[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]
Versions: (draft-sheffer-acme-star) 00 01 02
03 04 05
ACME Working Group Y. Sheffer
Internet-Draft Intuit
Intended status: Standards Track D. Lopez
Expires: June 2, 2018 O. Gonzalez de Dios
A. Pastor Perales
Telefonica I+D
T. Fossati
Nokia
November 29, 2017
Support for Short-Term, Automatically-Renewed (STAR) Certificates in
Automated Certificate Management Environment (ACME)
draft-ietf-acme-star-02
Abstract
Public-key certificates need to be revoked when they are compromised,
that is, when the associated private key is exposed to an attacker.
However the revocation process is often unreliable. An alternative
to revocation is issuing a sequence of certificates, each with a
short validity period, and terminating this sequence upon compromise.
This memo proposes an ACME extension to enable the issuance of short-
term and automatically renewed (STAR) certificates.
[RFC Editor: please remove before publication]
While the draft is being developed, the editor's version can be found
at https://github.com/yaronf/I-D/tree/master/STAR.
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 http://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 June 2, 2018.
Sheffer, et al. Expires June 2, 2018 [Page 1]
Internet-Draft ACME STAR November 2017
Copyright Notice
Copyright (c) 2017 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
(http://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. Name Delegation Use Case . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Conventions used in this document . . . . . . . . . . . . 4
2. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Bootstrap . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Refresh . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Termination . . . . . . . . . . . . . . . . . . . . . . . 6
3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 7
3.1. ACME Extensions . . . . . . . . . . . . . . . . . . . . . 7
3.1.1. Extending the Order Resource . . . . . . . . . . . . 7
3.1.2. Canceling a Recurrent Order . . . . . . . . . . . . . 8
3.2. Capability Discovery . . . . . . . . . . . . . . . . . . 9
3.3. Fetching the Certificates . . . . . . . . . . . . . . . . 10
4. Operational Considerations . . . . . . . . . . . . . . . . . 11
4.1. Define "short" . . . . . . . . . . . . . . . . . . . . . 11
4.2. Clock Skew . . . . . . . . . . . . . . . . . . . . . . . 11
4.3. Certificate Transparency (CT) Logs . . . . . . . . . . . 11
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 11
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1.1. ACME Server with STAR extension . . . . . . . . . . . 12
5.1.2. STAR Proxy . . . . . . . . . . . . . . . . . . . . . 12
5.2. Level of Maturity . . . . . . . . . . . . . . . . . . . . 13
5.3. Coverage . . . . . . . . . . . . . . . . . . . . . . . . 13
5.4. Version Compatibility . . . . . . . . . . . . . . . . . . 13
5.5. Licensing . . . . . . . . . . . . . . . . . . . . . . . . 13
5.6. Implementation experience . . . . . . . . . . . . . . . . 13
5.7. Contact Information . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
6.1. New ACME Error Types . . . . . . . . . . . . . . . . . . 14
6.2. New ACME Order Object Fields . . . . . . . . . . . . . . 14
Sheffer, et al. Expires June 2, 2018 [Page 2]
Internet-Draft ACME STAR November 2017
6.3. Not-Before and Not-After HTTP Headers . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7.1. Denial of Service Considerations . . . . . . . . . . . . 15
7.2. Additional Considerations TBD . . . . . . . . . . . . . . 16
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Document History . . . . . . . . . . . . . . . . . . 18
A.1. draft-ietf-acme-star-02 . . . . . . . . . . . . . . . . . 18
A.2. draft-ietf-acme-star-01 . . . . . . . . . . . . . . . . . 18
A.3. draft-ietf-acme-star-00 . . . . . . . . . . . . . . . . . 18
A.4. draft-sheffer-acme-star-02 . . . . . . . . . . . . . . . 18
A.5. draft-sheffer-acme-star-01 . . . . . . . . . . . . . . . 18
A.6. draft-sheffer-acme-star-00 . . . . . . . . . . . . . . . 18
A.7. draft-sheffer-acme-star-lurk-00 . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
The ACME protocol [I-D.ietf-acme-acme] automates the process of
issuing a certificate to a named entity (an Identity Owner or IdO).
Typically, but not always, the identity is a domain name and we may
refer to the entity as a Domain Name Owner (DNO).
If the IdO wishes to obtain a string of short-term certificates
originating from the same private key (see [Topalovic] about why
using short-lived certificates might be preferable to explicit
revocation), she must go through the whole ACME protocol each time a
new short-term certificate is needed - e.g., every 2-3 days. If done
this way, the process would involve frequent interactions between the
registration function of the ACME Certification Authority (CA) and
the identity provider infrastructure (e.g.: DNS, web servers),
therefore making the issuance of short-term certificates exceedingly
dependent on the reliability of both.
This document presents an extension of the ACME protocol that
optimizes this process by making short-term certificates first class
objects in the ACME ecosystem. Once the order for a string of short-
term certificates is accepted, the CA is responsible for publishing
the next certificate at an agreed upon URL before the previous one
expires. The IdO can terminate the automatic renewal before the
natural deadline, if needed - e.g., on key compromise.
For a more generic treatment of STAR certificates, readers are
referred to [I-D.nir-saag-star].
Sheffer, et al. Expires June 2, 2018 [Page 3]
Internet-Draft ACME STAR November 2017
1.1. Name Delegation Use Case
The proposed mechanism can be used as a building block of an
efficient name-delegation protocol, for example one that exists
between a CDN or a cloud provider and its customers
[I-D.sheffer-acme-star-request]. At any time, the service customer
(i.e., the IdO) can terminate the delegation by simply instructing
the CA to stop the automatic renewal and letting the currently active
certificate expire shortly thereafter.
1.2. Terminology
IdO Identifier Owner, the owner of an identifier, e.g.: a domain
name, a telephone number.
DNO Domain Name Owner, a type of IdO whose identifier is a domain
name.
STAR Short-Term, Automatically Renewed X.509 certificates.
NDC Name Delegation Client, an entity to which the identifier owned
by the IdO is delegated for a limited time. Examples include a
CDN edge cache, a cloud provider's load balancer or Web
Application Firewall (WAF).
1.3. 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
The following subsections describe the three main phases of the
protocol:
o Bootstrap: the IdO asks an ACME CA to create a short-term and
automatically-renewed (STAR) certificate (Section 2.1);
o Auto-renewal: the ACME CA periodically re-issues the short-term
certificate and posts it to a public URL (Section 2.2);
o Termination: the IdO requests the ACME CA to discontinue the
automatic renewal of the certificate (Section 2.3).
This diagram presents the entities that are (or may be) involved in
the protocol and their interactions during the different phases.
Sheffer, et al. Expires June 2, 2018 [Page 4]
Internet-Draft ACME STAR November 2017
Refresh
. . . . . . . . . . . . . . . . . . . .
. ' ` v
.-----. Bootstrap / Terminate .---------.
| IdO |------------------------------------->| ACME CA |
`-----' `---------'
^ .- - -. ^
` . . . . . . . . : NDC : . . . . . . . . . '
Request `- - -' Refresh
Delegation
Note that there might be a distinct NDC entity (e.g., a CDN edge
cache) that uses a separate channel to request the IdO to set up a
name delegation. The protocol described in
[I-D.sheffer-acme-star-request] may be used for this purpose.
2.1. Bootstrap
The IdO, in its role as an ACME client, requests the CA to issue a
STAR certificate, i.e., one that:
o Has a short validity, e.g., 24 to 72 hours. Note that the exact
definition of "short" depends on the use case;
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 usual 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 URL for the issued STAR certificate to be used in subsequent
interaction with the CA (e.g., if the certificate needs to be
terminated.)
The bootstrap phase ends when the IdO obtains a confirmation from the
ACME CA that includes a certificate endpoint.
2.2. Refresh
The CA automatically re-issues the certificate using the same CSR
(and therefore the same identifier and public key) before it expires
and publishes it to the URL that was returned to the IdO at the end
of the bootstrap phase. The certificate user, which could be either
the IdO itself or a delegated third party, as described in
[I-D.sheffer-acme-star-request], obtains the certificate and uses it.
The refresh process (Figure 1) goes on until either:
Sheffer, et al. Expires June 2, 2018 [Page 5]
Internet-Draft ACME STAR November 2017
o IdO explicitly terminates the automatic renewal (Section 2.3); or
o Automatic renewal expires.
Certificate ACME/STAR
User Server
| Retrieve cert | [...]
|---------------------->| |
| +------. /
| | | /
| | Automatic renewal :
| | | \
| |<-----' \
| Retrieve cert | |
|---------------------->| 72 hours
| | |
| +------. /
| | | /
| | Automatic renewal :
| | | \
| |<-----' \
| Retrieve cert | |
|---------------------->| 72 hours
| | |
| +------. /
| | | /
| | Automatic renewal :
| | | \
| |<-----' \
| | |
| [...] | [...]
Figure 1: Auto renewal
2.3. Termination
The IdO may request early termination of the STAR certificate by
sending a cancellation request to the order resource, as described in
Section 3.1.2. 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 issuance;
o Change the status of the order to "canceled".
Note that it is not necessary to explicitly revoke the short-term
certificate.
Sheffer, et al. Expires June 2, 2018 [Page 6]
Internet-Draft ACME STAR November 2017
Certificate ACME/STAR
User IdO Server
| | |
| | Terminate order |
| +---------------------->|
| | +-------.
| | | |
| | | End auto renewal
| | | Remove cert link
| | | etc.
| | | |
| | Done |<------'
| |<----------------------+
| | |
| |
| Retrieve cert |
+---------------------------------------------->|
| Error: terminated |
|<----------------------------------------------+
| |
Figure 2: Termination
3. Protocol Details
This section describes the protocol details, namely the extensions to
the ACME protocol required to issue STAR certificates.
3.1. ACME Extensions
This protocol extends the ACME protocol, to allow for recurrent
orders.
3.1.1. Extending the Order Resource
The order resource is extended with the following attributes:
{
"recurrent": true,
"recurrent-start-date": "2016-01-01T00:00:00Z",
"recurrent-end-date": "2017-01-01T00:00:00Z",
"recurrent-certificate-validity": 604800
}
o recurrent: MUST be true for STAR certificates.
o recurrent-start-date: the earliest date of validity of the first
certificate issued, in [RFC3339] format. This attribute is
Sheffer, et al. Expires June 2, 2018 [Page 7]
Internet-Draft ACME STAR November 2017
optional. When omitted, the start date is as soon as
authorization is complete.
o recurrent-end-date: the latest date of validity of the last
certificate issued, in [RFC3339] format.
o recurrent-certificate-validity: the maximum validity period of
each STAR certificate, an integer that denotes a number of
seconds.
These attributes are included in a POST message when creating the
order, as part of the "payload" encoded object. They are returned
when the order has been created, and the ACME server MAY adjust them
at will, according to its local policy (see also Section 3.2).
The optional notBefore and notAfter fields MUST NOT be present in a
STAR order.
ACME defines the following values for the order resource's status:
"invalid", "pending", "processing", "valid". In the case of
recurrent orders, the status MUST be "valid" as long as STAR
certificates are being issued. We add a new status value:
"canceled", see Section 3.1.2.
3.1.2. Canceling a Recurrent Order
An important property of the recurrent order is that it can be
canceled by the IdO, with no need for certificate revocation. To
cancel the order, the ACME client sends a POST to the order URL:
POST /acme/order/1 HTTP/1.1
Host: acme-server.example.org
Content-Type: application/jose+json
{
"protected": base64url({
"alg": "ES256",
"kid": "https://example.com/acme/acct/1",
"nonce": "5XJ1L3lEkMG7tR6pA00clA",
"url": "https://example.com/acme/order/1"
}),
"payload": base64url({
"status": "canceled"
}),
"signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g"
}
The server MUST NOT issue any additional certificates for this order,
beyond the certificate that is available for collection at the time
of deletion.
Sheffer, et al. Expires June 2, 2018 [Page 8]
Internet-Draft ACME STAR November 2017
Immediately after the order is canceled, the server:
o MUST update the status of the order resource to "canceled" and
MUST set an appropriate "expires" date;
o MUST respond with 403 (Forbidden) to any requests to the
certificate endpoint. The response SHOULD provide additional
information using a problem document [RFC7807] with type
"urn:ietf:params:acme:error:recurrentOrderCanceled".
Issuing a cancellation for an order that is not in "valid" state has
undefined semantics. A client MUST NOT send such a request, and a
server MUST return an error response with status code 400 (Bad
Request) and type
"urn:ietf:params:acme:error:recurrentCancellationInvalid".
3.2. Capability Discovery
In order to support the discovery of STAR capabilities, The directory
object of an ACME STAR server MUST contain the following attributes
inside the "meta" field:
o star-enabled: boolean flag indicating STAR support. An ACME STAR
server MUST include this key, and MUST set it to true if the
feature is enabled.
o star-min-cert-validity: minimum acceptable value for recurrent-
certificate-validity, in seconds.
o star-max-renewal: maximum delta between recurrent-end-date and
recurrent-start-date, in seconds.
Example directory object advertising STAR support with one day star-
min-cert-validity and one year star-max-renewal:
{
"new-nonce": "https://example.com/acme/new-nonce",
"new-account": "https://example.com/acme/new-account",
"new-order": "https://example.com/acme/new-order",
"new-authz": "https://example.com/acme/new-authz",
"revoke-cert": "https://example.com/acme/revoke-cert",
"key-change": "https://example.com/acme/key-change",
"meta": {
"terms-of-service": "https://example.com/acme/terms/2017-5-30",
"website": "https://www.example.com/",
"caa-identities": ["example.com"],
"star-enabled": true,
"star-min-cert-validity": 86400,
"star-max-renewal": 31536000
}
}
Sheffer, et al. Expires June 2, 2018 [Page 9]
Internet-Draft ACME STAR November 2017
3.3. Fetching the Certificates
The certificate is fetched from the certificate endpoint, as per
[I-D.ietf-acme-acme], Section 7.4.2.
GET /acme/cert/asdf HTTP/1.1
Host: acme-server.example.org
Accept: application/pkix-cert
HTTP/1.1 200 OK
Content-Type: application/pem-certificate-chain
Link: <https://example.com/acme/some-directory>;rel="index"
Not-Before: Mon, 1 Feb 2016 00:00:00 GMT
Not-After: Mon, 8 Feb 2016 00:00:00 GMT
-----BEGIN CERTIFICATE-----
[End-entity certificate contents]
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
[Issuer certificate contents]
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
[Other certificate contents]
-----END CERTIFICATE-----
The Server SHOULD include the "Not-Before" and "Not-After" HTTP
headers in the response. When they exist, they MUST be equal to the
respective fields inside the end-entity certificate. Their format is
"HTTP-date" as defined in Section 7.1.1.2 of [RFC7231]. Their
purpose is to enable client implementations that do not parse the
certificate.
To improve robustness, the next certificate MUST be made available by
the ACME CA at the latest halfway through the lifetime of the
currently active certificate. It is worth noting that this has an
implication in case of cancellation: in fact, from the time the next
certificate is made available, the cancellation is not completely
effective until the latter also expires.
The server MUST NOT issue any additional certificates for this order
beyond its recurrent-end-date.
Immediately after the order expires, the server MUST respond with 403
(Forbidden) to any requests to the certificate endpoint. The
response SHOULD provide additional information using a problem
document [RFC7807] with type
"urn:ietf:params:acme:error:recurrentOrderExpired".
Sheffer, et al. Expires June 2, 2018 [Page 10]
Internet-Draft ACME STAR November 2017
4. Operational Considerations
4.1. Define "short"
TBD
o Short is a relative concept: defining a cut-off point in this
document would be arbitrary. The lifetime of a STAR certificate
is defined by the requirements for revocation on a case by case
basis.
4.2. Clock Skew
TBD
o tweaking notBefore (maybe reference [I-D.nir-saag-star])
o Browser use case: to select the lower bound for short-term (5-7
days) see Section 7.1 of [Acer].
4.3. Certificate Transparency (CT) Logs
TBD
o Browser use case only: STAR increase in CT log ingestion rate
(quantify). How to deal with it is not part of this document.
5. Implementation Status
Note to RFC Editor: please remove this section before publication,
including the reference to [RFC7942].
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
Sheffer, et al. Expires June 2, 2018 [Page 11]
Internet-Draft ACME STAR November 2017
It is up to the individual working groups to use this information as
they see fit".
5.1. Overview
The implementation is constructed around 3 elements: STAR Client for
NDC, STAR Proxy for IdO and ACME Server for CA. The communication
between them is over an IP network and the HTTPS protocol.
The software of the implementation is available at:
https://github.com/mami-project/lurk
The following subsections offer a basic description, detailed
information is available in https://github.com/mami-
project/lurk/blob/master/proxySTAR_v2/README.md
5.1.1. ACME Server with STAR extension
This is a fork of the Let's Encrypt Boulder project that implements
an ACME compliant CA. It includes modifications to extend the ACME
protocol as it is specified in this draft, to support recurrent
orders and cancelling orders.
The implementation understands the new "recurrent" attributes as part
of the Certificate issuance in the POST request for a new resource.
An additional process "renewalManager.go" has been included in
parallel that reads the details of each recurrent request,
automatically produces a "cron" Linux based task that issues the
recurrent certificates, until the lifetime ends or the order is
canceled. This process is also in charge of maintaining a fixed URI
to enable the NDC to download certificates, unlike Boulder's regular
process of producing a unique URI per certificate.
5.1.2. STAR Proxy
The STAR Proxy has a double role as ACME client and STAR Server. The
former is a fork of the EFF Certbot project that implements an ACME
compliant client with the STAR extension. The latter is a basic HTTP
REST API server.
The STAR Proxy understands the basic API request with a server. The
current implementation of the API is defined in draft-ietf-acme-star-
01. Registration or order cancellation triggers the modified Certbot
client that requests, or cancels, the recurrent generation of
certificates using the STAR extension over ACME protocol. The URI
with the location of the recurrent certificate is delivered to the
STAR client as a response.
Sheffer, et al. Expires June 2, 2018 [Page 12]
Internet-Draft ACME STAR November 2017
5.2. Level of Maturity
This is a prototype.
5.3. Coverage
A STAR Client is not included in this implementation, but done by
direct HTTP request with any open HTTP REST API tool. This is
expected to be covered as part of the [I-D.sheffer-acme-star-request]
implementation.
This implementation completely covers STAR Proxy and ACME Server with
STAR extension
5.4. Version Compatibility
The implementation is compatible with version draft-ietf-acme-star-
01. The implementation is based on the Boulder and Certbot code
release from 7-Aug-2017.
5.5. Licensing
This implementation inherits the Boulder license (Mozilla Public
License 2.0) and Certbot license (Apache License Version 2.0 ).
5.6. Implementation experience
To prove the concept all the implementation has been done with a
self-signed CA, to avoid impact on real domains. To be able to do it
we use the FAKE_DNS property of Boulder and static /etc/hosts entries
with domains names. Nonetheless this implementation should run with
real domains.
Most of the implementation has been made to avoid deep changes inside
of Boulder or Certbot, for example, the recurrent certificates
issuance by the CA is based on an external process that auto-
configures the standard Linux "cron" daemon in the ACME CA server.
The reference setup recommended is one physical host with 3 virtual
machines, one for each of the 3 components (client, proxy and server)
and the connectivity based on host bridge.
Network security is not enabled (iptables default policies are
"accept" and all rules removed) in this implementation to simplify
and test the protocol.
Sheffer, et al. Expires June 2, 2018 [Page 13]
Internet-Draft ACME STAR November 2017
5.7. Contact Information
See author details below.
6. IANA Considerations
[[RFC Editor: please replace XXXX below by the RFC number.]]
6.1. New ACME Error Types
This document adds the following entries to the ACME Error Type
registry:
+------------------------------+------------------------+-----------+
| Type | Description | Reference |
+------------------------------+------------------------+-----------+
| recurrentOrderCanceled | The short-term | RFC XXXX |
| | certificate is no | |
| | longer available | |
| | because the recurrent | |
| | order has been | |
| | explicitly canceled by | |
| | the IdO | |
| recurrentOrderExpired | The short-term | RFC XXXX |
| | certificate is no | |
| | longer available | |
| | because the recurrent | |
| | order has expired | |
| recurrentCancellationInvalid | A request to cancel a | RFC XXXX |
| | recurrent order that | |
| | is not in state | |
| | "valid" has been | |
| | received | |
+------------------------------+------------------------+-----------+
6.2. New ACME Order Object Fields
This document adds the following entries to the ACME Order Object
Fields registry:
Sheffer, et al. Expires June 2, 2018 [Page 14]
Internet-Draft ACME STAR November 2017
+-------------------------------+--------+--------------+-----------+
| Field Name | Field | Configurable | Reference |
| | Type | | |
+-------------------------------+--------+--------------+-----------+
| recurrent | string | true | RFC XXXX |
| recurrent-start-date | string | true | RFC XXXX |
| recurrent-end-date | string | true | RFC XXXX |
| recurrent-certificate- | string | true | RFC XXXX |
| validity | | | |
+-------------------------------+--------+--------------+-----------+
6.3. Not-Before and Not-After HTTP Headers
The "Message Headers" registry should be updated with the following
additional values:
+-------------------+----------+----------+-----------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+-----------+
| Not-Before | http | standard | RFC XXXX |
| Not-After | http | standard | RFC XXXX |
+-------------------+----------+----------+-----------+
7. Security Considerations
7.1. Denial of Service Considerations
STAR adds a new attack vector that increases the threat of denial of
service attacks, caused by the change to the CA's behavior. Each
STAR request amplifies the resource demands upon the CA, where one
order produces not one, but potentially dozens or hundreds of
certificates, depending on the "recurrent-certificate-validity"
parameter. An attacker can use this property to aggressively reduce
the "recurrent-certificate-validity" (e.g. 1 sec.) jointly with other
ACME attack vectors identified in Sec. 10 of [I-D.ietf-acme-acme].
Other collateral impact is related to the certificate endpoint
resource where the client can retrieve the certificates periodically.
If this resource is external to the CA (e.g. a hosted web server),
the previous attack will be reflected to that resource.
Mitigation recommendations from ACME still apply, but some of them
need to be adjusted. For example, applying rate limiting to the
initial request, by the nature of the recurrent behavior cannot solve
the above problem. The CA server needs complementary mitigation and
specifically, it SHOULD enforce a minimum value on "recurrent-
certificate-validity". Alternatively, the CA can set an internal
certificate generation processes rate limit.
Sheffer, et al. Expires June 2, 2018 [Page 15]
Internet-Draft ACME STAR November 2017
7.2. Additional Considerations TBD
8. 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.
Thanks to Jon Peterson and Martin Thomson for helpful comments and
discussions that have shaped this document.
9. References
9.1. Normative References
[I-D.ietf-acme-acme]
Barnes, R., Hoffman-Andrews, J., and J. Kasten, "Automatic
Certificate Management Environment (ACME)", draft-ietf-
acme-acme-08 (work in progress), October 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<https://www.rfc-editor.org/info/rfc3339>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014, <https://www.rfc-
editor.org/info/rfc7231>.
[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>.
9.2. Informative References
[Acer] Acer, M., Stark, E., Felt, A., Fahl, S., Bhargava, R.,
Dev, B., Braithwaite, M., Sleevi, R., and P. Tabriz,
"Where the Wild Warnings Are: Root Causes of Chrome HTTPS
Certificate Errors", DOI 10.1145/3133956.3134007, 2017,
<https://acmccs.github.io/papers/p1407-acerA.pdf>.
Sheffer, et al. Expires June 2, 2018 [Page 16]
Internet-Draft ACME STAR November 2017
[I-D.nir-saag-star]
Nir, Y., Fossati, T., and Y. Sheffer, "Considerations For
Using Short Term Certificates", draft-nir-saag-star-00
(work in progress), October 2017.
[I-D.sheffer-acme-star-request]
Sheffer, Y., Lopez, D., Dios, O., Pastor, A., and T.
Fossati, "Generating Certificate Requests for Short-Term,
Automatically-Renewed (STAR) Certificates", draft-sheffer-
acme-star-request-01 (work in progress), June 2017.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
[Topalovic]
Topalovic, E., Saeta, B., Huang, L., Jackson, C., and D.
Boneh, "Towards Short-Lived Certificates", 2012,
<http://www.w2spconf.com/2012/papers/w2sp12-final9.pdf>.
Sheffer, et al. Expires June 2, 2018 [Page 17]
Internet-Draft ACME STAR November 2017
Appendix A. Document History
[[Note to RFC Editor: please remove before publication.]]
A.1. draft-ietf-acme-star-02
o Discovery of STAR capabilities via the directory object
o Use the more generic term Identifier Owner (IdO) instead of Domain
Name Owner (DNO)
o More precision about what goes in the order
o Detail server side behavior on cancellation
A.2. draft-ietf-acme-star-01
o Generalized the introduction, separating out the specifics of
CDNs.
o Clean out LURK-specific text.
o Using a POST to ensure cancellation is authenticated.
o First and last date of recurrent cert, as absolute dates.
Validity of certs in seconds.
o Use RFC7807 "Problem Details" in error responses.
o Add IANA considerations.
o Changed the document's title.
A.3. draft-ietf-acme-star-00
o Initial working group version.
o Removed the STAR interface, the protocol between NDC and DNO.
What remains is only the extended ACME protocol.
A.4. draft-sheffer-acme-star-02
o Using a more generic term for the delegation client, NDC.
o Added an additional use case: public cloud services.
o More detail on ACME authorization.
A.5. draft-sheffer-acme-star-01
o A terminology section.
o Some cleanup.
A.6. draft-sheffer-acme-star-00
o Renamed draft to prevent confusion with other work in this space.
o Added an initial STAR protocol: a REST API.
o Discussion of CDNI use cases.
Sheffer, et al. Expires June 2, 2018 [Page 18]
Internet-Draft ACME STAR November 2017
A.7. draft-sheffer-acme-star-lurk-00
o Initial version.
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
Thomas Fossati
Nokia
EMail: thomas.fossati@nokia.com
Sheffer, et al. Expires June 2, 2018 [Page 19]
Html markup produced by rfcmarkup 1.129b, available from
https://tools.ietf.org/tools/rfcmarkup/