SCITT Transparency

Supply Chain Integrity, Transparency and Trust — IETF draft-ietf-scitt-scrapi. EPI implements Mode B (SCITT Producer) with Merkle inclusion proofs, independent service keys, and offline receipt verification.

Specification

EPI implements the IETF SCITT architecture as a COSE_Sign1 producer. The full specification is documented in the project repository.

Read SCITT Predicate Spec View Source (epi_core/scitt.py) Local Service Source

IETF draft-ietf-scitt-scrapi conformance

Implemented

COSE_Sign1 (CBOR tag 18) with Ed25519 (alg -8)
CWT claims: iss (1), sub (2) in protected header
Content-type: application/scitt-statement+cose
Content-type: application/scitt-receipt+cose
SHA-256 payload binding to manifest hash
Merkle tree inclusion proofs with audit paths
Independent service keypair (separation of duties)
Append-only JSONL transparency ledger
Offline receipt verification
Trust level upgrade on valid SCITT receipt

Roadmap

draft-ietf-scitt-architecture full compliance
IANA-registered CWT labels (currently using private -260)
Multiple concurrent transparency services
Cross-service receipt aggregation
Automatic re-registration on manifest update

Architecture

Two independent keypairs enforce separation of duties. The artifact signing key never touches the transparency service.

┌─────────────────────────────────────────────────────────┐
│                    EPI Artifact                         │
│  ┌──────────────┐  ┌──────────────────────────────┐   │
│  │ manifest.json │  │ artifacts/scitt/             │   │
│  │ Ed25519 signed│  │  statement.cbor (COSE_Sign1) │   │
│  │               │  │  receipt.cbor  (COSE_Sign1) │   │
│  └──────────────┘  └──────────────────────────────┘   │
└─────────────────────────────────────────────────────────┘
         │                                                    
         ▼                                                    
┌──────────────────────┐       ┌──────────────────────┐       
│ Artifact Signing Key │       │ SCITT Service Key    │       
│ (~/.epi/keys/)       │       │ (~/.epi/local-scitt/)│       
│ Signs manifest       │       │ Signs receipt        │       
└──────────────────────┘       └──────────────────────┘       

Registration flow

# Local (CI, air-gap, development)
$ epi scitt register case.epi --local
[OK] Local SCITT Registration Complete
  Service:  local
  Entry:    8c2576b5f92a348a74e5088fef295a02

# Production (remote transparency service)
$ epi scitt register case.epi --service https://scitt.epilabs.org
[OK] Registration Complete
  Entry ID:  ...
  Trust Level upgraded to MEDIUM

# Verification includes SCITT check
$ epi verify case.epi
  Integrity:    Verified
  Signature:    Valid
  Transparency: VERIFIED (Merkle inclusion)
  Trust Level:  MEDIUM (SCITT anchored)

Merkle inclusion proofs

Every receipt embeds a Merkle audit path that proves the statement was registered at a specific position in the transparency log. The proof is verified during epi verify without contacting the service.

Leaf hash    sha256(0x00 || tree_index || entry_hash)
Internal     sha256(0x01 || left || right)
Root         recomputed from leaf + audit path
Verification  audit_path → root == signed_tree_head

Local service

The built-in local SCITT service works offline with no extra dependencies. State is stored at ~/.epi/local-scitt/.

~/.epi/local-scitt/
  service.key     Ed25519 private key (independent from artifact key)
  service.pub     Ed25519 public key
  log.jsonl       Append-only transparency ledger

The service keypair is generated automatically on first use. It is separate from the artifact signing key, satisfying SCITT's separation-of-duties model.

Try it yourself.

View SCITT Tests (21 cases) pip install epi-recorder