trust-core

A small, language-neutral trust plane: Biscuit public-key capability tokens + a per-request Ed25519 proof-of-possession, plus a length-prefixed wire so the issuer private key can be isolated in its own signer process.

The engine holds zero app vocabulary — the policy (Datalog) and the request-facts are data passed in — so different services share it unchanged and each supplies its own rights/scopes and policy strings. No novel crypto: it composes the audited Rust biscuit-auth core (via biscuit-python) and libsodium (PyNaCl).

The model

Three tiers, assigned by the containment rule — process isolation buys containment only for a component that holds a secret:

Only tier 1 holds a secret, so only it needs to leave. Tiers 2–3 are a library the app links.

Layers

• trust_core.keys — IssuerKey (mint + job-sign) and WorkerKey (a holder's PoP key). One 32-byte Ed25519 seed each; the issuer seed doubles as the Biscuit root and the job signer.
• trust_core.proof — RequestParts / WorkerProof / make_proof + the header/query parsers. The canonical string binds method, path, and sha256(body), so a captured signature is valid only for the one request it was made for.
• trust_core.engine — mint_biscuit (bind a key + arbitrary Datalog facts + expiry), authenticate (issuer-sig → identity → revocation → freshness → proof-of-possession), check_policy (one authorizer decision), sign_job / verify_job.
• trust_core.wire — the signer sidecar's length-prefixed JSON framing (fail-closed: oversize cap, closed-connection, non-object body).
• trust_core.errors — the single fail-closed TrustError.

Why the facts are parameterized

mint_biscuit binds fact values as bound Datalog parameters (never string interpolation), so a value can never inject Datalog — a safer primitive than a raw mint(datalog_string) helper.

Example

from trust_core import IssuerKey, WorkerKey, RequestParts, make_proof, \
    mint_biscuit, authenticate, check_policy

issuer, worker = IssuerKey.generate(), WorkerKey.generate()

# Issuer mints a capability binding the worker's public key.
token = mint_biscuit(
    issuer, public_hex=worker.public_hex, holder_id="gpu-1",
    facts={"right": ["lease"], "lane": ["transcribe"]},
    revocation_id="rev-1", expires_at=now + 3600,
)

# Worker proves possession on each request; verifier authenticates then authorizes.
proof = make_proof(worker, token, RequestParts("POST", "/lease", b"{}"),
                   timestamp=str(now), nonce="n1")
parsed, identity = authenticate(
    issuer.public_hex, proof, RequestParts("POST", "/lease", b"{}"),
    now=now, revoked_ids=frozenset(), max_skew_seconds=300,
)
check_policy(parsed, request_facts={"req_right": "lease", "req_lane": "transcribe"},
             allow="allow if req_right($r), right($r), req_lane($l), lane($l)", now=now)

Status

Local package (no published release yet). Consumed by easy-podcast; designed to be reused by other services (e.g. antibody-analysis) — each writes a thin adapter that maps routes → rights, supplies the policy strings, and owns its replay + data-predicates.