Consumer Messaging Platform — WhatsApp-Class System  ·  View 13 of 23

Multi-Device Linking and Synchronisation

Linking a companion device, seeding its history, and keeping four devices consistent without making the phone a relay.

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Primary Device
Primary Device
Companion Device
Companion Device
Edge Gateway
Edge Gateway
Device Service
Device Service
Key Distribution
Key Distribution
Chat Service
Chat Service
Peer Device
Peer Device
1. generate its own identity key pair
1. generate its own identity key pair
2. request linking nonce
2. request linking nonce
3. issue challenge, 60 s TTL
3. issue challenge, 60 s TTL
4. QR payload
4. QR payload
5. scan QR, verify nonce and fingerprint
5. scan QR, verify nonce and fingerprint
6. authorise device, signed by account identity
6. authorise device, signed by account identity
7. register companion identity and prekeys
7. register companion identity and prekeys
8. encrypted history bundle
8. encrypted history bundle
9. backlog from its own device inbox
9. backlog from its own device inbox
10. new message, one ciphertext per device
10. new message, one ciphertext per device
11. deliver device copy
11. deliver device copy
12. deliver device copy
12. deliver device copy
13. read receipt
13. read receipt
14. sync read state across devices
14. sync read state across devices
15. revoke device, rotate sender keys
15. revoke device, rotate sender keys
Multi-Device Linking and Synchronisation
Multi-Device Linking and Synchronisation
Each device is an independent Signal session; the primary device is not a relay.
Each device is an independent Signal session; the primary device is not a relay.
v 1.0 · owner Platform Architecture · date 2026-08
v 1.0 · owner Platform Architecture · date 2026-08Text is not SVG - cannot display

Device independence

  • Each device holds its own identity key and its own Signal sessions
  • A sender encrypts once per recipient device, not once per account
  • The primary device can be offline without stopping companion delivery

History and state

  • History is seeded once from the primary as an encrypted bundle at link time
  • After linking, each device receives from its own server-side inbox
  • Read state, mutes, archives and deletions are synchronised as ordinary encrypted events

Revocation

  • Unlinking a device revokes its sessions and rotates every sender key it held
  • Linked devices expire after a period of inactivity and must be re-linked
  • The linking QR carries a nonce with a 60-second lifetime to resist relay attacks
Solution Architecture v1.0 · Platform Architecture · 2026-0813-multi-device-sync