Internet DRAFT - draft-sheffer-acme-star-request
draft-sheffer-acme-star-request
ACME Y. Sheffer
Internet-Draft Intuit
Intended status: Standards Track D. Lopez
Expires: December 31, 2018 O. Gonzalez de Dios
A. Pastor Perales
Telefonica I+D
T. Fossati
Nokia
June 29, 2018
Generating Certificate Requests for Short-Term, Automatically-Renewed
(STAR) Certificates
draft-sheffer-acme-star-request-02
Abstract
This memo proposes a protocol that allows a domain name owner to
delegate to a third party (such as a CDN) control over a certificate
that bears one or more names in that domain. Specifically the third
party creates a Certificate Signing Request for the domain, which can
then be used by the domain owner to request a short term and
automatically renewed (STAR) certificate.
This is a component in a solution where a third-party such as a CDN
can terminate TLS sessions on behalf of a domain name owner (e.g., a
content provider), and the domain owner can cancel this delegation at
any time without having to rely on certificate revocation mechanisms.
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
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This Internet-Draft will expire on December 31, 2018.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Conventions used in this document . . . . . . . . . . . . 4
2. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Preconditions . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Bootstrap . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Refresh . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4. Termination . . . . . . . . . . . . . . . . . . . . . . . 7
3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 8
3.1. STAR API . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1.1. Creating a Delegation Request . . . . . . . . . . . . 8
3.1.2. Polling the Delegation Request . . . . . . . . . . . 10
3.2. Transport Security for the STAR Protocol . . . . . . . . 11
4. CDNI Use Cases . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Multiple Parallel Delegates . . . . . . . . . . . . . . . 11
4.2. Chained Delegation . . . . . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
5.1. STAR Protocol Authentication . . . . . . . . . . . . . . 12
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Document History . . . . . . . . . . . . . . . . . . 14
A.1. draft-sheffer-acme-star-request-02 . . . . . . . . . . . 14
A.2. draft-sheffer-acme-star-request-01 . . . . . . . . . . . 14
A.3. draft-sheffer-acme-star-request-00 . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
This document is a companion document to [I-D.ietf-acme-star]. To
avoid duplication, we give here a bare-bones description of the
motivation for this solution. For more details and further use
cases, please refer to the introductory sections of
[I-D.ietf-acme-star].
A content provider (referred to in this document as Domain Name
Owner, DNO, or more generally as Identity Owner, IdO) has agreements
in place with one or more Content Delivery Networks (CDNs) that are
contracted to serve its content over HTTPS. The CDN terminates the
HTTPS connection at one of its edge cache servers and needs to
present its clients (browsers, set-top-boxes) a certificate whose
name matches the authority of the URL that is requested, i.e. that of
the DNO. However, many DNOs balk at sharing their long-term private
keys with another organization and, equally, delegates (henceforth
referred to as NDC, Name Delegation Consumer) would rather not have
to handle other parties' long-term secrets.
This document describes a protocol where the IdO and the NDC agree on
a CSR template and the NDC generates a CSR for a private key that it
holds. The IdO then uses the ACME protocol (as extended in
[I-D.ietf-acme-star]) to issue the STAR certificate.
The generated short-term certificate is automatically renewed by an
ACME Certification Authority (CA) [I-D.ietf-acme-acme] and
periodically fetched into the NDC and used for HTTPS connections.
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.
1.1. Terminology
IdO Identity Owner, the owner of an identity (e.g., a domain name)
that needs to be delegated.
DNO Domain Name Owner, a specific kind of IdO whose identity is a
domain name.
NDC Name Delegation Consumer, the entity to which the domain name is
delegated for a limited time. This is often a CDN (in fact,
readers may note the similarity of the two acronyms).
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 The IETF Automated Certificate Management Environment, a
certificate management protocol.
CA A Certificate Authority that implements the ACME protocol.
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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
[RFC2119].
2. Protocol Flow
This section presents the protocol flow. For completeness, we
include the STAR Interface proposed in this draft, as well as the
extended ACME protocol as described in [I-D.ietf-acme-star].
2.1. Preconditions
The protocol assumes the following preconditions are met:
o A mutually authenticated channel between NDC and IdO pre-exists.
This is called "STAR channel" and all STAR protocol exchanges
between NDC and IdO are run over it. It provides the guarantee
that requests and responses are authentic.
o NDC and IdO have agreed on a "CSR template" to use, including at a
minimum:
- Subject name (e.g., "somesite.example.com"),
- Requested algorithms,
- Key length,
- Key usage.
The NDC is required to use this template for every CSR created
under the same delegation.
o IdO has registered through the ACME interface exposed by the
Certificate Authority (CA) using the usual ACME registration
procedure. In ACME terms, the IdO has an Account on the server
and is ready to issue Orders.
2.2. Bootstrap
The NDC (STAR Client) generates a key-pair, wraps it into a
Certificate Signing Request (CSR) according to the agreed upon CSR
template, and sends it to the IdO (STAR Proxy) over the pre-
established STAR channel. The IdO uses the NDC identity provided on
the STAR channel to look up the CSR template that applies to the
requesting NDC and decides whether or not to accept the request.
Assuming everything is in order, it then "forwards" the NDC request
to the ACME CA by means of the usual ACME application procedure.
Specifically, the IdO, in its role as an ACME client, requests the CA
to issue a STAR certificate, i.e., one that:
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o Has a short validity (e.g., 24 to 72 hours);
o Is automatically renewed by the CA for a certain period of time;
o Is downloadable from a (highly available) public link without
requiring any special authorization.
Other than that, the ACME protocol flows as normal between IdO and
CA, in particular IdO is responsible for satisfying the requested
ACME challenges until the CA is willing to issue the requested
certificate. Per normal ACME processing, the IdO is given back an
Order ID for the issued STAR certificate to be used in subsequent
interaction with the CA (e.g., if the certificate needs to be
terminated.)
Concurrently, a response is sent back to the NDC with an endpoint to
poll for completion of the certificate generation process.
The bootstrap phase ends when the IdO obtains the OK from the ACME CA
and posts the certificate's URL to the "completion endpoint" where
the NDC can retrieve it.
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...........................
STAR : STAR Proxy / : ACME/STAR
Client : ACME Client : Server
| : | | : |
| : | | ACME registration |
+-------. : | |<--------------------->|
| | : | | STAR capabilities |
| generate CSR : | | : |
| | : | | : |
|<------' : | | : |
| : | | : |
| Request new : | | : |
+---------------------->| | : |
| cert for CSR : | | : |
| : +-------. | : |
| : | | | : |
| : | Verify CSR | : |
| : | | | : |
| : +<------' | : |
| Accepted, poll at | | : |
|<----------------------+ | : |
| "completion URL" |- - - - - - - >| Application for |
| : | +---------------------->|
| : | | STAR certificate |
| : | | : |
| GET "completion URL" | | : Challenge |
|<--------------------->| |<--------------------->|
| in progress : | | : Response |
| : | | : |
| : | | Finalize/Certificate |
| : | |<----------------------+
| GET "completion URL" |< - - - - - - -| : + Order Id |
+---------------------->| | : |
| : | | : |
| 200, certificate URL | | : |
|<----------------------+ | : |
| and other metadata | | : |
| : | | : |
`.........................'
Figure 1: Bootstrap
2.3. Refresh
The CA automatically re-issues the certificate (using the same CSR)
before it expires and publishes it to the URL that the NDC has come
to know at the end of the bootstrap phase. The NDC downloads and
installs it. This process goes on until either:
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o IdO terminates the delegation, or
o Automatic renewal expires.
STAR ACME/STAR
Client Server
| Retrieve cert | [...]
|<--------------------->| |
| +------. /
| | | /
| | Automatic renewal :
| | | \
| |<-----' \
| Retrieve cert | |
|<--------------------->| 72 hours
| | |
| +------. /
| | | /
| | Automatic renewal :
| | | \
| |<-----' \
| Retrieve cert | |
|<--------------------->| 72 hours
| | |
| +------. /
| | | /
| | Automatic renewal :
| | | \
| |<-----' \
| | |
| [...] | [...]
Figure 2: Auto renewal
2.4. Termination
The IdO may request early termination of the STAR certificate by
including the Order ID in a certificate termination request to the
ACME interface, defined below. After the CA receives and verifies
the request, it shall:
o Cancel the automatic renewal process for the STAR certificate;
o Change the certificate publication resource to return an error
indicating the termination of the delegation to external clients,
including the NDC.
Note that it is not necessary to explicitly revoke the short-term
certificate.
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STAR STAR ACME/STAR
Client Proxy Server
| | |
| | Terminate Order ID |
| +---------------------->|
| | +-------.
| | | |
| | | End auto renewal
| | | Remove cert link
| | | etc.
| | | |
| | Done |<------'
| |<----------------------+
| | |
| |
| Retrieve cert |
+---------------------------------------------->|
| Error: terminated |
|<----------------------------------------------+
| |
Figure 3: Termination
No facility is provided for the NDC to directly initiate the
termination of a STAR certificate.
3. Protocol Details
This section describes the STAR API between the STAR Client and the
STAR Proxy.
3.1. STAR API
This API allows an IdO (STAR Proxy) to control the long-term
delegation of one of its names to an authorized third-party (STAR
Client).
3.1.1. Creating a Delegation Request
To create a new delegation request, the client wraps the following
parameters in a POST to the '/star/delegation' path:
o csr (required, string): A CSR encoding the parameters for the
certificate being requested [RFC2986]. The CSR is sent in the
base64url-encoded version of the DER format. (Note: Because this
field uses base64url, and does not include headers, it is
different from PEM.)
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o duration (optional, integer): How long the delegation should last
(in seconds). If not specified, a local default applies.
o certificate-lifetime (optional, integer): How long each short-term
certificate should last (in seconds). If not specified, a local
default applies.
Note that the STAR Proxy MAY treat both "duration" and "certificate-
lifetime" as hints, and MAY update any of them due to local policy
decisions or as a result of the interaction with the ACME server.
POST /star/delegation
Host: star-proxy.example.net
Content-Type: application/json
{
"csr": "jcRf4uXra7FGYW5ZMewvV...rhlnznwy8YbpMGqwidEXfE",
"duration": 31536000,
"certificate-lifetime": 604800
}
On success, the service returns a 201 Created status with the URL of
the newly generated delegation order in the Location header field.
The current state of the delegation order is returned in the body of
the response in JSON format:
HTTP/1.1 201 Created
Content-Type: application/json
Location: http://example.net/star/delegation/567
{
"id": "567",
"certificate-lifetime": 604800,
"duration": 31536000,
"status": "new"
}
If an error occurs, an error response (4XX or 5XX) is generated with
an appropriate problem detail [RFC7807] body, e.g.:
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HTTP/1.1 400 Bad Request
Content-Type: application/problem+json
{
"type": "https://example.net/validation-error",
"title": "Your request parameters didn't validate.",
"invalid-params": [ {
"name": "csr",
"reason": "missing mandatory parameter"
} ]
}
3.1.2. Polling the Delegation Request
The returned delegation order URL can be polled until the dialog
between the STAR Proxy and the ACME server is complete (i.e., the
"status" attribute changes from "new" or "pending" to one of "failed"
or "success"):
GET /star/delegation/567
Host: star-proxy.example.net
In responding to poll requests while the validation is still in
progress, the server MUST return a 200 (OK) response and MAY include
a Retry-After header field to suggest a polling interval to the
client. The Retry-After value MUST be expressed in seconds. If the
Retry-After header is present, in order to avoid surprising
interactions with heuristic expiration times, a max-age Cache-Control
SHOULD also be present and set to a value slightly smaller than the
Retry-After value:
HTTP/1.1 200 OK
Content-Type: application/json
Retry-After: 10
Cache-Control: max-age=9
{
"id": "5",
"certificate-lifetime": 604800,
"creation-date": "2017-11-12T01:38:09Z",
"duration": 31536000,
"status": "pending"
}
When the operation is successfully completed, the ACME Proxy returns:
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HTTP/1.1 200 OK
{
"status": "success", // or "failed"
"lifetime": 365, // lifetime of the registration in days,
// possibly less than requested
"certificates": "https://ca.example.org/certificates/A51A3"
}
The "certificates" attribute contains a URL of the certificate pull
endpoint, received from the ACME Server.
If the registration fails for any reason, the server returns a "200
OK" response, with the status as "failed" and a "reason" attribute
containing a human readable error message.
3.2. Transport Security for the STAR Protocol
Traffic between the STAR Client and the STAR Proxy MUST be protected
with HTTPS. For interoperability, all implementations MUST support
HTTP Basic Authentication [RFC7617]. However some deployments MAY
prefer mutually-authenticated HTTPS or two-legged OAUTH.
4. CDNI Use Cases
Members of the IETF CDNI (Content Delivery Network Interconnection)
working group are interested in delegating authority over web content
to CDNs. Their requirements are described in a draft
[I-D.fieau-cdni-https-delegation] that compares several solutions.
This section discusses two particular requirements in the context of
the STAR protocol.
4.1. Multiple Parallel Delegates
In some cases the DNO would like to delegate authority over a web
site to multiple CDNs. This could happen if the DNO has agreements
in place with different regional CDNs for different geographical
regions. STAR enables this use case naturally, since each CDN can
authenticate separately to the DNO specifying its CSR, and the DNO is
free to allow or deny each certificate request according to its own
policy.
4.2. Chained Delegation
In other cases, a content owner (DNO) delegates some domains to a
large CDN (CDN1), which in turn delegates to a smaller regional CDN,
CDN2. The DNO has a contractual relationship with CDN1, and CDN1 has
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a similar relationship with CDN2. However DNO may not even know
about CDN2.
The STAR protocol does not prevent this use case, although there is
no special support for it. CDN1 can forward requests from CDN2 to
DNO, and forward responses back to CDN2. Whether such proxying is
allowed is governed by policy and contracts between the parties.
5. Security Considerations
5.1. STAR Protocol Authentication
The STAR protocol allows its client to obtain certificates bearing
the IdO's identity. Therefore strong client authentication is
mandatory.
When multiple NDCs may connect to the same IdO, the STAR protocol's
authentication MUST allow the IdO to distinguish between different
NDCs, and the IdO MUST associate different Registration objects to
different clients. Among other benefits, this allows the IdO to
cancel a STAR registration for one of its clients instead of all of
them.
6. Acknowledgments
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.
7. References
7.1. Normative References
[I-D.ietf-acme-acme]
Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", draft-ietf-acme-acme-12 (work in progress), April
2018.
[I-D.ietf-acme-star]
Sheffer, Y., Lopez, D., Dios, O., Pastor, A., and T.
Fossati, "Support for Short-Term, Automatically-Renewed
(STAR) Certificates in Automated Certificate Management
Environment (ACME)", draft-ietf-acme-star-03 (work in
progress), March 2018.
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[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>.
[RFC7617] Reschke, J., "The 'Basic' HTTP Authentication Scheme",
RFC 7617, DOI 10.17487/RFC7617, September 2015,
<https://www.rfc-editor.org/info/rfc7617>.
[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>.
7.2. Informative References
[I-D.fieau-cdni-https-delegation]
Fieau, F., Emile, S., and S. Mishra, "HTTPS delegation in
CDNI", draft-fieau-cdni-https-delegation-02 (work in
progress), July 2017.
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Appendix A. Document History
[[Note to RFC Editor: please remove before publication.]]
A.1. draft-sheffer-acme-star-request-02
o Clarifications and minor changes based on implementation
experience.
o More detail on error cases.
A.2. draft-sheffer-acme-star-request-01
o Correct reference to WG draft.
A.3. draft-sheffer-acme-star-request-00
o Initial version, the STAR API extracted from draft-sheffer-acme-
star-02.
Authors' Addresses
Yaron Sheffer
Intuit
EMail: yaronf.ietf@gmail.com
Diego Lopez
Telefonica I+D
EMail: diego.r.lopez@telefonica.com
Oscar Gonzalez de Dios
Telefonica I+D
EMail: oscar.gonzalezdedios@telefonica.com
Antonio Agustin Pastor Perales
Telefonica I+D
EMail: antonio.pastorperales@telefonica.com
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Thomas Fossati
Nokia
EMail: thomas.fossati@nokia.com
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