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 '../3rdparty/Crypt_Blowfish/Blowfish.php';
require_once realpath( dirname( __FILE__ ) . '/../3rdparty/Crypt_Blowfish/Blowfish.php' );

/**
 * 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 string 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 string 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
	 * @param $content
	 * @return boolean
	 * @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 $data
	 * @param string $relPath The path of the file, relative to user/data;
	 *        e.g. filename or /Docs/filename, NOT admin/files/filename
	 * @return boolean
	 */
	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
	 * @param $plainContent
	 * @param $iv
	 * @param string $passphrase
	 * @return string encrypted file content
	 */
	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
	 * @param $encryptedContent
	 * @param $iv
	 * @param $passphrase
	 * @throws \Exception
	 * @return string decrypted file content
	 */
	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' );

		}

	}

	/**
	 * @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 string $plainContent content to be encrypted in keyfile
	 * @param string $passphrase
	 * @return bool|string
	 * @return string 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 $keyfileContent
	 * @param string $passphrase
	 * @throws \Exception
	 * @return bool|string
	 * @internal param string $source
	 * @internal param string $target
	 * @internal param string $key the decryption key
	 * @returns string 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;

		} else {
			return false;
		}

	}

	/**
	 * @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 ) ) {

			throw new \Exception( 'Cannot mutliKeyEncrypt empty plain content' );

		}

		// Set empty vars to be set by openssl by reference
		$sealed = '';
		$shareKeys = array();
		$mappedShareKeys = 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 $encryptedContent
	 * @param $shareKey
	 * @param $privateKey
	 * @return bool
	 * @internal 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
	 * @return string 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
	 * @return string 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;

		}

	}

	/**
	 * @param $passphrase
	 * @return mixed
	 */
	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 string $content the cleartext message you want to encrypt
	 * @param string $passphrase
	 * @return
	 * @internal param \OCA\Encryption\the $key encryption key (optional)
	 * @returns string 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 string $content the cleartext message you want to decrypt
	 * @param string $passphrase
	 * @return string
	 * @internal param \OCA\Encryption\the $key encryption key (optional)
	 * @return string 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" );;

	}

	/**
	 * @param $data
	 * @param string $key
	 * @param int $maxLength
	 * @return string
	 */
	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" );
		}
	}

	/**
	 * @param $legacyEncryptedContent
	 * @param $legacyPassphrase
	 * @param $publicKeys
	 * @param $newPassphrase
	 * @param $path
	 * @return array
	 */
	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'] );

	}

}