CoAP Transport for CMPV2
draft-ietf-ace-cmpv2-coap-transport-01
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (ace WG) | |
|---|---|---|---|
| Authors | Mohit Sahni , Saurabh Tripathi | ||
| Last updated | 2021-04-22 | ||
| Replaces | draft-msahni-ace-cmpv2-coap-transport | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text xml htmlized pdfized bibtex | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-ace-cmpv2-coap-transport-01
ACE M. Sahni, Ed.
Internet-Draft S. Tripathi, Ed.
Intended status: Standards Track Palo Alto Networks
Expires: October 25, 2021 April 23, 2021
CoAP Transport for CMPV2
draft-ietf-ace-cmpv2-coap-transport-01
Abstract
This document specifies the use of Constrained Application Protocol
(CoAP) as a transport medium for the Certificate Management Protocol
(CMP). CMP defines the interaction between various PKI entities for
the purpose of certificate creation and management. CoAP is an HTTP
like client-server protocol used by various constrained devices in
the IoT space.
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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and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 25, 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
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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
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. CoAP Transport For CMP . . . . . . . . . . . . . . . . . . . 3
2.1. CoAP URI Format . . . . . . . . . . . . . . . . . . . . . 3
2.2. Discovery of CMP RA/CA . . . . . . . . . . . . . . . . . 3
2.3. CoAP Request Format . . . . . . . . . . . . . . . . . . . 4
2.4. CoAP Content-Format . . . . . . . . . . . . . . . . . . . 4
2.5. Announcement PKIMessage . . . . . . . . . . . . . . . . . 4
2.6. CoAP Block-Wise Transfer Mode . . . . . . . . . . . . . . 4
2.7. Multicast CoAP . . . . . . . . . . . . . . . . . . . . . 5
3. Using CoAP over DTLS . . . . . . . . . . . . . . . . . . . . 5
4. Proxy support . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The Certificate Management Protocol (CMP) [RFC4210] is used by the
PKI entities for the generation and management of certificates. One
of the requirements of Certificate Management Protocol is to be
independent of the transport protocol in use. CMP has mechanisms to
take care of required transactions, error reporting and encryption of
messages. The Constrained Application Protocol (CoAP) defined in
[RFC7252], [RFC7959] and [RFC8323] is a client-server protocol like
HTTP. It is designed to be used by constrained devices over
constrained networks. The recommended transport for CoAP is UDP,
however [RFC8323] specifies the support of CoAP over TCP, TLS and
Websockets. This document specifies the use of CoAP over UDP as a
transport medium for the CMP version 2 [RFC4210], CMP version 3
[Certificate-Management-Protocol-Updates] and Lightweight CMP Profile
[Lightweight-CMP-Profile]. This document, in general, follows the
HTTP transport specifications for CMP defined in [RFC6712] and
specifies the additional requirements for using CoAP as a transport
medium. This document also provides guidance on how to use a "CoAP-
to-HTTP" proxy for a better adaptation of CoAP transport without
significant changes to the existing PKI entities. Although CoAP
transport can be used for communication between Registration
Authority (RA) and Certification Authority (CA) or between CAs, the
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scope of this document is for communication between End Entity (EE)
and RA or EE and CA. This document is applicable only when the CoAP
transport is used for the CMP transactions.
1.1. 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.
2. CoAP Transport For CMP
A CMP transaction consists of exchanging PKIMessages [RFC4210]
between PKI End Entities (EEs), Registration Authorities (RAs), and
Certification Authorities (CAs). If the EEs are constrained devices
then they may prefer, as a CMP client, the use of CoAP instead of
HTTP as the transport medium, while the RAs and CAs, in general, are
not constrained and can support both CoAP and HTTP Client and Server
implementations. This section specifies how to use CoAP as the
transport medium for the Certificate Management Protocol.
2.1. CoAP URI Format
The CoAP URI format is described in section 6 of [RFC7252]. The CoAP
endpoints MUST support use of the path prefix "/.well-known/" as
defined in [RFC8615] and the registered name "cmp" to help with
endpoint discovery and interoperability. Optional path segments MAY
be added after the registered application name (i.e. after "/.well-
known/cmp") to provide path specific to a CA, certificate profile or
PKI management operations. A valid full operation path segment can
look like this:
coap://www.example.com/.well-known/cmp
coap://www.example.com/.well-known/cmp/operationalLabel
coap://www.example.com/.well-known/cmp/profileLabel
coap://www.example.com/.well-known/cmp/profileLabel/operationalLabel
2.2. Discovery of CMP RA/CA
The EEs can be configured with enough information to form the CMP
server URI. The minimum information that can be configured is the
scheme i.e. "coap://" or "coaps://" and the authority portion of the
URI, e.g. "example.com:5683". If the port number is not specified in
the authority, then port 5683 MUST be assumed for the "coap://"
scheme and port 5684 MUST be assumed for the "coaps://" scheme.
Optionally, in the environments where a Local Registration Authority
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(LRA) or a Local CA is deployed, EEs can also use the CoAP service
discovery mechanism [RFC7252] to discover the URI of the Local RA or
CA's CMP endpoint. The CoAP CMP endpoints supporting service
discovery MUST also support resource discovery in the CoRE Link
Format as described in [RFC6690].
2.3. CoAP Request Format
The CMP PKIMessages MUST be DER encoded and sent as the body of the
CoAP POST request. If the CoAP request is successful then the server
MUST return a "2.05 Content" response code. If the CoAP request is
not successful then an appropriate CoAP Client Error 4.xx or a Server
Error 5.xx response code MUST be returned.
2.4. CoAP Content-Format
When transferring CMP PKIMesssage over CoAP the media type
"application/pkixcmp" MUST be used.
2.5. Announcement PKIMessage
When using the CoAP protocol, a PKI EE SHOULD poll for the potential
changes via "PKI Information" request using "PKI General Message"
defined in the PKIMessage [RFC4210] for various type of changes like
CA key update or to get current CRL [RFC5280] to check revocation or
using Support messages defined in section 5.4 of Lightweight CMP
Profile [Lightweight-CMP-Profile]. This will help constrained
devices that are acting as EEs conserve resources by eliminating the
need to create an endpoint for receiving notifications from RA or CA.
It will also simplify the implementation of CoAP-to-HTTP proxy.
2.6. CoAP Block-Wise Transfer Mode
A CMP PKIMesssage consists of a header, body, protection, and
extraCerts structures. These structures may contain many optional
and potentially large fields, a CMP message can be much larger than
the Maximum Transmission Unit (MTU) of the outgoing interface of the
device. In order to avoid IP fragmentation of messages exchanged
between EEs and RAs or CAs, the Block-Wise transfer [RFC7959] mode
MUST be used for the CMP Transactions over CoAP. If a CoAP-to-HTTP
proxy is in the path between EEs and CA or EEs and RA then it MUST
receive the entire body from the client before sending the HTTP
request to the server. This will avoid unnecessary errors in case
the entire content of the PKIMesssage is not received and the proxy
opens a connection with the server.
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2.7. Multicast CoAP
CMP PKIMessages sent over CoAP transport MUST NOT use a Multicast
destination address.
3. Using CoAP over DTLS
Although CMP protocol does not depend upon the underlying transport
for protecting the messages but in cases when an end to end secrecy
is desired for the CoAP transport, CoAP over DTLS [RFC6347] as a
transport medium SHOULD be used. Section 9.1 of [RFC7252] defines
how to use DTLS [RFC6347] for securing the CoAP. Once a DTLS
[RFC6347] connection is established it SHOULD be used for as long as
possible to avoid the frequent overhead of setting up a DTLS
[RFC6347] connection for constrained devices.
4. Proxy support
This section provides guidance on using a CoAP-to-HTTP proxy between
EEs and RAs or CAs in order to avoid changes to the existing PKI
implementation. Since the CMP payload is same over CoAP and HTTP
transport, a CoAP-to-HTTP cross protocol proxy can be implemented
based on section 10 of [RFC7252]. The CoAP-to-HTTP proxy can be
either located closer to the EEs or closer to the RA or CA. In case
the proxy is deployed closer to the EEs then it may also support
service discovery and resource discovery as described in section 2.2.
The CoAP-to-HTTP proxy MUST function as a reverse proxy, only
permitting connections to a limited set of pre configured servers.
It is out of scope of this document on how a reverse proxy can route
CoAP client requests to one of the configured servers. Some
recommended mechanisms are as follows:
o Use Uri-Path option to identify a server.
o Use separate hostnames for each of the configured servers and then
use Uri-Host option for routing the CoAP requests.
o Use separate hostnames for each of the configured servers and then
use Server Name Indication ([RFC8446]) in case of "coaps://"
scheme for routing CoAP requests.
5. Security Considerations
The CMP protocol depends upon various mechanisms in the protocol
itself for making the transactions secure therefore security issues
of CoAP due to using UDP do not carry over to the CMP layer. However
the CoAP is vulnerable to many issues due to the connectionless
characteristics of UDP itself. The Security considerations for CoAP
protocol are mentioned in the [RFC7252].
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In order to protect themselves against DDoS attacks, the
implementations SHOULD avoid sending or receiving very small packets
containing partial CMP PKIMessage data. A CoAP-to-HTTP proxy can
also protect the PKI entities from various attacks by enforcing basic
checks and validating messages before sending them to PKI entities.
Proxy can be deployed at the edge of End Entities" network or in
front of an RA and CA to protect them.
6. IANA Considerations
This document requires a new entry to the CoAP Content-Formats
Registry code for the content-type "application/pkixcmp" and a new
entry in Well-Known URIs for URI Suffix "cmp".
7. Acknowledgments
The authors would like to thank Hendrik Brockhaus, David von Oheimb,
and Andreas Kretschmer for their guidance in writing the content of
this document and providing valuable feedback.
8. References
8.1. 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>.
[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210,
DOI 10.17487/RFC4210, September 2005,
<https://www.rfc-editor.org/info/rfc4210>.
[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>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
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[RFC6712] Kause, T. and M. Peylo, "Internet X.509 Public Key
Infrastructure -- HTTP Transfer for the Certificate
Management Protocol (CMP)", RFC 6712,
DOI 10.17487/RFC6712, September 2012,
<https://www.rfc-editor.org/info/rfc6712>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/info/rfc7959>.
[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>.
[RFC8323] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained
Application Protocol) over TCP, TLS, and WebSockets",
RFC 8323, DOI 10.17487/RFC8323, February 2018,
<https://www.rfc-editor.org/info/rfc8323>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/info/rfc8615>.
8.2. Informative References
[Certificate-Management-Protocol-Updates]
Brockhaus, H. and D. von Oheimb, "Certificate Management
Protocol (CMP) Updates", Work in Progress, draft-
brockhaus-lamps-cmp-updates-03, 2021,
<https://tools.ietf.org/html/draft-brockhaus-lamps-cmp-
updates-03>.
[Lightweight-CMP-Profile]
Brockhaus, H., Fries, S., and D. von Oheimb, "Lightweight
CMP Profile", Work in Progress, draft-ietf-lamps-
lightweight-cmp-profile-05, 2021,
<https://tools.ietf.org/html/draft-ietf-lamps-lightweight-
cmp-profile-05>.
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[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
Authors' Addresses
Mohit Sahni (editor)
Palo Alto Networks
3000 Tannery Way
Santa Clara, CA 95054
US
EMail: msahni@paloaltonetworks.com
Saurabh Tripathi (editor)
Palo Alto Networks
3000 Tannery Way
Santa Clara, CA 95054
US
EMail: stripathi@paloaltonetworks.com
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