Internet DRAFT - draft-ietf-acme-star-delegation
draft-ietf-acme-star-delegation
ACME Y. Sheffer
Internet-Draft Intuit
Intended status: Standards Track D. López
Expires: 13 December 2021 A. Pastor Perales
Telefonica I+D
T. Fossati
ARM
11 June 2021
An ACME Profile for Generating Delegated Certificates
draft-ietf-acme-star-delegation-09
Abstract
This document defines a profile of the Automatic Certificate
Management Environment (ACME) protocol by which the holder of an
identifier (e.g., a domain name) can allow a third party to obtain an
X.509 certificate such that the certificate subject is the delegated
identifier while the certified public key corresponds to a private
key controlled by the third party. A primary use case is that of a
Content Delivery Network (CDN, the third party) terminating TLS
sessions on behalf of a content provider (the holder of a domain
name). The presented mechanism allows the holder of the identifier
to retain control over the delegation and revoke it at any time.
Importantly, this mechanism does not require any modification to the
deployed TLS clients and servers.
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/.
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 13 December 2021.
Sheffer, et al. Expires 13 December 2021 [Page 1]
Internet-Draft ACME Delegation June 2021
Copyright Notice
Copyright (c) 2021 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
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Conventions used in this document . . . . . . . . . . . . 5
2. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Preconditions . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Delegated Identity Profile . . . . . . . . . . . . . . . 8
2.3.1. Delegation Configuration . . . . . . . . . . . . . . 8
2.3.2. Order Object Transmitted from NDC to IdO and to ACME
Server (STAR) . . . . . . . . . . . . . . . . . . . . 11
2.3.3. Order Object Transmitted from NDC to IdO and to ACME
Server (non-STAR) . . . . . . . . . . . . . . . . . . 15
2.3.4. Capability Discovery . . . . . . . . . . . . . . . . 18
2.3.5. Negotiating an Unauthenticated GET . . . . . . . . . 19
2.3.6. Terminating the Delegation . . . . . . . . . . . . . 20
2.4. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . 21
3. CA Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 22
4. CSR Template . . . . . . . . . . . . . . . . . . . . . . . . 22
4.1. Template Syntax . . . . . . . . . . . . . . . . . . . . . 22
4.2. Example . . . . . . . . . . . . . . . . . . . . . . . . . 23
5. Further Use Cases . . . . . . . . . . . . . . . . . . . . . . 24
5.1. CDN Interconnection (CDNI) . . . . . . . . . . . . . . . 24
5.1.1. Multiple Parallel Delegates . . . . . . . . . . . . . 25
5.1.2. Chained Delegation . . . . . . . . . . . . . . . . . 25
5.2. Secure Telephone Identity Revisited (STIR) . . . . . . . 28
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
6.1. New Fields in the "meta" Object within a Directory
Object . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.2. New Fields in the Order Object . . . . . . . . . . . . . 30
6.3. New Fields in the Account Object . . . . . . . . . . . . 30
6.4. New Error Types . . . . . . . . . . . . . . . . . . . . . 30
6.5. CSR Template Extensions . . . . . . . . . . . . . . . . . 31
Sheffer, et al. Expires 13 December 2021 [Page 2]
Internet-Draft ACME Delegation June 2021
7. Security Considerations . . . . . . . . . . . . . . . . . . . 32
7.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 32
7.2. Delegation Security Goal . . . . . . . . . . . . . . . . 32
7.3. New ACME Channels . . . . . . . . . . . . . . . . . . . . 33
7.4. Restricting CDNs to the Delegation Mechanism . . . . . . 35
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.1. Normative References . . . . . . . . . . . . . . . . . . 36
9.2. Informative References . . . . . . . . . . . . . . . . . 37
Appendix A. Document History . . . . . . . . . . . . . . . . . . 38
A.1. draft-ietf-acme-star-delegation-09 . . . . . . . . . . . 38
A.2. draft-ietf-acme-star-delegation-08 . . . . . . . . . . . 39
A.3. draft-ietf-acme-star-delegation-07 . . . . . . . . . . . 39
A.4. draft-ietf-acme-star-delegation-06 . . . . . . . . . . . 39
A.5. draft-ietf-acme-star-delegation-05 . . . . . . . . . . . 39
A.6. draft-ietf-acme-star-delegation-04 . . . . . . . . . . . 39
A.7. draft-ietf-acme-star-delegation-03 . . . . . . . . . . . 40
A.8. draft-ietf-acme-star-delegation-02 . . . . . . . . . . . 40
A.9. draft-ietf-acme-star-delegation-01 . . . . . . . . . . . 40
A.10. draft-ietf-acme-star-delegation-00 . . . . . . . . . . . 40
A.11. draft-sheffer-acme-star-delegation-01 . . . . . . . . . . 40
A.12. draft-sheffer-acme-star-delegation-00 . . . . . . . . . . 40
Appendix B. CSR Template: CDDL . . . . . . . . . . . . . . . . . 40
Appendix C. CSR Template: JSON Schema . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47
1. Introduction
This document is related to [RFC8739], in that some important use
cases require both documents to be implemented. To avoid
duplication, we give here a bare-bones description of the motivation
for this solution. For more details, please refer to the
introductory sections of [RFC8739].
An Identifier Owner (IdO) has agreements in place with one or more
NDC (Name Delegation Consumer) to use and attest its identity.
In the primary use case the IdO is a content provider, and we
consider a Content Delivery Network (CDN) provider contracted to
serve the content over HTTPS. The CDN terminates the HTTPS
connection at one of its edge cache servers and needs to present its
clients (browsers, mobile apps, set-top-boxes) a certificate whose
name matches the domain name of the URL that is requested, i.e., that
of the IdO. Understandably, some IdOs may balk at sharing their
long-term private keys with another organization and, equally,
delegates would rather not have to handle other parties' long-term
secrets. Other relevant use cases are discussed in Section 5.
Sheffer, et al. Expires 13 December 2021 [Page 3]
Internet-Draft ACME Delegation June 2021
This document describes a profile of the ACME protocol [RFC8555] that
allows the NDC to request from the IdO, acting as a profiled ACME
server, a certificate for a delegated identity - i.e., one belonging
to the IdO. The IdO then uses the ACME protocol (with the extensions
described in [RFC8739]) to request issuance of a Short-Term,
Automatically Renewed (STAR) certificate for the same delegated
identity. The generated short-term certificate is automatically
renewed by the ACME Certification Authority (CA), periodically
fetched by the NDC and used to terminate HTTPS connections in lieu of
the IdO. The IdO can end the delegation at any time by simply
instructing the CA to stop the automatic renewal and letting the
certificate expire shortly thereafter.
While the primary use case we address is delegation of STAR
certificates, the mechanism proposed here accommodates also long-
lived certificates managed with the ACME protocol. The most
noticeable difference between long-lived and STAR certificates is the
way the termination of the delegation is managed. In the case of
long-lived certificates, the IdO uses the revokeCert URL exposed by
the CA and waits for the explicit revocation based on Certificate
Revocation List (CRL) and Online Certificate Status Protocol (OCSP)
to propagate to the relying parties.
In case the delegated identity is a domain name, this document also
provides a way for the NDC to inform the IdO about the CNAME mappings
that need to be installed in the IdO's DNS zone to enable the
aliasing of the delegated name, thus allowing the complete name
delegation workflow to be handled using a single interface.
We note that other standardization efforts address the problem of
certificate delegation for TLS connections, specifically
[I-D.ietf-tls-subcerts] and [I-D.mglt-lurk-tls13]. The former
extends the TLS certificate chain with a customer-owned signing
certificate; the latter separates the server's private key into a
dedicated, more secure component. Compared to these other
approaches, the current document does not require changes to the TLS
network stack of the client or the server, nor does it introduce
additional latency to the TLS connection.
1.1. Terminology
IdO Identifier Owner, the holder (current owner) of an identifier
(e.g., a domain name) that needs to be delegated. Depending on
the context, the term IdO may also be used to designate the
(profiled) ACME server deployed by the Identifier Owner or the
ACME client used by the Identifier Owner to interact with the CA.
NDC Name Delegation Consumer, the entity to which the domain name is
Sheffer, et al. Expires 13 December 2021 [Page 4]
Internet-Draft ACME Delegation June 2021
delegated for a limited time. This is a CDN in the primary use
case (in fact, readers may note the similarity of the two
acronyms). Depending on the context, the term NDC may also be
used to designate the (profiled) ACME client used by the Name
Delegation Consumer.
CDN Content Delivery Network, a widely distributed network that
serves the domain's web content to a wide audience at high
performance.
STAR Short-Term, Automatically Renewed X.509 certificates.
ACME Automated Certificate Management Environment, a certificate
management protocol [RFC8555].
CA A Certification Authority that implements the ACME protocol. In
this document, the term is synonymous with "ACME server deployed
by the Certification Authority".
CSR A PKCS#10 [RFC2986] Certificate Signing Request, as supported by
ACME.
FQDN Fully Qualified Domain Name.
1.2. Conventions used in this document
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.
2. Protocol Flow
This section presents the protocol flow. For completeness, we
include the ACME profile proposed in this document as well as the
ACME STAR protocol described in [RFC8739].
2.1. Preconditions
The protocol assumes the following preconditions are met:
* The IdO exposes an ACME server interface to the NDC(s) comprising
the account management interface;
* The NDC has registered an ACME account with the IdO;
Sheffer, et al. Expires 13 December 2021 [Page 5]
Internet-Draft ACME Delegation June 2021
* NDC and IdO have agreed on a "CSR template" to use, including at a
minimum: subject name (e.g., "abc.ido.example"), requested
algorithms and key length, key usage, extensions. The NDC will
use this template for every CSR created under the same delegation;
* IdO has registered an ACME account with the Certification
Authority (CA)
Note that even if the IdO implements the ACME server role, it is not
acting as a CA: in fact, from the point of view of the certificate
issuance process, the IdO only works as a "policing" forwarder of the
NDC's key-pair and is responsible for completing the identity
verification process towards the CA.
2.2. Overview
For clarity, the protocol overview presented here covers the main use
case of this protocol, namely delegation of STAR certificates.
Protocol behavior for non-STAR certificates is similar, and the
detailed differences are listed in the following sections.
The interaction between the NDC and the IdO is governed by the
profiled ACME workflow detailed in Section 2.3. The interaction
between the IdO and the CA is ruled by ACME [RFC8555], ACME STAR
[RFC8739] as well as any other ACME extension that applies (e.g.,
[I-D.ietf-acme-authority-token-tnauthlist] for STIR).
The outline of the combined protocol for STAR certificates is as
follow (Figure 1):
* NDC sends an order Order1 for the delegated identifier to IdO;
* IdO creates an Order1 resource in state "ready" with a "finalize"
URL;
* NDC immediately sends a finalize request (which includes the CSR)
to the IdO;
* IdO verifies the CSR according to the agreed upon CSR template;
* If the CSR verification fails, Order1 is moved to an "invalid"
state and everything stops;
* If the CSR verification is successful, IdO moves Order1 to state
"processing", and sends a new Order2 (using its own account) for
the delegated identifier to the CA;
* If the ACME STAR protocol fails, Order2 moves to "invalid" and the
same state is reflected in Order1 (i.e., the NDC Order);
* If the ACME STAR run is successful (i.e., Order2 is "valid"), IdO
copies the "star-certificate" URL from Order2 to Order1 and
updates the Order1 state to "valid".
Sheffer, et al. Expires 13 December 2021 [Page 6]
Internet-Draft ACME Delegation June 2021
The NDC can now download, install and use the short-term certificate
bearing the name delegated by the IdO. This can continue until the
STAR certificate expires or the IdO decides to cancel the automatic
renewal process with the CA.
Note that the interactive identifier authorization phase described in
Section 7.5 of [RFC8555] is suppressed on the NDC-IdO side because
the delegated identity contained in the CSR presented to the IdO is
validated against the configured CSR template (Section 4.1).
Therefore, the NDC sends the finalize request, including the CSR, to
the IdO immediately after Order1 has been acknowledged. The IdO
SHALL buffer a (valid) CSR until the Validation phase completes
successfully.
Also note that the successful negotiation of the "unauthenticated
GET" (Section 3.4 of [RFC8739]) is required in order to allow the NDC
to access the "star-certificate" URL on the CA.
.------. .---------------. .------.
| NDC | | IdO | | ACME |
+--------+ +--------+--------+ +--------+
| Client | | Server | Client | | Server |
'---+----' '----+---+---+----' '----+---'
| | | |
| Order1 | | |
| Signature | | |
o------------------->| | |
| | | |
| [ No identity ] | | |
| [ validation via ] | | |
| [ authorizations ] | | |
| | | |
| CSR | | |
| Signature | | |
o------------------->| | |
| Acknowledgement | | Order2 |
|<-------------------o | Signature |
| | o------------------->|
| | | Required |
| | | Authorizations |
| | |<-------------------o
| | | Responses |
| | | Signature |
| | o------------------->|
| | | |
| | |<~~~~Validation~~~~>|
| | | |
| | | CSR |
Sheffer, et al. Expires 13 December 2021 [Page 7]
Internet-Draft ACME Delegation June 2021
| | | Signature |
| | o------------------->|
| | | Acknowledgement |
| | |<-------------------o
| | | |
|<~~Await issuance~->| |<~~Await issuance~~>|
| |
| (unauthenticated) GET STAR certificate |
o------------------------------------------------>|
| Certificate #1 |
|<------------------------------------------------o
| (unauthenticated) GET STAR certificate |
o------------------------------------------------>|
| Certificate #2 |
|<------------------------------------------------o
| [...] |
| (unauthenticated) GET STAR certificate |
o------------------------------------------------>|
| Certificate #n |
|<------------------------------------------------o
Figure 1: End to end STAR delegation flow
2.3. Delegated Identity Profile
This section defines a profile of the ACME protocol, to be used
between the NDC and IdO.
2.3.1. Delegation Configuration
The IdO must be preconfigured to recognize one or more NDCs, and
present them with details about certificate delegations that apply to
each one.
2.3.1.1. Account Object Extensions
An NDC identifies itself to the IdO as an ACME account. The IdO can
delegate multiple names to a NDC, and these configurations are
described through "delegation" objects associated with the NDC's
Account object on the IdO.
As shown in Figure 2, the ACME account resource on the IdO is
extended with a new "delegations" attribute:
* delegations (required, string): A URL from which a list of
delegations configured for this account (Section 2.3.1.3) can be
fetched via a POST-as-GET request.
Sheffer, et al. Expires 13 December 2021 [Page 8]
Internet-Draft ACME Delegation June 2021
{
"status": "valid",
"contact": [
"mailto:delegation-admin@ido.example"
],
"termsOfServiceAgreed": true,
"orders": "https://example.com/acme/orders/saHpfB",
"delegations": "https://acme.ido.example/acme/delegations/adFqoz"
}
Figure 2: Example Account object with delegations
2.3.1.2. Delegation Lists
Each account object includes a "delegations" URL from which a list of
delegation configurations created by the IdO can be fetched via POST-
as-GET request. The result of the request MUST be a JSON object
whose "delegations" field is an array of URLs, each identifying a
delegation configuration made available to the NDC account
(Section 2.3.1.3). The server MAY return an incomplete list, along
with a Link header field with a "next" link relation indicating where
further entries can be acquired.
HTTP/1.1 200 OK
Content-Type: application/json
Link: <https://acme.ido.example/acme/directory>;rel="index"
Link: <https://acme.ido.example/acme/delegations/adFqoz?cursor=2>;rel="next"
{
"delegations": [
"https://acme.ido.example/acme/delegation/ogfr8EcolOT",
"https://acme.ido.example/acme/delegation/wSi5Lbb61E4",
/* more URLs not shown for example brevity */
"https://acme.ido.example/acme/delegation/gm0wfLYHBen"
]
}
2.3.1.3. Delegation Objects
This profile extends the ACME resource model with a new read-only
delegation object that represents a delegation configuration that
applies to a given NDC.
A delegation object contains the CSR template (see Section 4) that
applies to that delegation, and optionally any related CNAME mapping
for the delegated identifiers. Its structure is as follows:
Sheffer, et al. Expires 13 December 2021 [Page 9]
Internet-Draft ACME Delegation June 2021
* csr-template (required, object): CSR template as defined in
Section 4.
* cname-map (optional, object): a map of FQDN pairs. In each pair,
the name is the delegated identifier, the value is the
corresponding NDC name that is aliased in the IdO's zone file to
redirect the resolvers to the delegated entity. Both names and
values MUST be FQDNs with a terminating '.'. This field is only
meaningful for identifiers of type "dns".
An example delegation object in JSON format is shown in Figure 3.
{
"csr-template": {
"keyTypes": [
{
"PublicKeyType": "id-ecPublicKey",
"namedCurve": "secp256r1",
"SignatureType": "ecdsa-with-SHA256"
}
],
"subject": {
"country": "CA",
"stateOrProvince": "**",
"locality": "**"
},
"extensions": {
"subjectAltName": {
"DNS": [
"abc.ido.example"
]
},
"keyUsage": [
"digitalSignature"
],
"extendedKeyUsage": [
"serverAuth"
]
}
},
"cname-map": {
"abc.ido.example.": "abc.ndc.example."
}
}
Figure 3: Example Delegation Configuration object
Sheffer, et al. Expires 13 December 2021 [Page 10]
Internet-Draft ACME Delegation June 2021
In order to indicate which specific delegation applies to the
requested certificate a new "delegation" attribute is added to the
request object on the NDC-IdO side (see Figure 4 and Figure 7). The
value of this attribute is the URL pointing to the delegation
configuration object that is to be used for this certificate request.
If the "delegation" attribute in the Order object contains a URL that
does not correspond to a configuration available to the requesting
ACME account, the IdO MUST return an error response with status code
403 (Forbidden), providing a problem document [RFC7807] with type
"urn:ietf:params:acme:error:unknownDelegation".
2.3.2. Order Object Transmitted from NDC to IdO and to ACME Server
(STAR)
If the delegation is for a STAR certificate, the request object
created by the NDC:
* MUST have a "delegation" attribute indicating the preconfigured
delegation that applies to this Order;
* MUST have entries in the "identifiers" field for each delegated
name present in the configuration;
* MUST NOT contain the "notBefore" and "notAfter" fields;
* MUST contain an "auto-renewal" object and inside it, the fields
listed in Section 3.1.1 of [RFC8739]. In particular, the "allow-
certificate-get" attribute MUST be present and set to true.
Sheffer, et al. Expires 13 December 2021 [Page 11]
Internet-Draft ACME Delegation June 2021
POST /acme/new-order HTTP/1.1
Host: acme.ido.example
Content-Type: application/jose+json
{
"protected": base64url({
"alg": "ES256",
"kid": "https://acme.ido.example/acme/acct/evOfKhNU60wg",
"nonce": "Alc00Ap6Rt7GMkEl3L1JX5",
"url": "https://acme.ido.example/acme/new-order"
}),
"payload": base64url({
"identifiers": [
{
"type": "dns",
"value": "abc.ido.example"
}
],
"auto-renewal": {
"end-date": "2021-04-20T00:00:00Z",
"lifetime": 345600, // 4 days
"allow-certificate-get": true
},
"delegation":
"https://acme.ido.example/acme/delegation/gm0wfLYHBen"
}),
"signature": "g454e3hdBlkT4AEw...nKePnUyZTjGtXZ6H"
}
Figure 4: New STAR Order from NDC
The Order object that is created on the IdO:
* MUST start in the "ready" state;
* MUST contain an "authorizations" array with zero elements;
* MUST contain the indicated "delegation" configuration;
* MUST contain the indicated "auto-renewal" settings;
* MUST NOT contain the "notBefore" and "notAfter" fields.
Sheffer, et al. Expires 13 December 2021 [Page 12]
Internet-Draft ACME Delegation June 2021
{
"status": "ready",
"expires": "2021-05-01T00:00:00Z",
"identifiers": [
{
"type": "dns",
"value": "abc.ido.example"
}
],
"auto-renewal": {
"end-date": "2021-04-20T00:00:00Z",
"lifetime": 345600,
"allow-certificate-get": true
},
"delegation":
"https://acme.ido.example/acme/delegation/gm0wfLYHBen",
"authorizations": [],
"finalize": "https://acme.ido.example/acme/order/TO8rfgo/finalize"
}
Figure 5: STAR Order Resource Created on IdO
The Order is then finalized by the NDC supplying the CSR containing
the delegated identifiers. The IdO checks the provided CSR against
the template contained in the delegation object that applies to this
request, as described in Section 4.1. If the CSR fails validation
for any of the identifiers, the IdO MUST return an error response
with status code 403 (Forbidden) and an appropriate type, e.g.,
"rejectedIdentifier" or "badCSR". The error response SHOULD contain
subproblems (Section 6.7.1 of [RFC8555]) for each failed identifier.
If the CSR is successfully validated, the Order object status moves
to "processing" and the twin ACME protocol instance is initiated on
the IdO-CA side.
The request object created by the IdO:
* MUST copy the identifiers sent by the NDC;
* MUST strip the "delegation" attribute;
* MUST carry a copy of the "auto-renewal" object sent by the NDC.
When the identifiers' authorization has been successfully completed
and the certificate has been issued by the CA, the IdO:
Sheffer, et al. Expires 13 December 2021 [Page 13]
Internet-Draft ACME Delegation June 2021
* MUST move its Order resource status to "valid";
* MUST copy the "star-certificate" field from the STAR Order
returned by the CA into its Order resource. When dereferenced,
the "star-certificate" URL includes (via the Cert-Not-Before and
Cert-Not-After HTTP header fields) the renewal timers needed by
the NDC to inform its certificate reload logic.
{
"status": "valid",
"expires": "2021-05-01T00:00:00Z",
"identifiers": [
{
"type": "dns",
"value": "abc.ido.example"
}
],
"auto-renewal": {
"end-date": "2021-04-20T00:00:00Z",
"lifetime": 345600,
"allow-certificate-get": true
},
"delegation":
"https://acme.ido.example/acme/delegation/gm0wfLYHBen",
"authorizations": [],
"finalize": "https://acme.ido.example/acme/order/TO8rfgo/finalize",
"star-certificate": "https://acme.ca.example/acme/order/yTr23sSDg9"
}
Figure 6: STAR Order Resource Updated on IdO
This delegation protocol is predicated on the NDC being able to fetch
certificates periodically using an unauthenticated HTTP GET, since in
general the NDC does not possess an account on the CA and therefore
cannot issue the standard POST-as-GET ACME request. Therefore,
before forwarding the Order request to the CA, the IdO SHOULD ensure
that the selected CA supports "unauthenticated GET" by inspecting the
relevant settings in the CA's "directory" object, as per Section 3.4
of [RFC8739]. If the CA does not support "unauthenticated GET" of
STAR certificates, the IdO MUST NOT forward the Order request.
Instead, it MUST move the Order status to "invalid" and set the
"allow-certificate-get" in the "auto-renewal" object to "false". The
same occurs in case the Order request is forwarded and the CA does
Sheffer, et al. Expires 13 December 2021 [Page 14]
Internet-Draft ACME Delegation June 2021
not reflect the "allow-certificate-get" setting in its Order
resource. The combination of "invalid" status and denied "allow-
certificate-get" in the Order resource at the IdO provides an
unambiguous (asynchronous) signal to the NDC about the failure
reason.
2.3.2.1. CNAME Installation
If an identifier object of type "dns" was included, the IdO can add
the CNAME records specified in the delegation object to its zone,
e.g.:
abc.ido.example. CNAME abc.ndc.example.
2.3.3. Order Object Transmitted from NDC to IdO and to ACME Server
(non-STAR)
If the delegation is for a non-STAR certificate, the request object
created by the NDC:
* MUST have a "delegation" attribute indicating the preconfigured
delegation that applies to this Order;
* MUST have entries in the "identifiers" field for each delegated
name present in the configuration;
* MUST have the "allow-certificate-get" attribute set to true.
Sheffer, et al. Expires 13 December 2021 [Page 15]
Internet-Draft ACME Delegation June 2021
POST /acme/new-order HTTP/1.1
Host: acme.ido.example
Content-Type: application/jose+json
{
"protected": base64url({
"alg": "ES256",
"kid": "https://acme.ido.example/acme/acct/evOfKhNU60wg",
"nonce": "IYBkoQfaCS80UcCn9qH8Gt",
"url": "https://acme.ido.example/acme/new-order"
}),
"payload": base64url({
"identifiers": [
{
"type": "dns",
"value": "abc.ido.example"
}
],
"delegation":
"https://acme.ido.example/acme/delegation/gm0wfLYHBen",
"allow-certificate-get": true
}),
"signature": "j9JBUvMigi4zodud...acYkEKaa8gqWyZ6H"
}
Figure 7: New Non-STAR Order from NDC
The Order object that is created on the IdO:
* MUST start in the "ready" state;
* MUST contain an "authorizations" array with zero elements;
* MUST contain the indicated "delegation" configuration;
* MUST contain the indicated "allow-certificate-get" setting.
Sheffer, et al. Expires 13 December 2021 [Page 16]
Internet-Draft ACME Delegation June 2021
{
"status": "ready",
"expires": "2021-05-01T00:00:00Z",
"identifiers": [
{
"type": "dns",
"value": "abc.ido.example"
}
],
"delegation":
"https://acme.ido.example/acme/delegation/gm0wfLYHBen",
"allow-certificate-get": true,
"authorizations": [],
"finalize": "https://acme.ido.example/acme/order/3ZDlhYy/finalize"
}
Figure 8: Non-STAR Order Resource Created on IdO
The Order finalization by the NDC and the subsequent validation of
the CSR by the IdO proceed in the same way as for the STAR case. If
the CSR is successfully validated, the Order object status moves to
"processing" and the twin ACME protocol instance is initiated on the
IdO-CA side.
The request object created by the IdO:
* MUST copy the identifiers sent by the NDC;
* MUST strip the "delegation" attribute;
* MUST copy the "allow-certificate-get" attribute.
When the identifiers' authorization has been successfully completed
and the certificate has been issued by the CA, the IdO:
* MUST move its Order resource status to "valid";
* MUST copy the "certificate" field from the Order returned by the
CA into its Order resource, as well as "notBefore" and "notAfter"
if these fields exist.
Sheffer, et al. Expires 13 December 2021 [Page 17]
Internet-Draft ACME Delegation June 2021
{
"status": "valid",
"expires": "2021-05-01T00:00:00Z",
"identifiers": [
{
"type": "dns",
"value": "abc.ido.example"
}
],
"delegation":
"https://acme.ido.example/acme/delegation/gm0wfLYHBen",
"allow-certificate-get": true,
"authorizations": [],
"finalize": "https://acme.ido.example/acme/order/3ZDlhYy/finalize",
"certificate": "https://acme.ca.example/acme/order/YtR23SsdG9"
}
Figure 9: Non-STAR Order Resource Updated on IdO
At this point of the protocol flow, the same considerations as in
Section 2.3.2.1 apply.
Before forwarding the Order request to the CA, the IdO SHOULD ensure
that the selected CA supports "unauthenticated GET" by inspecting the
relevant settings in the CA's "directory" object, as per
Section 2.3.5. If the CA does not support "unauthenticated GET" of
certificate resources, the IdO MUST NOT forward the Order request.
Instead, it MUST move the Order status to "invalid" and set the
"allow-certificate-get" attribute to "false". The same occurs in
case the Order request is forwarded and the CA does not reflect the
"allow-certificate-get" setting in its Order resource. The
combination of "invalid" status and denied "allow-certificate-get" in
the Order resource at the IdO provides an unambiguous (asynchronous)
signal to the NDC about the failure reason.
2.3.4. Capability Discovery
In order to help a client to discover support for this profile, the
directory object of an ACME server (typically, one deployed by the
IdO) contains the following attribute in the "meta" field:
Sheffer, et al. Expires 13 December 2021 [Page 18]
Internet-Draft ACME Delegation June 2021
* delegation-enabled (optional, boolean): Boolean flag indicating
support for the profile specified in this memo. An ACME server
that supports this delegation profile MUST include this key, and
MUST set it to true.
The IdO MUST declare its support for delegation using "delegation-
enabled" regardless of whether it supports delegation of STAR
certificates, non-STAR certificates or both.
In order to help a client to discover support for certificate
fetching using unauthenticated HTTP GET, the directory object of an
ACME server (typically, one deployed by the CA) contains the
following attribute in the "meta" field:
* allow-certificate-get (optional, boolean): See Section 2.3.5.
2.3.5. Negotiating an Unauthenticated GET
In order to enable the name delegation of non-STAR certificates, this
document defines a mechanism that allows a server to advertise
support for accessing certificate resources via unauthenticated GET
(in addition to POST-as-GET), and a client to enable this service
with per-Order granularity.
It is worth pointing out that the protocol elements described in this
section have the same names and semantics as those introduced in
Section 3.4 of [RFC8739] for the STAR use case (except, of course,
they apply to the certificate resource rather than the star-
certificate resource). However, they differ in terms of their
position in the directory meta and order objects: rather than being
wrapped in an auto-renewal sub-object they are located at the top-
level.
A server states its availability to grant unauthenticated access to a
client's Order certificate by setting the "allow-certificate-get"
attribute to "true" in the "meta" field inside the directory object:
* allow-certificate-get (optional, boolean): If this field is
present and set to "true", the server allows GET (and HEAD)
requests to certificate URLs.
A client states its desire to access the issued certificate via
unauthenticated GET by adding an "allow-certificate-get" attribute to
the payload of its newOrder request and setting it to "true".
Sheffer, et al. Expires 13 December 2021 [Page 19]
Internet-Draft ACME Delegation June 2021
* allow-certificate-get (optional, boolean): If this field is
present and set to "true", the client requests the server to allow
unauthenticated GET (and HEAD) to the certificate associated with
this Order.
If the server accepts the request, it MUST reflect the attribute
setting in the resulting order object.
Note that even when the use of unauthenticated GET has been agreed
upon, the server MUST also allow POST-as-GET requests to the
certificate resource.
2.3.6. Terminating the Delegation
Identity delegation is terminated differently depending on whether
this is a STAR certificate or not.
2.3.6.1. By Cancellation (STAR)
The IdO can terminate the delegation of a STAR certificate by
requesting its cancellation (see Section 3.1.2 of [RFC8739]).
Cancellation of the ACME STAR certificate is a prerogative of the
IdO. The NDC does not own the relevant account key on the CA,
therefore it can't issue a cancellation request for the STAR
certificate. Potentially, since it holds the STAR certificate's
private key, it could request the revocation of a single STAR
certificate. However, STAR explicitly disables the revokeCert
interface.
Shortly after the automatic renewal process is stopped by the IdO,
the last issued STAR certificate expires and the delegation
terminates.
2.3.6.2. By Revocation (non-STAR)
The IdO can terminate the delegation of a non-STAR certificate by
requesting it to be revoked using the revokeCert URL exposed by the
CA.
Sheffer, et al. Expires 13 December 2021 [Page 20]
Internet-Draft ACME Delegation June 2021
According to Section 7.6 of [RFC8555], the revocation endpoint can be
used with either the account keypair, or the certificate keypair. In
other words, an NDC that learns the revokeCert URL of the CA (which
is publicly available via the CA's Directory object) would be able to
revoke the certificate using the associated private key. However,
given the trust relationship between NDC and IdO expected by the
delegation trust model (Section 7.1), as well as the lack of
incentives for the NDC to prematurely terminate the delegation, this
does not represent a significant security risk.
2.4. Proxy Behavior
There are cases where the ACME Delegation flow should be proxied,
such as the use case described in Section 5.1.2. This section
describes the behavior of such proxies.
An entity implementing the IdO server role - an "ACME Delegation
server" - may behave, on a per-identity case, either as a proxy into
another ACME Delegation server, or it may behave as an IdO and obtain
a certificate directly. The determining factor is whether it can
successfully be authorized by the next-hop ACME server for the
identity associated with the certificate request.
The identities supported by each server and the disposition for each
of them are preconfigured.
Following is the proxy's behavior for each of the messages exchanged
in the ACME Delegation process:
* New-order request:
- The complete "identifiers" object MUST be copied as-is.
- Similarly, the "auto-renewal" object MUST be copied as-is.
* New-order response:
- The "status", "expires", "authorizations", "identifiers" and
"auto-renewal" attributes/objects MUST be copied as-is.
- The "finalize" URL is rewritten, so that the "finalize" request
will be made to the proxy.
- Similarly, the "Location" header MUST be rewritten to point to
an Order object on the proxy.
- Any "Link" relations MUST be rewritten to point to the proxy.
* Get Order response:
- The "status", "expires", "authorizations", "identifiers" and
"auto-renewal" attributes/objects MUST be copied as-is.
- Similarly, the "star-certificate" URL (or the "certificate" URL
in case of non-STAR requests) MUST be copied as-is.
- The "finalize" URL is rewritten, so that the "finalize" request
will be made to the proxy.
Sheffer, et al. Expires 13 December 2021 [Page 21]
Internet-Draft ACME Delegation June 2021
- The "Location" header MUST be rewritten to point to an Order
object on the proxy.
- Any "Link" relations MUST be rewritten to point to the proxy.
* Finalize request:
- The CSR MUST be copied as-is.
* Finalize response:
- The "Location" header, "Link" relations and the "finalize" URLs
are rewritten as for Get Order.
We note that all the above messages are authenticated, and therefore
each proxy must be able to authenticate any subordinate server.
3. CA Behavior
Although most of this document, and in particular Section 2 is
focused on the protocol between the NDC and to IdO, the protocol does
affect the ACME server running in the CA. A CA that wishes to
support certificate delegation MUST also support unauthenticated
certificate fetching, which it declares using "allow-certificate-get"
(Section 2.3.5, Paragraph 3).
4. CSR Template
The CSR template is used to express and constrain the shape of the
CSR that the NDC uses to request the certificate. The CSR is used
for every certificate created under the same delegation. Its
validation by the IdO is a critical element in the security of the
whole delegation mechanism.
Instead of defining every possible CSR attribute, this document takes
a minimalist approach by declaring only the minimum attribute set and
deferring the registration of further, more specific, attributes to
future documents.
4.1. Template Syntax
The template is a JSON document. Each field (with the exception of
"keyTypes", see below) denotes one of:
* A mandatory field, where the template specifies the literal value
of that field. This is denoted by a literal string, such as
"abc.ido.example".
* A mandatory field, where the content of the field is defined by
the client. This is denoted by "**".
* An optional field, where the client decides whether the field is
included in the CSR and if so, what its value is. This is denoted
by "*".
Sheffer, et al. Expires 13 December 2021 [Page 22]
Internet-Draft ACME Delegation June 2021
The NDC MUST NOT include in the CSR any fields, including any
extensions, unless they are specified in the template.
The structure of the template object is defined by the CDDL [RFC8610]
document in Appendix B. An alternative, non-normative JSON Schema
syntax is given in Appendix C. While the CSR template must follow
the syntax defined here, neither the IdO nor the NDC are expected to
validate it at run-time.
The "subject" field and its subfields are mapped into the "subject"
field of the CSR, as per [RFC5280], Section 4.1.2.6. Other extension
fields of the CSR template are mapped into the CSR according to the
table in Section 6.5.
The "subjectAltName" field is currently defined for the following
identifiers: DNS names, email addresses, and URIs. New identifier
types may be added in the future by documents that extend this
specification. Each new identifier type SHALL have an associated
identifier validation challenge that the CA can use to obtain proof
of the requester's control over it.
The "keyTypes" property is not copied into the CSR. Instead, this
property constrains the "SubjectPublicKeyInfo" field of the CSR,
which MUST have the type/size defined by one of the array members of
the "keyTypes" property.
When the IdO receives the CSR, it MUST verify that the CSR is
consistent with the template contained in the "delegation" object
referenced in the Order. The IdO MAY enforce additional constraints,
e.g., by restricting field lengths. In this regard, note that a
"subjectAltName" of type "DNS" can be specified using the wildcard
notation, meaning that the NDC can be required ("**") or offered the
possibility ("*") to define the delegated domain name by itself. If
this is the case, the IdO MUST apply application-specific checks on
top of the control rules already provided by the CSR template to
ensure the requested domain name is legitimate according to its local
policy.
4.2. Example
The CSR template in Figure 10 represents one possible CSR template
governing the delegation exchanges provided in the rest of this
document.
Sheffer, et al. Expires 13 December 2021 [Page 23]
Internet-Draft ACME Delegation June 2021
{
"keyTypes": [
{
"PublicKeyType": "rsaEncryption",
"PublicKeyLength": 2048,
"SignatureType": "sha256WithRSAEncryption"
},
{
"PublicKeyType": "id-ecPublicKey",
"namedCurve": "secp256r1",
"SignatureType": "ecdsa-with-SHA256"
}
],
"subject": {
"country": "CA",
"stateOrProvince": "**",
"locality": "**"
},
"extensions": {
"subjectAltName": {
"DNS": [
"abc.ido.example"
]
},
"keyUsage": [
"digitalSignature"
],
"extendedKeyUsage": [
"serverAuth",
"clientAuth"
]
}
}
Figure 10: Example CSR template
5. Further Use Cases
This non-normative section describes additional use cases that use
STAR certificate delegation in non-trivial ways.
5.1. CDN Interconnection (CDNI)
[I-D.ietf-cdni-interfaces-https-delegation] discusses several
solutions addressing different delegation requirements for the CDNI
(CDN Interconnection) environment. This section discusses two of the
stated requirements in the context of the STAR delegation workflow.
Sheffer, et al. Expires 13 December 2021 [Page 24]
Internet-Draft ACME Delegation June 2021
This section uses specifically CDNI terminology, e.g., "uCDN" and
"dCDN", as defined in [RFC7336].
5.1.1. Multiple Parallel Delegates
In some cases the content owner (IdO) would like to delegate
authority over a web site to multiple NDCs (CDNs). This could happen
if the IdO has agreements in place with different regional CDNs for
different geographical regions, or if a "backup" CDN is used to
handle overflow traffic by temporarily altering some of the CNAME
mappings in place. The STAR delegation flow enables this use case
naturally, since each CDN can authenticate separately to the IdO (via
its own separate account) specifying its CSR, and the IdO is free to
allow or deny each certificate request according to its own policy.
5.1.2. Chained Delegation
In other cases, a content owner (IdO) delegates some domains to a
large CDN (uCDN), which in turn delegates to a smaller regional CDN,
dCDN. The IdO has a contractual relationship with uCDN, and uCDN has
a similar relationship with dCDN. However IdO may not even know
about dCDN.
If needed, the STAR protocol can be chained to support this use case:
uCDN could forward requests from dCDN to IdO, and forward responses
back to dCDN. Whether such proxying is allowed is governed by policy
and contracts between the parties.
A mechanism is necessary at the interface between uCDN and dCDN by
which the uCDN can advertise:
* The names that the dCDN is allowed to use;
* The policy for creating the key material (allowed algorithms,
minimum key lengths, key usage, etc.) that the dCDN needs to
satisfy.
Note that such mechanism is provided by the CSR template.
5.1.2.1. Two-Level Delegation in CDNI
A User Agent (UA), browser or set-top-box, wants to fetch the video
resource at the following URI: "https://video.cp.example/movie".
Redirection between Content Provider (CP), upstream, and downstream
CDNs is arranged as a CNAME-based aliasing chain as illustrated in
Figure 11.
Sheffer, et al. Expires 13 December 2021 [Page 25]
Internet-Draft ACME Delegation June 2021
.------------.
video.cp.example ? | .-----. |
.---------------------------------->| | |
| (a) | | DNS | CP |
| .-------------------------------+ | |
| | CNAME video.ucdn.example | '-----' |
| | '------------'
| |
| |
.-----------|---v--. .------------.
| .-----.-+-----. | video.ucdn.example ? | .-----. |
| | | +----------------------------->| | |
| UA | TLS | DNS | | (b) | | DNS | uCDN |
| | | |<-----------------------------+ | |
| '--+--'-----+-' | CNAME video.dcdn.example | '-----' |
'------|----^---|--' '------------'
| | |
| | |
| | | .------------.
| | | video.dcdn.example ? | .-----. |
| | '------------------------------>| | |
| | (c) | | DNS | |
| '-----------------------------------+ | |
| A 192.0.2.1 | +-----+ dCDN |
| | | | |
'--------------------------------------->| TLS | |
SNI: video.cp.example | | | |
| '-----' |
'------------'
Figure 11: DNS Redirection
Unlike HTTP-based redirection, where the original URL is supplanted
by the one found in the Location header of the 302 response, DNS
redirection is completely transparent to the User Agent. As a
result, the TLS connection to the dCDN edge is done with a Server
Name Indication (SNI) equal to the "host" in the original URI - in
the example, "video.cp.example". So, in order to successfully
complete the handshake, the landing dCDN node has to be configured
with a certificate whose subjectAltName matches "video.cp.example",
i.e., a Content Provider's name.
Figure 12 illustrates the cascaded delegation flow that allows dCDN
to obtain a STAR certificate that bears a name belonging to the
Content Provider with a private key that is only known to the dCDN.
Sheffer, et al. Expires 13 December 2021 [Page 26]
Internet-Draft ACME Delegation June 2021
.--------------------.
| .------.------. |
| | STAR | ACME |<-------------.
| CP | dele | STAR | | |
| | srv | cli +-----. |
| '---+--'------' | | 6
'---------|------^---' 5 |
| | | .--|-------.
| | | | .-+----. |
7 | '---->| ACME | |
| | | | STAR | C |
| 4 | +------| A |
| | | | HTTP | |
| | | '----+-' |
| .-' '--^--|----'
.--------------v--|--. | |
| .------.----+-. | | 10
| | | STAR | | | |
| uCDN | CDNI | dele | | | |
| | | fwd | | | |
| '----+-'-+----' | | |
'-------^--|---|--^--' | |
| | | | | |
| 2 8 | | |
1 | | 3 | |
| | | | 9 |
.-------|--v---v--|---------. | |
| .-+----.----+-.------. | | |
| | | STAR | +------------' |
| dCDN | CDNI | dele | HTTP | | |
| | | cli | |<--------------'
| '------'------'------' |
'---------------------------'
Figure 12: Two levels delegation in CDNI
uCDN is configured to delegate to dCDN, and CP is configured to
delegate to uCDN, both as defined in Section 2.3.1.
1. dCDN requests CDNI path metadata to uCDN;
2. uCDN replies with, among other CDNI metadata, the STAR
delegation configuration, which includes the delegated Content
Provider's name;
3. dCDN creates a key-pair and the CSR with the delegated name. It
then places an order for the delegated name to uCDN;
4. uCDN forwards the received order to the Content Provider (CP);
Sheffer, et al. Expires 13 December 2021 [Page 27]
Internet-Draft ACME Delegation June 2021
5. CP creates an order for a STAR certificate and sends it to the
CA. The order also requests unauthenticated access to the
certificate resource;
6. After all authorizations complete successfully, the STAR
certificate is issued;
7. CP notifies uCDN that the STAR certificate is available at the
order's star-certificate URL;
8. uCDN forwards the information to dCDN. At this point the ACME
signalling is complete;
9. dCDN requests the STAR certificate using unauthenticated GET
from the CA;
10. the CA returns the certificate. Now dCDN is fully configured to
handle HTTPS traffic in-lieu of the Content Provider.
Note that 9. and 10. repeat until the delegation expires or is
terminated.
5.2. Secure Telephone Identity Revisited (STIR)
As a second use case, we consider the delegation of credentials in
the STIR ecosystem [I-D.ietf-stir-cert-delegation].
This section uses STIR terminology. The term PASSPorT is defined in
[RFC8225], and "TNAuthList" in [RFC8226].
In the STIR "delegated" mode, a service provider SP2 - the NDC -
needs to sign PASSPorT's [RFC8225] for telephone numbers (e.g.,
TN=+123) belonging to another service provider, SP1 - the IdO. In
order to do that, SP2 needs a STIR certificate, and private key, that
includes TN=+123 in the TNAuthList [RFC8226] certificate extension.
In details (Figure 13):
1. SP1 and SP2 agree on the configuration of the delegation - in
particular, the CSR template that applies;
2. SP2 generates a private/public key-pair and sends a CSR to SP1
requesting creation of a certificate with: SP1 name, SP2 public
key, and a TNAuthList extension with the list of TNs that SP1
delegates to SP2. (Note that the CSR sent by SP2 to SP1 needs to
be validated against the CSR template agreed upon in step 1.);
3. SP1 sends an order for the CSR to the CA. The order also
requests unauthenticated access to the certificate resource;
4. Subsequently, after the required TNAuthList authorizations are
successfully completed, the CA moves the order to a "valid"
state; at the same time the star-certificate endpoint is
populated;
5. The order contents are forwarded from SP1 to SP2 by means of the
paired "delegation" order;
Sheffer, et al. Expires 13 December 2021 [Page 28]
Internet-Draft ACME Delegation June 2021
6. SP2 dereferences the star-certificate URL in the order to fetch
the rolling STAR certificate bearing the delegated identifiers;
7. The STAR certificate is returned to SP2.
.-------------------.
| .------.------. |
| | STAR | STAR |<--------------.
.-->| SP1 | dele | dele | | |
| | | srv | cli +-----. |
| | '----+-'------' | | 4
| '------^--|---------' 3 |
| | | | .----|-----.
| | 5 | | .---+--. |
| | | '--->| ACME | |
| | | | | STAR | C |
1 | | | +------| A |
| | | .--->| HTTP | |
| 2 | | | '---+--' |
| | | | '----|-----'
| .------|--v---------. 6 |
| | .-+----.------. | | 7
| | | STAR | +-----' |
'-->| SP2 | dele | HTTP | | |
| | cli | |<--------------'
| '----+-'-+----' |
'-------------------'
Figure 13: Delegation in STIR
As shown, the STAR delegation profile described in this document
applies straightforwardly, the only extra requirement being the
ability to instruct the NDC about the allowed TNAuthList values.
This can be achieved by a simple extension to the CSR template.
6. IANA Considerations
[[RFC Editor: please replace XXXX below by the RFC number.]]
6.1. New Fields in the "meta" Object within a Directory Object
This document adds the following entries to the ACME Directory
Metadata Fields registry:
Sheffer, et al. Expires 13 December 2021 [Page 29]
Internet-Draft ACME Delegation June 2021
+=======================+============+===========+
| Field Name | Field Type | Reference |
+=======================+============+===========+
| delegation-enabled | boolean | RFC XXXX |
+-----------------------+------------+-----------+
| allow-certificate-get | boolean | RFC XXXX |
+-----------------------+------------+-----------+
Table 1
6.2. New Fields in the Order Object
This document adds the following entries to the ACME Order Object
Fields registry:
+=======================+============+==============+===========+
| Field Name | Field Type | Configurable | Reference |
+=======================+============+==============+===========+
| allow-certificate-get | boolean | true | RFC XXXX |
+-----------------------+------------+--------------+-----------+
| delegation | string | true | RFC XXXX |
+-----------------------+------------+--------------+-----------+
Table 2
6.3. New Fields in the Account Object
This document adds the following entries to the ACME Account Object
Fields registry:
+=============+============+==========+===========+
| Field Name | Field Type | Requests | Reference |
+=============+============+==========+===========+
| delegations | string | none | RFC XXXX |
+-------------+------------+----------+-----------+
Table 3
Note that the "delegations" field is only reported by ACME servers
that have "delegation-enabled" set to true in their meta Object.
6.4. New Error Types
This document adds the following entries to the ACME Error Type
registry:
Sheffer, et al. Expires 13 December 2021 [Page 30]
Internet-Draft ACME Delegation June 2021
+===================+================================+===========+
| Type | Description | Reference |
+===================+================================+===========+
| unknownDelegation | An unknown configuration is | RFC XXXX |
| | listed in the "delegations" | |
| | attribute of the request Order | |
+-------------------+--------------------------------+-----------+
Table 4
6.5. CSR Template Extensions
IANA is requested to establish a registry "STAR Delegation CSR
Template Extensions", with "Specification Required" as its
registration procedure.
Each extension registered must specify:
* An extension name.
* An extension syntax, as a reference to a CDDL document that
defines this extension.
* The extension's mapping into an X.509 certificate extension.
The initial contents of this registry are the extensions defined by
the CDDL in Appendix B.
+==================+===========+===============================+
| Extension Name | Extension | Mapping to X.509 Certificate |
| | Syntax | Extension |
+==================+===========+===============================+
| keyUsage | See | [RFC5280], Section 4.2.1.3 |
| | Appendix | |
| | B | |
+------------------+-----------+-------------------------------+
| extendedKeyUsage | See | [RFC5280], Section 4.2.1.12 |
| | Appendix | |
| | B | |
+------------------+-----------+-------------------------------+
| subjectAltName | See | [RFC5280], Section 4.2.1.6 |
| | Appendix | (note that only specific name |
| | B | formats are allowed: URI, DNS |
| | | name, email address) |
+------------------+-----------+-------------------------------+
Table 5
When evaluating a request for an assignment in this registry, the
designated expert should follow this guidance:
Sheffer, et al. Expires 13 December 2021 [Page 31]
Internet-Draft ACME Delegation June 2021
* The definition must include a full CDDL definition, which the
expert will validate.
* The definition must include both positive and negative test cases.
* Additional requirements that are not captured by the CDDL
definition are allowed but must be explicitly specified.
7. Security Considerations
7.1. Trust Model
The ACME trust model needs to be extended to include the trust
relationship between NDC and IdO. Note that once this trust link is
established, it potentially becomes recursive. Therefore, there has
to be a trust relationship between each of the nodes in the
delegation chain; for example, in case of cascading CDNs this is
contractually defined. Note that using standard [RFC6125] identity
verification there are no mechanisms available to the IdO to restrict
the use of the delegated name once the name has been handed over to
the first NDC. It is therefore expected that contractual measures
are in place to get some assurance that re-delegation is not being
performed.
7.2. Delegation Security Goal
Delegation introduces a new security goal: only an NDC that has been
authorised by the IdO, either directly or transitively, can obtain a
certificate with an IdO identity.
From a security point of view, the delegation process has five
separate parts:
1. Enabling a specific third party (the intended NDC) to submit
requests for delegated certificates;
2. Making sure that any request for a delegated certificate matches
the intended "shape" in terms of delegated identities as well as
any other certificate metadata, e.g., key length, x.509
extensions, etc.;
3. Serving the certificate back to the NDC;
4. A process for handling revocation of the delegation;
5. A process for handling revocation of the certificate itself.
The first part is covered by the NDC's ACME account that is
administered by the IdO, whose security relies on the correct
handling of the associated key pair. When a compromise of the
private key is detected, the delegate MUST use the account
deactivation procedures defined in Section 7.3.6 of [RFC8555].
Sheffer, et al. Expires 13 December 2021 [Page 32]
Internet-Draft ACME Delegation June 2021
The second part is covered by the act of checking an NDC's
certificate request against the intended CSR template. The steps of
shaping the CSR template correctly, selecting the right CSR template
to check against the presented CSR, and making sure that the
presented CSR matches the selected CSR template are all security
relevant.
The third part builds on the trust relationship between NDC and IdO
that is responsible for correctly forwarding the certificate URL from
the Order returned by the CA.
The fourth part is associated with the ability of the IdO to
unilaterally remove the delegation object associated with the revoked
identity, therefore disabling any further NDC requests for such
identity. Note that, in more extreme circumstances, the IdO might
decide to disable the NDC account thus entirely blocking any further
interaction.
The fifth is covered by two different mechanisms, depending on the
nature of the certificate. For STAR, the IdO shall use the
cancellation interface defined in Section 2.3 of [RFC8739]. For non-
STAR, the certificate revocation interface defined in Section 7.6 of
[RFC8555]) is used.
The ACME account associated with the delegation plays a crucial role
in the overall security of the presented protocol. This, in turn,
means that in delegation scenarios the security requirements and
verification associated with an ACME account may be more stringent
than in traditional ACME, since the out-of-band configuration of
delegations that an account is authorized to use, combined with
account authentication, takes the place of the normal ACME
authorization challenge procedures. Therefore, the IdO MUST ensure
that each account is associated with the exact policies (via their
matching "delegation" objects) that define which domain names can be
delegated to the account and how. The IdO is expected to use out of
band means to pre-register each NDC to the corresponding account.
7.3. New ACME Channels
Using the model established in Section 10.1 of [RFC8555], we can
decompose the interactions of the basic delegation workflow as shown
in Figure 14.
Sheffer, et al. Expires 13 December 2021 [Page 33]
Internet-Draft ACME Delegation June 2021
.-----. ACME Channel .--------.
| NDC +------------->| IdO |
'--+--' | server |
| '--o-----'
| |
| | ACME Channel
| | .------------>-------------.
| | | |
| .--o--+--. .--+---.
| | IdO | | CA |
| | client | '--+-+-'
| '-----+--' | |
| '-----------<--------------' |
| Validation Channel |
'-------------------->-------------------------------'
(subset of) ACME Channel [1]
[1] Unauthenticated certificate fetch and non-STAR certificate
revocation.
Figure 14: Delegation Channels Topology
The considerations regarding the security of the ACME Channel and
Validation Channel discussed in [RFC8555] apply verbatim to the IdO-
CA leg. The same can be said for the ACME channel on the NDC-IdO
leg. A slightly different set of considerations apply to the ACME
Channel between NDC and CA, which consists of a subset of the ACME
interface comprising two API endpoints: the unauthenticated
certificate retrieval and, potentially, non-STAR revocation via
certificate private key. No specific security considerations apply
to the former, but the privacy considerations in Section 6.3 of
[RFC8739] do. With regards to the latter, it should be noted that
there is currently no means for an IdO to disable authorising
revocation based on certificate private keys. So, in theory, an NDC
could use the revocation API directly with the CA, therefore
bypassing the IdO. The NDC SHOULD NOT directly use the revocation
interface exposed by the CA unless failing to do so would compromise
the overall security, for example if the certificate private key is
compromised and the IdO is not currently reachable.
All other security considerations from [RFC8555] and [RFC8739] apply
as-is to the delegation topology.
Sheffer, et al. Expires 13 December 2021 [Page 34]
Internet-Draft ACME Delegation June 2021
7.4. Restricting CDNs to the Delegation Mechanism
When a web site is delegated to a CDN, the CDN can in principle
modify the web site at will, create and remove pages. This means
that a malicious or breached CDN can pass the ACME (as well as common
non-ACME) HTTPS-based validation challenges and generate a
certificate for the site. This is true regardless of whether the
CNAME mechanisms defined in the current document is used or not.
In some cases, this is the desired behavior: the domain holder trusts
the CDN to have full control of the cryptographic credentials for the
site. The current document however assumes a scenario where the
domain holder only wants to delegate restricted control, and wishes
to retain the capability to cancel the CDN's credentials at a short
notice.
The following is a possible mitigation when the IdO wishes to ensure
that a rogue CDN cannot issue unauthorized certificates:
* The domain holder makes sure that the CDN cannot modify the DNS
records for the domain. The domain holder should ensure it is the
only entity authorized to modify the DNS zone. Typically, it
establishes a CNAME resource record from a subdomain into a CDN-
managed domain.
* The domain holder uses a CAA record [RFC8659] to restrict
certificate issuance for the domain to specific CAs that comply
with ACME and are known to implement [RFC8657].
* The domain holder uses the ACME-specific CAA mechanism [RFC8657]
to restrict issuance to a specific account key which is controlled
by it, and MUST require "dns-01" as the sole validation method.
We note that the above solution may need to be tweaked depending on
the exact capabilities and authorisation flows supported by the
selected CA. In addition, this mitigation may be bypassed if a
malicious or misconfigured CA does not comply with CAA restrictions.
8. Acknowledgments
We would like to thank the following people who contributed
significantly to this document with their review comments and design
proposals: Richard Barnes, Carsten Bormann, Roman Danyliw, Lars
Eggert, Frédéric Fieau, Russ Housley, Ben Kaduk, Eric Kline, Sanjay
Mishra, Francesca Palombini, Jon Peterson, Ryan Sleevi, Emile
Stephan, Éric Vyncke.
Sheffer, et al. Expires 13 December 2021 [Page 35]
Internet-Draft ACME Delegation June 2021
This work is partially supported by the European Commission under
Horizon 2020 grant agreement no. 688421 Measurement and Architecture
for a Middleboxed Internet (MAMI). This support does not imply
endorsement.
9. References
9.1. Normative References
[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>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/info/rfc2986>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP
APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
<https://www.rfc-editor.org/info/rfc7807>.
[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>.
[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
<https://www.rfc-editor.org/info/rfc8555>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
Sheffer, et al. Expires 13 December 2021 [Page 36]
Internet-Draft ACME Delegation June 2021
[RFC8739] Sheffer, Y., Lopez, D., Gonzalez de Dios, O., Pastor
Perales, A., and T. Fossati, "Support for Short-Term,
Automatically Renewed (STAR) Certificates in the Automated
Certificate Management Environment (ACME)", RFC 8739,
DOI 10.17487/RFC8739, March 2020,
<https://www.rfc-editor.org/info/rfc8739>.
9.2. Informative References
[I-D.ietf-acme-authority-token-tnauthlist]
Wendt, C., Hancock, D., Barnes, M., and J. Peterson,
"TNAuthList profile of ACME Authority Token", Work in
Progress, Internet-Draft, draft-ietf-acme-authority-token-
tnauthlist-08, 27 March 2021,
<https://www.ietf.org/archive/id/draft-ietf-acme-
authority-token-tnauthlist-08.txt>.
[I-D.ietf-cdni-interfaces-https-delegation]
Fieau, F., Stephan, E., and S. Mishra, "CDNI extensions
for HTTPS delegation", Work in Progress, Internet-Draft,
draft-ietf-cdni-interfaces-https-delegation-05, 12 March
2021, <https://www.ietf.org/archive/id/draft-ietf-cdni-
interfaces-https-delegation-05.txt>.
[I-D.ietf-stir-cert-delegation]
Peterson, J., "STIR Certificate Delegation", Work in
Progress, Internet-Draft, draft-ietf-stir-cert-delegation-
04, 22 February 2021, <https://www.ietf.org/archive/id/
draft-ietf-stir-cert-delegation-04.txt>.
[I-D.ietf-tls-subcerts]
Barnes, R., Iyengar, S., Sullivan, N., and E. Rescorla,
"Delegated Credentials for TLS", Work in Progress,
Internet-Draft, draft-ietf-tls-subcerts-10, 24 January
2021, <https://www.ietf.org/archive/id/draft-ietf-tls-
subcerts-10.txt>.
[I-D.mglt-lurk-tls13]
Migault, D., "LURK Extension version 1 for (D)TLS 1.3
Authentication", Work in Progress, Internet-Draft, draft-
mglt-lurk-tls13-04, 25 January 2021,
<https://www.ietf.org/archive/id/draft-mglt-lurk-
tls13-04.txt>.
Sheffer, et al. Expires 13 December 2021 [Page 37]
Internet-Draft ACME Delegation June 2021
[json-schema-07]
Wright, A., Andrews, H., and G. Luff, "JSON Schema
Validation: A Vocabulary for Structural Validation of
JSON", 2018, <https://datatracker.ietf.org/doc/html/draft-
handrews-json-schema-validation-01>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC7336] Peterson, L., Davie, B., and R. van Brandenburg, Ed.,
"Framework for Content Distribution Network
Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336,
August 2014, <https://www.rfc-editor.org/info/rfc7336>.
[RFC8225] Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
<https://www.rfc-editor.org/info/rfc8225>.
[RFC8226] Peterson, J. and S. Turner, "Secure Telephone Identity
Credentials: Certificates", RFC 8226,
DOI 10.17487/RFC8226, February 2018,
<https://www.rfc-editor.org/info/rfc8226>.
[RFC8657] Landau, H., "Certification Authority Authorization (CAA)
Record Extensions for Account URI and Automatic
Certificate Management Environment (ACME) Method Binding",
RFC 8657, DOI 10.17487/RFC8657, November 2019,
<https://www.rfc-editor.org/info/rfc8657>.
[RFC8659] Hallam-Baker, P., Stradling, R., and J. Hoffman-Andrews,
"DNS Certification Authority Authorization (CAA) Resource
Record", RFC 8659, DOI 10.17487/RFC8659, November 2019,
<https://www.rfc-editor.org/info/rfc8659>.
Appendix A. Document History
[[Note to RFC Editor: please remove before publication.]]
A.1. draft-ietf-acme-star-delegation-09
* A few remaining comments by Ben Kaduk.
Sheffer, et al. Expires 13 December 2021 [Page 38]
Internet-Draft ACME Delegation June 2021
A.2. draft-ietf-acme-star-delegation-08
Extensive reviews by multiple IETF contributors and IESG members
(many thanks to all involved, your names are in the Acknowledgments).
Specifically:
* More clarity in the Terminology, and correct distinction between
CA and ACME server.
* Explicit description of "delegations list", the object returned by
the "delegations" URL.
* The "delegation" is no longer part of the identifier, rather it is
a property of the order.
* Clarified the negotiation of unauthenticated GET for fetching
certificates. This includes some normative changes.
* Explicit description of the changes required on the CA: support
for unauthenticated GET.
* Some changes to IANA registrations and a change to the
registration policy of a new registry.
* More detail about security considerations related to pre-
registration of the NDC as an ACME account on IdO.
* Minor changes to the CSR Template schemas.
* Many editorial changes.
A.3. draft-ietf-acme-star-delegation-07
* SecDir comments by Russ Housley.
* In particular, reorganized some parts of the document to clarify
handling of non-STAR certificates.
* And changed the document's title accordingly.
A.4. draft-ietf-acme-star-delegation-06
* CDDL schema to address Roman's remaining comments.
A.5. draft-ietf-acme-star-delegation-05
* Detailed AD review by Roman Danyliw.
* Some comments that were left unaddressed in Ryan Sleevi's review.
* Numerous other edits for clarity and consistency.
A.6. draft-ietf-acme-star-delegation-04
* Delegation of non-STAR certificates.
* More IANA clarity, specifically on certificate extensions.
* Add delegation configuration object and extend account and order
objects accordingly.
* A lot more depth on Security Considerations.
Sheffer, et al. Expires 13 December 2021 [Page 39]
Internet-Draft ACME Delegation June 2021
A.7. draft-ietf-acme-star-delegation-03
* Consistency with the latest changes in the base ACME STAR
document, e.g. star-delegation-enabled capability renamed and
moved.
* Proxy use cases (recursive delegation) and the definition of proxy
behavior.
* More detailed analysis of the CDNI and STIR use cases, including
sequence diagrams.
A.8. draft-ietf-acme-star-delegation-02
* Security considerations: review by Ryan Sleevi.
* CSR template simplified: instead of being a JSON Schema document
itself, it is now a simple JSON document which validates to a JSON
Schema.
A.9. draft-ietf-acme-star-delegation-01
* Refinement of the CDNI use case.
* Addition of the CSR template (partial, more work required).
* Further security considerations (work in progress).
A.10. draft-ietf-acme-star-delegation-00
* Republished as a working group draft.
A.11. draft-sheffer-acme-star-delegation-01
* Added security considerations about disallowing CDNs from issuing
certificates for a delegated domain.
A.12. draft-sheffer-acme-star-delegation-00
* Initial version, some text extracted from draft-sheffer-acme-star-
requests-02
Appendix B. CSR Template: CDDL
Following is the normative definition of the CSR template, using CDDL
[RFC8610]. The CSR template MUST be a valid JSON document, compliant
with the syntax defined here.
There are additional constraints not expressed in CDDL that MUST be
validated by the recipient, including:
* The value of each "subjectAltName" entry is compatible with its
type;
Sheffer, et al. Expires 13 December 2021 [Page 40]
Internet-Draft ACME Delegation June 2021
* The parameters in each "keyTypes" entry form an acceptable
combination.
csr-template-schema = {
keyTypes: [ + $keyType ]
? subject: non-empty<distinguishedName>
extensions: extensions
}
non-empty<M> = (M) .and ({ + any => any })
mandatory-wildcard = "**"
optional-wildcard = "*"
wildcard = mandatory-wildcard / optional-wildcard
; regtext matches all text strings but "*" and "**"
regtext = text .regexp "([^\*].*)|([\*][^\*].*)|([\*][\*].+)"
regtext-or-wildcard = regtext / wildcard
distinguishedName = {
? country: regtext-or-wildcard
? stateOrProvince: regtext-or-wildcard
? locality: regtext-or-wildcard
? organization: regtext-or-wildcard
? organizationalUnit: regtext-or-wildcard
? emailAddress: regtext-or-wildcard
? commonName: regtext-or-wildcard
}
$keyType /= rsaKeyType
$keyType /= ecdsaKeyType
rsaKeyType = {
PublicKeyType: "rsaEncryption" ; OID: 1.2.840.113549.1.1.1
PublicKeyLength: rsaKeySize
SignatureType: $rsaSignatureType
}
rsaKeySize = uint
; RSASSA-PKCS1-v1_5 with SHA-256
$rsaSignatureType /= "sha256WithRSAEncryption"
; RSASSA-PCKS1-v1_5 with SHA-384
$rsaSignatureType /= "sha384WithRSAEncryption"
; RSASSA-PCKS1-v1_5 with SHA-512
$rsaSignatureType /= "sha512WithRSAEncryption"
; RSASSA-PSS with SHA-256, MGF-1 with SHA-256, and a 32 byte salt
Sheffer, et al. Expires 13 December 2021 [Page 41]
Internet-Draft ACME Delegation June 2021
$rsaSignatureType /= "sha256WithRSAandMGF1"
; RSASSA-PSS with SHA-384, MGF-1 with SHA-384, and a 48 byte salt
$rsaSignatureType /= "sha384WithRSAandMGF1"
; RSASSA-PSS with SHA-512, MGF-1 with SHA-512, and a 64 byte salt
$rsaSignatureType /= "sha512WithRSAandMGF1"
ecdsaKeyType = {
PublicKeyType: "id-ecPublicKey" ; OID: 1.2.840.10045.2.1
namedCurve: $ecdsaCurve
SignatureType: $ecdsaSignatureType
}
$ecdsaCurve /= "secp256r1" ; OID: 1.2.840.10045.3.1.7
$ecdsaCurve /= "secp384r1" ; OID: 1.3.132.0.34
$ecdsaCurve /= "secp521r1" ; OID: 1.3.132.0.3
$ecdsaSignatureType /= "ecdsa-with-SHA256" ; paired with secp256r1
$ecdsaSignatureType /= "ecdsa-with-SHA384" ; paired with secp384r1
$ecdsaSignatureType /= "ecdsa-with-SHA512" ; paired with secp521r1
subjectaltname = {
? DNS: [ + regtext-or-wildcard ]
? Email: [ + regtext ]
? URI: [ + regtext ]
* $$subjectaltname-extension
}
extensions = {
? keyUsage: [ + keyUsageType ]
? extendedKeyUsage: [ + extendedKeyUsageType ]
subjectAltName: non-empty<subjectaltname>
}
keyUsageType /= "digitalSignature"
keyUsageType /= "nonRepudiation"
keyUsageType /= "keyEncipherment"
keyUsageType /= "dataEncipherment"
keyUsageType /= "keyAgreement"
keyUsageType /= "keyCertSign"
keyUsageType /= "cRLSign"
keyUsageType /= "encipherOnly"
keyUsageType /= "decipherOnly"
extendedKeyUsageType /= "serverAuth"
extendedKeyUsageType /= "clientAuth"
extendedKeyUsageType /= "codeSigning"
extendedKeyUsageType /= "emailProtection"
extendedKeyUsageType /= "timeStamping"
Sheffer, et al. Expires 13 December 2021 [Page 42]
Internet-Draft ACME Delegation June 2021
extendedKeyUsageType /= "OCSPSigning"
extendedKeyUsageType /= oid
oid = text .regexp "([0-2])((\.0)|(\.[1-9][0-9]*))*"
Appendix C. CSR Template: JSON Schema
This appendix includes an alternative, non-normative, JSON Schema
definition of the CSR template. The syntax used is that of draft 7
of JSON Schema, which is documented in [json-schema-07]. Note that
later versions of this (now expired) draft describe later versions of
the JSON Schema syntax. At the time of writing, a stable reference
for this syntax is not yet available, and we have chosen to use the
draft version which is currently best supported by tool
implementations.
The same considerations about additional constraints checking
discussed in Appendix B apply here as well.
{
"title": "JSON Schema for the STAR Delegation CSR template",
"$schema": "http://json-schema.org/draft-07/schema#",
"$id": "http://ietf.org/acme/drafts/star-delegation/csr-template",
"$defs": {
"distinguished-name": {
"$id": "#distinguished-name",
"type": "object",
"minProperties": 1,
"properties": {
"country": {
"type": "string"
},
"stateOrProvince": {
"type": "string"
},
"locality": {
"type": "string"
},
"organization": {
"type": "string"
},
"organizationalUnit": {
"type": "string"
},
"emailAddress": {
"type": "string"
},
"commonName": {
Sheffer, et al. Expires 13 December 2021 [Page 43]
Internet-Draft ACME Delegation June 2021
"type": "string"
}
},
"additionalProperties": false
},
"rsaKeyType": {
"$id": "#rsaKeyType",
"type": "object",
"properties": {
"PublicKeyType": {
"type": "string",
"const": "rsaEncryption"
},
"PublicKeyLength": {
"type": "integer"
},
"SignatureType": {
"type": "string",
"enum": [
"sha256WithRSAEncryption",
"sha384WithRSAEncryption",
"sha512WithRSAEncryption",
"sha256WithRSAandMGF1",
"sha384WithRSAandMGF1",
"sha512WithRSAandMGF1"
]
}
},
"required": [
"PublicKeyType",
"PublicKeyLength",
"SignatureType"
],
"additionalProperties": false
},
"ecdsaKeyType": {
"$id": "#ecdsaKeyType",
"type": "object",
"properties": {
"PublicKeyType": {
"type": "string",
"const": "id-ecPublicKey"
},
"namedCurve": {
"type": "string",
"enum": [
"secp256r1",
"secp384r1",
Sheffer, et al. Expires 13 December 2021 [Page 44]
Internet-Draft ACME Delegation June 2021
"secp521r1"
]
},
"SignatureType": {
"type": "string",
"enum": [
"ecdsa-with-SHA256",
"ecdsa-with-SHA384",
"ecdsa-with-SHA512"
]
}
},
"required": [
"PublicKeyType",
"namedCurve",
"SignatureType"
],
"additionalProperties": false
}
},
"type": "object",
"properties": {
"keyTypes": {
"type": "array",
"minItems": 1,
"items": {
"anyOf": [
{
"$ref": "#rsaKeyType"
},
{
"$ref": "#ecdsaKeyType"
}
]
}
},
"subject": {
"$ref": "#distinguished-name"
},
"extensions": {
"type": "object",
"properties": {
"keyUsage": {
"type": "array",
"minItems": 1,
"items": {
"type": "string",
"enum": [
Sheffer, et al. Expires 13 December 2021 [Page 45]
Internet-Draft ACME Delegation June 2021
"digitalSignature",
"nonRepudiation",
"keyEncipherment",
"dataEncipherment",
"keyAgreement",
"keyCertSign",
"cRLSign",
"encipherOnly",
"decipherOnly"
]
}
},
"extendedKeyUsage": {
"type": "array",
"minItems": 1,
"items": {
"anyOf": [
{
"type": "string",
"enum": [
"serverAuth",
"clientAuth",
"codeSigning",
"emailProtection",
"timeStamping",
"OCSPSigning"
]
},
{
"type": "string",
"pattern": "^([0-2])((\\.0)|(\\.[1-9][0-9]*))*$",
"description": "Used for OID values"
}
]
}
},
"subjectAltName": {
"type": "object",
"minProperties": 1,
"properties": {
"DNS": {
"type": "array",
"minItems": 1,
"items": {
"anyOf": [
{
"type": "string",
"enum": [
Sheffer, et al. Expires 13 December 2021 [Page 46]
Internet-Draft ACME Delegation June 2021
"*",
"**"
]
},
{
"type": "string",
"format": "hostname"
}
]
}
},
"Email": {
"type": "array",
"minItems": 1,
"items": {
"type": "string",
"format": "email"
}
},
"URI": {
"type": "array",
"minItems": 1,
"items": {
"type": "string",
"format": "uri"
}
}
},
"additionalProperties": false
}
},
"required": [
"subjectAltName"
],
"additionalProperties": false
}
},
"required": [
"extensions",
"keyTypes"
],
"additionalProperties": false
}
Authors' Addresses
Sheffer, et al. Expires 13 December 2021 [Page 47]
Internet-Draft ACME Delegation June 2021
Yaron Sheffer
Intuit
Email: yaronf.ietf@gmail.com
Diego López
Telefonica I+D
Email: diego.r.lopez@telefonica.com
Antonio Agustín Pastor Perales
Telefonica I+D
Email: antonio.pastorperales@telefonica.com
Thomas Fossati
ARM
Email: thomas.fossati@arm.com
Sheffer, et al. Expires 13 December 2021 [Page 48]
