Software Distribution Platform

Conception for a software distribution platform for a distributed network of WRT54GS nodes.

The identified requirements are as follows:

• dynamic network of homogenous nodes (no privileged nodes)
  • nodes may be turned off or disconnected for any period of time from the remaining network
  • network may be split for any period of time
  • nodes may be added at any time
• no centralized datastore
  • avoids single point of failure
  • less administration
• robust and reliable updates
  • allow updates even with broken routing
  • cross-compatible beginning with version 1.0.0 (e.g. allow update of a node running 1.0.0 with version 1.5.99)
• broken, untrustworthy and malicious nodes must not be able to install unwanted software (optional: not interfere with the updating process)
• trustworthy developer team and CA
• all nodes should have the same software version running most of the time (ideally every second)
• implementation must fit into limited hardware (e.g. 32MB RAM + 8MB flash (optional: WRT54G))

The ideas to meet those requirements:

• discovery mechanism for newer versions on neighbours
  • push and/or pull
  • broadcast(push) and/or query
• if newer version is available, fetch it (e.g. over existing TFTP)
• infection based distribution mechanism
  • obtain code from neighbour
  • new version can be injected on any connected node
  • distributed step by step to each connected node
• notification and update protocol never changes after 1.0.0 is released
• sign each software update package with a CA key
• CA public key is preinstalled with the base system on every node to check authenticity of new files
• synchronize system clocks over NTP (using UDP port 123) with neighbours
  • guaranteeing similar system times
• include software starting time (and end time for experimental software) in each update package
• coordinated switch over to new version if system_time > start_time
• coordinated switch-back to non-experimental version if system_time > end_time