nextcloud/apps/files_encryption/lib/crypt.php

<?php

/**
 * ownCloud
 *
 * @author Sam Tuke, Frank Karlitschek, Robin Appelman
 * @copyright 2012 Sam Tuke samtuke@owncloud.com, 
 * Robin Appelman icewind@owncloud.com, Frank Karlitschek 
 * frank@owncloud.org
 *
 * 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/>.
 *
 */

namespace OCA\Encryption;

require_once 'Crypt_Blowfish/Blowfish.php';

// Todo:
//  - Add a setting "Don´t encrypt files larger than xx because of performance"
//  - Don't use a password directly as encryption key. but a key which is 
//    stored on the server and encrypted with the user password. -> change pass 
//    faster

/**
 * Class for common cryptography functionality
 */

class Crypt {

	/**
	 * @brief return encryption mode client or server side encryption
	 * @param string user name (use system wide setting if name=null)
	 * @return string 'client' or 'server'
	 */
	public static function mode( $user = null ) {

		return 'server';
		
	}
	
        /**
         * @brief Create a new encryption keypair
         * @return array publicKey, privatekey
         */
	public static function createKeypair() {
		
		$res = openssl_pkey_new(array('private_key_bits' => 4096));

		// Get private key
		openssl_pkey_export( $res, $privateKey );

		// Get public key
		$publicKey = openssl_pkey_get_details( $res );
		
		$publicKey = $publicKey['key'];
		
		return( array( 'publicKey' => $publicKey, 'privateKey' => $privateKey ) );
	
	}
	
        /**
         * @brief Add arbitrary padding to encrypted data
         * @param string $data data to be padded
         * @return padded data
         * @note In order to end up with data exactly 8192 bytes long we must 
         * add two letters. It is impossible to achieve exactly 8192 length 
         * blocks with encryption alone, hence padding is added to achieve the 
         * required length. 
         */
	public static function addPadding( $data ) {
	
		$padded = $data . 'xx';
		
		return $padded;
	
	}
	
        /**
         * @brief Remove arbitrary padding to encrypted data
         * @param string $padded padded data to remove padding from
         * @return unpadded data on success, false on error
         */
	public static function removePadding( $padded ) {
	
		if ( substr( $padded, -2 ) == 'xx' ) {
	
			$data = substr( $padded, 0, -2 );
			
			return $data;
		
		} else {
		
			// TODO: log the fact that unpadded data was submitted for removal of padding
			return false;
			
		}
	
	}
	
        /**
         * @brief Check if a file's contents contains an IV and is symmetrically encrypted
         * @return true / false
         * @note see also OCA\Encryption\Util->isEncryptedPath()
         */
	public static function isCatfileContent( $content ) {
	
		if ( !$content ) {
		
			return false;
			
		}
		
		$noPadding = self::removePadding( $content );
		
		// Fetch encryption metadata from end of file
		$meta = substr( $noPadding, -22 );
		
		// Fetch IV from end of file
		$iv = substr( $meta, -16 );
		
		// Fetch identifier from start of metadata
		$identifier = substr( $meta, 0, 6 );
		
		if ( $identifier == '00iv00') {
		
			return true;
			
		} else {
		
			return false;
			
		}
	
	}
	
	/**
	 * Check if a file is encrypted according to database file cache
	 * @param string $path
	 * @return bool
	 */
	public static function isEncryptedMeta( $path ) {
	
		// TODO: Use DI to get \OC\Files\Filesystem out of here
	
		// Fetch all file metadata from DB
		$metadata = \OC\Files\Filesystem::getFileInfo( $path);
		
		// Return encryption status
		return isset( $metadata['encrypted'] ) and ( bool )$metadata['encrypted'];
	
	}
	
        /**
         * @brief Check if a file is encrypted via legacy system
         * @param string $relPath The path of the file, relative to user/data;
         *        e.g. filename or /Docs/filename, NOT admin/files/filename
         * @return true / false
         */
	public static function isLegacyEncryptedContent( $data, $relPath ) {

		// Fetch all file metadata from DB
		$metadata = \OC\Files\Filesystem::getFileInfo( $relPath, '' );
		
		// If a file is flagged with encryption in DB, but isn't a 
		// valid content + IV combination, it's probably using the 
		// legacy encryption system
		if ( 
			isset( $metadata['encrypted'] ) 
			and $metadata['encrypted'] === true 
			and ! self::isCatfileContent( $data ) 
		) {
		
			return true;
		
		} else {
		
			return false;
			
		}
	
	}
	
        /**
         * @brief Symmetrically encrypt a string
         * @returns encrypted file
         */
	public static function encrypt( $plainContent, $iv, $passphrase = '' ) {
		
		if ( $encryptedContent = openssl_encrypt( $plainContent, 'AES-128-CFB', $passphrase, false, $iv ) ) {

			return $encryptedContent;
			
		} else {
		
			\OC_Log::write( 'Encryption library', 'Encryption (symmetric) of content failed', \OC_Log::ERROR );
			
			return false;
			
		}
	
	}
	
        /**
         * @brief Symmetrically decrypt a string
         * @returns decrypted file
         */
	public static function decrypt( $encryptedContent, $iv, $passphrase ) {
		
		if ( $plainContent = openssl_decrypt( $encryptedContent, 'AES-128-CFB', $passphrase, false, $iv ) ) {

			return $plainContent;
		
			
		} else {
		
			throw new \Exception( 'Encryption library: Decryption (symmetric) of content failed' );
			
			return false;
			
		}
	
	}
	
        /**
         * @brief Concatenate encrypted data with its IV and padding
         * @param string $content content to be concatenated
         * @param string $iv IV to be concatenated
         * @returns string concatenated content
         */
	public static function concatIv ( $content, $iv ) {
	
		$combined = $content . '00iv00' . $iv;
		
		return $combined;
	
	}
	
        /**
         * @brief Split concatenated data and IV into respective parts
         * @param string $catFile concatenated data to be split
         * @returns array keys: encrypted, iv
         */
	public static function splitIv ( $catFile ) {
	
		// Fetch encryption metadata from end of file
		$meta = substr( $catFile, -22 );
		
		// Fetch IV from end of file
		$iv = substr( $meta, -16 );
		
		// Remove IV and IV identifier text to expose encrypted content
		$encrypted = substr( $catFile, 0, -22 );
	
		$split = array(
			'encrypted' => $encrypted
			, 'iv' => $iv
		);
		
		return $split;
	
	}
	
        /**
         * @brief Symmetrically encrypts a string and returns keyfile content
         * @param $plainContent content to be encrypted in keyfile
         * @returns encrypted content combined with IV
         * @note IV need not be specified, as it will be stored in the returned keyfile
         * and remain accessible therein.
         */
	public static function symmetricEncryptFileContent( $plainContent, $passphrase = '' ) {
		
		if ( !$plainContent ) {
		
			return false;
			
		}
		
		$iv = self::generateIv();
		
		if ( $encryptedContent = self::encrypt( $plainContent, $iv, $passphrase ) ) {
			
				// Combine content to encrypt with IV identifier and actual IV
				$catfile = self::concatIv( $encryptedContent, $iv );
				
				$padded = self::addPadding( $catfile );
				
				return $padded;
		
		} else {
		
			\OC_Log::write( 'Encryption library', 'Encryption (symmetric) of keyfile content failed', \OC_Log::ERROR );
			
			return false;
			
		}
		
	}


	/**
	* @brief Symmetrically decrypts keyfile content
	* @param string $source
	* @param string $target
	* @param string $key the decryption key
	* @returns decrypted content
	*
	* This function decrypts a file
	*/
	public static function symmetricDecryptFileContent( $keyfileContent, $passphrase = '' ) {
	
		if ( !$keyfileContent ) {
		
			throw new \Exception( 'Encryption library: no data provided for decryption' );
			
		}
		
		// Remove padding
		$noPadding = self::removePadding( $keyfileContent );
		
		// Split into enc data and catfile
		$catfile = self::splitIv( $noPadding );
		
		if ( $plainContent = self::decrypt( $catfile['encrypted'], $catfile['iv'], $passphrase ) ) {
		
			return $plainContent;
			
		}
	
	}
	
	/**
	* @brief Creates symmetric keyfile content using a generated key
	* @param string $plainContent content to be encrypted
	* @returns array keys: key, encrypted
	* @note symmetricDecryptFileContent() can be used to decrypt files created using this method
	*
	* This function decrypts a file
	*/
	public static function symmetricEncryptFileContentKeyfile( $plainContent ) {
	
		$key = self::generateKey();
	
		if( $encryptedContent = self::symmetricEncryptFileContent( $plainContent, $key ) ) {
		
			return array(
				'key' => $key
				, 'encrypted' => $encryptedContent
			);
		
		} else {
		
			return false;
			
		}
	
	}
	
	/**
	* @brief Create asymmetrically encrypted keyfile content using a generated key
	* @param string $plainContent content to be encrypted
	* @param array $publicKeys array keys must be the userId of corresponding user
	* @returns array keys: keys (array, key = userId), data
	* @note symmetricDecryptFileContent() can decrypt files created using this method
	*/
	public static function multiKeyEncrypt( $plainContent, array $publicKeys ) {
		
		// openssl_seal returns false without errors if $plainContent 
		// is empty, so trigger our own error
		if ( empty( $plainContent ) ) {
		
			trigger_error( "Cannot mutliKeyEncrypt empty plain content" );
			throw new \Exception( 'Cannot mutliKeyEncrypt empty plain content' );
		
		}
		
		// Set empty vars to be set by openssl by reference
		$sealed = '';
		$shareKeys = array();
	
		if( openssl_seal( $plainContent, $sealed, $shareKeys, $publicKeys ) ) {
			
			$i = 0;
			
			// Ensure each shareKey is labelled with its 
			// corresponding userId
			foreach ( $publicKeys as $userId => $publicKey ) {
			
				$mappedShareKeys[$userId] = $shareKeys[$i];
				$i++;
			
			}
		
			return array(
				'keys' => $mappedShareKeys
				, 'data' => $sealed
			);
		
		} else {
		
			return false;
			
		}
	
	}
	
	/**
	* @brief Asymmetrically encrypt a file using multiple public keys
	* @param string $plainContent content to be encrypted
	* @returns string $plainContent decrypted string
	* @note symmetricDecryptFileContent() can be used to decrypt files created using this method
	*
	* This function decrypts a file
	*/
	public static function multiKeyDecrypt( $encryptedContent, $shareKey, $privateKey ) {
	
		if ( !$encryptedContent ) {
		
			return false;
			
		}
		
		if ( openssl_open( $encryptedContent, $plainContent, $shareKey, $privateKey ) ) {
		
			return $plainContent;
			
		} else {
		
			\OC_Log::write( 'Encryption library', 'Decryption (asymmetric) of sealed content failed', \OC_Log::ERROR );
			
			return false;
			
		}
	
	}
	
        /**
         * @brief Asymetrically encrypt a string using a public key
         * @returns encrypted file
         */
	public static function keyEncrypt( $plainContent, $publicKey ) {

		openssl_public_encrypt( $plainContent, $encryptedContent, $publicKey );
		
		return $encryptedContent;
	
	}
	
        /**
         * @brief Asymetrically decrypt a file using a private key
         * @returns decrypted file
         */
	public static function keyDecrypt( $encryptedContent, $privatekey ) {
	
		$result = @openssl_private_decrypt( $encryptedContent, $plainContent, $privatekey );
		
		if ( $result ) {
			return $plainContent;
		}

		return $result;
	
	}
		
	/**
	 * @brief Generates a pseudo random initialisation vector
	 * @return String $iv generated IV
	 */
	public static function generateIv() {
		
		if ( $random = openssl_random_pseudo_bytes( 12, $strong ) ) {
		
			if ( !$strong ) {
			
				// If OpenSSL indicates randomness is insecure, log error
				\OC_Log::write( 'Encryption library', 'Insecure symmetric key was generated using openssl_random_pseudo_bytes()', \OC_Log::WARN );
			
			}
			
			// We encode the iv purely for string manipulation 
			// purposes - it gets decoded before use
			$iv = base64_encode( $random );
			
			return $iv;
			
		} else {
		
			throw new Exception( 'Generating IV failed' );
			
		}
		
	}
	
	/**
	 * @brief Generate a pseudo random 1024kb ASCII key
	 * @returns $key Generated key
	 */
	public static function generateKey() {
		
		// Generate key
		if ( $key = base64_encode( openssl_random_pseudo_bytes( 183, $strong ) ) ) {
		
			if ( !$strong ) {
			
				// If OpenSSL indicates randomness is insecure, log error
				throw new Exception ( 'Encryption library, Insecure symmetric key was generated using openssl_random_pseudo_bytes()' );
			
			}
		
			return $key;
			
		} else {
		
			return false;
			
		}
		
	}

	/**
	 * @brief Get the blowfish encryption handeler for a key
	 * @param $key string (optional)
	 * @return Crypt_Blowfish blowfish object
	 *
	 * if the key is left out, the default handeler will be used
	 */
	public static function getBlowfish( $key = '' ) {
	
		if ( $key ) {
		
			return new \Crypt_Blowfish( $key );
		
		} else {
		
			return false;
			
		}
		
	}
	
	public static function legacyCreateKey( $passphrase ) {
	
		// Generate a random integer
		$key = mt_rand( 10000, 99999 ) . mt_rand( 10000, 99999 ) . mt_rand( 10000, 99999 ) . mt_rand( 10000, 99999 );

		// Encrypt the key with the passphrase
		$legacyEncKey = self::legacyEncrypt( $key, $passphrase );

		return $legacyEncKey;
	
	}

	/**
	 * @brief encrypts content using legacy blowfish system
	 * @param $content the cleartext message you want to encrypt
	 * @param $key the encryption key (optional)
	 * @returns encrypted content
	 *
	 * This function encrypts an content
	 */
	public static function legacyEncrypt( $content, $passphrase = '' ) {
	
		$bf = self::getBlowfish( $passphrase );
		
		return $bf->encrypt( $content );
		
	}
	
	/**
	* @brief decrypts content using legacy blowfish system
	* @param $content the cleartext message you want to decrypt
	* @param $key the encryption key (optional)
	* @returns cleartext content
	*
	* This function decrypts an content
	*/
	public static function legacyDecrypt( $content, $passphrase = '' ) {
		
		$bf = self::getBlowfish( $passphrase );
		
		$decrypted = $bf->decrypt( $content );
		
		return rtrim($decrypted, "\0");;
		
	}

	private static function legacyBlockDecrypt($data, $key='',$maxLength=0) {
		$result = '';
		while (strlen($data)) {
			$result.=self::legacyDecrypt(substr($data, 0, 8192), $key);
			$data = substr($data, 8192);
		}
		if ($maxLength > 0) {
			return substr($result, 0, $maxLength);
		} else {
			return rtrim($result, "\0");
		}
	}
	
	public static function legacyKeyRecryptKeyfile( $legacyEncryptedContent, $legacyPassphrase, $publicKeys, $newPassphrase, $path ) {
	
		$decrypted = self::legacyBlockDecrypt( $legacyEncryptedContent, $legacyPassphrase );

		// Encrypt plain data, generate keyfile & encrypted file
		$cryptedData = self::symmetricEncryptFileContentKeyfile( $decrypted );

		// Encrypt plain keyfile to multiple sharefiles
		$multiEncrypted = Crypt::multiKeyEncrypt( $cryptedData['key'], $publicKeys );

		return array( 'data' => $cryptedData['encrypted'], 'filekey' => $multiEncrypted['data'], 'sharekeys' => $multiEncrypted['keys'] );
	
	}

}