ACE

Internet Engineering Task Force (IETF)                     M. Sahni, Ed.
Internet-Draft
Request for Comments: 9482                              S. Tripathi, Ed.
Intended status:
Category: Standards Track                             Palo Alto Networks
Expires: 16 November
ISSN: 2070-1721                                             October 2023                                    15 May 2023

         CoAP

  Constrained Application Protocol (CoAP) Transfer for the Certificate
                          Management Protocol
                 draft-ietf-ace-cmpv2-coap-transport-10

Abstract

   This document specifies the use of the Constrained Application
   Protocol (CoAP) as a transfer mechanism 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 Internet of Things 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 an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list  It represents the consensus of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid the IETF community.  It has
   received public review and has been approved for a maximum publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of six months this document, any errata,
   and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained 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 16 November 2023.
   https://www.rfc-editor.org/info/rfc9482.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3  Requirements Language
   2.  CoAP Transfer Mechanism for CMP . . . . . . . . . . . . . . .   3
     2.1.  CoAP URI Format . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Discovery of CMP RA/CA  . . . . . . . . . . . . . . . . .   4
     2.3.  CoAP Request Format . . . . . . . . . . . . . . . . . . .   4
     2.4.  CoAP Block-Wise Transfer Mode . . . . . . . . . . . . . .   4
     2.5.  Multicast CoAP  . . . . . . . . . . . . . . . . . . . . .   5
     2.6.  Announcement PKIMessage . . . . . . . . . . . . . . . . .   5
   3.  Proxy Support . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Acknowledgements
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

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 CMP is to be independent of the transport
   protocol in use.  CMP has mechanisms to take care of required
   transactions, error reporting reporting, and protection of messages.

   The Constrained Application Protocol (CoAP) defined in [RFC7252],
   [RFC7959]
   [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 UDP; however,
   [RFC8323] specifies the support of CoAP over TCP, TLS TLS, and Websockets.
   WebSockets.

   This document specifies the use of CoAP over UDP as a transport
   medium for the CMP version 2 [RFC4210], CMP version 3
   [I-D.ietf-lamps-cmp-updates] designated [RFC9480]
   (designated as CMP in this document document), and the Lightweight CMP Profile [I-D.ietf-lamps-lightweight-cmp-profile].
   This document, in
   [RFC9483].  In general, this document follows the HTTP transfer for
   CMP specifications defined in [RFC6712] and specifies the
   requirements for using CoAP as a transfer mechanism for the CMP.

   This document also provides guidance on how to use a "CoAP-to-HTTP"
   proxy to ease adoption of a CoAP transfer mechanism by enabling the
   interconnection with existing PKI entities already providing CMP over
   HTTP.

1.1.  Terminology  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY",and "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 Transfer Mechanism for CMP

   A CMP transaction consists of exchanging PKIMessages [RFC4210]
   between PKI End Entities end entities (EEs), Registration Authorities registration authorities (RAs), and
   Certification Authorities
   certification authorities (CAs).  If the EEs are constrained devices devices,
   then they may prefer, as a CMP client, the use of CoAP instead of
   HTTP as the transfer mechanism.  The  In general, the RAs and CAs, in general, CAs are not
   constrained and can support both CoAP and HTTP Client client and Server server
   implementations.  This section specifies how to use CoAP as the
   transfer mechanism for the Certificate Management Protocol. CMP.

2.1.  CoAP URI Format

   The CoAP URI format is described in section 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. (i.e., after "/.well-
   known/cmp") to provide distinction.  The path segment 'p' followed by
   an arbitraryLabel <name> could could, for example example, support the
   differentiation of specific CAs or certificate profiles.  Further
   path segments, e.g., for example, as specified in the Lightweight CMP Profile [I-
   D.ietf-lamps-lightweight-cmp-profile],
   [RFC9483], could indicate PKI management operations using an
   operationLabel <operation>.  A valid full CMP URI can look like this:

     coap://www.example.com/.well-known/cmp
     coap://www.example.com/.well-known/cmp/<operation>
     coap://www.example.com/.well-known/cmp/p/<profileLabel>
     coap://www.example.com/.well-known/cmp/p/<profileLabel>/<operation>

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.
   scheme, i.e., "coap:" or "coaps:" "coaps:", and the authority portion of the
   URI,
   e.g. e.g., "example.com:5683".  If the port number is not specified
   in the authority, then the default ports port numbers MUST be assumed for
   the "coap:" and the "coaps:" scheme URIs.  The default port for coap: "coap:"
   scheme URIs is 5683 and the default port for coaps: "coaps:" scheme URIs is
   5684 [RFC7252].

   Optionally, in the environments where a Local Registration Authority
   (LRA) RA 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.  The CoAP CMP endpoints
   supporting service discovery MUST also support resource discovery in
   the CoRE Constrained RESTful Environments (CoRE) Link Format Format, as described
   in [RFC6690].  The Link link MUST include the 'ct' attribute defined in
   section
   Section 7.2.1 of [RFC7252] with the value of "application/pkixcmp" "application/pkixcmp",
   as defined in the CoAP Content-Formats "CoAP Content-Formats" IANA registry.

2.3.  CoAP Request Format

   The CMP PKIMessages MUST be DER encoded and sent as the body of the
   CoAP POST request.  A CMP client MUST send each CoAP requests request marked
   as a Confirmable message [RFC7252].  If the CoAP request is
   successful
   successful, then the CMP RA or CA MUST return a Success 2.xx response
   code otherwise
   code; otherwise, the CMP RA or CA MUST return an appropriate Client
   Error 4.xx or Server Error 5.xx response code.  A CMP RA or CA may
   choose to send a Piggybacked piggybacked response [RFC7252] to the client client, or it
   MAY send a Separate separate response [RFC7252] in case it takes some time for CA or
   the RA or CA to process the CMP transaction.

   When transferring CMP PKIMesssage PKIMessage over CoAP CoAP, the content-format
   "application/pkixcmp" MUST be used.

2.4.  CoAP Block-Wise Transfer Mode

   A CMP PKIMesssage PKIMessage consists of a header, body, protection, and
   extraCerts structures structure, which may contain many optional and potentially
   large fields.  Thus, a CMP message can be much larger than the
   Maximum Transmission Unit (MTU) of the outgoing interface of the
   device.  The EEs and RAs or CAs, CAs MUST use the Block-Wise block-wise transfer mode
   [RFC7959] to transfer such large messages instead of relying on IP
   fragmentation.

   If a CoAP-to-HTTP proxy is in the path between EEs and CA an RA or EEs
   and
   RA then, a CA and if the server supports, then it MUST use the chunked
   transfer encoding [RFC9112] to send data over the HTTP transport.
   The proxy MUST try to reduce the number of packets sent by using an
   optimal chunk length for the HTTP transport.

2.5.  Multicast CoAP

   CMP PKIMessages sent over CoAP MUST NOT use a Multicast destination
   address.

2.6.  Announcement PKIMessage

   A CMP server may publish announcements, announcements that can be event triggered by an
   event or periodic, periodicly for the other PKI entities.  Here is the list of
   CMP announcement messages prefixed by their respective ASN.1
   identifier
   (section (see Section 5.1.2 [RFC4210]) of [RFC4210]):

         [15] CA Key Update Announcement
         [16] Certificate Announcement
         [17] Revocation Announcement
         [18] CRL Announcement

   An EE MAY use the CoAP Observe option Option [RFC7641] to register itself to
   get any announcement messages from the RA or CA.  The EE can send a
   GET request to the server's URI suffixed by "/ann".  For example example, a
   path to register for announcement messages may look like this:

       coap://www.example.com/.well-known/cmp/ann
       coap://www.example.com/.well-known/cmp/p/<profileLabel>/ann

   If the server supports CMP Announcements announcement messages, then it MUST send
   an appropriate Success 2.xx response code, otherwise code; otherwise, it MUST send an
   appropriate Client Error 4.xx or Server Error 5.xx response code.  If
   for some reason the server cannot add the client to its list of
   observers for the announcements, it can omit the Observe option Option
   [RFC7641] in the response to the client.  A client on  Upon receiving a Success
   2.xx success response without the Observe option [RFC7641] MAY try Option [RFC7641], after some time time,
   a client MAY try to register again for announcements from the CMP
   server.  Since a server can remove the EE from the list of observers
   for announcement messages, an EE SHOULD periodically re-register reregister
   itself for announcement messages.

   Alternatively, an EE MAY periodically poll for the current status of
   the CA via the "PKI Information Request" message, message; see section Section 6.5 of
   [RFC4210].  If supported, EEs MAY also use "Support Messages" "support messages" defined
   in section Section 4.3 of Lightweight CMP Profile
   [I-D.ietf-lamps-lightweight-cmp-profile] [RFC9483] to get
   information about the CA status.  These mechanisms will help
   constrained devices, devices that are acting as EEs, EEs to conserve resources by
   eliminating the need to create an endpoint for receiving
   notifications from the RA or CA.  It will also simplify the
   implementation of a CoAP-to-HTTP proxy.

3.  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 the same over CoAP and HTTP transfer
   mechanisms, a CoAP-to-HTTP cross-protocol proxy can be implemented
   based on
   section Section 10 of [RFC7252].  The CoAP-to-HTTP proxy can either
   be located closer to the EEs or closer to the RA or CA.  The proxy
   MAY support service discovery and resource discovery discovery, as described in
   section
   Section 2.2.  The CoAP-to-HTTP proxy MUST function as a reverse
   proxy, only permitting connections to a limited set of pre-configured preconfigured
   servers.  It is out of scope of this document to specify how a
   reverse proxy can route CoAP client requests to one of the configured
   servers.  Some recommended mechanisms are as follows:

   *  Use the Uri-Path option to identify a server.

   *  Use separate hostnames for each of the configured servers and then
      use the Uri-Host option for routing the CoAP requests.

   *  Use separate hostnames for each of the configured servers and then
      use Server Name Indication [RFC8446] in case of the "coaps://"
      scheme for routing CoAP requests.

4.  Security Considerations

   *  If PKIProtection is used, the PKIHeader and PKIBody of the CMP
      protocol are
      cryptographically protected against malicious modifications.  As
      such, UDP can be used without compromising the security of the CMP protocol.
      CMP.  Security Considerations considerations for CoAP are defined in [RFC7252].
   *  The CMP protocol does not provide confidentiality of the CMP payloads.  If
      confidentiality is desired, CoAP over DTLS [RFC9147] SHOULD be
      used to provide confidentiality for the CMP payloads,
      although payloads; although, it
      cannot conceal that the CMP protocol is used within the DTLS layer.
   *  Section 9.1 of [RFC7252] defines how to use DTLS [RFC9147] for
      securing the CoAP.  DTLS [RFC9147] associations SHOULD be kept alive
      and re-used reused where possible to amortize on the additional overhead
      of DTLS on constrained devices.
   *  An EE might not witness all of the Announcement announcement messages when
      using the CoAP Observe option Option [RFC7641], since the Observe option Option
      is a "best-effort" approach and the server might lose its state
      for subscribers to its announcement messages.  The EEs may use an
      alternate method described in section Section 2.6 to obtain time critical
      changes
      changes, such as CRL Certificate Revocation List (CRL) [RFC5280]
      updates.
   *  Implementations SHOULD use the available datagram size and avoid
      sending small datagrams containing partial CMP PKIMessage data in
      order to reduce memory usage for packet buffering.
   *  A CoAP-to-HTTP proxy can also protect the PKI entities by handling
      UDP and CoAP messages.  The proxy can mitigate attacks attacks, like denial
      of service
      denial-of-service attacks, replay attacks attacks, and resource-exhaustion attacks
      attacks, by enforcing basic checks checks, like validating that the ASN.1
      syntax is compliant to CMP messages and validating the PKIMessage
      protection before sending them to PKI entities.
   *  Since the Proxy proxy may have access to the CMP-Level CMP-level metadata and
      control over the flow of CMP messages therefore messages, proper role based role-based access
      control should be in place.  The proxy can be deployed at the edge
      of the "End Entities" "end entities" network or in front of an RA and CA to
      protect them.  The  However, the proxy however may itself be vulnerable to
      resource-exhaustion attacks as it's required to buffer the CMP
      messages received over CoAP transport before sending it to the
      HTTP endpoint.  This can be mitigated by using short timers for
      discarding the buffered messages and rate limiting clients based
      on the resource usage.

5.  IANA Considerations

   This document adds a new entry to the CoAP Content-Formats

   IANA
   Registry (https://www.iana.org/assignments/core-parameters/core-
   parameters.xhtml#content-formats) for has registered "application/pkixcmp" (ID 259) in the code of content-type
   "application/pkixcmp", for transferring "CoAP
   Content-Formats" registry <https://www.iana.org/assignments/core-
   parameters> to transfer CMP transactions over CoAP,
   from the identifier range 256-9999 reserved for IETF specifications. CoAP.

   Type name:  application
   Subtype name:  pkixcmp
   Encoding: Content may contain arbitrary octet values.  The octet
   values are the ASN.1 DER encoding of a PKI message, as defined in the
   [RFC4210] specifications.
   Reference: This document and  RFC 9482 [RFC4210]

   This document

   IANA has also adds registered a new path segment "ann" to in the CMP "CMP Well-
   Known URI Path Segments (https://www.iana.org/assignments/cmp/
   cmp.xhtml#cmp-well-known-uri) IANA Segments" registry <https://www.iana.org/assignments/
   cmp> for the EEs to register themselves for the announcement
   messages.

   Path Segment:  ann
   Description:  The path to send a GET request with the CoAP Observer Observe
      Option to register for CMP announcement messages.
   Reference: This document.

   This  RFC 9482

   IANA has added this document references as a reference for the cmp, "cmp" entry in
   the Well-Known URIs
   (https://www.iana.org/assignments/well-known-uris/well-known-
   uris.xhtml) "Well-Known URIs" registry <https://www.iana.org/assignments/
   well-known-uris>.

   IANA registry.  Please add a reference of has also added this document
   to the Well-Known URIs (https://www.iana.org/assignments/well-known-
   uris/well-known-uris.xhtml) IANA registry as a reference for that entry.

   This document also refers the path segment "p" entry in
   the CMP "CMP Well-Known URI Path Segments (https://www.iana.org/assignments/cmp/
   cmp.xhtml#cmp-well-known-uri) IANA registry.  Please add a reference
   of this document to the CMP Well-Known URI Path Segments
   (https://www.iana.org/assignments/cmp/cmp.xhtml#cmp-well-known-uri)
   for that path segment.

   [Note RFC Editor]: This document should be published together or
   after the CMP version 3 [I-D.ietf-lamps-cmp-updates] as it references
   IANA entries created by that Internet draft. Segments" registry
   <https://www.iana.org/assignments/cmp/>.

6.  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.

7.  References

7.1.

6.1.  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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119

   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Words", BCP 14, Infrastructure Certificate
              Management Protocol (CMP)", RFC 8174, 4210,
              DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>. 10.17487/RFC4210, September 2005,
              <https://www.rfc-editor.org/info/rfc4210>.

   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
              <https://www.rfc-editor.org/info/rfc6690>.

   [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>.

   [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>.

   [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>.

   [RFC7641]  Hartke, K., "Observing Resources in the Constrained
              Application Protocol (CoAP)", RFC 7641,
              DOI 10.17487/RFC7641, September 2015,
              <https://www.rfc-editor.org/info/rfc7641>.

   [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>.

   [I-D.ietf-lamps-cmp-updates]
              Brockhaus, H., von Oheimb, D., and J. Gray, "Certificate
              Management Protocol (CMP) Updates", Work in Progress,
              Internet-Draft, draft-ietf-lamps-cmp-updates-23, 29 June
              2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
              lamps-cmp-updates-23>.

   [I-D.ietf-lamps-lightweight-cmp-profile]
              Brockhaus, H., von Oheimb, D., and S. Fries, "Lightweight
              Certificate Management Protocol (CMP) Profile", Work

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in
              Progress, Internet-Draft, draft-ietf-lamps-lightweight-
              cmp-profile-21, 17 February 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
              lightweight-cmp-profile-21>. RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8615]  Nottingham, M., "Well-Known Uniform Resource Identifiers
              (URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
              <https://www.rfc-editor.org/info/rfc8615>.

   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
              <https://www.rfc-editor.org/info/rfc6690>.

   [RFC7641]  Hartke, K., "Observing Resources in the Constrained
              Application Protocol (CoAP)",

   [RFC9112]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP/1.1", STD 99, RFC 7641, 9112, DOI 10.17487/RFC7641, September 2015,
              <https://www.rfc-editor.org/info/rfc7641>. 10.17487/RFC9112,
              June 2022, <https://www.rfc-editor.org/info/rfc9112>.

   [RFC9147]  Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
              <https://www.rfc-editor.org/info/rfc9147>.

   [RFC9112]  Fielding, R., Ed., Nottingham, M.,

   [RFC9480]  Brockhaus, H., Ed., von Oheimb, D., and J. Reschke,
              Ed., "HTTP/1.1", STD 99, Gray,
              "Certificate Management Protocol (CMP) Updates", RFC 9112, 9480,
              DOI 10.17487/RFC9112,
              June 2022, <https://www.rfc-editor.org/info/rfc9112>.

7.2. 10.17487/RFC9480, October 2023,
              <https://www.rfc-editor.org/info/rfc9480>.

   [RFC9483]  Brockhaus, H., von Oheimb, D., and S. Fries, "Lightweight
              Certificate Management Protocol (CMP) Profile", RFC 9483,
              DOI 10.17487/RFC9483, October 2023,
              <https://www.rfc-editor.org/info/rfc9483>.

6.2.  Informative References

   [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>.

   [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>.

   [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>.

   [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>.

Acknowledgements

   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.

Authors' Addresses

   Mohit Sahni (editor)
   Palo Alto Networks
   3000 Tannery Way
   Santa Clara, CA 95054
   United States of America
   Email: msahni@paloaltonetworks.com

   Saurabh Tripathi (editor)
   Palo Alto Networks
   3000 Tannery Way
   Santa Clara, CA 95054
   United States of America
   Email: stripathi@paloaltonetworks.com