sdls

Overview ¶

Example: Encrypting and authenticating a link

Every other example here sends plaintext. Anyone with a dish can read a downlink, and worse, anyone with a transmitter can forge an uplink. SDLS is the layer that fixes both.

Downlink (clause E1 baseline):
  AES-256-GCM. The telemetry is encrypted and authenticated together.

Uplink (clause E2 baseline):
  AES-CMAC. The telecommand travels in the clear but cannot be forged,
  which is what commanding actually needs.

Three attacks that fail:
  1. A flipped bit in the ciphertext
  2. A replayed frame
  3. A valid frame injected on the wrong virtual channel

SDLS protects the data field of a frame. The carrier packages need no changes: this package builds the protected data field and the frame constructor takes it as ordinary octets.