Multi-Party Quorum Authorization for High-Risk Agent Actions (EP-QUORUM)
draft-schrock-ep-quorum-03

Network Working Group                                         I. Schrock
Internet-Draft                                     EMILIA Protocol, Inc.
Intended status: Informational                              19 July 2026
Expires: 20 January 2027

Multi-Party Quorum Authorization for High-Risk Agent Actions (EP-QUORUM)
                       draft-schrock-ep-quorum-03

Abstract

   This document defines EP-QUORUM, a multi-party authorization profile
   for the EMILIA Protocol (EP) authorization receipt (draft-schrock-ep-
   authorization-receipts).  Where the base receipt binds a single
   accountable human to one exact high-risk action, EP-QUORUM binds a
   set of distinct accountable humans -- the "two-person rule,"
   generalized to M-of-N and to ordered approval trails -- to one exact
   action, such that the quorum predicate is not satisfied until the
   full quorum holds.  The profile is purely additive: each quorum
   member is an unmodified EP signoff over the same action hash, and a
   single-approver policy is the degenerate one-member case.  EP-QUORUM
   specifies a fail-closed quorum predicate (all member signatures
   valid, every member bound to the exact action, approvers pairwise
   distinct, every approver admitted by role, the threshold met, the
   declared order respected, and all signatures within a bounded time
   window), an incremental server-side admission rule that rejects a
   non-conforming signer before it enters the trail, and a set of
   adversarial conformance vectors.  The predicate is offline-verifiable
   under the base draft's verification model and is maintained as cross-
   language conformance vectors that three reference verifiers
   (JavaScript, Python, Go) are required to agree on.  Those verifiers
   live in one repository -- a cross-language consistency check, not
   clean-room independent implementations; independent implementations
   remain future interoperability evidence.  The document also
   describes, informatively, the multi-handshake composition process:
   how individual signing ceremonies -- fresh one-time challenge, exact-
   action binding, user-verified device signature -- compose into one
   ordered, offline-verifiable, at-most-once-consumable multi-party
   decision.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Design Goals  . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  The Quorum Policy . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Approval Modes  . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  The Quorum Gate (fail-closed predicate) . . . . . . . . . . .   8
   6.  Incremental Admission (canAccept) . . . . . . . . . . . . . .   9
   7.  Multi-Handshake Composition . . . . . . . . . . . . . . . . .  10
   8.  Member Representation in the Receipt  . . . . . . . . . . . .  12
   9.  Conformance . . . . . . . . . . . . . . . . . . . . . . . . .  12
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  14
     10.1.  What multi-party authorization does and does not
            prevent  . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.2.  Fail-closed is the only safe default . . . . . . . . . .  14
     10.3.  Partial trails confer no authority . . . . . . . . . . .  15
     10.4.  Window and replay  . . . . . . . . . . . . . . . . . . .  15
     10.5.  Divide-and-misinform across members  . . . . . . . . . .  15
     10.6.  Approver fatigue, at quorum scale  . . . . . . . . . . .  15
     10.7.  Rubber-stamping and review-latency evidence  . . . . . .  16
     10.8.  Human quorum is not threshold secret custody . . . . . .  16

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   11. Changes from -02  . . . . . . . . . . . . . . . . . . . . . .  16
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   13. Normative References  . . . . . . . . . . . . . . . . . . . .  16
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   The base EP authorization receipt closes the gap between "is this
   actor authorized in general?" and "should this exact action happen,
   and which accountable human said yes?" by binding one named
   approver's device-held signature to one exact action (see
   [EP-RECEIPTS], Section 1).  For the highest-consequence actions, one
   approver is not the right control.  The discipline that governs
   nuclear release, large-value treasury movement, and production-
   credential change is the _two-person rule_: no single human --
   however well-authenticated, however senior -- can unilaterally cause
   the action.  Two or more distinct, accountable humans must each
   independently authorize, and the action proceeds only when all of
   them have.

   As autonomous agents acquire credentials sufficient for irreversible
   operations, the two-person rule is exactly the control that lets an
   organization grant an agent real authority without creating a single
   point of failure: a compromised, misaligned, or prompt-injected agent
   cannot act alone, and neither can a single compromised or coerced
   approver.  EP-QUORUM specifies how to express that control as a
   cryptographic predicate over EP signoffs and how to enforce it both
   at the moment each approver signs and at the moment the action would
   execute.

   The base draft already contemplates multi-approver policies
   ([EP-RECEIPTS], Section 7): each approver signs an individual
   Authorization Context sharing the same action hash, and commitment
   occurs only when k valid, distinct signoffs exist before expiry.
   This document makes that sketch normative and testable.  It adds:
   ordered approval trails (Section 4); an explicit role roster and
   admission semantics (Section 3); a bounded approval window with a
   monotonic-time constraint for ordered mode (Section 4); an
   incremental server-side admission rule that keeps a non-conforming
   signer out of the trail in the first place (Section 6); the
   consolidated fail-closed quorum predicate (Section 5); and an
   adversarial conformance suite (Section 9).

1.1.  Design Goals

   EP-QUORUM inherits design goals G1-G7 of the base draft and adds:

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   *  *Q1 -- Additivity.* A quorum is a set of unmodified EP signoffs
      over the same action hash.  No new signature type, no new signing
      ceremony, and no change to the receipt verifier are introduced.  A
      single-approver policy is the one-member quorum.

   *  *Q2 -- Fail-closed.* The quorum predicate is not satisfied unless
      _every_ element of the predicate holds.  Absence of evidence, an
      unparseable member, a malformed policy, or any single failed check
      yields "not satisfied," never "satisfied."

   *  *Q3 -- Distinctness (separation of duties at the human level).* A
      quorum of size k requires k pairwise-distinct human approvers,
      each distinct from the initiator.  One human MUST NOT fill two
      slots.

   *  *Q4 -- Incremental enforcement.* The protocol enforces conformance
      as each approver signs, not only at consume time, so that a wrong-
      action, wrong-role, duplicate, out-of-order, stale, or invalid
      signature never becomes part of the trail.

   *  *Q5 -- Offline-verifiable quorum.* The satisfied/not-satisfied
      judgment is computable from the receipt's members and the policy
      alone, under the same offline verification model as the base draft
      ([EP-RECEIPTS], Section 6.3).

2.  Terminology

   In addition to the terminology of [EP-RECEIPTS]:

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHOULD",
   "MAY" are to be interpreted as described in BCP 14 [RFC2119]
   [RFC8174] when, and only when, they appear in all capitals.

   Quorum.  The set of distinct approver signoffs required to satisfy
      one human-authorization evidence requirement for an action under a
      Quorum Policy.

   Quorum Policy.  A named, versioned rule set declaring the approval
      mode, the required count, the roster of eligible (role, approver)
      slots, the distinct-humans rule, and the approval window.  Carried
      in the policy that governs the action; see Section 3.

   Member.  One element of a candidate quorum: a (role, approver public
      key, signoff) triple, where the signoff is an unmodified EP
      signoff ([EP-RECEIPTS], Section 5.3) over the Authorization
      Context the approver signed.

   Trail.  The ordered sequence of members admitted so far for one

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      action -- the partial quorum under construction.

   Quorum Gate.  The fail-closed predicate (Section 5) that decides
      whether a trail is a satisfied quorum.  The Verifying Executor
      ([EP-RECEIPTS], Section 9) MUST consult it before performing the
      action.

3.  The Quorum Policy

   A Quorum Policy is a JSON object:

   {
     "mode": "ordered",
     "required": 3,
     "approvers": [
       {
         "role": "program_officer",
         "approver": "ep:approver:po_rivera"
       },
       {
         "role": "authorizing_official",
         "approver": "ep:approver:ao_chen"
       },
       {
         "role": "inspector_general",
         "approver": "ep:approver:ig_okafor"
       }
     ],
     "distinct_humans": true,
     "window_sec": 900
   }

   Members:

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   +=================+==========+=========+===========================+
   | Field           | Required | Type    | Meaning                   |
   +=================+==========+=========+===========================+
   | mode            | REQUIRED | string  | threshold or ordered      |
   |                 |          | (enum)  | (Section 4).              |
   +-----------------+----------+---------+---------------------------+
   | required        | REQUIRED | integer | The quorum size k.        |
   |                 |          | >= 1    |                           |
   +-----------------+----------+---------+---------------------------+
   | approvers       | REQUIRED | array   | The roster of eligible    |
   |                 |          |         | {role, approver} slots.   |
   |                 |          |         | MUST be non-empty.        |
   +-----------------+----------+---------+---------------------------+
   | distinct_humans | OPTIONAL | boolean | When true, no approver    |
   |                 | (default |         | identifier may fill more  |
   |                 | true)    |         | than one slot, AND no     |
   |                 |          |         | single device key may     |
   |                 |          |         | fill more than one slot   |
   |                 |          |         | (Section 5, checks 5 and  |
   |                 |          |         | 5a).  Implementations     |
   |                 |          |         | MUST treat a missing      |
   |                 |          |         | value as true.            |
   +-----------------+----------+---------+---------------------------+
   | window_sec      | OPTIONAL | integer | Maximum span, in seconds, |
   |                 | (default | > 0     | between the first and any |
   |                 | 900)     |         | later admitted signature. |
   +-----------------+----------+---------+---------------------------+
   | ordered_chain   | OPTIONAL | boolean | Strong ordered mode       |
   |                 | (default |         | (Section 4).  When true   |
   |                 | false)   |         | (ordered mode only), each |
   |                 |          |         | signoff after the first   |
   |                 |          |         | MUST commit, inside its   |
   |                 |          |         | own signed context, to    |
   |                 |          |         | the hash of its           |
   |                 |          |         | predecessor's context     |
   |                 |          |         | (prev_context_hash), so   |
   |                 |          |         | approval order is proven  |
   |                 |          |         | by the signatures rather  |
   |                 |          |         | than by issued_at         |
   |                 |          |         | timestamps.               |
   +-----------------+----------+---------+---------------------------+

                                 Table 1

   Rules:

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   *  An approver slot identifies an eligible approver in the Approver
      Directory ([EP-RECEIPTS], Section 5.2).  The role is the
      organizational role under which that approver is admitted to this
      quorum; it is the unit of role eligibility (Section 5, check 4).

   *  A member is admitted only if its (role, approver) pair is present
      in the roster.  A correct signature by a real, enrolled approver
      who is not on the roster for this action MUST be rejected
      (wrong_role).

   *  required MUST NOT exceed the number of distinct human approvers
      the roster can supply under distinct_humans.  A policy that cannot
      be satisfied is a misconfiguration; verifiers treat an
      unsatisfiable trail as not satisfied, as always.

   *  The Quorum Policy is part of the action's governing policy and is
      therefore committed by the policy_hash of every member's
      Authorization Context ([EP-RECEIPTS], Section 4).  A signature
      collected under one Quorum Policy version MUST NOT satisfy a
      requirement evaluated under another.

4.  Approval Modes

   *Threshold mode ("threshold").* Any required distinct approvers drawn
   from the roster, in any order, satisfy the quorum.  This is the
   classic M-of-N rule.

   *Ordered mode ("ordered").* Approvals MUST occur in the roster's
   listed order: the i-th admitted member MUST match approvers[i-1] in
   both role and approver.  In addition, signature times MUST be
   strictly increasing -- each member's issued_at MUST be later than the
   previous admitted member's issued_at (non_increasing_time).  Ordered
   mode expresses escalation chains in which a later authority signs
   _after, and in knowledge of,_ an earlier one (e.g., Program Officer,
   then Authorizing Official, then Inspector General).

   In both modes, every admitted member's issued_at MUST fall within
   window_sec of the first admitted member's issued_at
   (window_exceeded).  The window bounds the lifetime of a partial
   quorum so that a long-dormant partial trail cannot be completed much
   later by an attacker who has since compromised a remaining approver.

   *Strong ordered mode ("ordered_chain": true).* Ordering by issued_at
   alone is asserted by whoever stamps the time.  To prove order by the
   signatures themselves, a policy MAY require a cryptographic chain:
   each signoff after the first carries, inside its signed Authorization
   Context, a prev_context_hash equal to the SHA-256 of the canonical
   context of its predecessor in the trail; the first signoff carries

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   none.  Because each approver's device signs over its own context, the
   i-th approver thereby attests to having signed _after_ the exact (i-
   1)-th approval, and no party -- including the operator -- can
   reorder, insert, or backdate a signoff without invalidating a
   signature (broken_chain).  This is RECOMMENDED for the highest-
   consequence ordered actions.  Implementations that do not set
   ordered_chain retain timestamp ordering and remain conformant.

5.  The Quorum Gate (fail-closed predicate)

   A trail is a *satisfied quorum* for an action with hash H under
   policy P if and only if ALL of the following hold.  A verifier MUST
   return "satisfied" only when every check passes, and MUST return "not
   satisfied" on the first failure, on a malformed policy or member, or
   on any unrecognized condition (Q2):

   1.   *Well-formed policy.* P has a recognized mode, an integer
        required >= 1, and a non-empty approvers roster.  Otherwise: not
        satisfied.

   2.   *All signatures valid.* For every member, the EP signoff
        verifies under [EP-RECEIPTS], Section 5.3 / 6.3 -- the WebAuthn
        [WEBAUTHN] assertion (Class A) verifies against the member's
        approver_public_key, with the assertion challenge equal to the
        member's context hash and user verification asserted.  One
        invalid signature (one_bad_signature) fails the whole quorum.

   3.   *Action binding.* Every member's Authorization Context carries
        action_hash == H (action_mismatch).  A member bound to any other
        action does not count.

   4.   *Role admission.* Every member's (role, approver) pair is
        present in the roster (wrong_role).

   5.   *Distinct humans.* When distinct_humans is true (the default),
        approvers are pairwise distinct and (per the base draft's
        SelfApprovalImpossible) distinct from the initiator
        (duplicate_human).

   6.   *Distinct keys (check 5a).* When distinct_humans is true, the
        admitted members' approver_public_key values are pairwise
        distinct (duplicate_key).  This defends against a single device
        key enrolled under two approver identifiers, which would
        otherwise pass the distinct-humans check by name while being one
        signer.

   7.   *Threshold.* At least required admitted members exist
        (under_threshold).

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   8.   *Order (ordered mode only).* The i-th admitted member matches
        approvers[i-1]; signature times are strictly increasing
        (out_of_order, non_increasing_time).

   9.   *Ordering chain (strong ordered mode only, check 7a).* When
        ordered_chain is true, the first admitted member carries no
        prev_context_hash and every later member's prev_context_hash
        equals the SHA-256 of the canonical context of its predecessor
        (broken_chain).  When ordered_chain is false this check is not
        applicable.

   10.  *Window.* Every admitted member's issued_at is within window_sec
        of the first member's issued_at (window_exceeded).

   The predicate is the same whether computed by the orchestrating
   operator before consumption or by an independent Verifying Executor
   or auditor offline (Q5): it is a pure function of (P, H, members).
   Because each member is an unmodified EP signoff, check 2 is exactly
   the base draft's verifier invoked per member; EP-QUORUM adds the set-
   level checks 1, 3-10 on top.

6.  Incremental Admission (canAccept)

   To keep a non-conforming signer out of the trail rather than
   discovering it only at consume time (Q4), an orchestrator MUST
   evaluate an incremental admission rule before recording each new
   signoff.  Given the policy P, the action hash H, the already-admitted
   trail, and one incoming candidate member, the rule ADMITS the
   candidate only if all of the following hold, and otherwise REJECTS it
   with the named reason:

   1.  P is well-formed and its roster is non-empty (else no_policy /
       no_eligible_approvers).

   2.  The candidate's context carries action_hash == H (else
       action_mismatch).

   3.  The candidate's (role, approver) is on the roster (else
       ineligible_role).

   4.  When distinct_humans is true, no already-admitted member shares
       the candidate's approver (else duplicate_human).

   5.  In ordered mode, the candidate matches the next unfilled roster
       slot (approvers[len(trail)]) in both role and approver (else
       out_of_order).

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   6.  If the trail is non-empty, the candidate's issued_at is within
       window_sec of the first member's issued_at (else
       window_exceeded); and in ordered mode it is strictly greater than
       the last admitted member's issued_at (else non_increasing_time).

   7.  The candidate's signature verifies (else invalid_signature).

   A rejected candidate MUST NOT be written into the trail.  Incremental
   admission is an enforcement convenience and an early-rejection UX; it
   is not a substitute for the Quorum Gate.  A conforming Verifying
   Executor MUST re-evaluate the full Quorum Gate (Section 5) over the
   assembled trail before performing the action, regardless of
   incremental admission, because the executor does not trust the
   orchestrator to have applied admission honestly (this mirrors the
   base draft's execution-side enforcement, [EP-RECEIPTS], Section 9).

7.  Multi-Handshake Composition

   This section is informative.  It describes, end to end, the process
   by which the normative machinery of Section 3 through Section 6
   composes individual signing ceremonies into one multi-party decision.
   Every property named here is required elsewhere in this document or
   in the base draft; this section introduces no new requirements.

   *The handshake is the unit of approval.* Each quorum member is one
   complete run of the base draft's single-approver signing ceremony
   ([EP-RECEIPTS], Section 5.3): a fresh, one-time challenge is issued
   for that approver against a verified handshake, bound to the exact
   action bytes through the action hash and binding hash it commits to,
   and bounded by an explicit validity window; the approver answers it
   with a user-verified, device-held signature whose WebAuthn assertion
   challenge is the member's context hash (the per-member requirement is
   check 2 of the Quorum Gate, Section 5).  Nothing about the ceremony
   is weakened or amortized when the action needs several approvers:
   there is no batch signature and no shared signing session; k
   approvals are k separate ceremonies, each independently verifiable
   and each independently refusable.

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   *A malformed trail never exists.* Composition is incremental and
   server-side.  Each candidate member is evaluated against the
   admission rule of Section 6 before it is recorded, so a wrong-action,
   off-roster, duplicate, out-of-order, stale, or invalidly signed
   member handshake is refused at the moment it is presented and never
   enters the trail.  The stored trail is therefore, at every instant, a
   prefix of a potentially satisfiable quorum; there is no later
   cleaning pass that removes bad members, because bad members are never
   written.  The Verifying Executor still re-evaluates the full Quorum
   Gate over the assembled trail, as Section 6 requires, precisely
   because it does not trust the orchestrator to have admitted honestly.

   *Order is a signed commitment, not a claim.* In strong ordered mode
   (Section 4), each member's signed context after the first commits to
   the hash of its predecessor's context.  Because that commitment sits
   inside the bytes the approver's device signed, and each predecessor
   in turn committed to its own predecessor, the i-th signature
   transitively covers the entire prior trail: the order of approvals is
   non-repudiable, and no party -- including the operator -- can
   reorder, insert, or backdate a member without invalidating a
   signature (check 7a, Section 5).  Plain ordered mode retains the
   weaker, timestamp-based ordering described in Section 4.

   *Denial is a first-class terminal outcome.* Any approver in the trail
   can refuse, and a refusal is not the mere absence of an approval.
   Under the base draft a denial is signed over the same context hash
   with a decision of "denied" and is terminal: a denied authorization
   can never later become approved ([EP-RECEIPTS], Sections 5.3 and
   6.1).  At the composition level, one dissenting approver leaves
   durable, attributable evidence of the dissent, which a relying party
   can weigh as adverse evidence rather than as a gap in the trail.

   *The composed decision is accepted at most once.* A satisfied quorum
   is authorization evidence for one exact action and is consumable at
   most once within its atomic consumption domain; the relying party
   separately decides AUTHORIZED.  Each member's signoff individually
   retains the base draft's one-time-consumption rule (Section 10.4),
   and consumption of the composed decision is refused until the Quorum
   Gate is satisfied; a partial trail confers no partial authority
   (Section 10.3).

   *The whole composition is verifiable offline.* Because the satisfied/
   not-satisfied judgment is a pure function of the policy, the action
   hash, and the members (Section 5, Q5), an auditor holding only the
   quorum receipt can recompute every check above -- per-member
   signatures, action binding, distinctness of humans and keys, roster
   admission, threshold, order and ordering chain, and window -- without
   contacting the operator.  As in the base draft, such offline

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   verification establishes the integrity and authenticity of the
   recorded composition as of signing time; it does not by itself
   establish current validity, such as the present enrollment or
   revocation status of the approvers involved.

8.  Member Representation in the Receipt

   A quorum receipt is an ordinary EP Trust Receipt ([EP-RECEIPTS],
   Section 6.2) whose contexts and signoffs arrays carry one entry per
   admitted member, plus the Quorum Policy (by reference via
   policy_hash, and optionally inline for convenience).  For the offline
   quorum computation, each member is the triple:

   {
     "role": "program_officer",
     "approver_public_key": "<SPKI of the approver's enrolled key>",
     "signoff": {
       "@type": "ep.signoff",
       "context": {
         "context_type": "ep.signoff.v1",
         "action_hash": "...",
         "approver": "...",
         "issued_at": "...",
         "...": "..."
       },
       "webauthn": {
         "authenticator_data": "...",
         "client_data_json": "...",
         "signature": "..."
       }
     }
   }

   The context and webauthn members are exactly as defined by the base
   draft; EP-QUORUM does not alter their canonicalization, hashing, or
   signature verification.  The role and approver_public_key are the
   join keys against the Quorum Policy roster and the Approver
   Directory.

9.  Conformance

   An implementation conforms to EP-QUORUM if, for the published
   adversarial conformance vectors, it returns the expected satisfied/
   not-satisfied verdict for every vector and rejects every non-
   conforming candidate at incremental admission with the expected
   reason.  The reference suite (EP-QUORUM-v1) comprises the following
   vectors, each carrying real Class-A WebAuthn assertions:

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    +==========================+===========+=========================+
    | Vector                   | Expect    | Exercises               |
    +==========================+===========+=========================+
    | accept_ordered_3of3      | satisfied | Ordered PO, AO, IG;     |
    |                          |           | distinct; increasing    |
    |                          |           | time; all action-bound  |
    +--------------------------+-----------+-------------------------+
    | accept_threshold_2of3    | satisfied | Any 2 distinct          |
    |                          |           | approvers from a 3-slot |
    |                          |           | roster                  |
    +--------------------------+-----------+-------------------------+
    | reject_under_threshold   | not       | Fewer than required     |
    |                          | satisfied | valid members           |
    +--------------------------+-----------+-------------------------+
    | reject_duplicate_human   | not       | One human filling two   |
    |                          | satisfied | slots                   |
    +--------------------------+-----------+-------------------------+
    | reject_out_of_order      | not       | Ordered mode, members   |
    |                          | satisfied | out of roster order     |
    +--------------------------+-----------+-------------------------+
    | reject_action_mismatch   | not       | A member bound to a     |
    |                          | satisfied | different action hash   |
    +--------------------------+-----------+-------------------------+
    | reject_expired_window    | not       | A member outside        |
    |                          | satisfied | window_sec              |
    +--------------------------+-----------+-------------------------+
    | reject_one_bad_signature | not       | One invalid member      |
    |                          | satisfied | signature               |
    +--------------------------+-----------+-------------------------+
    | reject_wrong_role        | not       | A correct signature by  |
    |                          | satisfied | an off-roster approver  |
    +--------------------------+-----------+-------------------------+
    | reject_duplicate_key     | not       | One device key signing  |
    |                          | satisfied | under two approver      |
    |                          |           | identifiers (check 5a)  |
    +--------------------------+-----------+-------------------------+
    | reject_broken_chain      | not       | Strong ordered mode, a  |
    |                          | satisfied | member committing to    |
    |                          |           | the wrong predecessor   |
    |                          |           | context hash (check 7a) |
    +--------------------------+-----------+-------------------------+

                                 Table 2

   The reference suite is maintained such that three cross-language
   reference verifiers (JavaScript, Python, Go), which share one
   repository and are therefore a consistency check rather than clean-
   room independent implementations, MUST agree on every vector;

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   divergence is a conformance defect in at least one verifier.
   Independent implementations remain future interoperability evidence.
   The "accept" vectors guard against a verifier that is too strict
   (denying valid quorums); the "reject" vectors guard against a
   verifier that is too lenient (the security-critical direction).

   Separate symbolic evidence covers a fixed 2-of-2 quorum instance.  It
   does not prove this document's general k-of-n construction, the
   reference implementations, WebAuthn internals, directory correctness,
   parser behavior, collusion resistance, or deployment behavior.  A CI
   regression gate over an existing prover result improves
   reproducibility but does not enlarge the modeled system.

10.  Security Considerations

   EP-QUORUM inherits all Security Considerations of [EP-RECEIPTS] and
   adds the following.  Several restate, honestly, what a quorum does
   _not_ buy.

10.1.  What multi-party authorization does and does not prevent

   A satisfied quorum proves that k pairwise-distinct enrolled approvers
   each produced a valid, action-bound, in-window, in-order (where
   required) signature with their own device-held keys, and that the
   orchestrator could not have forged any of them ([EP-RECEIPTS],
   Section 11.1).  It raises the cost of unilateral action: a single
   compromised agent, a single stolen key, a single coerced or malicious
   approver is insufficient.  It does _not_ defeat collusion among the
   required number of distinct humans, nor one human who controls
   multiple enrolled identities (an enrollment control -- base draft
   Section 5.2), nor simultaneous coercion of a full quorum.  As in the
   base draft, EP-QUORUM makes such events _attributable_ -- named,
   signed, and evidenced for every member -- which is a deterrent and an
   audit primitive, not an impossibility proof.  Implementations MUST
   NOT claim a quorum is collusion-proof.

10.2.  Fail-closed is the only safe default

   The dangerous error in a multi-party gate is to treat ambiguity as
   approval.  EP-QUORUM is specified so that a malformed policy, a
   missing or unparseable member, a partial trail, or any single failed
   check yields "not satisfied."  A verifier MUST NOT default to
   satisfied on any unrecognized condition.  The "reject" conformance
   vectors exist to catch a regression in this direction.

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10.3.  Partial trails confer no authority

   A trail short of the threshold, or one in which incremental admission
   has accepted some but not all required slots, authorizes nothing.  A
   Verifying Executor presented with a partial trail MUST refuse,
   exactly as it refuses a missing single signoff.  This is the multi-
   party form of the base draft's NoBypassWrite invariant.

10.4.  Window and replay

   The approval window (window_sec) bounds how long a partial quorum
   remains completable, limiting the value to an attacker of
   compromising a _remaining_ approver after some approvals already
   exist.  Each member's signoff retains the base draft's one-time-
   consumption nonce (G3); the window is an additional, quorum-level
   constraint, not a substitute for per-signoff replay protection.  The
   monotonic-time rule in ordered mode additionally prevents back-dating
   a later authority's signature to appear to precede an earlier one.

10.5.  Divide-and-misinform across members

   Because each approver signs their own Authorization Context, a
   malicious orchestrator can attempt to show different approvers
   different renderings or different initiator attestations
   ([EP-RECEIPTS], Section 11.9) while each individual signature remains
   valid.  EP-QUORUM does not change the base draft's cross-context
   consistency requirement; verifiers SHOULD surface per-member context
   differences, and high-value ordered policies SHOULD render the prior
   approvers' decisions to each subsequent approver so that the trail is
   a chain of informed approvals rather than parallel ones.  The
   presentation-attack mitigations of base draft Section 11.3 apply per
   member.

10.6.  Approver fatigue, at quorum scale

   Requiring more humans does not help if each rubber-stamps; it can
   hurt, by diffusing responsibility across a group in which no member
   feels decisive (base draft Section 11.8).  Quorum policies MUST be
   scoped to genuinely high-consequence, low-frequency actions, and
   deployments SHOULD monitor per-role time-to-sign and deny rates
   rather than assume that more signers means more scrutiny.

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10.7.  Rubber-stamping and review-latency evidence

   Signing-ceremony telemetry -- the times at which each member's
   challenge was issued, first viewed, and approved -- SHOULD be
   retained alongside the trail as evidence of how much review each
   approval actually received.  A relying party MAY apply a minimum-
   review-latency policy when weighing an approval: an approval recorded
   a very short interval after the challenge was first viewed is
   evidence of rubber-stamping rather than review, and a relying party
   may discount it or treat the bundle as containing conflicting
   evidence accordingly.  This raises the probability that rubber-
   stamping is detected after the fact and makes it attributable to a
   named approver; it does not prevent rubber-stamping, and it does not
   defeat collusion or coercion, for which Section 10.1 applies.
   Ceremony telemetry originates with the orchestrator, so a relying
   party that depends on it should weigh unsigned telemetry with the
   same skepticism as any other operator-supplied metadata; deployments
   that need it to serve as evidence rather than log data can have the
   operator sign the ceremony record so that its integrity is
   independently checkable.

10.8.  Human quorum is not threshold secret custody

   EP-QUORUM verifies distinct enrolled approvers, action-bound
   signatures, roles, order, and timing.  Reconstructing a capability
   holder secret from m-of-n shares proves only that enough shares were
   combined.  Unless each share holder separately performs the EP-QUORUM
   ceremony, threshold reconstruction does not prove that distinct
   humans reviewed or approved the action.  Implementations and public
   claims MUST NOT describe threshold secret custody as EP-QUORUM
   authorization.

11.  Changes from -02

   Clarified that EP-QUORUM's distinct-human, action-bound approval
   ceremony is not interchangeable with m-of-n reconstruction of a
   capability holder secret.

12.  IANA Considerations

   This document has no IANA actions.

13.  Normative References

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   [EP-RECEIPTS]
              Schrock, I., "Authorization Receipts for High-Risk Agent
              Actions (EP)", Work in Progress, Internet-Draft, draft-
              schrock-ep-authorization-receipts, June 2026,
              <https://datatracker.ietf.org/doc/draft-schrock-ep-
              authorization-receipts/>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [WEBAUTHN] W3C, "Web Authentication: An API for accessing Public Key
              Credentials, Level 2", April 2021,
              <https://www.w3.org/TR/webauthn-2/>.

Author's Address

   Iman Schrock
   EMILIA Protocol, Inc.
   United States of America
   Email: team@emiliaprotocol.ai

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