#The decision boundary
TOFU is not one problem. It is a continuity hint after a first observation. TalkCo also needs to bind a key to a user or context, enroll and revoke devices, survive offline changes, recover from loss, and detect a malicious directory or relay. Any proposal that claims to replace TOFU must say which of those jobs it actually performs.
#Evidence comparison
| Mechanism | Establishes or detects | Does not establish | Useful TalkCo role |
|---|---|---|---|
| QR/SAS/safety number | Possession of a specific key during a ceremony | Human identity, future rotation, or recovery | High-assurance introduction and re-verification |
| Device root and cross-signing | A verified device set can authorize device succession | The first human binding or a globally consistent directory | Default device continuity |
| Key transparency | Auditable directory history and consistency evidence | Real-world identity, instant freshness, or private lookups by itself | Optional monitors, checkpoints, and split-view detection |
| Witness/gossip network | Independent observation of conflicting checkpoints | Identity and immediate availability | Scoped equivocation detection |
| WebAuthn/passkeys | User verification and possession at the TalkCo origin | Correspondent identity or authorization to read a remote context | Protect local roots and recovery ceremonies |
| Signed local membership history | Offline-verifiable membership, roles, invitations, and revocations | Global agreement without an explicit witness policy | Canonical context authority |
| DID/VC, KERI, PGP web of trust | Portable claims, key-event histories, or social evidence | A universal trust root and simple UX | Interoperability or optional high-risk profiles |
| UCAN/capabilities | Attenuated action authority | Key discovery and decryption | Bind operations to scopes after identity is known |
| libp2p/iroh peer identity | Endpoint or transport continuity | TalkCo account or human identity | Transport binding only |
The primary references are the IETF Key Transparency architecture, IETF protocol draft, Matrix cross-signing API, Signal Sesame, and WebAuthn Level 3.
#Working trust ladder
- An authenticated invitation or local QR exchange creates the context and records the initial device key.
- A user root or verified device set signs device additions, rotations, and revocations.
- A signed, append-only context membership history carries roles and causal evidence across replicas.
- A scoped key directory supplies signed records, checkpoints, freshness, and proofs of consistency.
- Monitors and independent witnesses gossip checkpoints; the client warns on equivocation instead of silently choosing a view.
- Sensitive contexts require user-visible re-verification; passkeys protect local root use and recovery.
- Recovery uses an explicit bundle or quorum policy. A restored backup cannot silently resurrect a revoked device.
This ladder is a complement to TOFU, not a universal identity oracle. Ordinary contexts can stop at invitation plus device continuity; high-risk contexts add a ceremony and independent observation.
#Falsifiers
- A malicious relay substitutes the first key or shows two directory heads to two devices.
- A stale checkpoint is accepted after a rotation, or a restored backup authorizes a revoked device.
- A device is enrolled offline by a compromised member and the replicas disagree about membership.
- Witness gossip leaks the social graph or cannot detect a deliberately partitioned view within the declared freshness window.
- A passkey ceremony is mistaken for proof of a correspondent's identity.
#Remaining questions
- Which freshness window and witness quorum are usable on mobile and during prolonged partitions?
- Is the first deployment a context-local directory backed by signed events, or an adapter to a transparency log such as Tessera?
- Which recovery profiles can be explained without turning social recovery into a reputation score?
#Open Threads
- Define the wire format for device succession, checkpoint gossip, and recovery receipts.
- Measure directory query metadata under direct, relay, and witness-assisted discovery.