
 295
 296                 if ( strlen( $buffer ) < $bytes ) {
 297                         // If available make use of openssl's random_pesudo_bytes method to attempt to generate randomness.
 298                         // However don't do this on Windows with PHP < 5.3.4 due to a bug:
 299                         // http://stackoverflow.com/questions/1940168/openssl-random-pseudo-bytes-is-slow-php
 300                         if ( function_exists( 'openssl_random_pseudo_bytes' )
 301                                 && ( !wfIsWindows() || version_compare( PHP_VERSION, '5.3.4', '>=' ) )
 302                         ) {
 303                                 wfProfileIn( __METHOD__ . '-openssl' );
 304                                 $rem = $bytes - strlen( $buffer );
 305                                 $openssl_bytes = openssl_random_pseudo_bytes( $rem, $openssl_strong );
 306                                 if ( $openssl_bytes === false ) {
 307                                         wfDebug( __METHOD__ . ": openssl_random_pseudo_bytes returned false.\n" );
 308                                 } else {
 309                                         $buffer .= $openssl_bytes;
 310                                         wfDebug( __METHOD__ . ": openssl_random_pseudo_bytes generated " . strlen( $openssl_bytes ) . " bytes of " . ( $openssl_strong ? "strong" : "weak" ) . " randomness.\n" );
 311                                 }
 312                                 if ( strlen( $buffer ) >= $bytes ) {
 313                                         // openssl tells us if the random source was strong, if some of our data was generated
 314                                         // using it use it's say on whether the randomness is strong
 315                                         $this->strong = !!$openssl_strong;
 316                                 }
 317                                 wfProfileOut( __METHOD__ . '-openssl' );
 318                         }
 319                 }
 320
 321                 // Only read from urandom if we can control the buffer size or were passed forceStrong
 322                 if ( strlen( $buffer ) < $bytes && ( function_exists( 'stream_set_read_buffer' ) || $forceStrong ) ) {
 323                         wfProfileIn( __METHOD__ . '-fopen-urandom' );
 324                         $rem = $bytes - strlen( $buffer );
 325                         if ( !function_exists( 'stream_set_read_buffer' ) && $forceStrong ) {
 326                                 wfDebug( __METHOD__ . ": Was forced to read from /dev/urandom without control over the buffer size.\n" );
 327                         }
 328                         // /dev/urandom is generally considered the best possible commonly
 329                         // available random source, and is available on most *nix systems.
 330                         wfSuppressWarnings();
 331                         $urandom = fopen( "/dev/urandom", "rb" );
 332                         wfRestoreWarnings();
 333
 334                         // Attempt to read all our random data from urandom
 335                         // php's fread always does buffered reads based on the stream's chunk_size
 336                         // so in reality it will usually read more than the amount of data we're
 337                         // asked for and not storing that risks depleting the system's random pool.
 338                         // If stream_set_read_buffer is available set the chunk_size to the amount
 339                         // of data we need. Otherwise read 8k, php's default chunk_size.
 340                         if ( $urandom ) {
 341                                 // php's default chunk_size is 8k
 342                                 $chunk_size = 1024 * 8;
 343                                 if ( function_exists( 'stream_set_read_buffer' ) ) {
 344                                         // If possible set the chunk_size to the amount of data we need
 345                                         stream_set_read_buffer( $urandom, $rem );
 346                                         $chunk_size = $rem;
 347                                 }
 348                                 $random_bytes = fread( $urandom, max( $chunk_size, $rem ) );
 349                                 $buffer .= $random_bytes;
 350                                 fclose( $urandom );
 351                                 wfDebug( __METHOD__ . ": /dev/urandom generated " . strlen( $random_bytes ) . " bytes of randomness.\n" );
 352                                 if ( strlen( $buffer ) >= $bytes ) {
 353                                         // urandom is always strong, set to true if all our data was generated using it
 354                                         $this->strong = true;
 355                                 }
 356                         } else {
 357                                 wfDebug( __METHOD__ . ": /dev/urandom could not be opened.\n" );
 358                         }
 359                         wfProfileOut( __METHOD__ . '-fopen-urandom' );
 360                 }
 361
 362                 // If we cannot use or generate enough data from a secure source
 363                 // use this loop to generate a good set of pseudo random data.
 364                 // This works by initializing a random state using a pile of unstable data
 365                 // and continually shoving it through a hash along with a variable salt.
 366                 // We hash the random state with more salt to avoid the state from leaking
 367                 // out and being used to predict the /randomness/ that follows.
 368                 if ( strlen( $buffer ) < $bytes ) {
 369                         wfDebug( __METHOD__ . ": Falling back to using a pseudo random state to generate randomness.\n" );
 370                 }
 371                 while ( strlen( $buffer ) < $bytes ) {
 372                         wfProfileIn( __METHOD__ . '-fallback' );
 373                         $buffer .= $this->hmac( $this->randomState(), mt_rand() );
 374                         // This code is never really cryptographically strong, if we use it
 375                         // at all, then set strong to false.
 376                         $this->strong = false;
 377                         wfProfileOut( __METHOD__ . '-fallback' );
 378                 }
 379
 380                 // Once the buffer has been filled up with enough random data to fulfill
 381                 // the request shift off enough data to handle the request and leave the
 382                 // unused portion left inside the buffer for the next request for random data
 383                 $generated = substr( $buffer, 0, $bytes );
 384                 $buffer = substr( $buffer, $bytes );
 385
 386                 wfDebug( __METHOD__ . ": " . strlen( $buffer ) . " bytes of randomness leftover in the buffer.\n" );
 387
 388                 wfProfileOut( __METHOD__ );
 389                 return $generated;
 390         }
 391
 392         /**
 393          * @see self::generateHex()
 394          */
 395         public function realGenerateHex( $chars, $forceStrong = false ) {
 396                 // hex strings are 2x the length of raw binary so we divide the length in half
 397                 // odd numbers will result in a .5 that leads the generate() being 1 character
 398                 // short, so we use ceil() to ensure that we always have enough bytes
 399                 $bytes = ceil( $chars / 2 );
 400                 // Generate the data and then convert it to a hex string
 401                 $hex = bin2hex( $this->generate( $bytes, $forceStrong ) );
 402                 // A bit of paranoia here, the caller asked for a specific length of string
 403                 // here, and it's possible (eg when given an odd number) that we may actually
 404                 // have at least 1 char more than they asked for. Just in case they made this
 405                 // call intending to insert it into a database that does truncation we don't
 406                 // want to give them too much and end up with their database and their live
 407                 // code having two different values because part of what we gave them is truncated
 408                 // hence, we strip out any run of characters longer than what we were asked for.
 409                 return substr( $hex, 0, $chars );
 410         }
 411
 412         /** Publicly exposed static methods **/
 413
 414         /**
 415          * Return a singleton instance of MWCryptRand
 416          * @return MWCryptRand
 417          */
 418         protected static function singleton() {
 419                 if ( is_null( self::$singleton ) ) {
 420                         self::$singleton = new self;
 421                 }
 422                 return self::$singleton;
 423         }
 424
 425         /**
 426          * Return a boolean indicating whether or not the source used for cryptographic
 427          * random bytes generation in the previously run generate* call
 428          * was cryptographically strong.
 429          *
 430          * @return bool Returns true if the source was strong, false if not.
 431          */
 432         public static function wasStrong() {
 433                 return self::singleton()->realWasStrong();
 434         }
 435
 436         /**
 437          * Generate a run of (ideally) cryptographically random data and return
 438          * it in raw binary form.
 439          * You can use MWCryptRand::wasStrong() if you wish to know if the source used
 440          * was cryptographically strong.
 441          *
 442          * @param $bytes int the number of bytes of random data to generate
 443          * @param $forceStrong bool Pass true if you want generate to prefer cryptographically
 444          *                          strong sources of entropy even if reading from them may steal
 445          *                          more entropy from the system than optimal.
 446          * @return String Raw binary random data
 447          */
 448         public static function generate( $bytes, $forceStrong = false ) {
 449                 return self::singleton()->realGenerate( $bytes, $forceStrong );
 450         }
 451
 452         /**
 453          * Generate a run of (ideally) cryptographically random data and return
 454          * it in hexadecimal string format.
 455          * You can use MWCryptRand::wasStrong() if you wish to know if the source used
 456          * was cryptographically strong.
 457          *
 458          * @param $chars int the number of hex chars of random data to generate
 459          * @param $forceStrong bool Pass true if you want generate to prefer cryptographically
 460          *                          strong sources of entropy even if reading from them may steal
 461          *                          more entropy from the system than optimal.
 462          * @return String Hexadecimal random data
 463          */
 464         public static function generateHex( $chars, $forceStrong = false ) {
 465                 return self::singleton()->realGenerateHex( $chars, $forceStrong );
 466         }
 467
 468 }