ACME Integrations
draft-friel-acme-integrations-01
The information below is for an old version of the document.
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|---|---|---|---|
| Authors | Owen Friel , Richard Barnes | ||
| Last updated | 2019-07-02 (Latest revision 2019-05-13) | ||
| Replaced by | draft-ietf-acme-integrations, draft-ietf-acme-integrations | ||
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draft-friel-acme-integrations-01
Network Working Group O. Friel
Internet-Draft R. Barnes
Intended status: Standards Track Cisco
Expires: January 3, 2020 July 02, 2019
ACME Integrations
draft-friel-acme-integrations-01
Abstract
This document outlines multiple advanced use cases and integrations
that ACME facilitates without any modifications or enhancements
required to the base ACME specification. These use cases are not
immediately obvious from reading the ACME specification and thus are
explicitly documented here. The use cases include ACME issuance of
subdomain certificates, and ACME integration with EST and TEAP.
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 3, 2020.
Copyright Notice
Copyright (c) 2019 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. ACME Issuance of Subdomain Certificates . . . . . . . . . . . 3
4. ACME Integration with EST . . . . . . . . . . . . . . . . . . 5
5. ACME Integration with BRSKI . . . . . . . . . . . . . . . . . 8
6. ACME Integration with TEAP . . . . . . . . . . . . . . . . . 10
7. ACME Integration with TEAP-BRSKI . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. Informative References . . . . . . . . . . . . . . . . . . . 16
Appendix A. Comments . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
ACME [RFC8555] defines a protocol that a certificate authority (CA)
and an applicant can use to automate the process of domain name
ownership validation and X.509 (PKIX) certificate issuance. The
protocol is rich and flexible and enables multiple use cases that are
not immediately obvious from reading the specification. This
document explicitly outlines multiple advanced ACME use cases
including:
o ACME issuance of subdomain certificates
o ACME integration with EST [RFC7030]
o ACME integration with BRSKI
[I-D.ietf-anima-bootstrapping-keyinfra]
o ACME integration with TEAP [RFC7170]
o ACME integration with TEAP-BRSKI draft-lear-eap-teap-brski
2. Terminology
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.
The following terms are used in this document:
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o BRSKI: Bootstrapping Remote Secure Key Infrastructures
[I-D.ietf-anima-bootstrapping-keyinfra]
o CA: Certificate Authority
o CMC: Certificate Management over CMS
o CSR: Certificate Signing Request
o EST: Enrollment over Secure Transport [RFC7030]
o FQDN: Fully Qualified Domain Name
o RA: PKI Registration Authority
o TEAP: Tunneled Extensible Authentication Protocol [RFC7170]
3. ACME Issuance of Subdomain Certificates
A typical ACME workflow for issuance of certificates is as follows:
1. client POSTs a newOrder request that contains a set of
"identifiers"
2. server replies with a set of "authorizations" and a "finalize"
URI
3. client sends POST-as-GET requests to retrieve the
"authorizations", with the downloaded "authorization" object(s)
containing the "identifier" that the client must prove control of
4. client proves control over the "identifier" in the
"authorization" object by completing the specified challenge, for
example, by publishing a DNS TXT record
5. client POSTs a CSR to the "finalize" API
ACME places the following restrictions on "identifiers":
o section 7.1.4: the only type of "identifier" defined by the ACME
specification is a fully qualified domain name: "The only type of
identifier defined by this specification is a fully qualified
domain name (type: "dns"). The domain name MUST be encoded in the
form in which it would appear in a certificate."
o Section 7.4: the "identifier" in the CSR request must match the
"identifier" in the newOrder request: "The CSR MUST indicate the
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exact same set of requested identifiers as the initial newOrder
request."
o Sections 8.3: the "identifier", or FQDN, in the "authorization"
object must be used when fulfilling challenges via HTTP:
"Construct a URL by populating the URL template ... where the
domain field is set to the domain name being verified"
o Section 8.4: the "identifier", or FQDN, in the "authorization"
object must be used when fulfilling challenges via DNS: "The
client constructs the validation domain name by prepending the
label "_acme-challenge" to the domain name being validated."
ACME does not mandate that the "identifier" in a newOrder request
matches the "identifier" in "authorization" objects. This means that
the ACME specification does not preclude an ACME server processing
newOrder requests and issuing certificates for a subdomain without
requiring a challenge to be fulfilled against that explicit
subdomain. ACME server policy could allow issuance of certificates
for a subdomain to a client where the client only has to fulfill an
authorization challenge for the parent domain.
This allows a flow where a client proves ownership of "domain.com"
and then successfully obtains a certificate for "sub.domain.com".
The ACME pre-authorization flow makes most sense for this use case,
and that is what is illustrated in the following call flow.
The client could pre-authorize for the parent domain once, and then
issue multiple newOrder requests for certificates for multiple
subdomains. This call flow illustrates the client only placing one
newOrder request.
+--------+ +------+ +-----+
| Client | | ACME | | DNS |
+--------+ +------+ +-----+
| | |
STEP 1: Pre-Authorization of parent domain
| | |
| POST /newAuthz | |
| "domain.com" | |
|--------------------->| |
| | |
| 201 authorizations | |
|<---------------------| |
| | |
| Publish DNS TXT | |
| "domain.com" | |
|--------------------------------->|
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| | |
| POST /challenge | |
|--------------------->| |
| | Verify |
| |---------->|
| 200 status=valid | |
|<---------------------| |
| | |
| Delete DNS TXT | |
| "domain.com" | |
|--------------------------------->|
| | |
STEP 2: Place order for subdomain
| | |
| POST /newOrder | |
| "sub.domain.com" | |
|--------------------->| |
| | |
| 201 status=ready | |
|<---------------------| |
| | |
| POST /finalize | |
| CSR "sub.domain.com" | |
|--------------------->| |
| | |
| 200 OK status=valid | |
|<---------------------| |
| | |
| POST /certificate | |
|--------------------->| |
| | |
| 200 OK | |
| PKI "sub.domain.com" | |
|<---------------------| |
4. ACME Integration with EST
EST [RFC7030] defines a mechanism for clients to enroll with a PKI
Registration Authority by sending CMC messages over HTTP. EST
section 1 states:
"Architecturally, the EST service is located between a Certification
Authority (CA) and a client. It performs several functions
traditionally allocated to the Registration Authority (RA) role in a
PKI."
EST section 1.1 states that:
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"For certificate issuing services, the EST CA is reached through the
EST server; the CA could be logically "behind" the EST server or
embedded within it."
When the CA is logically "behind" the EST RA, EST does not specify
how the RA communicates with the CA. EST section 1 states:
"The nature of communication between an EST server and a CA is not
described in this document."
This section outlines how ACME could be used for communication
between the EST RA and the CA. The example call flow shows the RA
proving ownership of a parent domain, with individual client
certificates being subdomains under that parent domain. This is an
optimisation that reduces DNS and ACME traffic overhead. The RA
could of course prove ownership of every explicit client certificate
identifier.
The call flow also illustrates how the Pledge inserts relevant domain
information into the CSR Subject and Subject Alternative Name fields.
[todo: The details of how the pledge determines what information to
include in the CSR are TBD. For example, the pledge could discover
the DNS domain via DHCP Option 15, and prepend the identifier from
the IDevID to this.
Note also that EST https://tools.ietf.org/html/rfc7030#section-4.2.1
states that the ChangeSubjectName attribute MAY be used, for example,
if the Pledge uses its IDevID when requesting a CSR/LDevID with a
different Subject, however this field does not appear to have
widespread support across CAs.]
+--------+ +--------+ +------+ +-----+
| Pledge | | EST RA | | ACME | | DNS |
+--------+ +--------+ +------+ +-----+
| | | |
STEP 1: Pre-Authorization of parent domain
| | | |
| | POST /newAuthz | |
| | "domain.com" | |
| |--------------------->| |
| | | |
| | 201 authorizations | |
| |<---------------------| |
| | | |
| | Publish DNS TXT | |
| | "domain.com" | |
| |--------------------------------->|
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| | | |
| | POST /challenge | |
| |--------------------->| |
| | | Verify |
| | |---------->|
| | 200 status=valid | |
| |<---------------------| |
| | | |
| | Delete DNS TXT | |
| | "domain.com" | |
| |--------------------------------->|
| | | |
STEP 2: Pledge enrolls against RA
| | | |
| POST /simpleenroll | | |
| PCSK#10 CSR | | |
| "pledgeid.domain.com"| | |
|--------------------->| | |
| | | |
| 202 Retry-After | | |
|<---------------------| | |
| | | |
STEP 3: RA places ACME order
| | | |
| | POST /newOrder | |
| | "pledgeid.domain.com"| |
| |--------------------->| |
| | | |
| | 201 status=ready | |
| |<---------------------| |
| | | |
| | POST /finalize | |
| | PKCS#10 CSR | |
| | "pledgeid.domain.com"| |
| |--------------------->| |
| | | |
| | 200 OK status=valid | |
| |<---------------------| |
| | | |
| | POST /certificate | |
| |--------------------->| |
| | | |
| | 200 OK | |
| | PEM | |
| | "pledgeid.domain.com"| |
| |<---------------------| |
| | | |
STEP 4: Pledge retries enroll
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| | | |
| POST /simpleenroll | | |
| PCSK#10 CSR | | |
| "pledgeid.domain.com"| | |
|--------------------->| | |
| | | |
| 200 OK | | |
| PKCS#7 | | |
| "pledgeid.domain.com"| | |
|<---------------------| | |
5. ACME Integration with BRSKI
BRSKI [I-D.ietf-anima-bootstrapping-keyinfra] is based upon EST
[RFC7030] and defines how to autonomically bootstrap PKI trust
anchors into devices via means of signed vouchers. EST certificate
enrollment may then optionally take place after trust has been
established. BRKSI voucher exchange and trust establishment are
based on EST extensions and the certificate enrollment part of BRSKI
is fully based on EST. Similar to EST, BRSKI does not define how the
EST RA communicates with the CA. Therefore, the mechanisms outlined
in the previous section for using ACME as the communications protocol
between the EST RA and the CA are equally applicable to BRSKI.
The following call flow shows how ACME may be integrated into a full
BRSKI voucher plus EST enrollment workflow. For brevity, it assumes
that the EST RA has previously proven ownership of a parent domain
and that pledge certificate identifiers are a subdomain of that
parent domain. The domain ownership exchanges between the RA, ACME
and DNS are not shown. Similarly, not all BRSKI interactions are
shown and only the key protocol flows involving voucher exchange and
EST enrollment are shown.
[todo: similar to the EST section above, it is TBD exactly how the
pledge determines what domain information to insert in the CSR. A
possibility is that the Voucher response includes domain information
and explicitly instructs the pledge what information to insert in the
CSR. The RA could also instruct the Pledge to include a guid or a
new unique random identifier in place of its MAC address, serial
number, or whatever other identifying information is included in the
IDevID.
+--------+ +--------+ +------+ +------+
| Pledge | | EST RA | | ACME | | MASA |
+--------+ +--------+ +------+ +------+
| | | |
NOTE: Pre-Authorization of "domain.com" is complete
| | | |
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STEP 1: Pledge requests Voucher
| | | |
| POST /requestvoucher | | |
|--------------------->| | |
| | POST /requestvoucher | |
| |--------------------------------->|
| | | |
| | 200 OK Voucher | |
| |<---------------------------------|
| 200 OK Voucher | | |
|<---------------------| | |
| | | |
STEP 2: Pledge enrolls against RA
| | | |
| POST /simpleenroll | | |
| PCSK#10 CSR | | |
| "pledgeid.domain.com"| | |
|--------------------->| | |
| | | |
| 202 Retry-After | | |
|<---------------------| | |
| | | |
STEP 3: RA places ACME order
| | | |
| | POST /newOrder | |
| | "pledgeid.domain.com"| |
| |--------------------->| |
| | | |
| | 201 status=ready | |
| |<---------------------| |
| | | |
| | POST /finalize | |
| | PKCS#10 CSR | |
| | "pledgeid.domain.com"| |
| |--------------------->| |
| | | |
| | 200 OK status=valid | |
| |<---------------------| |
| | | |
| | POST /certificate | |
| |--------------------->| |
| | | |
| | 200 OK | |
| | PEM | |
| | "pledgeid.domain.com"| |
| |<---------------------| |
| | | |
STEP 4: Pledge retries enroll
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| | | |
| POST /simpleenroll | | |
| PCSK#10 CSR | | |
| "pledgeid.domain.com"| | |
|--------------------->| | |
| | | |
| 200 OK | | |
| PKCS#7 | | |
| "pledgeid.domain.com"| | |
|<---------------------| | |
6. ACME Integration with TEAP
TEAP [RFC7170] define a tunnel-based EAP method that enables secure
communication between a peer and a server by using TLS to establish a
mutually authenticated tunnel. TEAP enables certificate provisioning
within the tunnel. TEAP does not define how the TEAP server
communicates with the CA.
This section outlines how ACME could be used for communication
between the TEAP server and the CA. The example call flow shows the
TEAP server proving ownership of a parent domain, with individual
client certificates being subdomains under that parent domain. This
is an optimisation that reduces DNS and ACME traffic overhead. The
TEAP server could of course prove ownership of every explicit client
certificate identifier.
[todo: Similar to the previous section, it is TBD exactly how the
Pledge determines what Subject/SAN to put in the CSR request.]
+--------+ +-------------+ +------+ +-----+
| Pledge | | TEAP-Server | | ACME | | DNS |
+--------+ +-------------+ +------+ +-----+
| | | |
STEP 1: Pre-Authorization of parent domain
| | | |
| | POST /newAuthz | |
| | "domain.com" | |
| |--------------------->| |
| | | |
| | 201 authorizations | |
| |<---------------------| |
| | | |
| | Publish DNS TXT | |
| | "domain.com" | |
| |--------------------------------->|
| | | |
| | POST /challenge | |
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| |--------------------->| |
| | | Verify |
| | |---------->|
| | 200 status=valid | |
| |<---------------------| |
| | | |
| | Delete DNS TXT | |
| | "domain.com" | |
| |--------------------------------->|
| | | |
| | | |
STEP 2: Establsh EAP Outer Tunnel
| | | |
| EAP-Request/ | | |
| Type=Identity | | |
|<------------------------| | |
| | | |
| EAP-Response/ | | |
| Type=Identity | | |
|------------------------>| | |
| | | |
| EAP-Request/ | | |
| Type=TEAP, | | |
| TEAP Start, | | |
| Authority-ID TLV | | |
|<------------------------| | |
| | | |
| EAP-Response/ | | |
| Type=TEAP, | | |
| TLS(ClientHello) | | |
|------------------------>| | |
| | | |
| EAP-Request/ | | |
| Type=TEAP, | | |
| TLS(ServerHello, | | |
| Certificate, | | |
| ServerKeyExchange, | | |
| CertificateRequest, | | |
| ServerHelloDone) | | |
|<------------------------| | |
| | | |
| EAP-Response/ | | |
| Type=TEAP, | | |
| TLS(Certificate, | | |
| ClientKeyExchange, | | |
| CertificateVerify, | | |
| ChangeCipherSpec, | | |
| Finished) | | |
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|------------------------>| | |
| | | |
| EAP-Request/ | | |
| Type=TEAP, | | |
| TLS(ChangeCipherSpec, | | |
| Finished), | | |
| {Crypto-Binding TLV, | | |
| Result TLV=Success} | | |
|<------------------------| | |
| | | |
| EAP-Response/ | | |
| Type=TEAP, | | |
| {Crypto-Binding TLV, | | |
| Result TLV=Success} | | |
|------------------------>| | |
| | | |
| EAP-Request/ | | |
| Type=TEAP, | | |
| {Request-Action TLV: | | |
| Status=Failure, | | |
| Action=Process-TLV, | | |
| TLV=PKCS#10} | | |
|<------------------------| | |
| | | |
STEP 3: Enroll for certificate
| | | |
| EAP-Response/ | | |
| Type=TEAP, | | |
| {PKCS#10 TLV: | | |
| "pledgeid.domain.com"}| | |
|------------------------>| | |
| | POST /newOrder | |
| | "pledgeid.domain.com"| |
| |--------------------->| |
| | | |
| | 201 status=ready | |
| |<---------------------| |
| | | |
| | POST /finalize | |
| | PKCS#10 CSR | |
| | "pledgeid.domain.com"| |
| |--------------------->| |
| | | |
| | 200 OK status=valid | |
| |<---------------------| |
| | | |
| | POST /certificate | |
| |--------------------->| |
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| | | |
| | 200 OK | |
| | PEM | |
| | "pledgeid.domain.com"| |
| |<---------------------| |
| | | |
| EAP-Request/ | | |
| Type=TEAP, | | |
| {PKCS#7 TLV, | | |
| Result TLV=Success} | | |
|<------------------------| | |
| | | |
| EAP-Response/ | | |
| Type=TEAP, | | |
| {Result TLV=Success} | | |
|------------------------>| | |
| | | |
| EAP-Success | | |
|<------------------------| | |
7. ACME Integration with TEAP-BRSKI
TEAP-BRSKI [I-D.lear-eap-teap-brski] defines how to execute BRSKI at
layer 2 inside a TEAP tunnel. Similar to the TEAP proposal in the
previous section, BRSKI-TEAP leverages the existing TEAP PKXS#10 and
PKCS#7 mechanisms for certificate enrollment, and does not define how
the TEAP server communicates with the CA.
This section outlines how ACME could be used for communication
between the TEAP server and the CA, and how this fits in with the
TEAP-BRSKI proposal.
[todo: Similar to the previous section, it is TBD exactly how the
Pledge determines what Subject/SAN to put in the CSR request.]
+--------+ +-------------+ +------+ +------+
| Pledge | | TEAP-Server | | ACME | | MASA |
+--------+ +-------------+ +------+ +------+
| | | |
NOTE: Pre-Authorization of "domain.com" is complete
and EAP outer tunnel is established as outlined in
the previous section
| | | |
STEP 1: Perform BRSKI Flow
| | | |
| EAP-Request/ | | |
| Type=TEAP, | | |
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| {Request-Action TLV: | | |
| Status=Failure, | | |
| Action=Process-TLV, | | |
| TLV=Request-Voucher, | | |
| TLV=Trusted-Server-Root,| | |
| TLV=CSR-Attributes, | | |
| TLV=PKCS#10} | | |
|<---------------------------| | |
| | | |
| EAP-Response/ | | |
| Type=TEAP, | | |
| {Request-Voucher TLV} | | |
|--------------------------->| RequestVoucher | |
| |-------------------/ | \------>|
| | Voucher | |
| |<------------------/ | \-------|
| EAP-Request/ | | |
| Type=TEAP, | | |
| {Voucher TLV} | | |
|<---------------------------| | |
| | | |
STEP 2: Retrieve CA Configuration
| | | |
| EAP-Response/ | | |
| Type=TEAP, | | |
| {Trusted-Server-Root TLV} | | |
|--------------------------->| | |
| | | |
| EAP-Request/ | | |
| Type=TEAP, | | |
| {Trusted-Server-Root TLV} | | |
|<---------------------------| | |
| | | |
| EAP-Response/ | | |
| Type=TEAP, | | |
| {CSR-Attributes TLV} | | |
|--------------------------->| | |
| | | |
| EAP-Request/ | | |
| Type=TEAP, | | |
| {CSR-Attributes TLV} | | |
|<---------------------------| | |
| | | |
STEP 3: Enroll for certificate
| | | |
| EAP-Response/ | | |
| Type=TEAP, | | |
| {PKCS#10 TLV: | | |
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| "pledgeid.domain.com"} | | |
|--------------------------->| | |
| |POST /newOrder | |
| |"pledgeid.domain.com"| |
| |-------------------->| |
| | | |
| | 201 status=ready | |
| |<--------------------| |
| | | |
| |POST /finalize | |
| |PKCS#10 CSR | |
| |"pledgeid.domain.com"| |
| |-------------------->| |
| | | |
| | 200 OK status=valid | |
| |<--------------------| |
| | | |
| | POST /certificate | |
| |-------------------->| |
| | | |
| |200 OK | |
| |PEM | |
| |"pledgeid.domain.com"| |
| |<--------------------| |
| | | |
| EAP-Request/ | | |
| Type=TEAP, | | |
| {PKCS#7 TLV, | | |
| Result TLV=Success} | | |
|<---------------------------| | |
| | | |
| EAP-Response/ | | |
| Type=TEAP, | | |
| {Result TLV=Success} | | |
|--------------------------->| | |
| | | |
| EAP-Success | | |
|<---------------------------| | |
8. IANA Considerations
[todo]
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9. Security Considerations
[todo]
10. Informative References
[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
S., and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-22 (work in progress), June 2019.
[I-D.lear-eap-teap-brski]
Lear, E., Friel, O., and N. Cam-Winget, "Bootstrapping Key
Infrastructure over EAP", draft-lear-eap-teap-brski-02
(work in progress), February 2019.
[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>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[RFC7170] Zhou, H., Cam-Winget, N., Salowey, J., and S. Hanna,
"Tunnel Extensible Authentication Protocol (TEAP) Version
1", RFC 7170, DOI 10.17487/RFC7170, May 2014,
<https://www.rfc-editor.org/info/rfc7170>.
[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>.
Appendix A. Comments
Authors' Addresses
Friel & Barnes Expires January 3, 2020 [Page 16]
Internet-Draft ATLS July 2019
Owen Friel
Cisco
Email: ofriel@cisco.com
Richard Barnes
Cisco
Email: rlb@ipv.sx
Friel & Barnes Expires January 3, 2020 [Page 17]