LCMsec - Security for the Lightweight Communications and Marshalling Protocol (LCM)

LCM is a set of libraries and tools for message passing and data marshalling, targeted at real-time systems where high-bandwidth and low latency are critical. It provides a publish/subscribe message passing model and automatic marshalling/unmarshalling code generation with bindings for applications in a variety of programming languages.

This fork, LCMsec, is a security extensions for LCM. It:

• provides confidentiality, integrity and authenticity to LCM messages
• provides an attribute-based acces control mechanism with multicastgroup, port and channel granularity
• aims to minimize both overhead and computational complexity - as such, LCMsec is designed to be usable in most environments in which LCM is used.
• maintains the decentralized, peer-to-peer nature of LCM: no broker, no central instance to facilitate keyexchange
• is scalable to many peers and capable of dealing with dynamic communication topologies (hosts leaving and joining a channel) efficiently

This is achieved with the use of:

• a hybrid cryptosystem: a symmetric key is shared between all publishers and subscribers to a channel on a specific multicastgroup
• No distinction between subscribers and publishers, each subscriber is also allowed to publish messages. This makes it possible to use a single shared symmetric key, and avoids issues typically associated with multicast authentication
• A built-in, decentralized discovery protocol
• AES/GCM or ChaChaPoly1305 as the underlying authenticated encryption algorithm.
• The Dutta-Barua group key agreement (modified to use EC-Cryptography) to agree on the symmetric key while minimizing the number of network interactions when a publisher or subscriber joins a topic (i.e., is turned on)

For more informations please take a look at the paper on LCMsec.

Limitations of LCMsec

• Additional dependencies are Botan and libstdc++.
• Not yet adressed are the issues of rekeying and certificate revocation, which will be a next step.
• Only C, C++ and Python bindings are available, Python bindings have not been tested recently
• lcm-logger and lcm-spy are not availe
• Only the udpm provider is available

LCMsec Quickstart guide

• To use security features, you will need generate a root certificate and x509v3 certificate/key-pairs for each node that should communicate. Permissions are written into SAN of those certificates. For a way to generate certificates automatically, refer to examples/cpp_security/gen_certificates.py
• The format of the SAN is a URI of the form: urn:lcmsec:gkexchg:<mcastgroup>:<port>:<channelname>:<user_id>
  • example: urn:lcmsec:gkexchg:239.255.76.67:7667:channel1:4 (for a channel)
  • for the permission to be part of a multicast group, use the special string "gkexchg_g" and omit the channelname, for instance: urn:lcmsec:gkexchg_g:239.255.76.67:7667:4
• use lcm_create_with_security(...) (or use the c++ API in lcm-sec.hpp) to create an LCM instance that has security enabled. This call will block until the group key agreement has finished on all channels for which there are permissions in the certificate
• At this point, just use the created lcm instance as you normally would.

An Example for an application using LCMsec can be found in examples/cpp_security folder.

Roadmap

The LCM project is active again. The current near-term plan is to:

• Clear deprecation warnings from build for all language targets
• Flush backlog of PRs
• Cut a new release

Quick Links

• LCM downloads
• Website and documentation

Features

• Low-latency inter-process communication
• Efficient broadcast mechanism using UDP Multicast
• Type-safe message marshalling
• User-friendly logging and playback
• No centralized "database" or "hub" -- peers communicate directly
• No daemons
• Few dependencies

Supported platforms and languages

• Platforms:
  • GNU/Linux
    • Ubuntu (20.04 and 22.04)
    • Fedora (37)
  • macOS (11 and 12)
  • Windows (2019 and 2022) via MSYS2
• Languages
  • C
  • C++
  • Java
  • Lua
  • MATLAB
  • Python

Unmaintained languages

The following languages are currently unmaintained. PRs for these languages are still welcome and if you are interested in maintaining them please let us know.

• Go
• C#/.NET