Crate mls_rs

An implementation of the IETF Messaging Layer Security end-to-end encryption (E2EE) protocol.

What is MLS?

MLS is a new IETF end-to-end encryption standard that is designed to provide transport agnostic, asynchronous, and highly performant communication between a group of clients.

MLS Protocol Features

• Multi-party E2EE group evolution via a propose-then-commit mechanism.
• Asynchronous by design with pre-computed key packages, allowing members to be added to a group while offline.
• Customizable credential system with built in support for X.509 certificates.
• Extension system allowing for application specific data to be negotiated via the protocol.
• Strong forward secrecy and post compromise security.
• Crypto agility via support for multiple cipher suites.
• Pre-shared key support.
• Subgroup branching.
• Group reinitialization for breaking changes such as protocol upgrades.

Features

• Easy to use client interface that can manage multiple MLS identities and groups.
• 100% RFC 9420 conformance with support for all default credential, proposal, and extension types.
• Support for WASM builds.
• Configurable storage for key packages, secrets and group state via traits along with provided “in memory” and SQLite implementations.
• Support for custom user proposal and extension types.
• Ability to create user defined credentials with custom validation routines that can bridge to existing credential schemes.
• OpenSSL and Rust Crypto based cipher suite implementations.
• Crypto agility with support for user defined cipher suite.
• Extensive test suite including security and interop focused tests against pre-computed test vectors.

Crypto Providers

For cipher suite descriptions see the RFC documentation here

Name	Cipher Suites	X509 Support
OpenSSL	1-7	Stable
AWS-LC	1,2,3,5,7	Stable
Rust Crypto	1,2,3	⚠️ Experimental

Security Notice

This library has been validated for conformance to the RFC 9420 specification but has not yet received a full security audit by a 3rd party.

Re-exports

• pub use crate::client::Client;
• pub use crate::group::mls_rules::MlsRules;
• pub use crate::group::Group;
• pub use mls_rs_codec;

Modules

• client
• client_builder
  Definitions to build a Client.
• crypto
  Dependencies of CryptoProvider and CipherSuiteProvider
• error
  Error types.
• extension
  Extension utilities and built-in extension types.
• external_clientexternal_client
  Tools to observe groups without being a member, useful for server implementations.
• group
  E2EE group created by a Client.
• identity
  Identity providers to use with ClientBuilder.
• mls_rules
  Dependencies of MlsRules.
• psk
  Pre-shared key support.
• storage_provider
  Storage providers to use with ClientBuilder.
• time
  WASM compatible timestamp.

Structs

• CipherSuite
  Wrapper type representing a ciphersuite identifier along with default values defined by the MLS RFC. Custom ciphersuites can be defined using a custom CryptoProvider.
• Extension
  An MLS protocol extension.
• ExtensionList
  A collection of MLS Extensions.
• KeyPackage
• KeyPackageRef
• MlsMessage
  A MLS protocol message for sending data over the wire.
• ProtocolVersion
  Wrapper type representing a protocol version identifier.

Enums

• WireFormat
  Content description of an MlsMessage

Traits

• CipherSuiteProvider
  Provides all cryptographic operations required by MLS for a given cipher suite.
• CryptoProvider
  Provides implementations for several ciphersuites via CipherSuiteProvider.
• GroupStateStorage
  Storage that can persist and reload a group state.
• IdentityProvider
  Identity system that can be used to validate a SigningIdentity
• KeyPackageStorage
  Storage trait that maintains key package secrets.
• PreSharedKeyStorage
  Storage trait to maintain a set of pre-shared key values.