jackandClaude Fable 5 ee148a018b Prekey bundles: forward-secret async first contact for courier mail ...

Courier envelopes were sealed with one-way Noise X to the recipient's
long-lived static key, so a later compromise of that key exposed every
envelope captured in transit. This adds one-time prekey bundles:

- PrekeyBundle (MessageType 0x24): 8 one-time Curve25519 public prekeys
  bound to the owner's Noise static key by an Ed25519 signature over
  "bitchat-prekey-bundle-v1" canonical bytes; gossiped mesh-wide on its
  own 60s sync round (SyncTypeFlags bit 9, 200-peer cap, 24h freshness)
  and verified against the announce-bound signing key before caching.
- Sealed envelope v2: Noise X where the responder static is the one-time
  prekey, prologue "bitchat-prekey-v1" || prekeyID. Sender identity rides
  encrypted inside and is authenticated exactly like v1 (blocked-sender
  check included). CourierEnvelope gains an optional prekeyID TLV that
  v1 decoders skip as unknown.
- Local prekeys live in the Keychain; consumed privates survive a 48h
  grace window for spray-and-wait redeliveries, then are deleted (the
  forward-secrecy clock starts at deletion). The batch tops back up and
  re-gossips when unconsumed count drops below 3, and everything is
  wiped in panic mode.
- Routing: courier sealing picks a cached verified bundle when one
  exists (one prekey per message, reused across deposit retries), with
  the advertised .prekeys capability as a veto for on-mesh peers, and
  falls back to static sealing otherwise.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

2026-07-06 20:14:05 +02:00

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BitFoundation

Prekey bundles: forward-secret async first contact for courier mail

2026-07-06 20:14:05 +02:00