Overview

libsignal contains platform-agnostic APIs used by the official Signal clients and servers, exposed as a Java, Swift, or TypeScript library. The underlying implementations are written in Rust:

libsignal-protocol: Implements the Signal protocol, including the Double Ratchet algorithm. A replacement for libsignal-protocol-java and libsignal-metadata-java.
signal-crypto: Cryptographic primitives such as AES-GCM. We use RustCrypto's where we can but sometimes have differing needs.
device-transfer: Support logic for Signal's device-to-device transfer feature.
attest: Functionality for remote attestation of SGX enclaves and server-side HSMs.
zkgroup: Functionality for zero-knowledge groups and related features available in Signal.
zkcredential: An abstraction for the sort of zero-knowledge credentials used by zkgroup, based on the paper "The Signal Private Group System" by Chase, Perrin, and Zaverucha.
poksho: Utilities for implementing zero-knowledge proofs (such as those used by zkgroup); stands for "proof-of-knowledge, stateful-hash-object".
pin: Functionality for consistently using PINs as passwords in Signal's Secure Value Recovery system.
usernames: Functionality for username generation, hashing, and proofs.
media: Utilities for manipulating media.

This repository is used by the Signal client apps (Android, iOS, and Desktop) as well as server-side. Use outside of Signal is unsupported. In particular, the products of this repository are the Java, Swift, and TypeScript libraries that wrap the underlying Rust implementations. All APIs and implementations are subject to change without notice, as are the JNI, C, and Node add-on "bridge" layers. However, backwards-incompatible changes to the Java, Swift, TypeScript, and non-bridge Rust APIs will be reflected in the version number on a best-effort basis, including increases to the minimum supported tools versions.

Building

To build anything in this repository you must have Rust installed, as well as Clang, libclang, CMake, Make, protoc, and git. On a Debian-like system, you can get these extra dependencies through apt:

$ apt-get install clang libclang-dev cmake make protobuf-compiler git

The build currently uses a specific version of the Rust nightly compiler, which will be downloaded automatically by cargo. To build and test the basic protocol libraries:

$ cargo build
...
$ cargo test
...

Java/Android

To build for Android you must install several additional packages including a JDK, the Android NDK/SDK, and add the Android targets to the Rust compiler, using

rustup target add armv7-linux-androideabi aarch64-linux-android i686-linux-android x86_64-linux-android

To build the Java/Android jar and aar, and run the tests:

$ cd java
$ ./gradlew test
$ ./gradlew build # if you need AAR outputs

Alternately, a build system using Docker is available:

$ cd java
$ make java_test

When exposing new APIs to Java, you will need to run rust/bridge/jni/bin/gen_java_decl.py in addition to rebuilding.

Maven Central

Signal publishes Java packages on Maven Central for its own use, under the names org.signal:libsignal-server, org.signal:libsignal-client, and org.signal:libsignal-android. libsignal-client and libsignal-server contain native libraries for Debian-flavored x86_64 Linux as well as Windows (x86_64) and macOS (x86_64 and arm64). libsignal-android contains native libraries for armeabi-v7a, arm64-v8a, x86, and x86_64 Android.

When building for Android you need both libsignal-android and libsignal-client, but the Windows and macOS libraries in libsignal-client won't automatically be excluded from your final app. You can explicitly exclude them using packagingOptions:

android {
  // ...
  packagingOptions {
    resources {
      exclude "libsignal_jni.dylib"
      exclude "signal_jni.dll"
    }
  }
  // ...
}

Swift

To learn about the Swift build process see swift/README.md

Node

You'll need Node installed to build. If you have nvm, you can run nvm use to select an appropriate version automatically.

We use yarn as our package manager. The Rust library will automatically be built when you run yarn install.

$ cd node
$ nvm use
$ yarn install
$ yarn tsc
$ yarn test

When testing changes locally, you can use yarn build to do an incremental rebuild of the Rust library.

When exposing new APIs to Node, you will need to run rust/bridge/node/bin/gen_ts_decl.py in addition to rebuilding.

NPM

Signal publishes the NPM package @signalapp/libsignal-client for its own use, including native libraries for Windows, macOS, and Debian-flavored Linux. Both x64 and arm64 builds are included for all three platforms, but the arm64 builds for Windows and Linux are considered experimental, since there are no official builds of Signal for those architectures.

Contributions

Signal does accept external contributions to this project. However unless the change is simple and easily understood, for example fixing a bug or portability issue, adding a new test, or improving performance, first open an issue to discuss your intended change as not all changes can be accepted.

Contributions that will not be used directly by one of Signal's official client apps may still be considered, but only if they do not pose an undue maintenance burden or conflict with the goals of the project.

Signing a CLA (Contributor License Agreement) is required for all contributions.

Legal things

Cryptography Notice

This distribution includes cryptographic software. The country in which you currently reside may have restrictions on the import, possession, use, and/or re-export to another country, of encryption software. BEFORE using any encryption software, please check your country's laws, regulations and policies concerning the import, possession, or use, and re-export of encryption software, to see if this is permitted. See http://www.wassenaar.org/ for more information.

The U.S. Government Department of Commerce, Bureau of Industry and Security (BIS), has classified this software as Export Commodity Control Number (ECCN) 5D002.C.1, which includes information security software using or performing cryptographic functions with asymmetric algorithms. The form and manner of this distribution makes it eligible for export under the License Exception ENC Technology Software Unrestricted (TSU) exception (see the BIS Export Administration Regulations, Section 740.13) for both object code and source code.