---
title: Temporal Causal Binding (TCB) — SCITT Companion Profile for Policy-Replay
category: std
work-in-progress: true
expires: 2027-02-10
---

# Temporal Causal Binding (TCB) — A SCITT Companion Profile for Offline Policy-Replay

**Work in Progress — Velaru / Nisaba LLC**  
**Intended status:** Informational (companion to draft-noa-scitt-ai-agent-receipt)  
**Date:** August 10, 2026

## Abstract

This document specifies **Temporal Causal Binding (TCB)**, a companion profile to the IETF SCITT AI-agent action receipt work. Where [draft-noa-scitt-ai-agent-receipt] deliberately excludes deterministic offline **policy-replay** (re-deriving a verdict from recorded inputs without access to the agent), TCB defines the **Counterfactual Receipt (CCR)**: a signed, hash-chained attestation that a specific counterfactual path was evaluated under a **frozen Handler Receipt** (pre-incident policy commitment) and was **not selected** as the executed path.

TCB does not claim model correctness. It claims **causal binding**: the counterfactual digest, source receipt, and handler commitment are cryptographically linked and independently verifiable.

## 1. Motivation

[draft-noa-scitt-ai-agent-receipt] Section 9 states policy-replay is **out of scope** for the base AI-agent receipt profile. [draft-kamimura-scitt-refusal-events] Section 5.3 states logged refusal **does not prove** that no unlogged generation occurred.

TCB addresses the **policy-replay companion** slot left open by draft-noa, and the **rejected-alternative audit** need in EPL, hiring, and carrier underwriting — without claiming lone-generator completeness.

## 2. Terminology

- **Handler Receipt (HR):** Pre-incident policy lock; hash of classifier rules frozen before dispute window.
- **Source Receipt (SR):** Signed record of the actual outcome (GEN, DENY, ERROR, SILENCE).
- **Counterfactual Receipt (CCR):** Signed record binding SR + HR + counterfactual_digest + intervention metadata.
- **causal_binding_hash:** SHA-256 over canonical JSON of `{source_entry_id, handler_receipt_id, counterfactual_digest, tcb_version}`.

## 3. Relationship to SCITT

TCB receipts SHOULD be registrable in a SCITT Transparency Service per [RFC 9943] for non-equivocation. COSE_Sign1 (RFC 9052) over JCS-canonical payload is RECOMMENDED for cross-profile interoperability.

This profile is **complementary** to:
- [draft-noa-scitt-ai-agent-receipt] — action receipts (verdict recorded, replay out of scope)
- [draft-kamimura-scitt-refusal-events] — ATTEMPT/DENY correlation (refusal logged, completeness not claimed)

## 4. CCR Claim Set (normative sketch)

| Field | Required | Description |
|-------|----------|-------------|
| `ccr_id` | YES | Unique CCR identifier (hash of signed payload) |
| `source_entry_id` | YES | SR entry_id being replayed against |
| `handler_receipt_id` | YES | HR lock entry in Policy Registry |
| `counterfactual_digest` | YES | Hash of counterfactual evaluation inputs |
| `counterfactual_reply` | REC | Human-readable or structured counterfactual output |
| `causal_binding_hash` | YES | Binding per Section 2 |
| `tcb_version` | YES | Profile version (e.g. `1.0`) |
| `deontic` | REC | DRP-1 binding if SR carries O/F/P modalities |

## 5. Verification (independent of Velaru)

A verifier MUST:

1. Validate Ed25519 signature(s) on CCR and referenced SR/HR.
2. Recompute `causal_binding_hash` from declared fields.
3. Confirm HR timestamp precedes SR timestamp (pre-incident commitment).
4. Optionally invoke SR/HR verification per sibling profiles.

Implementations MUST NOT represent CCR as proof that no other counterfactual existed — only that **this** bound counterfactual was attested.

## 6. API Mapping (Velaru reference implementation)

```
POST /tcb/counterfactual-replay
  { "entry_id": "<SR hash>", "session_id": "..." }

GET  /tcb/ccr/{ccr_id}/verify.json
  → portable CCR for client-side /verify (CHECK 9)
```

Public verifier: `GET /verify` — twelve checks including DRP-1 (CHECK 8) and TCB (CHECK 9).

## 7. Security Considerations

- HR must be frozen before incident; retroactive HR invalidates causal claim.
- Counterfactual generation MUST use committed policy hash, not live policy.
- Quorum observers (employer BYOK, vendor cosign, external anchor) strengthen non-repudiation but do not resolve lone-generator completeness — see POSS-2 impossibility theorem.

## 8. IANA / Registry

TBD — request `velaru-tcb` or `nisaba-tcb` profile URI under SCITT claim registry when draft-noa companion slot opens.

## 9. References

- [draft-noa-scitt-ai-agent-receipt] — Policy-replay explicitly deferred to companion profile
- [draft-kamimura-scitt-refusal-events] — Refusal logged ≠ completeness
- [RFC 9943] — SCITT Architecture
- [RFC 9052] — COSE Sign1
- Velaru TCB spec: `/standards/tcb`
- Velaru POSS-2: `/standards/poss-2`
- Velaru DRP-1: `/standards/drp-1`

## Authors

Nisaba LLC · Velaru Relay · Patent #64/124,027  
Contact: demond@velaru.xyz

## Appendix A — Found Scripture Export

Carrier-facing dossiers SHOULD include: HR → living chain summary → optional CCR → `/verify` links → standards read order. See `/export/found-scripture-template.txt`.