Concepts

Concepts

Ten terms cover the whole system. Section numbers refer to spec/SPEC.md.

Leaf (§2–3). One event. Eight types: PassiveMemory (0x00), ActiveIntent (0x01), ActiveResult (0x02), Redaction (0x03), KeyRevocation (0x04), HandoffAttestation (0x05), AuthorizationEvent (0x06), ExternalAnchor (0x07). A leaf carries its index, type, timestamp, the session key that wrote it, and payload_hash; the payload itself is never stored in the tree.

payload_hash (§8). SHA256(bucket_pad(payload) || salt || index). The salt is random per leaf and lives outside the tree. Forgetting the salt is how an entry is erased: the hash stays, the content is unrecoverable, every proof still verifies.

Merkle tree (§4). RFC 6962 construction over leaf hashes. The root commits to every leaf and their order. Inclusion proofs show one leaf is in a root; consistency proofs show a newer root extends an older one without rewriting anything.

Identity key and session key (§5). The identity key is the agent's name: generated once, kept forever, signs checkpoints. Each process run gets a fresh session key; a signed key binding ties it to the identity. Restart = new session, same identity, provably continuous.

Checkpoint / Signed Tree Head (§6). (tree_size, root, timestamp) signed by the identity key. This is what witnesses cosign and what a verifier rebuilds the tree against.

Journal. The persistence format: one JSON line per leaf, header holds the identity key, <journal>.salts holds the salts. Append-only, torn tails healed on resume, locked against double writers.

Witness (§7, §9.3). A separate process, ideally run by a separate organisation, that cosigns checkpoints over c2sp.org/tlog-witness. It remembers the last head per log, demands a consistency proof, and refuses forks. Its cosignatures become receipts in a dossier.

Dossier (§9). The portable, offline-verifiable file: identity, leaves, checkpoint, key bindings, revocations, receipts, and a display-only copy of the directory. JSON Schema in spec/dossier.schema.json.

Directory. The list of witnesses the verifier trusts, obtained out-of-band (the public registry/ is one source). Receipts are scored only against it, never against the dossier's own list.

Verdict (§9.2). Exactly one of WITNESSED (0; 11 when the cosigners are not a strict majority of the directory), CONSISTENT-UNWITNESSED (10), UNANCHORED (20), DIVERGED (30: valid, but contradicts a head or an equivocation proof the verifier brought), INVALID (40: a check failed). See Verification and verdicts.

The flow, end to end

agent process                          witnesses (≥2 operators)        anyone, later
─────────────                          ────────────────────────        ─────────────
intent leaf ─┐
result leaf ─┼─► journal + salts
   …         ┘
checkpoint (signed) ──► POST /add-checkpoint + consistency proof ──► cosignature
                                                                    │
dossier.json  ◄────────────────────── receipts ─────────────────────┘
      │
      └──────────────────────────────────────────────────────────────► witness-log verify
                                                                        --identity <key> --directory <trusted>
                                                                        → WITNESSED / exit 0