Messaging Protocols

Candidate Protocols for Messaging and Encapsulation

Low-level Signalling

The purpose of the low-level protocol is to provide primatives such as:

• Message Encapsulation appropriate for different mediums
  • RS-232
  • RS-485
  • Ethernet
  • SMS/Cellular
• Polling, and unique identification protocol
  • Uniquely identify all devices on the network
  • Handle collisions

Protocol Candidates

• MODBUS - Industrial Control protocol, works over serial or Ethernet
  • MODBUS over Serial

End to end session protocol

Considerations

• Ideally, session is encrypted and authenticated at all levels
  • User should know they are interacting with a legitimate terminal
  • Token should know that it is talking to a legitimate reader
  • Reader should not leak any secrets during transaction
  • Secrets should not be subject to interception between reader and server/panel
    • Physically secure wiring/network
    • Secure/encrypted protocols
• Messages should be not be able to vulnerable to session replay
  • Time stamping/serializing of messages
• Messages should not be subject to intentional or accidental alteration in transit
  • Message CRC and cryptographic signing/MAC protocol

Protocols and Session Flow

• Example Message Flow