buzz/docs/nips/NIP-FI.md

NIP-FI

Federated identity authorization — core

draft optional relay

Protocol dependencies: NIP-01 and either NIP-42 or NIP-98. Optional profiles are defined by NIP-FI-EDGE, NIP-FI-LIFECYCLE, NIP-FI-DELEG, and NIP-FI-CONF.

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", and "MAY" in this document are to be interpreted as described in BCP 14 (RFC 2119 and RFC 8174) when, and only when, they appear in all capitals.

Abstract

NIP-FI authorizes a Nostr key only when four independent facts agree: a valid issuer-qualified identity assertion, fresh proof of that Nostr key, current identity-to-key binding state, and current local policy for the exact operation. The identity provider never signs Nostr events, and an assertion never replaces Nostr proof.

Bindings outlive individual assertions. Assertions and authorization leases do not outlive their evidence. This core defines the portable client-attached assertion transport, direct enrollment, atomic final admission, bounded sessions, privacy-preserving denial responses, and the smallest useful binding lifecycle. Companion profiles add trusted edges, extended lifecycle operations, and delegation without changing the core admission rule.

This NIP does not define an identity provider, database schema, operator API, public identity projection, application membership policy, or user interface.

Terms and identifier classes

• domain (D): an authorization boundary selected only by authenticated server routing and configuration.
• identity (i): the exact tuple (iss, sub) returned by assertion validation. Email, display name, employee number, and a bare sub are not identities.
• target context (R_t): the server-resolved method, authority, path and query, body semantics, transport, operation, and resource.
• actor (k): the 32-byte public key returned by Nostr-proof validation.
• request context (R): R_t sealed with k.
• binding: a durable, versioned association (D, i, k) with immutable provenance attested-key, tofu, or provisioned.
• retired pair: a durable denial fact for an exact (D, i, k).
• revoked key: a durable denial fact for (D, k).
• prepared authorization: immutable, read-only evidence and witnesses for a possible admission.
• committed authorization: authority returned only after final revalidation and atomic commit.
• lease: a cached committed decision for one actor and bounded operation set. A lease is not a binding.

Identity and authorization-state comparisons preserve every tuple component. Equal sub values under different iss values are distinct identities; equal (i, k) pairs under different domains are distinct bindings, retired pairs, and authorization state. [FI-TRACE-CROSS-DOMAIN-COLLISION]

Every identifier is either interoperability-critical or deployment-local. Header names, public response bytes, token type values, and trace identifiers are interoperability-critical and fixed here. assertion_policy_id, transport_contract_id, domain IDs, snapshot versions, binding versions, policy versions, and correlation IDs are deployment-local; their values are opaque outside a deployment, while their stability and invalidation behavior are normative.

Core security invariants

These labels are the normative home of the NIP-FI invariants. Companion profiles may add witnesses and bounds but cannot weaken them.

1. FI-INV-01 — partial bijection. Active bindings are one-to-one within a domain: one identity has at most one active key and one key has at most one active identity. [FI-TRACE-BINDING-CONFLICT]
2. FI-INV-02 — durable binding. Assertion expiry removes neither a binding nor its provenance. Fresh eligible evidence may authorize the same binding later. [FI-TRACE-ASSERTION-REFRESH]
3. FI-INV-03 — tombstone monotonicity. Ordinary authorization never removes a retired-pair or revoked-key fact and never recreates a retired pair. [FI-TRACE-TOMBSTONE-REPLAY]
4. FI-INV-04 — server-owned context. Every admitted operation uses one server-resolved domain, target, resource, operation, and proven actor. Unauthenticated input cannot replace them. [FI-TRACE-DOMAIN-SPOOF]
5. FI-INV-05 — independent evidence. Direct authorization requires a current assertion and fresh Nostr proof. If the assertion names a key, it equals the proven actor. [FI-TRACE-ASSERTION-KEY-MISMATCH]
6. FI-INV-06 — stable assertion policy. Assertion-policy identity changes when accepted assertion semantics change, but not when only authenticated key or status snapshot contents rotate. [FI-TRACE-VERIFIER-PARITY]
7. FI-INV-07 — current-snapshot verification. Evidence cannot survive removal of the key or policy snapshot that authenticated it; a changed snapshot requires revalidation. [FI-TRACE-JWKS-REMOVE]
8. FI-INV-08 — read-only preparation. Preparation creates no binding, tombstone, replay claim, receipt, lease, publication, last-seen value, audit authority, or application mutation. [FI-TRACE-FINAL-DENIAL-NO-MUTATION]
9. FI-INV-09 — atomic final admission. Enrollment, replay claims, receipts, and required authorization evidence commit only after complete final revalidation, all or none. [FI-TRACE-PREPARED-STALE]
10. FI-INV-10 — explicit lifecycle authority. Retirement, revocation, rotation, and profile-defined lifecycle changes occur only through their separately authorized transition. [FI-TRACE-LIFECYCLE-AUTHORITY]
11. FI-INV-11 — evidence-bounded leases. A lease ends no later than every evidence, snapshot, proof, binding, local-policy, and implementation bound on which it depends. [FI-TRACE-LEASE-BOUND]
12. FI-INV-12 — current-owner delegation. When NIP-FI-DELEG is claimed, delegation requires the exact current eligible owner binding, fresh delegate proof, capability intersection, and a positive finite deadline. [FI-DELEG-OWNER-CURRENT]
13. FI-INV-13 — privacy-safe denial. Public rejection is many-to-one and reveals no identity, key, claim, binding, tombstone, enrollment mode, key identifier, or private policy fact. [FI-TRACE-DENIAL-ORACLE]
14. FI-INV-14 — fail closed. Unreadable, ambiguous, stale beyond policy, or inconsistent evidence or authoritative state cannot produce authority. [FI-TRACE-DEPENDENCY-FAIL-CLOSED]
15. FI-INV-15 — uniform authority. Every protected ingress in a domain uses the same current domain policy and final-admission authority. An uncovered or competing path is unavailable. [FI-TRACE-AUTHORITY-UNIFORM]
16. FI-INV-16 — canonical verifier. Assertion transports feed one closed, provider-neutral normalized-result contract and cannot fork final admission. [FI-TRACE-VERIFIER-PARITY]

Client-attached transport

Server configuration selects client-attached before protected traffic is accepted. Request fields cannot select, negotiate, or downgrade transport. Failure never falls back to another transport. [FI-TRACE-TRANSPORT-CLOSED]

The client sends exactly one field on the request or WebSocket upgrade:

Nostr-Federated-Identity: Bearer <compact-JWS>

Authorization remains reserved for NIP-98. Assertion and provenance fields from any other profile are absent. Missing, repeated, comma-combined, empty, malformed, non-Bearer, or mixed-profile fields deny. Assertions never appear in URLs, query parameters, Nostr events, tags, filters, application history, or public identity projections. [FI-TRACE-TRANSPORT-CLOSED]

The core transport contract has deployment-local identity transport_contract_id. It deterministically identifies the exact field, parsing, request-attachment, no-fallback, and context-preservation semantics. Changing any of those semantics changes the ID; changing request data does not. [FI-TRACE-CONTRACT-IDENTITIES]

Assertion validation

A configured assertion policy accepts exactly one bounded compact JWS and returns this closed result:

VerifiedAssertion = (
  identity = (iss, sub),
  asserted_key?,
  claims_or_capabilities,
  authority_deadlines,          // non-empty
  assertion_policy_id,
  transport_contract_id,
  revalidation_dependencies
)

The verifier rejects ambiguous protected-header or claim members, unknown critical headers, alg=none, symmetric algorithms, algorithm/key mismatch, incompatible JWK usage, ambiguous key selection, and signatures not valid under exactly one accepted asymmetric key. It bounds the assertion, headers, claims, subject, key identifiers, and authenticated key set before lookup or logging. [FI-TRACE-ASSERTION-VALIDATION]

The exact iss selects an authenticated policy and key source; iss and at least one aud value exactly match configured values. sub is a non-empty bounded string. Each policy configures a non-negative finite skew, a positive finite maximum_assertion_age, and, for current-status, a positive finite maximum_status_age; a missing value denies. exp and iat are finite NumericDate values satisfying now < exp, iat <= now + skew, and now < iat + maximum_assertion_age. Optional nbf satisfies nbf <= now + skew. Arithmetic is overflow-safe and equality at an expiry is expired. [FI-TRACE-ASSERTION-VALIDATION]

The Nostr-key claim is named nostr_pubkey. When present it MUST be a lowercase hexadecimal encoding of exactly one 32-byte Nostr public key; other encodings and aliases deny. In attested-key enrollment policy and wherever current matching issuer attestation is required, this exact claim MUST be present and equal the proven actor; authorization claims or capabilities use a closed bounded input set and deterministic canonical encoding. Unchecked claims never enter the result. [FI-TRACE-VERIFIER-PARITY]

Token class

Policy selects exactly one token class before parsing claims:

• at+jwt access token: a Buzz-resource access token whose protected typ is exactly at+jwt and whose aud contains the configured Buzz resource audience. This class selects tokens carrying the RFC 9068 at+jwt type but validates them under this document's claim contract; it does not implement the full RFC 9068 validation profile, and the long-form media type application/at+jwt is not accepted;
• dedicated Buzz assertion: a separately minted assertion whose protected typ is exactly nip-fi+jwt;
• named compatibility access token: absent or generic protected typ=JWT only under an explicit issuer policy whose required and forbidden claims, audience, issuer, key source, and validation rules are mutually exclusive with every accepted ID-token and other JWT class.

OIDC ID Tokens always deny, even when iss, aud, and sub match. A generic or absent type has no stock fallback. Failure under one class never triggers validation under another. An at+jwt access token MUST contain one non-empty bounded client_id. Issuer policy MUST distinguish a resource-owner token from a token whose subject represents the OAuth client, including a client-credentials token, using authenticated claim semantics and mutually exclusive validation rules. A token that admits both interpretations denies. If client-subject tokens are accepted, the issuer MUST guarantee that their (iss, sub) coordinates cannot collide with resource-owner coordinates; otherwise that token class is ineligible. Token class and every class-specific validation rule are inputs to assertion_policy_id. [FI-TRACE-TOKEN-CLASS]

Policy identity and snapshots

Core has exactly two semantic contract identities:

assertion_policy_id  = H(canonical assertion-policy contract)
transport_contract_id = H(canonical transport contract)

Each uses one implementation-defined but deterministic, versioned encoding and collision-resistant hash within a deployment. assertion_policy_id covers the canonical issuer, audience, token class, allowed algorithms, authenticated key/status-source contracts, identity/key/claim mapping, time and size rules, normalization, freshness class, and compiled verifier behavior. The verifier fingerprint is an input, not a third identity. transport_contract_id covers the client-attached field, parsing, attachment, context preservation, and no-fallback semantics; a companion transport may define its own canonical contract under that same identity slot. A semantic change changes exactly its owning ID. [FI-TRACE-CONTRACT-IDENTITIES]

Mutable contents and deployment state are not contract identities. They remain in revalidation_dependencies: authenticated assertion-snapshot version, verification-key identity, key-snapshot hard deadline, optional status source/version/deadline, binding/lifecycle/local-policy/resource versions, proof and replay witnesses, and a confidential handle to the exact compact JWS. Adding, removing, or replacing an accepted key changes the snapshot version, not assertion_policy_id. Changed dependencies require revalidation under current state; a retained key may continue, while an absent key denies. Unknown-key refresh is bounded and coalesced and has no attacker-triggered stale-key fallback. [FI-TRACE-JWKS-ADD] [FI-TRACE-JWKS-REMOVE]

The base contract compares the current authenticated snapshot and makes no anti-rollback promise. A deployment claiming rollback prevention records a separately authenticated monotonic floor and tests it. [deployment artifact: assertion-policy review]

Freshness class

Each policy declares exactly one server-owned freshness class, included in assertion_policy_id:

• offline-jwt validates the JWT and authenticated key snapshot only. upstream_authority_deadline is the minimum of exp, iat + maximum_assertion_age, and the key-snapshot hard deadline. Token age bounds assertions minted before revocation; it cannot bound an issuer that continues minting accepted assertions afterward. Enabling this class therefore requires deployment evidence that revocation stops new accepted issuance, and discovery reports the unconditional residual bound as unknown (null). It MUST NOT advertise a finite unconditional residual bound. [deployment artifact: issuer revocation review]
• current-status additionally requires an authenticated witness (iss, sub, token_or_session_id?, active=true, observed_at, valid_until, status_version, authenticated_source_id). Issuer, subject, and optional session identifier exactly match the assertion. Ambiguous, unauthenticated, inactive, or expired status denies. valid_until is finite and no later than observed_at + maximum_status_age. The upstream deadline is the minimum of the offline assertion deadlines and valid_until. Source outage cannot mint or extend a witness; an already verified witness remains usable only until its existing valid_until. [FI-TRACE-CURRENT-STATUS-STALE]

A current-status deployment advertises a tested positive maximum_residual_upstream_revocation_seconds. Prepared evidence and leases close within that value after upstream revocation, including a revocation racing final admission. Poll/cache age, event-delivery and processing delay, and enforcement delay all fit within the advertised value. A push implementation may close authority sooner but cannot claim a value below its tested worst case. [FI-TRACE-CURRENT-STATUS-REVOKED]

An external capability projection whose removal is required to close authority within a declared revocation bound MUST enter authoritative local-policy state, not claims_or_capabilities from the assertion. That state is reread during preparation, final admission, and protected lease use. A deployment that carries such a projection only in assertions cannot claim a revocation bound for its changes. [FI-TRACE-CAPABILITY-REVOCATION]

Before enabling an issuer, the operator records authoritative evidence that sub is stable for the account lifetime, never reassigned, and not intentionally derived from mutable profile data. An issuer that cannot provide this property is ineligible. [deployment artifact: issuer subject-stability review]

Nostr proof and body semantics

The actor is always returned by fresh Nostr-proof validation, never by an assertion or unsigned field. NIP-42 binds its AUTH event to the current challenge, relay URL, connection, and freshness window. NIP-98 binds its event to the exact server-resolved URL, method, and freshness window. All evidence agrees with the same D and R_t. [FI-TRACE-DOMAIN-SPOOF]

Each protected HTTP operation declares in server policy whether its body is authorization-relevant; clients cannot select the declaration.

For a relevant body, the NIP-98 event contains exactly one payload tag equal to lowercase hexadecimal SHA-256 of the body bytes: the complete content after transfer decoding and before any content decoding. Absence, duplication, mismatch, validation of only a prefix, or substitution of the body bytes after validation denies. For an irrelevant body, no authorization decision, target, capability, or effect selector derives from a body field not bound by NIP-98. A payload tag present on an operation whose body is declared authorization-irrelevant is validated identically against the body bytes; duplication or mismatch denies. [FI-TRACE-BODY-BINDING]

Every operation has finite body and spool bounds. A known oversized body is rejected before hashing; a stream is rejected at octet limit + 1; admission waits for EOF. Before EOF there is no application effect, replay mutation, receipt, or partial digest authority. Quota failure cleans up staged bytes and denies. [FI-TRACE-BODY-BOUNDS]

Direct preparation

The following is normative pseudocode; every read is from authoritative state.

PrepareDirect(request, assertion, proof):
  (D, R_t, operation, resource) := ResolveTargetContext(request) or DENY
  e := ValidateClientAttached(assertion, D, R_t) or DENY
  k := ValidateNostrProof(proof, D, R_t) or DENY
  R := SealActor(R_t, k)
  i := e.identity

  if e.asserted_key exists and e.asserted_key != k: DENY(key_mismatch)
  atomically read B_D(i), B_D(k), T_D(i,k), Y_D(k), enrollment policy,
                      local policy, resource, and all dependency versions
  if k in Y_D: DENY(key_revoked)
  if (i,k) in T_D: DENY(pair_retired)

  if B_D(i) = B_D(k) = binding(i,k):
      proposal := existing(binding.version, binding.provenance)
  else if B_D(i) exists or B_D(k) exists:
      DENY(binding_conflict)
  else if enrollment policy = attested-key:
      if e.asserted_key != k: DENY(attestation_required)
      proposal := enroll(i, k, attested-key)
  else if enrollment policy = tofu:
      proposal := enroll(i, k, e.asserted_key = k ? attested-key : tofu)
  else:
      DENY(binding_required)

  EvaluateLocalPolicy(D, R, operation, resource, k,
                      e.claims_or_capabilities) or DENY
  return PreparedAuthorization(evidence, proposal, witnesses, deadlines)

TOFU is optional private deployment posture and is not self-advertised. It accepts that a stolen assertion for a never-enrolled identity can bind an attacker's proven key; deployments enabling it retain a passing FI-TRACE-TOFU-THEFT artifact. Binding provenance is immutable. A policy change affects only future creation. [deployment artifact: TOFU risk review]

Preparation, including first-use enrollment, is read-only and produces no authoritative mutation. [FI-TRACE-FINAL-DENIAL-NO-MUTATION]

Final admission

A prepared value is consumed at most once. Final admission first requires an exact domain, context, operation, resource, actor, and transport match; both contract IDs unchanged; and every bound live. A changed dependency is reread and re-evaluated from authoritative evidence. [FI-TRACE-PREPARED-STALE]

Two verified assertion results are equivalent when:

1. identity-class fields are byte-equal: iss, sub, asserted-key presence and value, canonical claims/capabilities, assertion_policy_id, and transport_contract_id;
2. each bounds-class deadline — every authority_deadlines member, the key-snapshot hard deadline, and any status deadline — is live now and is no later than its prepared value; and
3. provenance-class fields — snapshot version, verification-key identity, status source and version, binding, lifecycle, local-policy, and resource versions, proof and replay witnesses, the confidential JWS handle, cache metadata, ordering, and retrieval time — are ignored after successful current revalidation.

Every revalidation_dependencies member is bounds-class if it is a deadline and provenance-class otherwise. Any new or unclassified assertion-content field belongs to the identity class. A fresher assertion cannot silently extend a prepared decision. [FI-TRACE-PREPARED-STALE]

Final admission atomically rereads binding, tombstone, revocation, enrollment, policy, resource, status, replay, receipt, and invalidation witnesses; recomputes the complete decision; claims applicable proof replay identities; creates an eligible proposed binding; and appends its request-bound receipt and required authorization evidence. All commit or none. A concurrent identical enrollment may recompute as the same existing binding; conflicting enrollment commits at most one winner. [FI-TRACE-CONCURRENT-ENROLLMENT]

A failed admission rolls back all authority mutation. The application operation runs only after committed authorization. If it cannot share the transaction, a request-bound idempotent receipt prevents the same proof from creating a second effect. [FI-TRACE-FINAL-DENIAL-NO-MUTATION]

Base lifecycle

Retirement, revocation, and rotation require separate privileged authority bound to the exact domain, transition, identity, old binding version when present, target key when present, and request. Each atomically rechecks current state, appends immutable lifecycle history, and invalidates dependent leases after commit. Every new target key supplies fresh target-bound Nostr proof and any policy-required current matching issuer attestation. [FI-TRACE-LIFECYCLE-AUTHORITY]

• RetirePair removes one exact active binding and durably retires its pair.
• RevokeKey records the key as revoked even if inactive; if active, it also removes the binding and retires that pair. Repeating the same authorized revocation is idempotent.
• Rotate replaces one exact active binding with one unused, unrevoked, non-retired target key, retires the old pair, and creates a fresh binding version. The replacement provenance is attested-key when current matching issuer attestation was validated and provisioned otherwise. Rotation does not globally revoke the old key. Rotation continues one grant onto a new key rather than establishing a new one: the replacement preserves every profile-defined administrative bound carried by the binding it replaces, as an opaque field core neither interprets nor clears. Only the authority that set such a bound can change it. [FI-TRACE-LIFECYCLE-AUTHORITY]

Failure or stale state causes no partial mutation. Ordinary authorization cannot perform or undo these transitions. Extended disablement, re-enablement, provisioning, and administrative expiry are defined only by NIP-FI-LIFECYCLE.

Request and session bounds

HTTP authority covers one exact request and is never reusable.

A WebSocket lease is scoped to one actor, domain, operation set, binding version, normalized result, policy/resource versions, and invalidation witnesses. Its deadline is the earliest assertion, upstream-authority, key-snapshot, proof/connection, local-policy, and implementation deadline. Arithmetic is overflow-safe and equality is expired. [FI-TRACE-LEASE-BOUND]

Before each protected use, the service checks actor, domain, operation, resource, deadline, binding version, contract IDs, snapshot/status versions, policy versions, and invalidation state. Changed dependencies require current revalidation to an equivalent result; unreadable or ineligible state denies. A lease for one key never authorizes another key on the same connection. [FI-TRACE-MULTI-KEY-SESSION]

Expiry ends the lease, not the binding. Renewal requires a new connection with a fresh assertion attached to its WebSocket upgrade, fresh Nostr proof, preparation, and final admission; there is no in-band renewal path. Confidential assertion revalidation material is destroyed on expiry, close, or invalidation.

Rejection and privacy

Public class is a function only of evidence the requester supplied, never of private per-principal server state; authorization_unavailable is the sole exception and reveals only that a required authoritative dependency is unreadable, never any per-principal fact. Replay status is a function of committed per-principal server state, not of the supplied evidence alone; replayed evidence is therefore classed authorization_denied, indistinguishable from any other private-state denial, so that resubmitting captured evidence reveals nothing about whether the original request committed. Under the private-posture rule, even key_mismatch joins the private-state anonymity set.

Private condition	Public class	Nostr prefix and exact text	HTTP response
assertion/proof absent	missing_evidence	auth-required: authentication required	401; WWW-Authenticate: Nostr; Content-Type: text/plain; charset=utf-8; authentication required\n
malformed, invalid, or expired evidence	evidence_rejected	restricted: evidence rejected	403; Content-Type: text/plain; charset=utf-8; evidence rejected\n
replayed evidence; key mismatch; attestation required; binding conflict; retired pair; revoked key; lifecycle gate; binding required/expired; local policy denial	authorization_denied	restricted: authorization denied	403; Content-Type: text/plain; charset=utf-8; authorization denied\n
required current dependency unreadable	authorization_unavailable	restricted: authorization unavailable	503; Content-Type: text/plain; charset=utf-8; authorization unavailable\n

Nostr text is the exact UTF-8 text after an applicable NIP-42/NIP-01 prefix. A denial decided on a WebSocket upgrade request, before any NIP-42 proof exists, is the HTTP response in the table, sent instead of 101; a denial decided after the connection is established is the Nostr text. For HTTP, the compared denial contract is closed over the status, complete body, and exact values of only the header fields named in the table; header order and other fields are outside that contract and their values cannot depend on the private condition. The body is the shown UTF-8 bytes with one LF and no other bytes. The Nostr challenge satisfies RFC 9110 Section 15.5.2. Responses contain no free text, reason code, request ID, issuer, subject, key, claim, binding state, enrollment posture, token material, or timing hint. All private conditions in authorization_denied produce byte-identical responses. [FI-TRACE-DENIAL-ORACLE]

NIP-FI defines no public identity projection. Public events, tags, filters, discovery, responses, logs, metrics, and traces contain no raw assertions or unredacted iss, sub, email, display name, or private claim. Access-controlled authoritative stores retain only what enforcement and investigation require. A separate presentation protocol cannot confer NIP-FI authority. [FI-TRACE-PRIVACY-NONPUBLIC]

Discovery

A relay SHOULD advertise core support in NIP-11 as:

{
  "limitation": { "federated_identity": true },
  "federated_identity": {
    "core": "client-attached",
    "assertion_freshness": {
      "class": "offline-jwt",
      "maximum_residual_upstream_revocation_seconds": null
    }
  }
}

NIP-FI-EDGE owns the optional edge_transports member and its exact type, placement, and value semantics. For current-status, the final value is a tested positive integer. Discovery never states enrollment mode or TOFU posture and never exposes issuer URLs, audiences, claim names, tenant IDs, or deployment-local identifiers. For a fixed set of claimed profiles, the complete public discovery output is byte-identical for every enrollment policy, including attested-key, private tofu, and any companion profile mode: no field, flag, value, omission, ordering, or object shape may distinguish the configured mode. Profile documents own only non-enrollment public claims. [FI-TRACE-DISCOVERY-PRIVATE]

Worked example (non-normative)

A protected HTTP POST under client-attached with NIP-98 proof and an authorization-relevant body. Credentials are elided; the NIP-FI-CONF exit fixture pins the complete request compared objects.

POST /media HTTP/1.1
Host: relay.example
Nostr-Federated-Identity: Bearer eyJhbGciOiJFUzI1NiIsInR5cCI6ImF0K2p3dCIs...
Authorization: Nostr eyJpZCI6IjE1ZTI3ZDc0Li4uIiwicHVia2V5IjoiOTljNzQ4Li4u...
Content-Type: application/octet-stream
Content-Length: 4

abcd

The bearer JWS validates under the configured assertion policy: exact iss and aud, token class at+jwt, live time claims, and nostr_pubkey equal to the NIP-98 event's pubkey. The NIP-98 event binds the server-resolved method and URL, and its single payload tag equals the SHA-256 of the four body bytes. Admission then follows Direct preparation and Final admission; success returns the application response, and every failure class returns exactly the bytes fixed in the Rejection table. On a WebSocket upgrade the same header attaches to the upgrade request and NIP-42 supplies the proof after connect.

Core behavioral oracles

A core claim covers every applicable oracle below at one implementation and policy revision. NIP-FI-CONF defines evidence and mutation-adequacy rules.

ID	Required outcome
FI-TRACE-TRANSPORT-CLOSED	Exact one-header input succeeds; missing, repeated, combined, malformed, mixed, URL, and fallback variants deny.
FI-TRACE-ASSERTION-VALIDATION	Valid boundary input passes; each signature, key-selection, issuer, audience, time, size, ambiguity, and missing-configuration negative denies.
FI-TRACE-TOKEN-CLASS	An at+jwt access token and a dedicated nip-fi+jwt assertion pass only their selected class. ID tokens, wrong/generic types outside a named compatibility policy, client-only audiences, absent or ambiguous client_id, resource-owner/client-subject ambiguity, and every attempted cross-class fallback deny.
FI-TRACE-CONTRACT-IDENTITIES	Mutate each assertion semantic, transport semantic, and mutable dependency independently: semantic mutations change only their owning contract ID; snapshot/binding/lifecycle/policy/resource/status mutations change neither ID but force current revalidation.
FI-TRACE-VERIFIER-PARITY	Equal authoritative input and policy produce the same canonical normalized result.
FI-TRACE-JWKS-ADD	Retained-key rotation revalidates successfully under the changed snapshot version.
FI-TRACE-JWKS-REMOVE	Evidence and leases under a removed key deny after snapshot change.
FI-TRACE-CURRENT-STATUS-REVOKED	Revocation, including one racing final admission, closes authority within the advertised tested bound.
FI-TRACE-CURRENT-STATUS-STALE	Inactive/ambiguous status denies; an issuer, subject, or session-identifier mismatch denies; expiry equality, outage, delayed events, and changed status versions cannot mint or extend a witness.
FI-TRACE-CAPABILITY-REVOCATION	Removal of a revocation-bounded external capability projection from authoritative local policy closes prepared evidence and lease use within the declared bound; assertion-only projection cannot satisfy this oracle.
FI-TRACE-BODY-BINDING	Exact complete relevant body passes; absent/duplicate/mutated/partial/substituted payload variants deny without effects; a payload tag on an irrelevant-body operation validates identically and denies on duplication or mismatch.
FI-TRACE-BODY-BOUNDS	Oversized, over-quota, and pre-EOF variants deny with bounded work, cleanup, and no effects.
FI-TRACE-DOMAIN-SPOOF	Client routing and forwarded authority cannot replace server-owned context.
FI-TRACE-ASSERTION-KEY-MISMATCH	Mismatch denies with no mutation and the private-state response.
FI-TRACE-BINDING-CONFLICT	A binding conflict denies without replacing either existing binding.
FI-TRACE-TOMBSTONE-REPLAY	Fresh eligible evidence for a retired pair or revoked key denies without recreation.
FI-TRACE-ASSERTION-REFRESH	Fresh evidence reuses the same eligible durable binding after prior assertion expiry.
FI-TRACE-PREPARED-STALE	Changed identity-class witnesses or extended bounds deny; provenance-only rotation revalidates.
FI-TRACE-CONCURRENT-ENROLLMENT	Identical first use converges; conflicting first use commits at most one winner.
FI-TRACE-FINAL-DENIAL-NO-MUTATION	Every failed phase leaves all authoritative stores and effects unchanged.
FI-TRACE-LIFECYCLE-AUTHORITY	Unprivileged/stale transitions deny; authorized retirement/revocation/rotation is atomic.
FI-TRACE-LEASE-BOUND	A lease ends at its earliest bound; equality at any bound is expired.
FI-TRACE-MULTI-KEY-SESSION	One actor's lease never authorizes another key on the same connection.
FI-TRACE-DENIAL-ORACLE	Each private row produces its exact fixed bytes on every surface where its condition can be decided — HTTP, a WebSocket upgrade, or after connect; all private-state rows compare byte-identical.
FI-TRACE-DEPENDENCY-FAIL-CLOSED	Each unreadable authoritative dependency denies.
FI-TRACE-AUTHORITY-UNIFORM	Every protected ingress reaches one current final-admission authority.
FI-TRACE-CROSS-DOMAIN-COLLISION	Equal subjects across issuers and equal pairs across domains remain distinct.
FI-TRACE-PRIVACY-NONPUBLIC	Private identity does not enter public surfaces.
FI-TRACE-DISCOVERY-PRIVATE	Complete discovery bytes remain identical across attested-key, TOFU, and companion enrollment modes.
FI-TRACE-TOFU-THEFT	Stolen-assertion first use denies unless private TOFU is enabled and the attacker also proves its chosen key.

Relationship to other work (non-normative)

NIP-FI binds an access token to a key the resource server itself verifies, the goal DPoP (RFC 9449) and mTLS-bound tokens (RFC 8705) reach through a cnf claim. Here the proof is the NIP-42 or NIP-98 event the relay already validates, so no second proof is defined and the issuer need not attest the key; nostr_pubkey is the optional cnf analogue. Unlike those profiles the binding is durable server state rather than a per-token claim: a stolen assertion cannot reach an enrolled identity without its key, and revocation is a local fact rather than a token-lifetime race. One identity, one key per domain is stricter than WebAuthn's many-credentials-per-account model because the Nostr key is itself the public identity; additional devices do not create additional active bindings. Two contract identities plus explicit dependency versions exist because folding a mutable key snapshot into policy identity would make benign rotation change policy lineage, while omitting it would let evidence under a removed key survive. Denial responses deliberately collapse the conditions that RFC 6750 error codes distinguish. trusted-proxy-hmac-v2 in NIP-FI-EDGE is a fixed-component request MAC in the family of HTTP Message Signatures (RFC 9421) and AWS SigV4, without negotiation and with length-prefixed canonicalization.

Security considerations

Issuer compromise can impersonate a principal but cannot prove an uncompromised bound Nostr key. Assertion theft cannot use an existing binding without that key; private TOFU intentionally retains first-use theft risk. Snapshot revalidation limits removed-key reuse but the base policy accepts authenticated key-source rollback as residual issuer risk. Two-phase admission closes the binding and policy TOCTOU window only when every authoritative witness is reread atomically. Availability failures deny rather than degrade to Nostr-only access.

Sources

• NIP-42 authentication: https://github.com/nostr-protocol/nips/blob/6d2979b3f503a8539c983efbcdcf901bbcf9ed23/42.md
• NIP-98 HTTP authentication: https://github.com/nostr-protocol/nips/blob/6d2979b3f503a8539c983efbcdcf901bbcf9ed23/98.md
• JWT BCP: https://www.rfc-editor.org/rfc/rfc8725
• JWT access-token profile: https://www.rfc-editor.org/rfc/rfc9068
• DPoP: https://www.rfc-editor.org/rfc/rfc9449
• OAuth 2.0 mTLS client certificate-bound tokens: https://www.rfc-editor.org/rfc/rfc8705
• HTTP Message Signatures: https://www.rfc-editor.org/rfc/rfc9421
• Non-normative composed model: NIP-FI-MODEL.md