Encrypted Core Data SQLite Store

Core Data encrypted SQLite store using SQLCipher. Use this security control to encrypt data stored in Core Data with SQLite by leveraging the great work at SQLCipher. With this control one no longer has to translate each query result in/out of data models.

Vulnerabilities Addressed

1. SQLite database is not encrypted, contents are in plain text

• CWE-311: Missing Encryption of Sensitive Data

2. SQLite database file protected with 4 digit system passcode

• CWE-326: Inadequate Encryption Strength
• SRG-APP-000129-MAPP-000029 Severity-CAT II: The mobile application must implement automated mechanisms to enforce access control restrictions which are not provided by the operating system

Caveat

This library is a work in progress and will probably not work in every case or with highly complex models. There is also what I believe to be a bug in the implementation of NSIncrementalStoreNode and its use through the Core Data framework. I have an open DTS ticket with Apple and am working on this. The issue can be seen by changing the value of and searching for USE_CUSTOM_NODE_CACHE in CMDEncryptedSQLiteStore.m.

Project Setup

Add this repository as a submodule to your project.

git submodule add https://github.com/calebmdavenport/encrypted-core-data.git vendor/encrypted-core-data
git submodule update --init --recursive

Configure OpenSSL Source for Xcode

• Download the OpenSSL source code from http://www.openssl.org/source/. This has been tested against 1.0.1c.
• Untar the source and place in a known location.
• Add a new source tree in Xcode > Preferences > Locations > Source Trees called OPENSSL_SRC pointing to the OpenSSL source folder.

Build the OpenSSL and SQLCipher Libraries

Add the Xcode projects found in vendor/encrypted-core-data/vendor/sqlcipher and vendor/encrypted-core-data/vendor/openssl as subprojects to your Xcode project.

Add the source files found in vendor/encrypted-core-data/Incremental Store to your Xcode project. Pick the appropriate targets and uncheck "copy files".

Add the crypto and sqlcipher libraries as dependencies and linked libraries to all appropriate targets.

Add the flag -DSQLITE_HAS_CODEC to all configurations of all appropriate targets

Using CMDEncryptedSQLiteStore

CMDEncryptedSQLiteStore is a subclass of NSIncrementalStore that enables communication between CoreData and an SQLCipher encrypted database. It registers itself at runtime so you do not have to call registerStoreClass:forStoreType: on NSPersistentStoreCoordinator.

Using it is easy. Just set the appropriate type and a database key when you load your persistent store:

NSDictionary *options = @{ CMDEncryptedSQLiteStorePassphraseKey : @"DB_KEY_HERE" };
NSPersistentStore *store = [coordinator
                            addPersistentStoreWithType:CMDEncryptedSQLiteStoreType
                            configuration:nil
                            URL:databaseURL
                            options:options
                            error:&error];

Debugging

CMDEncryptedSQLiteStore responds to the standard CoreData SQL debug flag. Add -com.apple.CoreData.SQLDebug 1 as an argument to the "run" phase of your scheme to see all generated statements logged to the console.

Improvements

This project has several areas that could be improved (in order of preference):

• Migrations The store currently supports a very small subset of lightweight migrations with inferred migration maps (changing columns, adding and removing whole objects). I would like to implement more migration map parsing.
• Relationships I currently only support one-to-many relationships. Work needs to be done in order to support many-to-many and one-to-one.
• Inheritance Table inheritance is not really supported or tested at this time.
• More Test Cases I built several test cases that helped find bugs and improve support for things like relationships. These cases currently do not touch every feature supported by the store.
• Persistent Store Options You have the option to pass a number of options when adding a new store a coordinator. I added my own option which provides the database key but would like to support system options as well. Things like data protection class, SQLite pragmas, and migration options would be nice to have.

Resources

• OpenSSL
• SQLCipher
• SQLCipher in Xcode

Use, Feedback, and Improvement

We strongly encourage developers to clone and use iMAS. Once you’ve had a chance to use iMAS, tell us what you think by providing us with feedback on your intended use. This information will enable us to address relevancy and need - which will help to keep our research funded in the long run. Lastly, feel free to enhance and improve the actual controls by submitting pull requests early and often!

Recognition

MITRE wishes to thank Caleb Davenport for creating, implementing, and pushing for the public release of this security control.

License

Copyright 2012 The MITRE Corporation, All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this work except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.