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` or `tofu`.
- **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.

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:

```text
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:

```text
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. `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]

If configured, a Nostr-key claim resolves without ambiguity to one 32-byte key.
Lowercase hexadecimal is canonical. 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:

- **RFC 9068 access token**: a Buzz-resource access token whose protected
  `typ` is exactly `at+jwt` and whose `aud` contains the configured Buzz
  resource audience;
- **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. 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:

```text
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]

Thus two contract identities do not mean two total version values. Folding a
mutable snapshot into policy identity would make benign rotation change policy
lineage; omitting it would let evidence under a removed key survive. Stable
semantic IDs plus explicit mutable dependency versions preserve both outcomes.

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)`. 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]

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 exact bytes consumed by the
application. Absence, duplication, mismatch, validation of only a prefix, or
post-validation transformation denies. For an irrelevant body, no
Authorization decision, target, capability, or effect selector derives from a
body field not bound by NIP-98. [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.

```text
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 is live now and is no later than its prepared
   value; and
3. provenance-class fields — snapshot version, verification-key identity,
   cache metadata, ordering, and retrieval time — are ignored after successful
   current revalidation.

Any new or unclassified 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, 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. Rotation does not globally revoke the old key.

Failure or stale state causes no partial mutation. Ordinary authorization cannot
perform or undo these transitions. Extended recovery, disablement, 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 fresh attached
assertion, fresh Nostr proof, preparation, and final admission. 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 server state. 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` + `authentication required\n` |
| malformed, invalid, expired, or replayed evidence | `evidence_rejected` | `restricted: evidence rejected` | `403` + `evidence rejected\n` |
| key mismatch; attestation required; binding conflict; retired pair; revoked key; lifecycle gate; binding required/expired; local policy denial | `authorization_denied` | `restricted: authorization denied` | `403` + `authorization denied\n` |
| required current dependency unreadable | `authorization_unavailable` | `restricted: authorization unavailable` | `503` + `authorization unavailable\n` |

Nostr text is the exact UTF-8 text after an applicable NIP-42/NIP-01 prefix;
HTTP body is exact UTF-8 `text/plain` with the shown LF and no other bytes.
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:

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

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 every
enrollment policy, including `attested-key`, private `tofu`, and any companion
profile mode, the complete public discovery output is byte-identical: 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]

## 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, and ambiguity negative denies. |
| `FI-TRACE-TOKEN-CLASS` | An RFC 9068 `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, 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` / `REMOVE` | Retained-key rotation can revalidate; removed-key evidence and leases deny. |
| `FI-TRACE-CURRENT-STATUS-REVOKED` / `STALE` | Revocation, including one racing final admission, closes authority within the advertised tested bound. Inactive/ambiguous status denies; expiry equality, outage, delayed events, and changed status versions cannot mint or extend a witness. |
| `FI-TRACE-BODY-BINDING` / `BOUNDS` | Exact complete relevant body passes; absent/duplicate/mutated/partial/transformed/oversized/quota variants deny without 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` / `TOMBSTONE-REPLAY` | Conflicts and fresh evidence for retired/revoked state deny without replacement. |
| `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` / `MULTI-KEY-SESSION` | Equality expires and one actor's lease never authorizes another. |
| `FI-TRACE-DENIAL-ORACLE` | Each private row produces its exact fixed bytes; 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` / `DISCOVERY-PRIVATE` | Private identity does not enter public surfaces; 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. |

## 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/6d2979b369329748734c66846989e453270ced03/42.md>
- NIP-98 HTTP authentication: <https://github.com/nostr-protocol/nips/blob/6d2979b369329748734c66846989e453270ced03/98.md>
- JWT BCP: <https://www.rfc-editor.org/rfc/rfc8725>
- JWT access-token profile: <https://www.rfc-editor.org/rfc/rfc9068>
- Non-normative composed model: [NIP-FI-MODEL.md](NIP-FI-MODEL.md)