nextcloud/apps/files_encryption/lib/stream.php

<?php
/**
 * ownCloud
 *
 * @author Robin Appelman
 * @copyright 2012 Sam Tuke <samtuke@owncloud.com>, 2011 Robin Appelman 
 * <icewind1991@gmail.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU AFFERO GENERAL PUBLIC LICENSE
 * License as published by the Free Software Foundation; either
 * version 3 of the License, or any later version.
 *
 * This library 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 AFFERO GENERAL PUBLIC LICENSE for more details.
 *
 * You should have received a copy of the GNU Affero General Public
 * License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

/**
 * transparently encrypted filestream
 *
 * you can use it as wrapper around an existing stream by setting CryptStream::$sourceStreams['foo']=array('path'=>$path,'stream'=>$stream)
 * and then fopen('crypt://streams/foo');
 */

namespace OCA\Encryption;

/**
 * @brief Provides 'crypt://' stream wrapper protocol.
 * @note We use a stream wrapper because it is the most secure way to handle 
 * decrypted content transfers. There is no safe way to decrypt the entire file
 * somewhere on the server, so we have to encrypt and decrypt blocks on the fly.
 * @note Paths used with this protocol MUST BE RELATIVE. Use URLs like:
 * crypt://filename, or crypt://subdirectory/filename, NOT 
 * crypt:///home/user/owncloud/data. Otherwise keyfiles will be put in 
 * [owncloud]/data/user/files_encryption/keyfiles/home/user/owncloud/data and 
 * will not be accessible to other methods.
 * @note Data read and written must always be 8192 bytes long, as this is the 
 * buffer size used internally by PHP. The encryption process makes the input 
 * data longer, and input is chunked into smaller pieces in order to result in 
 * a 8192 encrypted block size.
 */
class Stream {

	public static $sourceStreams = array();

	// TODO: make all below properties private again once unit testing is 
	// configured correctly
	public $rawPath; // The raw path received by stream_open
	public $path_f; // The raw path formatted to include username and data dir
	private $userId;
	private $handle; // Resource returned by fopen
	private $path;
	private $readBuffer; // For streams that dont support seeking
	private $meta = array(); // Header / meta for source stream
	private $count;
	private $writeCache;
	public $size;
	private $publicKey;
	private $keyfile;
	private $encKeyfile;
	private static $view; // a fsview object set to user dir
	private $rootView; // a fsview object set to '/'

	public function stream_open( $path, $mode, $options, &$opened_path ) {
		
		$this->userId = \OCP\User::getUser();
		
		if ( ! isset( $this->rootView ) ) {

			$this->rootView = new \OC_FilesystemView( '/' );

		}

		// Strip identifier text from path
		$this->rawPath = str_replace( 'crypt://', '', $path );
		
		// Set file path relative to user files dir
		$this->relPath = $this->userId . '/files/' . $this->rawPath;
		
		if ( 
		dirname( $this->rawPath ) == 'streams' 
		and isset( self::$sourceStreams[basename( $this->rawPath )] ) 
		) {
		
			// Is this just for unit testing purposes?

			$this->handle = self::$sourceStreams[basename( $this->rawPath )]['stream'];

			$this->path = self::$sourceStreams[basename( $this->rawPath )]['path'];

			$this->size = self::$sourceStreams[basename( $this->rawPath )]['size'];

		} else {

			if ( 
			$mode == 'w' 
			or $mode == 'w+' 
			or $mode == 'wb' 
			or $mode == 'wb+' 
			) {

				// We're writing a new file so start write counter with 0 bytes
				$this->size = 0;

			} else {
				
				$this->size = $this->rootView->filesize( $this->relPath, $mode );
				
				//$this->size = filesize( $this->rawPath );
				
			}

			// Disable fileproxies so we can open the source file without recursive encryption
			\OC_FileProxy::$enabled = false;

			//$this->handle = fopen( $this->rawPath, $mode );
			
			$this->handle = $this->rootView->fopen( $this->relPath, $mode );
			
			\OC_FileProxy::$enabled = true;

			if ( ! is_resource( $this->handle ) ) {

				\OCP\Util::writeLog( 'files_encryption', 'failed to open file "'.$this->rootView . '"', \OCP\Util::ERROR );

			} else {
			
				$this->meta = stream_get_meta_data( $this->handle );
				
			}

		}

		return is_resource( $this->handle );

	}
	
	public function stream_seek( $offset, $whence = SEEK_SET ) {
	
		$this->flush();
		
		fseek( $this->handle, $offset, $whence );
		
	}
	
	public function stream_tell() {
		return ftell($this->handle);
	}
	
	public function stream_read( $count ) {
	
		$this->writeCache = '';

		if ( $count != 8192 ) {
			
			// $count will always be 8192 https://bugs.php.net/bug.php?id=21641
			// This makes this function a lot simpler, but will break this class if the above 'bug' gets 'fixed'
			\OCP\Util::writeLog( 'files_encryption', 'PHP "bug" 21641 no longer holds, decryption system requires refactoring', OCP\Util::FATAL );

			die();

		}

// 		$pos = ftell( $this->handle );
// 
		// Get the data from the file handle
		$data = fread( $this->handle, 8192 );
 
		if ( strlen( $data ) ) {
			
			$this->getKey();
			
			$result = Crypt::symmetricDecryptFileContent( $data, $this->keyfile );
			
		} else {

			$result = '';

		}

// 		$length = $this->size - $pos;
// 
// 		if ( $length < 8192 ) {
// 
// 			$result = substr( $result, 0, $length );
// 
// 		}

		return $result;

	}
	
	/**
	 * @brief Encrypt and pad data ready for writting to disk
	 * @param string $plainData data to be encrypted
	 * @param string $key key to use for encryption
	 * @return encrypted data on success, false on failure
	 */
	public function preWriteEncrypt( $plainData, $key ) {
		
		// Encrypt data to 'catfile', which includes IV
		if ( $encrypted = Crypt::symmetricEncryptFileContent( $plainData, $key ) ) {
		
			return $encrypted; 
			
		} else {
		
			return false;
			
		}
		
	}
	
	/**
	 * @brief Get the keyfile for the current file, generate one if necessary
	 * @param bool $generate if true, a new key will be generated if none can be found
	 * @return bool true on key found and set, false on key not found and new key generated and set
	 */
	public function getKey() {
		
		// If a keyfile already exists for a file named identically to 
		// file to be written
		if ( $this->rootView->file_exists( $this->userId . '/'. 'files_encryption' . '/' . 'keyfiles' . '/' . $this->rawPath . '.key' ) ) {
		
			// TODO: add error handling for when file exists but no 
			// keyfile
			
			// Fetch existing keyfile
			$this->encKeyfile = Keymanager::getFileKey( $this->rootView, $this->userId, $this->rawPath );
			
			$this->getUser();
			
			$session = new Session();
			
			$privateKey = $session->getPrivateKey( $this->userId );
			
			$this->keyfile = Crypt::keyDecrypt( $this->encKeyfile, $privateKey );
			
			return true;
			
		} else {
		
			return false;
		
		}
		
	}
	
	public function getuser() {
	
		// Only get the user again if it isn't already set
		if ( empty( $this->userId ) ) {
	
			// TODO: Move this user call out of here - it belongs 
			// elsewhere
			$this->userId = \OCP\User::getUser();
		
		}
		
		// TODO: Add a method for getting the user in case OCP\User::
		// getUser() doesn't work (can that scenario ever occur?)
		
	}
	
	/**
	 * @brief Handle plain data from the stream, and write it in 8192 byte blocks
	 * @param string $data data to be written to disk
	 * @note the data will be written to the path stored in the stream handle, set in stream_open()
	 * @note $data is only ever be a maximum of 8192 bytes long. This is set by PHP internally. stream_write() is called multiple times in a loop on data larger than 8192 bytes
	 * @note Because the encryption process used increases the length of $data, a writeCache is used to carry over data which would not fit in the required block size
	 * @note Padding is added to each encrypted block to ensure that the resulting block is exactly 8192 bytes. This is removed during stream_read
	 * @note PHP automatically updates the file pointer after writing data to reflect it's length. There is generally no need to update the poitner manually using fseek
	 */
	public function stream_write( $data ) {
		
		// Disable the file proxies so that encryption is not 
		// automatically attempted when the file is written to disk - 
		// we are handling that separately here and we don't want to 
		// get into an infinite loop
		\OC_FileProxy::$enabled = false;
		
		// Get the length of the unencrypted data that we are handling
		$length = strlen( $data );
		
		// So far this round, no data has been written
		$written = 0;
		
		// Find out where we are up to in the writing of data to the 
		// file
		$pointer = ftell( $this->handle );
		
		// Make sure the userId is set
		$this->getuser();
		
		// TODO: Check if file is shared, if so, use multiKeyEncrypt and
		// save shareKeys in necessary user directories
		
		// Get / generate the keyfile for the file we're handling
		// If we're writing a new file (not overwriting an existing 
		// one), save the newly generated keyfile
		if ( ! $this->getKey() ) {
		
			// TODO: Reuse the keyfile, it it exists, instead of making a new one
			$this->keyfile = Crypt::generateKey();
			
			$this->publicKey = Keymanager::getPublicKey( $this->rootView, $this->userId );
			
			$this->encKeyfile = Crypt::keyEncrypt( $this->keyfile, $this->publicKey );
			
			$view = new \OC_FilesystemView( '/' );
			$userId = \OCP\User::getUser();
			
			// Save the new encrypted file key
			Keymanager::setFileKey( $view, $this->rawPath, $userId, $this->encKeyfile );
			
		}

		// If extra data is left over from the last round, make sure it 
		// is integrated into the next 6126 / 8192 block
		if ( $this->writeCache ) {
			
			// Concat writeCache to start of $data
			$data = $this->writeCache . $data;
			
			// Clear the write cache, ready for resuse - it has been
			// flushed and its old contents processed
			$this->writeCache = '';

		}
// 		
// 		// Make sure we always start on a block start
		if ( 0 != ( $pointer % 8192 ) ) { 
		// if the current position of 
		// file indicator is not aligned to a 8192 byte block, fix it 
		// so that it is

// 			fseek( $this->handle, - ( $pointer % 8192 ), SEEK_CUR );
// 			
// 			$pointer = ftell( $this->handle );
// 
// 			$unencryptedNewBlock = fread( $this->handle, 8192 );
// 			
// 			fseek( $this->handle, - ( $currentPos % 8192 ), SEEK_CUR );
// 
// 			$block = Crypt::symmetricDecryptFileContent( $unencryptedNewBlock, $this->keyfile );
// 
// 			$x =  substr( $block, 0, $currentPos % 8192 );
// 
// 			$data = $x . $data;
// 			
// 			fseek( $this->handle, - ( $currentPos % 8192 ), SEEK_CUR );
// 
		}

// 		$currentPos = ftell( $this->handle );
		
// 		// While there still remains somed data to be processed & written
		while( strlen( $data ) > 0 ) {
// 			
// 			// Remaining length for this iteration, not of the 
//			// entire file (may be greater than 8192 bytes)
// 			$remainingLength = strlen( $data );
// 			
// 			// If data remaining to be written is less than the 
//			// size of 1 6126 byte block
			if ( strlen( $data ) < 6126 ) {
				
				// Set writeCache to contents of $data
				// The writeCache will be carried over to the 
				// next write round, and added to the start of 
				// $data to ensure that written blocks are 
				// always the correct length. If there is still 
				// data in writeCache after the writing round 
				// has finished, then the data will be written 
				// to disk by $this->flush().
				$this->writeCache = $data;

				// Clear $data ready for next round
				$data = '';
// 
			} else {
				
				// Read the chunk from the start of $data
				$chunk = substr( $data, 0, 6126 );
				
				$encrypted = $this->preWriteEncrypt( $chunk, $this->keyfile );
				
				// Write the data chunk to disk. This will be 
				// addended to the last data chunk if the file 
				// being handled totals more than 6126 bytes
				fwrite( $this->handle, $encrypted );
				
				$writtenLen = strlen( $encrypted );
				//fseek( $this->handle, $writtenLen, SEEK_CUR );

				// Remove the chunk we just processed from 
				// $data, leaving only unprocessed data in $data
				// var, for handling on the next round
				$data = substr( $data, 6126 );

			}
		
		}

		$this->size = max( $this->size, $pointer + $length );
		
		return $length;

	}


	public function stream_set_option( $option, $arg1, $arg2 ) {
		switch($option) {
			case STREAM_OPTION_BLOCKING:
				stream_set_blocking( $this->handle, $arg1 );
				break;
			case STREAM_OPTION_READ_TIMEOUT:
				stream_set_timeout( $this->handle, $arg1, $arg2 );
				break;
			case STREAM_OPTION_WRITE_BUFFER:
				stream_set_write_buffer( $this->handle, $arg1, $arg2 );
		}
	}

	public function stream_stat() {
		return fstat($this->handle);
	}
	
	public function stream_lock( $mode ) {
		flock( $this->handle, $mode );
	}
	
	public function stream_flush() {
	
		return fflush( $this->handle ); 
		// Not a typo: http://php.net/manual/en/function.fflush.php
		
	}

	public function stream_eof() {
		return feof($this->handle);
	}

	private function flush() {
		
		if ( $this->writeCache ) {
			
			// Set keyfile property for file in question
			$this->getKey();
			
			$encrypted = $this->preWriteEncrypt( $this->writeCache, $this->keyfile );
			
			fwrite( $this->handle, $encrypted );
			
			$this->writeCache = '';
		
		}
	
	}

	public function stream_close() {
	
		$this->flush();

		if ( 
		$this->meta['mode']!='r' 
		and $this->meta['mode']!='rb' 
		) {

			\OC\Files\Filesystem::putFileInfo( $this->path, array( 'encrypted' => true, 'size' => $this->size ), '' );

		}

		return fclose( $this->handle );

	}

}