pyMLS - Message Layer Security (MLS) Implementation

pyMLS is a Python implementation of the Message Layer Security (MLS) protocol, designed for secure and efficient group messaging. This project aims to adhere to the RFC 9420 standard.

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Current Functionality

• HandshakeMessages: Add, Update, Remove, Commit message handling with RFC-compliant structures.
• KeyPackage: Construction, signing, serialization, and validation.
• KeySchedule: Epoch secret derivation with support for PSK injection.
• MessageFraming: Encoding/decoding for Public and Private messages with AES-GCM encryption.
• Proposals: AddProposal, UpdateProposal, RemoveProposal with validation.
• RatchetTree: Efficient group state management through tree-based cryptography.
• SecretTree: Secure key and nonce derivation for handshake and application messages.
• TranscriptHashManager: Ensures transcript consistency across group state transitions.
• WelcomeMessage: Secure group creation and member onboarding.

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TODO

KeyPackage

1. Add detailed validation for fields (e.g., HPKE key checks, signature expiration).
2. Incorporate support for pre-shared keys (PSKs) for external initialization.

KeySchedule

1. Complete integration with the SecretTree for encryption key derivation.
2. Validate derived secrets against expected outputs for compliance with RFC Section 9.1.

MessageFraming

1. Add robust nonce management to prevent AES-GCM nonce reuse.
2. Implement padding mechanisms to obscure message length (Section 15.1).

Proposals

1. Validate proposal inputs (e.g., KeyPackages in AddProposal) against group capabilities.
2. Implement proposal list validation checks (RFC Section 12.2).

RatchetTree

1. Add functions for validating parent and tree hash calculations (Sections 7.8 and 7.9).
2. Implement synchronization mechanisms for distributed tree views (Section 7.5).

SecretTree

1. Enforce deletion schedules for leaf nodes (Section 9.2).
2. Enhance support for epoch transitions and synchronization.

TranscriptHashManager

1. Add base hash integrity checks for stronger validation.

WelcomeMessage

1. Add support for group context extensions (Section 11.1).
2. Improve validation for encrypted fields (e.g., nonce and ciphertext checks) to ensure consistency.

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Contributions

Contributions are welcome! Please create an issue or submit a pull request.

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