- Originally posted on Freifunk Blog by Harry Pantazis
BMX7 is an IPv6 native dynamic routing protocol for mesh networks which offers advanced features and a small network overhead - thanks to the distance-vector strategy and a set of optimizations - and a great way to extend its functionality via plugins. BMX7 is also referenced as SEMTOR (Securely-Entrusted Multi-Topology Routing for Community Networks).
(For Axel Neumann’s presentation of BMX7 on BattleMesh, as well as the SEMTOR Whitepapers refer to the Further Info section).
BMX7 offers plugins which are used for the distribution of small files, settings up tunnels or offer stats of the network structure. The connection between a client node and the gateway establishes via IPIP (IPv4/6 over IPv6), which is unencrypted and possibly readable by attackers. As mesh networks usually operate on unencrypted wireless connections, the attack vector is considerably big.
Our proposed solution is to combine the current cryptographic stack of BMX7 with the one used by WireGuard. The process via which this will be achieved will be iterative; meaning that first binary calls from bmx7 to userland WG will be introduced, afterwards the efforts will be centered in the creation of a new plugin implementing WireGuard routing by using part of the existing cryptographic primitives and at last the effort to combine the tunnel plugin with the wg one. In all of these one rule must be set: do not implement cryptography yourself; mistakes will be made.
The detail that distinguishes our approach’s difficulty from hard to medium is cryptographic keys. It’s simpler to announce new public keys for WireGuard and have a separate plugin than replacing the existing BMX7 keys to allow signing of descriptive updates and encryption of traffic.
To portray some of the perks of the implementation, the following sections are quoted from the WireGuard Whitepaper.
WireGuard is a secure network tunnel, operating at layer 3, implementd as a kernel virtual network interface for Linux. (..) The virtual tunnel interface is based on a proposed fundamental principle of secure tunnels: an association between a peer public key and a tunnel source IP address. It uses a single round trip key exchange, based on NoiseIK, and handles all session creation transparently to the user using a novel timer state machine mechanism. Short pre-shared static keys–Curve25519 points–are used for mutual authentication. (..) Peers are identified strictly by their public key, a 32-byte Curve25519 point. (..) The protocol provides strong perfect forward secrecy in addition to a high degree of identity hiding. (..) An improved take-on IP-binding cookies is used for mitigating denial of service attacks, to add encryption and authentication. (..) Two WireGuard peers exchange their public keys through some unspecified mechanism, and afterwards they are able to communicate. (..) It intentionally lacks cipher and protocol agility (H: opinionated protocol).From the official WireGuard Technical Paper, Sections: Intro, 1 and 2
For further, technical details refer to Section 5 of the WG paper.
- Implementation of wrapper functions to native WireGuard API for the establishment of the WireGuard tunnel.
- Creation of a new WG tunnel plugin based on a simplified version of the existing tun plugin, by use the aforementioned wrapper functions.
- The ultimate goal is the combination of the current tunnel plugin of BMX7 that incorporates IPv4/6 over IPv6 tunnels with the cryptographic stack of Wireguard, offering each administrator’s node to choose whether to encrypt or not through a command line parameter (tun + wg == crypt-tun).
- Stretch Goal: Applying the optional 32-byte pre-shared key that is mixed into the public key cryptography supported by WG for an additional layer of symmetric-key crypto for the purposes of resistance against post-quantum attacks that are potential for Curve25519.
- Phase 1:
- Understand BMX7 functionality, descriptions (descriptive updates) and plugin system.
- Understand the WireGuard cryptographic stack and tunneling.
- Establish the following Testing setups for testing and later on continuous integration:
- LXC running OpenWrt bridged mesh.
- Qemu OpenWrt bridged mesh networks.
- Implement the initial wrapper functions to WG.
- Phase 2:
- Release a Debian package for BMX7 (as described in the issue referenced in Further Info section)
- Polish and test the wrapper function for the establishment of the WireGuard tunnel
- Create the WG tunnel plugin, based on the wrapper functions.
- Phase 3:
- Test extensively on the CI environments and troubleshoot.
- Try to combine/reuse the cryptographic primitives of BMX7 and WG.
- Refresh the user and developer documentation of BMX7.
I’m an open-source advocate, supporter of FOSS communities and student currently dwelling in Athens. My purposes span around the empowering of pro-consensus community networks (either technical or human), distributed and censorship resistant (focusing in the lower Balkan area communities, where adversaries for freedom in the mainstream Internet have begun to thrive).
A milestone for myself would be to meet the people that have created the software that our communities use and be able to interact and hack together.
For this reason my best efforts will go into making it to meetings such as Battlemesh in Paris, CC Camp and Bornhack happening this summer.
- Debian Packaging for BMX7 GH Issue
- WireGuard Network Namespaces and Routing
- BattleMesh 2016 BMX7 Presentation
- WireGuard Key Exchange
- WireGuard mailing list on roaming between IPv4 and IPv6
- WireGuard mailing list on HW-related Timestamps
- SEMTOR Overview
- SEMTOR in detail