+global\MWCryptRand::realGenerate()

Complexity

Conditions	20
Paths	2112

Size

Total Lines	124
Code Lines	64

Duplication

Lines	0
Ratio	0 %

Importance

Changes

0

<?php
	public function realGenerate( $bytes, $forceStrong = false ) {

		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' ) ) {
				$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" );
				}
			}
		}

		if ( strlen( $buffer ) < $bytes ) {
			if ( function_exists( 'openssl_random_pseudo_bytes' ) ) {
				$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;
				}
			}
		}

		// 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 )
		) {
			$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.
			MediaWiki\suppressWarnings();
			$urandom = fopen( "/dev/urandom", "rb" );
			MediaWiki\restoreWarnings();

			// 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" );
			}
		}

		// 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 ) {
			$buffer .= MWCryptHash::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;
		}

		// 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" );

		return $generated;
	}