Bounded Capability Receipts and Durable Spend Control for Agent Actions
draft-schrock-ep-bounded-capability-receipts-03
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Iman Schrock | ||
| Last updated | 2026-08-08 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources |
Pre-standard JavaScript prototype and durable capability stores
|
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| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
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draft-schrock-ep-bounded-capability-receipts-03
Network Working Group I. Schrock
Internet-Draft EMILIA Protocol, Inc.
Intended status: Experimental 8 August 2026
Expires: 9 February 2027
Bounded Capability Receipts and Durable Spend Control for Agent Actions
draft-schrock-ep-bounded-capability-receipts-03
Abstract
Agents sometimes need bounded authority to perform more than one
consequential action without obtaining a new human approval for every
operation. A signed token alone cannot enforce a shared budget
across replicas, survive retries safely, or distinguish an operation
that never crossed an effect boundary from one whose outcome is
unknown.
This document defines a bounded capability receipt and a durable
reserve-execute-commit protocol. The receipt binds an issuance
authorization, a closed action scope, a budget with explicit units, a
holder proof, an expiry, and any parent capability. The state
protocol atomically refuses overspend and replay, fences concurrent
owners, and charges an indeterminate operation when an external
effect may have occurred. Delegation transfers rather than copies
authority: all direct child allocations are funded by committed
parent operations before child registration, and their aggregate
cannot exceed the parent balance within one authoritative atomic
state domain. It also defines narrowing-only delegation, explicit
revocation inheritance for delegated authority, and evidence
interfaces. It does not make a bearer token into human approval,
does not provide cross-domain or offline global double-spend
prevention, and does not claim that an authorized action was safe,
lawful, or successfully executed.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 9 February 2027.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Scope and Non-Goals . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Trust Model . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. The Bounded Capability Receipt . . . . . . . . . . . . . . . 5
4.1. Required Fields . . . . . . . . . . . . . . . . . . . . . 6
4.2. Signature Input and Receipt Digest . . . . . . . . . . . 8
4.3. Receipt Verification . . . . . . . . . . . . . . . . . . 8
5. Issuance Authorization . . . . . . . . . . . . . . . . . . . 9
6. Per-Action Human Authorization Composition . . . . . . . . . 9
7. Action Scope . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Holder Proof and Threshold Custody . . . . . . . . . . . . . 10
9. Registration . . . . . . . . . . . . . . . . . . . . . . . . 11
10. Reserve, Execute, and Commit . . . . . . . . . . . . . . . . 11
10.1. Reserve . . . . . . . . . . . . . . . . . . . . . . . . 11
10.2. Effect Boundary . . . . . . . . . . . . . . . . . . . . 12
10.3. Commit . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.4. Crash Recovery and Reconciliation . . . . . . . . . . . 13
11. Executor and State-Domain Binding . . . . . . . . . . . . . . 13
12. Narrowing Delegation . . . . . . . . . . . . . . . . . . . . 13
12.1. Revocation Inheritance Across Delegation Lineage . . . . 14
13. Evidence and Decision Vocabulary . . . . . . . . . . . . . . 15
14. Failure Codes . . . . . . . . . . . . . . . . . . . . . . . . 16
15. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 17
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16. Relationship to Other Work . . . . . . . . . . . . . . . . . 18
17. Security Considerations . . . . . . . . . . . . . . . . . . . 19
18. Privacy Considerations . . . . . . . . . . . . . . . . . . . 21
19. Implementation Status . . . . . . . . . . . . . . . . . . . . 21
20. Changes Since -02 . . . . . . . . . . . . . . . . . . . . . . 23
21. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
22. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
22.1. Normative References . . . . . . . . . . . . . . . . . . 24
22.2. Informative References . . . . . . . . . . . . . . . . . 24
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
A single-action authorization receipt is intentionally narrow: it
records approval of one exact action and can be accepted at most once
within its atomic consumption domain. Some agent deployments also
need a different primitive. For example, an operator may authorize
an agent to purchase a bounded class of supplies, subject to an
aggregate monetary ceiling and an expiry, without asking a human to
approve each conforming purchase.
That primitive has two inseparable parts:
1. a signed capability receipt that states the immutable authority
boundary; and
2. a shared, durable state machine that serializes reservations and
committed consumption across retries, processes, replicas, and
restarts.
The signed object without the state machine is replayable budget
metadata. The state machine without a signed, scoped grant has no
portable statement of authority. This document specifies their
composition.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
BCP 14 is indexed by the RFC Editor at [BCP14].
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1.2. Scope and Non-Goals
This document defines issuance binding, action-scope evaluation,
budget accounting, holder proof, durable reservation and commitment,
and narrowing delegation. It does not define user authentication,
human-approval presentation, general policy syntax, payment clearing,
settlement, currency conversion, revocation distribution, or the
external effect adapter.
A capability receipt is machine authority evidence. It is not,
merely by being signed, evidence that a human reviewed each later
action. Deployments that require per-action human authorization
continue to require a per-action authorization artifact.
When a capability may be exercised by more than one executor, every
executor MUST use the same relying-party-pinned authoritative atomic
state domain. A deployment that cannot enforce that binding MUST
restrict the capability to one executor or state only a per-executor
budget guarantee.
2. Terminology
Issuance authorization: An independently verified authorization
artifact for the exact act of creating a bounded capability.
Capability receipt: The signed immutable grant defined by this
document.
Capability issuer: The principal whose pinned key signs a capability
receipt.
Holder proof: Proof that the requester controls the secret or key
named by the capability receipt. Holder proof is not proof that a
requested action is in scope.
Scope verifier: A verifier for a named scope profile, selected and
configured by the relying party.
Capability store: The authoritative shared transactional state for
registration, reservation, and committed consumption.
State domain: The relying-party-pinned atomic store and trust
configuration to which every authority-bearing participant for a
capability lineage is bound. A state-domain identifier is
deployment context, not portable proof of global uniqueness.
Operation ID: A globally unique identifier for one attempted
capability-funded operation within a capability-store domain.
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Reservation token: An unguessable owner-fencing value returned by a
successful reservation and required for its commitment.
Effect boundary: The point after which an external effect may have
occurred and therefore budget cannot safely be restored merely
because the caller did not receive a successful response.
Indeterminate outcome: An operation for which the executor cannot
prove that no effect occurred and cannot prove a successful
expected effect.
3. Trust Model
The relying party selects capability-issuer keys, accepted issuance
authorization profiles, scope profiles, state-store domain, and local
authorization policy. A key embedded in a presented capability
receipt MUST NOT, by itself, become a trust anchor. An empty trust
configuration MUST fail closed.
The capability store is trusted to serialize state transitions and
retain committed operation records. The effect adapter is trusted to
place the effect boundary correctly and to report outcomes honestly.
This protocol makes those trust dependencies explicit; it does not
remove them.
All capability-store participants that can authorize a capability or
allocate, register, reserve, commit, reconcile, suspend, revoke, or
report any ancestor or descendant drawing on that capability's
authority MUST use one shared authoritative atomic state domain.
Independent stores cannot prevent each other from accepting or
reallocating the same remaining authority. Conservation claims in
this document apply only inside that one domain.
A deployment may have multiple executor instances, settlement
adapters, or process replicas. If they can exercise the same
capability, each MUST resolve the same state domain before admission
and use that domain for the budget transition. An executor's local
record of prior spending is not an authoritative aggregate record.
If the deployment cannot make the shared-domain guarantee, it MUST
either name exactly one executor in the applicable scope or describe
the limit as per-executor and MUST NOT claim aggregate conservation
across executors.
4. The Bounded Capability Receipt
The receipt is a JSON object serialized using the JSON
Canonicalization Scheme (JCS) [RFC8785] before signing. The
following is illustrative:
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{
"@version": "EP-BOUNDED-CAPABILITY-v1",
"capability": {
"capability_id": "cap_01J...",
"issuer": "https://operator.example",
"subject": "agent:procurement-7",
"authorization": {
"receipt_id": "rcpt_01J...",
"receipt_digest": "sha256:4c..."
},
"scope": {
"profile": "urn:emilia:scope:caid-set-v1",
"value": {
"caids": ["caid1:sha256:..."]
},
"digest": "sha256:8a..."
},
"budget": {
"amount": 250000,
"unit": "iso4217:USD",
"scale": 2
},
"holder": {
"method": "sha-256-preimage",
"commitment": "sha256:91..."
},
"threshold": {"m": 2, "n": 3},
"revocation_mode": "cascade",
"parent": null,
"not_before": "2026-07-18T20:00:00Z",
"expires_at": "2026-07-19T20:00:00Z"
},
"capability_signature": {
"algorithm": "Ed25519",
"public_key": "base64url...",
"value": "base64url..."
}
}
4.1. Required Fields
@version: EP-BOUNDED-CAPABILITY-v1.
capability_id: A globally unique, opaque identifier. Uniqueness is
not used as a substitute for cryptographic binding.
issuer: The issuer identifier used to select a relying-party-pinned
verification key.
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subject: The intended holder or workload identifier. This
identifier does not replace holder proof or live workload
authentication.
authorization: The identifier and SHA-256 digest of the complete
issuance authorization artifact. The digest MUST cover the exact
bytes accepted by that artifact's native verifier.
scope: A named scope profile, its value, and the SHA-256 digest of
the JCS serialization of profile and value.
budget: A non-negative integer amount no greater than
9007199254740991, an explicit unit, and a decimal scale from 0
through 18. For iso4217:USD with scale 2, an amount of 250000
denotes USD 2500.00. Implementations MUST NOT infer a scale from
display conventions.
holder: A recognized holder-proof method and commitment.
threshold: Integers m and n satisfying 1 <= m <= n <= 255. This
field describes custody of the holder credential; it does not
assert approval by distinct humans.
revocation_mode: Exactly direct or cascade. A direct revocation
affects the named capability but does not withdraw authority
already transferred to a registered child. A cascade revocation
also blocks new authority claims by every descendant. The value
is signed and MUST NOT be inferred from the issuer, holder,
lineage depth, or a presenter-selected default. A missing or
unknown value MUST be rejected.
parent: null for a root capability. For a child capability, an
object containing the parent capability ID, the digest of the
complete signed parent receipt, and the identifier of an
authenticated parent delegation operation. That operation MUST
bind the child receipt digest and the delegated amount, unit,
scale, scope, validity interval, and revocation mode. A parent
identifier without digest-bound parent and delegation evidence is
insufficient.
not_before and expires_at: UTC timestamps in Internet Date/Time
format [RFC3339] using the canonical string form selected by the
deployment profile. Expiry is exclusive. Numeric epochs,
implementation-specific date strings, and values that do not
round-trip to the canonical form MUST be rejected.
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4.2. Signature Input and Receipt Digest
The issuer signature input is the JCS serialization of the object
containing exactly @version and capability. The signature algorithm
for this version is Ed25519 [RFC8032]. The receipt digest is:
SHA-256(JCS({
"@version": receipt["@version"],
"capability": receipt.capability,
"capability_signature": receipt.capability_signature
}))
The issuance authorization is bound by both its identifier and
digest. Binding only a caller-selected receipt identifier is
insufficient because two different artifacts can carry the same
identifier.
4.3. Receipt Verification
A verifier MUST perform all of the following and fail closed on any
error:
1. apply bounded parsing and reject duplicate JSON member names,
unknown critical versions, malformed encodings, and out-of-range
values;
2. select the issuer key from relying-party configuration, not from
the presented object alone;
3. verify the issuer signature over the exact signature input;
4. natively verify the issuance authorization under its own pinned
trust inputs and compare both receipt identifier and digest;
5. verify that the authorized action is issuance of this exact
capability object, or of a digest that commits to it;
6. verify the scope digest and require a recognized, relying-party-
enabled scope profile;
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7. verify the validity interval and, for a child, resolve and verify
the digest-bound parent lineage to a root capability or a locally
trusted, previously validated lineage checkpoint. Reject an
unresolved, truncated, reordered, or substituted link; a repeated
capability ID or receipt digest; the leaf appearing among its
ancestors; or a path exceeding deployment policy. At every hop,
verify that the child amount does not exceed the authenticated
delegated amount, unit and scale are unchanged, validity is
contained by the parent, and scope is no broader than the parent
scope; and
8. compute the capability receipt digest used for store
registration.
Receipt verification returns VERIFIED. It does not return
AUTHORIZED, prove remaining budget, or prove that a proposed
operation is in scope.
5. Issuance Authorization
The issuance authorization MUST authorize the act of creating the
capability, including the immutable digest of its subject, scope,
budget, holder commitment, revocation mode, parent, and validity
interval. It MUST NOT be reused as though it were a per-operation
authorization for later spends.
When the issuance artifact is an EMILIA Authorization Receipt, its
exact action is capability issuance and its one-time consumption
occurs when the capability is registered. Later capability-funded
operations are governed by this document's scope and durable state
protocol.
6. Per-Action Human Authorization Composition
A deployment may require a separately authenticated human
authorization for an individual capability-funded exercise. That
artifact MUST bind the exact canonical exercise-action digest used by
reservation and effect admission. If material terms are not
committed by that digest, the artifact MUST bind those terms
independently.
A capability signature, holder proof, threshold custody, or key
protected inside a workload is not evidence that a human reviewed the
later exercise. The capability verifier and human-authorization
verifier may remain separate. A relying-party composition policy may
require both results for the same action digest, but the two
verifiers MUST NOT treat the other's evidence as a trust anchor.
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This composition does not make human authorization part of every
bounded capability. A deployment that permits conforming exercises
without a per-action human artifact MUST state that the issuance
authorization established the bounded class rather than a human
reviewing each later action.
7. Action Scope
Before reserving budget, the enforcement point MUST compute the
proposed material action independently of presenter-supplied labels
and invoke the pinned verifier for scope.profile. A missing profile,
unknown action representation, lossy mapping, or indeterminate
comparison MUST refuse.
The mandatory-to-implement urn:emilia:scope:caid-set-v1 profile
contains a non-empty, duplicate-free array of Canonical Action
IDentifiers. It matches only exact identifier equality. Possession
of a CAID authorizes nothing outside this verified capability
context.
Application profiles can define closed constraints over typed action
fields. Such a profile MUST specify canonicalization, comparison,
unknown-field handling, numerical units, and an algorithm for proving
that a delegated scope is no broader than its parent. Profiles that
cannot decide either action membership or attenuation MUST return
INDETERMINATE.
8. Holder Proof and Threshold Custody
The mandatory-to-implement holder method is sha-256-preimage. The
holder presents exactly 32 bytes over a confidential, integrity-
protected channel, and the enforcement point compares SHA-
256(preimage) with the signed commitment using a constant-time
comparison. The preimage MUST NOT be logged, stored with the
receipt, or included in portable evidence.
The preimage may be divided using a threshold secret-sharing scheme
before presentation. Share format, participant authentication,
confidentiality, recovery, and distribution are outside this
document. Reconstructing m shares proves control of the holder
secret; it does not prove that m distinct humans reviewed or approved
the action. Human multi-party approval requires a protocol such as
[EP-QUORUM].
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9. Registration
After receipt verification and one-time consumption of the issuance
authorization, the issuer registers the capability in the
authoritative store. Registration MUST atomically create immutable
fields for capability ID, receipt digest, unit, scale, total budget,
scope digest, validity interval, revocation mode, and parent. It
MUST initialize consumed and reserved to zero.
A second registration of the same capability ID MUST succeed only
when every immutable field and receipt digest is identical. Any
mismatch is a collision and MUST refuse.
Mutable counters in a presented receipt are not authoritative.
Remaining budget is computed only from the shared store:
remaining = total - consumed - reserved
The authoritative state MUST maintain the invariant reserved +
consumed <= total for every capability. For a parent capability,
each registered child allocation MUST be covered by one or more
distinct terminal delegated operation committed against that parent
before child registration. The aggregate amount of registered direct
children MUST NOT exceed the amount committed by those distinct
parent delegation operations, and each operation identifier MUST NOT
fund more than one child receipt digest.
10. Reserve, Execute, and Commit
10.1. Reserve
A reservation request contains the capability ID, capability receipt
digest, globally unique operation ID, the immutable canonical
exercise-action digest and CAID where used, positive integer amount,
unit, scale, and authenticated holder proof. The same immutable
action snapshot MUST be used for scope evaluation, authorization,
reservation accounting, and the effect callback; a mutable caller
object MUST NOT cross those boundaries. In one serializable
transaction, or while holding an equivalent row lock, the store MUST:
1. load the registered capability and compare the receipt digest;
2. resolve the complete authority-bearing ancestor lineage in the
same authoritative state domain and reject unavailable,
inconsistent, or truncated state;
3. reject an unknown, not-yet-valid, expired, or revoked capability;
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4. reject when any revoked ancestor has revocation_mode equal to
cascade;
5. reject a unit or scale mismatch;
6. reject any already-seen operation ID, regardless of its previous
capability or outcome;
7. verify that the amount is positive and no greater than total -
consumed - reserved;
8. increase reserved by the amount; and
9. create an operation in state reserved with an unguessable
reservation token, exercise-action digest, and amount, and return
that token only to the owner.
Scope evaluation and local authorization policy MUST succeed before
the effect adapter is entered. Deployments SHOULD perform them
before reserving to reduce abandoned reservations.
10.2. Effect Boundary
The enforcement point enters the effect adapter only after a
successful reservation. It MUST NOT expose an alternate path to the
same effect that bypasses capability enforcement when the action
requires this profile.
10.3. Commit
A commit request contains the operation ID, reservation token, and
one of three outcomes: executed, indeterminate, or delegated. In one
atomic transaction, the store MUST verify ownership and reserved
state, decrease reserved, increase consumed by the same amount, and
make the operation terminal.
A repeated commit, wrong reservation token, or commit against a non-
reserved operation MUST refuse. A caller timeout does not justify
retrying with a new operation ID; the caller MUST query the original
operation or reconcile it.
If the executor cannot prove that the effect boundary was not
crossed, it MUST commit indeterminate and charge the budget.
Availability loss is safer than allowing the same authority to be
spent again after an unobserved external effect.
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10.4. Crash Recovery and Reconciliation
Reservations survive process and replica failure. A deployment MUST
define a reconciler for non-terminal operations. The reconciler may
commit executed only with authenticated effect evidence. It may
restore budget only when it can prove the effect boundary was never
crossed. In every other case it MUST commit indeterminate.
11. Executor and State-Domain Binding
The state domain is a relying-party trust input. A portable
capability receipt need not embed a globally meaningful domain
identifier, but the registration and operation records SHOULD
identify the domain and executor participant used for each admission
so that a relying party can detect an unsupported state fork.
When multiple executors are authorized to present one capability, the
store MUST serialize their reservations and commitments in one
domain. Merely replicating a signed receipt, copying a remaining
counter, or exchanging eventual spending logs does not satisfy this
requirement. A deployment that uses independent stores may still use
signed receipts, but it MUST NOT describe the resulting behavior as
one aggregate budget.
A scope that names one executor is a valid narrower deployment
choice. The applicable scope profile MUST define how that executor
participant is identified and compared at admission. This removes
the cross-executor guarantee requirement; it does not turn a local
record into a global budget or provide offline double-spend
prevention.
12. Narrowing Delegation
A child capability MUST NOT outlive its parent, exceed the
authenticated amount delegated from the parent, change unit or scale,
or broaden the parent's scope. Its delegation chain MUST be bounded
by deployment policy and MUST include the parent receipt digest.
Before registering a child, the verifier MUST validate complete
digest-linked ancestry to a trusted root within the configured depth
bound, or enforce equivalent authenticated parent-edge constraints in
one authoritative store. The verified lineage MUST form a simple
path. The verifier MUST reject a repeated capability identifier or
receipt digest, a missing or inconsistent parent, a substituted or
reordered edge, or a chain whose trusted root cannot be established.
A cycle, truncated lineage, or over-depth chain MUST fail closed.
Per-receipt identifier uniqueness or a self-declared list of
ancestors does not establish graph-wide acyclicity. An
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implementation MUST NOT infer acyclicity merely because its ordinary
issuance path constructs children from known parents; verification
applies the same check to imported and reconstructed chains.
Creating a child is itself a parent-funded operation. Before
registering the child, the issuer MUST reserve the delegated amount
from the parent and MUST commit that exact reservation once with
outcome delegated. The authenticated terminal operation record MUST
bind the exact child receipt digest, delegated amount, unit, scale,
scope, validity interval, and revocation mode before the child is
registered; otherwise a valid parent spend could be paired with a
different child. A shared store SHOULD perform parent commitment and
child registration atomically. If that is impossible and child
registration fails after the parent is committed, the parent budget
remains consumed and the orphaned delegation MUST be retained for
reconciliation. The system MUST NOT silently refund it.
12.1. Revocation Inheritance Across Delegation Lineage
Delegation transfers bounded authority rather than leaving every
child as a live reference to its parent. Direct revocation of an
ancestor therefore does not, by itself, determine whether authority
already transferred to registered descendants survives. The signed
revocation_mode field makes that choice explicit.
When a capability's revocation_mode is direct, revoking that
capability MUST prevent new reservations and child allocations funded
by that capability. It MUST NOT, solely because of that revocation,
invalidate a child registered before the revocation committed. The
child remains subject to its own validity, scope, budget, direct
revocation, and any cascade-mode ancestor.
When a capability's revocation_mode is cascade, revoking that
capability MUST prevent every descendant from making a new
reservation or funding a new child. The enforcement point MUST
establish the current revocation state of every authority-bearing
cascade-mode ancestor in the same authoritative atomic state domain
used for the descendant reservation. A cached status value or
eventually consistent notification does not establish immediate
cascade revocation.
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The ancestor revocation transition and a descendant reservation MUST
be serialized in that state domain. If revocation commits first, the
descendant request MUST refuse. If the reservation commits first,
the revocation is late for that operation and prevents later
authority claims; it MUST NOT retroactively release the reservation,
relabel an effect, or authorize a retry. Any operation whose effect
outcome is unresolved remains subject to the reconciliation rules in
Section 10.4.
If complete current ancestor state cannot be established before
reservation, the request MUST refuse without entering the effect
adapter. This is a pre-effect status failure, not evidence that an
external effect is indeterminate. A deployment using separate state
domains or freshness-bounded status distribution MUST NOT claim
immediate cascade revocation across those domains.
Neither mode grants a grace period after revocation. Continued or
wind-down authority MUST be established by a separate authorization
with its own exact scope, budget, holder, and validity interval; it
MUST NOT be inferred from an in-flight delegation. This document
defines the consequence of an authenticated revocation within one
state domain. It does not define who is entitled to revoke, how
revocation is distributed, or how independently operated domains
transfer exclusive admission ownership.
13. Evidence and Decision Vocabulary
A capability receipt can be VERIFIED. A scope verifier can return
the profile-local result IN_SCOPE, OUT_OF_SCOPE, or INDETERMINATE.
This containment result is not the architecture's MATCH state, which
is reserved for correlation of exact material actions. A relying-
party evidence requirement can be SATISFIED. Successful local policy
and an atomic reservation together can establish AUTHORIZED for one
exercise. Separately authenticated effect evidence can establish
EXECUTED. No earlier state implies a later one.
Portable evidence for a capability-funded operation SHOULD include
the capability receipt digest, issuance authorization digest, scope
profile and digest, operation ID, the exact exercise action digest
and CAID where used, amount, unit, scale, reservation timestamp,
terminal outcome, and any authenticated effect statement. The
integrity-protected operation record MUST bind the exercise action
and the capability receipt digest. Holder secrets and reservation
tokens MUST NOT be included.
An Authorization Evidence Chain may carry that operation record as a
native component whose verifier recursively verifies the capability
receipt, issuance authorization, scope result, and operation-record
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integrity. The static grant is not a same-action component for every
later exercise. Evidence satisfaction does not query or reserve
current budget; that state transition remains at the enforcement
point.
14. Failure Codes
Implementations SHOULD expose stable, non-authorizing failure codes
including:
* capability_untrusted_issuer
* capability_authorization_mismatch
* capability_scope_mismatch
* capability_scope_indeterminate
* capability_holder_proof_invalid
* capability_not_active
* capability_expired
* capability_revoked
* capability_revocation_mode_invalid
* capability_ancestor_revoked
* capability_ancestor_status_unavailable
* capability_budget_exceeded
* capability_delegation_lineage_invalid
* capability_delegation_not_narrowed
* capability_operation_replay
* capability_reservation_owner_mismatch
* capability_commit_indeterminate
A failure code is diagnostic output, not an authorization artifact.
Responses SHOULD avoid revealing secret, budget, or scope details to
an unauthenticated caller.
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15. Conformance
A conforming implementation MUST pass positive and adversarial
vectors for receipt canonicalization and signature, authorization-
digest substitution, untrusted issuer, unknown scope profile, action
mismatch, holder-proof failure, duplicate registration, concurrent
overspend, operation replay, wrong reservation token, double commit,
expiry, a cycle spread across separately signed receipts, repeated
ancestors, leaf-as-ancestor, missing or truncated lineage, reordered
or substituted parent links, parent-receipt and delegation-operation
substitution, a single-hop child exceeding the authenticated
delegated amount, unit or scale changes, scope or validity widening
at every hop, over-depth chains, parent over-allocation, crash
recovery, and indeterminate-effect charging.
The conformance set MUST exercise revocation inheritance over a root,
child, and grandchild. It MUST show that direct-mode revocation
leaves previously registered descendant authority independently
usable, while cascade-mode revocation refuses every later descendant
reservation and child allocation. It MUST reject a missing or
unknown revocation_mode, refuse when required ancestor state is
unavailable, and cover a race between ancestor revocation and
descendant reservation in which exactly one transition commits first.
A reservation that commits first remains owned and reconcilable; a
revocation that commits first prevents the reservation.
The conformance set MUST also include multiple executor participants
sharing one domain, an independent-store state fork, and a scope
restricted to one executor; only the shared-domain case may claim one
aggregate budget.
The parent-over-allocation case MUST include at least three sibling
child-creation attempts whose individually valid amounts collectively
exceed the parent's available balance, with concurrent reservation
ordering chosen by the implementation. At most a balance-preserving
subset may commit. The case MUST also cover one operation identifier
presented for two different child receipt digests and an orphaned
child-registration failure after parent commitment. The former
refuses as operation replay; the latter leaves the committed parent
amount consumed pending reconciliation.
A wire-format implementation that does not implement one shared
atomic store is a receipt verifier, not a conforming spend-control
implementation. A store implementation that accepts a capability
without pinned issuer verification, issuance authorization, and scope
matching is not conforming.
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16. Relationship to Other Work
Rich Authorization Requests [RFC9396] carries fine-grained
authorization details but deliberately leaves comparison semantics
for arbitrary detail types to their specifications. This document
defines an executor-side durable spend state machine and requires a
named closed scope profile.
OAuth Transaction Tokens [TXN-TOKENS] propagate transaction-specific
authorization context through a call chain. Bounded Capability
Receipts instead address an aggregate budget shared across multiple
operations and the reserve/commit boundary at the executor. A
deployment can use both.
The Delegation Receipt Protocol for AI Agent Authorization [DRP]
records delegation and narrowing. This document requires narrowing
for child capabilities and additionally accounts delegated budget as
a terminal parent spend.
Attenuating Authorization Tokens for Agentic Delegation Chains
[ATTENUATING] describes constrained, attenuable agent tokens. This
document's distinct contribution is not the existence of constrained
tokens; it is the composition of a signed grant with shared
reservation ownership, committed budget accounting, and conservative
treatment of indeterminate external effects.
The Agent Identity Protocol [AIP] defines per-token budget ceilings
and explicitly assigns cumulative spending enforcement to the
orchestration runtime. A bounded capability budget is instead a
balance-valued authority in one authoritative store: reservation and
consumption reduce the amount available to every sibling allocation
in that domain.
PEDIGREE [PEDIGREE] defines cryptographic delegation, mandate
narrowing, and an operator-controlled ceiling. This document
preserves that identity and policy role and addresses the adjacent
runtime question of how one parent balance funds multiple children
without multiplying aggregate authority.
The Credential Broker for Agents [CB4A] defines proxy and short-
lived-token delivery patterns that keep long-lived provider
credentials away from agents. A deployment can use such a broker as
the credential-owning effect adapter after this protocol grants one
valid reservation; this document does not duplicate credential
brokering.
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Condition-Bounded Credentials [CBC] binds workload-key use to live,
verifier-appraised conditions. That property composes with holder
proof and provider entry, especially for stable attestable workloads.
It does not replace aggregate balance accounting, and this document
does not extend its hardware assumptions to hardware-less or cross-
domain swarms.
The affine Token Budgets work [TOKEN-BUDGETS] studies LLM cost
overruns and uses Rust ownership to prevent cloning and use-after-
delegation in one process. It is adjacent prior art. This document
instead binds human- or policy-authorized consequential authority,
exact exercise actions, durable provider-entry reservations, and
conservative post-entry uncertainty across a transactional runtime.
It does not claim that balance-valued budgets or affine ownership
were invented here.
The Attested Payment Authorization for Autonomous Agents [HAWKINS]
binds an attested payment key and endorsed software identity to a
payment authorization scope and requires verification before
settlement. It is adjacent and complementary work: this document
does not define hardware attestation or transparency registration,
while that document does not define shared-domain aggregate
conservation, durable reserve-execute-commit, parent-funded narrowing
delegation, or indeterminate-effect charging. A deployment can
compose the two by binding their decisions to the same exact
exercise-action digest without making either verifier consume the
other's evidence as a trust anchor.
17. Security Considerations
*Identifier substitution.* Capability signatures bind the full
issuance authorization digest, not only an identifier. Scope, budget
units, parent, holder commitment, and validity are all inside the
issuer signature.
*State forks.* Two stores accepting the same capability lineage can
each spend or delegate its full budget. Global offline or cross-
domain double-spend prevention is therefore not provided.
Deployments that cannot name one authoritative atomic state domain
for a capability and every authority-bearing ancestor and descendant
MUST NOT claim aggregate sibling conservation or an enforced
aggregate budget.
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*Executor federation.* A multi-rail or multi-process deployment does
not, by itself, establish a shared budget. Every executor that can
admit an exercise must be bound to the same state domain, or the
scope must be restricted to one executor and the claim must be stated
as per-executor. Eventual reconciliation after independent
admissions cannot retroactively prevent overspend.
*Crash ambiguity.* Restoring budget after a timeout can authorize
duplicate external effects. Once the effect boundary may have been
crossed, uncertainty is charged as indeterminate.
*Bearer and share theft.* A raw holder secret or enough
unauthenticated shares can authorize possession. Secret shares
require confidential distribution, authenticated participants,
compromise response, and rate limiting. Threshold custody is not
human quorum.
*Revocation.* Expiry and exhausted budget are not revocation. A
deployment that requires early invalidation MUST consult a separately
authenticated revocation or status source before reservation and
define its freshness policy. Revocation inheritance is not inferred
from lineage alone: the signed mode determines whether already
transferred descendant authority survives. An immediate cascade
claim requires the ancestor revocation transition and descendant
reservation to be serialized in the same authoritative atomic state
domain. Notification or eventual cache refresh cannot supply that
guarantee.
*Units and arithmetic.* All accounting uses integers with signed unit
and scale. Floating-point arithmetic, implicit currency conversion,
and caller-selected rounding MUST NOT occur in the authoritative
budget path.
*Database authority.* The capability tables contain authorization
state. Deployments MUST restrict writes to the enforcement service,
use least-privilege credentials, protect backups, and audit
administrative changes.
*Delegation lineage.* Local uniqueness checks over one presented
receipt do not establish graph-wide acyclicity or complete ancestry.
Separately presented receipts can omit links, substitute a parent
operation, or form a cycle unless each parent edge is authenticated
and resolved by digest, or an authoritative store enforces equivalent
edge constraints. Implementations MUST fail closed on incomplete,
cyclic, substituted, or non-narrowing lineage. Verifiers apply the
complete traversal and refusal rules in Section 12 to imported chains
and chains reconstructed from storage.
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*Semantic limits.* A valid capability does not prove that an action
is safe, lawful, beneficial, or correctly executed. Local policy and
domain controls remain necessary.
*Cryptographic scope.* This version uses SHA-256 and Ed25519. It
does not provide a post-quantum signature profile or a zero-knowledge
receipt. Algorithm agility and long-term preservation are separate
concerns.
18. Privacy Considerations
Capability receipts and operation records can reveal spending limits,
organizational roles, intended action classes, counterparties, and
timing. Profiles SHOULD minimize identifiers, separate portable
evidence from operational secrets, and define retention and access
controls. Hashing a low-entropy scope or identifier does not make it
confidential.
19. Implementation Status
The Apache-2.0 TypeScript reference implementation includes a signed
pre-standard capability envelope, holder-secret commitment, optional
threshold secret reconstruction, and a durable PostgreSQL reservation
and commitment store. Its issuer-controlled delegation API, when
used with one shared capability store, reserves and commits a child
amount from the immediate parent before registering the child. The
store has adversarial tests for overspend, replay, ownership fencing,
expiry, terminal commitment, concurrent N-sibling aggregate over-
allocation, one operation identifier paired with different child
digests, orphaned registration after parent commitment, and an
explicit two-store state-fork counterexample. These are same-team
implementation and regression results, not independent implementation
or production deployment evidence.
The prototype wire format predates this document and does not yet
implement all mandatory fields in this version, including full
issuance authorization digest binding, an explicit action-scope
profile, and explicit budget unit scale, digest-linked parent
lineage, authenticated parent-delegation binding, not_before, and
complete ingest-time cycle validation. It is therefore
implementation experience, not a claim of conformance. There is no
independent implementation, interoperability event, production
transaction history, post-quantum profile, or zero-knowledge
implementation. The executor-domain participant binding and per-
action human-authorization composition added in -02 are protocol
requirements and composition rules. The reference execution path now
implements those two integrations: an aggregate budget claim requires
an exact match to a relying-party-pinned atomic state-domain digest;
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a mismatch may fall back only to an explicitly pinned single
executor; and a required per-action human authorization must pass a
native verifier under relying-party pins and bind the exact exercise-
action digest. Calls without an executor-domain binding are labeled
local_store_only and do not claim aggregate enforcement. A
configured state-domain digest is a deployment trust binding; the
code cannot by itself prove that two processes connect to the same
physical database.
The reference implementation now signs and requires revocation_mode,
records each capability's immediate parent, and implements direct and
cascade revocation in both the in-memory test store and PostgreSQL
store. A descendant reservation resolves the complete registered
ancestor lineage. The PostgreSQL path locks those state rows in the
reservation transaction, so an ancestor revocation that commits first
refuses the reservation, while a reservation that commits first
remains owned and reconcilable. Missing, malformed, or migration-
incomplete ancestor state refuses before provider entry. The tracked
migration quarantines legacy rows without an explicit mode rather
than inferring direct or cascade. Regression cases cover the signed
closed field, direct descendant survival, cascade refusal,
unavailable ancestor state, child allocation after revocation, and
both orderings of the revocation race. This is same-team
implementation evidence inside one authoritative atomic state domain;
it is not independent interoperability, revocation distribution, or
cross-domain cascade enforcement.
The reference implementation does reject repeated delegation
identifiers, repeated parent capability identifiers, a leaf named as
its own parent, and increasing amounts within the delegation chain
presented at mint or verification time. Those checks provide local
simple-path and monotonic amount enforcement. They do not discover
omitted parents or establish the digest-linked, graph-wide lineage
required by Section 12, so they do not close the remaining
conformance gap.
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The public repository contains two CI-gated bounded TLA+ models
relevant here. The capability-accounting model covers registration,
reservation, commitment, delegation, replay refusal, parent-funded
child registration, and aggregate sibling conservation. A separate
-03 revocation-inheritance model covers every direct/cascade
assignment over a root, child, and grandchild; complete ancestor-
state availability; future child allocation; and both serialized
orderings of revocation and reservation. Exact state and obligation
counts are emitted by governed proof-status artifacts. These are
bounded results about the models, not refinement proofs of the
TypeScript, SQL, transaction adapter, cryptography, lineage
verification, or complete protocol defined here. Arbitrary
implementation inputs still require the runtime traversal and refusal
rules in Section 12.
The main branch also runs a fixed-seed adversarial harness in per-
push CI over the actual JavaScript in-memory capability and
consumption stores. It includes a true-concurrency Promise.all race
target and a deliberately non-atomic comparison store that
demonstrates the race detector can expose over-commitment.
Additional targets exercise accounting and ownership invariants at
whole-method boundaries. This is regression evidence for those in-
process stores, not complete protocol conformance: it does not fuzz
the PostgreSQL capability transaction path, the atomic handshake RPC,
replica or connection failures, and no deeper nightly sweep is
scheduled.
20. Changes Since -02
* Added a signed revocation_mode that distinguishes direct
revocation from cascade revocation of future descendant authority
claims.
* Required ancestor revocation and descendant reservation to
serialize in one authoritative atomic state domain, with explicit
race and unavailable-status behavior.
* Separated revocation from in-flight reconciliation and from any
separately authorized wind-down authority, and added corresponding
failure codes and conformance cases.
21. IANA Considerations
This document has no IANA actions. A future revision may request a
media type and registries for receipt versions, scope profiles,
holder methods, and failure codes after implementation experience
stabilizes the protocol.
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22. References
22.1. Normative References
[BCP14] Internet Engineering Task Force, "Key Words for Use in
RFCs to Indicate Requirement Levels", BCP 14, 2017,
<https://www.rfc-editor.org/info/bcp14>.
[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>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<https://www.rfc-editor.org/info/rfc3339>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>.
[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>.
[RFC8785] Rundgren, A., Jordan, B., and S. Erdtman, "JSON
Canonicalization Scheme (JCS)", RFC 8785,
DOI 10.17487/RFC8785, June 2020,
<https://www.rfc-editor.org/info/rfc8785>.
22.2. Informative References
[AIP] Prakash, S., "Agent Identity Protocol (AIP): Verifiable
Delegation for AI Agent Systems", 2026,
<https://datatracker.ietf.org/doc/draft-prakash-aip/>.
[ATTENUATING]
Aimable, N., "Attenuating Authorization Tokens for Agentic
Delegation Chains", 2026,
<https://datatracker.ietf.org/doc/draft-niyikiza-oauth-
attenuating-agent-tokens/>.
[CB4A] Hartman, K. G., "Credential Broker for Agents (CB4A)",
2026, <https://datatracker.ietf.org/doc/draft-hartman-
credential-broker-4-agents/>.
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[CBC] Huu, T. N., Nikitin, S., and J. O'Leary, "Condition-
Bounded Credentials for Workload and Agent Identity: Non-
Exfiltratable Keys and Validity by Presence", 2026,
<https://datatracker.ietf.org/doc/draft-winmagic-wimse-
condition-bounded-credentials/>.
[DRP] Nelson, R., "Delegation Receipt Protocol for AI Agent
Authorization", 2026, <https://datatracker.ietf.org/doc/
draft-nelson-agent-delegation-receipts/>.
[EP-QUORUM]
Schrock, I., "Multi-Party Authorization (Quorum) for the
EMILIA Protocol", 2026, <https://datatracker.ietf.org/doc/
draft-schrock-ep-quorum/>.
[HAWKINS] Hawkins, W., "Attested Payment Authorization for
Autonomous Agents", Work in Progress, Internet-Draft,
draft-hawkins-scitt-attested-agent-payment-00, 2026,
<https://datatracker.ietf.org/doc/draft-hawkins-scitt-
attested-agent-payment/>.
[PEDIGREE] Rampalli, K., "PEDIGREE: Verifiable Delegation Identity
for Agentic AI Systems", 2026,
<https://datatracker.ietf.org/doc/draft-rampalli-
pedigree/>.
[RFC9396] Lodderstedt, T., Richer, J., and B. Campbell, "OAuth 2.0
Rich Authorization Requests", RFC 9396,
DOI 10.17487/RFC9396, May 2023,
<https://www.rfc-editor.org/info/rfc9396>.
[TOKEN-BUDGETS]
Khan, S., "Token Budgets: An Empirical Catalog of 63 LLM-
Agent Budget-Overrun Incidents, with an Affine-Typed Rust
Mitigation as a Case Study", arXiv 2606.04056, 2026,
<https://arxiv.org/abs/2606.04056>.
[TXN-TOKENS]
Tulshibagwale, A., Fletcher, G., and P. Kasselman,
"Transaction Tokens", 2026,
<https://datatracker.ietf.org/doc/draft-ietf-oauth-
transaction-tokens/>.
Author's Address
Iman Schrock
EMILIA Protocol, Inc.
United States of America
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Email: team@emiliaprotocol.ai
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