



Internet Engineering Task Force (IETF)                       K. Moriarty
Request for Comments: 8996                                           CIS
BCP: 195                                                      S. Farrell
Obsoletes: 5469, 7507                             Trinity College Dublin
Updates: 3261, 3329, 3436, 3470, 3501, 3552,                  March 2021
         3568, 3656, 3749, 3767, 3856, 3871,                            
         3887, 3903, 3943, 3983, 4097, 4111,                            
         4162, 4168, 4217, 4235, 4261, 4279,                            
         4497, 4513, 4531, 4540, 4582, 4616,                            
         4642, 4680, 4681, 4712, 4732, 4743,                            
         4744, 4785, 4791, 4823, 4851, 4964,                            
         4975, 4976, 4992, 5018, 5019, 5023,                            
         5024, 5049, 5054, 5091, 5158, 5216,                            
         5238, 5263, 5281, 5364, 5415, 5422,                            
         5456, 5734, 5878, 5953, 6012, 6042,                            
         6083, 6084, 6176, 6347, 6353, 6367,                            
         6460, 6614, 6739, 6749, 6750, 7030,                            
         7465, 7525, 7562, 7568, 8261, 8422                             
Category: Best Current Practice                                         
ISSN: 2070-1721


                    Deprecating TLS 1.0 and TLS 1.1

Abstract

   This document formally deprecates Transport Layer Security (TLS)
   versions 1.0 (RFC 2246) and 1.1 (RFC 4346).  Accordingly, those
   documents have been moved to Historic status.  These versions lack
   support for current and recommended cryptographic algorithms and
   mechanisms, and various government and industry profiles of
   applications using TLS now mandate avoiding these old TLS versions.
   TLS version 1.2 became the recommended version for IETF protocols in
   2008 (subsequently being obsoleted by TLS version 1.3 in 2018),
   providing sufficient time to transition away from older versions.
   Removing support for older versions from implementations reduces the
   attack surface, reduces opportunity for misconfiguration, and
   streamlines library and product maintenance.

   This document also deprecates Datagram TLS (DTLS) version 1.0 (RFC
   4347) but not DTLS version 1.2, and there is no DTLS version 1.1.

   This document updates many RFCs that normatively refer to TLS version
   1.0 or TLS version 1.1, as described herein.  This document also
   updates the best practices for TLS usage in RFC 7525; hence, it is
   part of BCP 195.

Status of This Memo

   This memo documents an Internet Best Current Practice.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   BCPs is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8996.

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
   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
     1.1.  RFCs Updated
     1.2.  Terminology
   2.  Support for Deprecation
   3.  SHA-1 Usage Problematic in TLS 1.0 and TLS 1.1
   4.  Do Not Use TLS 1.0
   5.  Do Not Use TLS 1.1
   6.  Updates to RFC 7525
   7.  Operational Considerations
   8.  Security Considerations
   9.  IANA Considerations
   10. References
     10.1.  Normative References
     10.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   Transport Layer Security (TLS) versions 1.0 [RFC2246] and 1.1
   [RFC4346] were superseded by TLS 1.2 [RFC5246] in 2008, which has now
   itself been superseded by TLS 1.3 [RFC8446].  Datagram Transport
   Layer Security (DTLS) version 1.0 [RFC4347] was superseded by DTLS
   1.2 [RFC6347] in 2012.  Therefore, it is timely to further deprecate
   TLS 1.0, TLS 1.1, and DTLS 1.0.  Accordingly, the aforementioned
   documents have been moved to Historic status.

   Technical reasons for deprecating these versions include:

   *  They require the implementation of older cipher suites that are no
      longer desirable for cryptographic reasons, e.g., TLS 1.0 makes
      TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA mandatory to implement.
   *  There is a lack of support for current recommended cipher suites,
      especially authenticated encryption with associated data (AEAD)
      ciphers, which were not supported prior to TLS 1.2.  Note that
      registry entries for no-longer-desirable ciphersuites remain in
      the registries, but many TLS registries were updated by [RFC8447],
      which indicates that such entries are not recommended by the IETF.
   *  The integrity of the handshake depends on SHA-1 hash.
   *  The authentication of the peers depends on SHA-1 signatures.
   *  Support for four TLS protocol versions increases the likelihood of
      misconfiguration.
   *  At least one widely used library has plans to drop TLS 1.1 and TLS
      1.0 support in upcoming releases; products using such libraries
      would need to use older versions of the libraries to support TLS
      1.0 and TLS 1.1, which is clearly undesirable.

   Deprecation of these versions is intended to assist developers as
   additional justification to no longer support older (D)TLS versions
   and to migrate to a minimum of (D)TLS 1.2.  Deprecation also assists
   product teams with phasing out support for the older versions, to
   reduce the attack surface and the scope of maintenance for protocols
   in their offerings.

1.1.  RFCs Updated

   This document updates the following RFCs that normatively reference
   TLS 1.0, TLS 1.1, or DTLS 1.0.  The update is to obsolete usage of
   these older versions.  Fallback to these versions is prohibited
   through this update.  Specific references to mandatory minimum
   protocol versions of TLS 1.0 or TLS 1.1 are replaced by TLS 1.2, and
   references to minimum protocol version DTLS 1.0 are replaced by DTLS
   1.2.  Statements that "TLS 1.0 is the most widely deployed version
   and will provide the broadest interoperability" are removed without
   replacement.

   [RFC3261] [RFC3329] [RFC3436] [RFC3470] [RFC3501] [RFC3552] [RFC3568]
   [RFC3656] [RFC3749] [RFC3767] [RFC3856] [RFC3871] [RFC3887] [RFC3903]
   [RFC3943] [RFC3983] [RFC4097] [RFC4111] [RFC4162] [RFC4168] [RFC4217]
   [RFC4235] [RFC4261] [RFC4279] [RFC4497] [RFC4513] [RFC4531] [RFC4540]
   [RFC4582] [RFC4616] [RFC4642] [RFC4680] [RFC4681] [RFC4712] [RFC4732]
   [RFC4785] [RFC4791] [RFC4823] [RFC4851] [RFC4964] [RFC4975] [RFC4976]
   [RFC4992] [RFC5018] [RFC5019] [RFC5023] [RFC5024] [RFC5049] [RFC5054]
   [RFC5091] [RFC5158] [RFC5216] [RFC5238] [RFC5263] [RFC5281] [RFC5364]
   [RFC5415] [RFC5422] [RFC5456] [RFC5734] [RFC5878] [RFC6012] [RFC6042]
   [RFC6083] [RFC6084] [RFC6176] [RFC6353] [RFC6367] [RFC6739] [RFC6749]
   [RFC6750] [RFC7030] [RFC7465] [RFC7525] [RFC7562] [RFC7568] [RFC8261]
   [RFC8422]

   The status of [RFC7562], [RFC6042], [RFC5456], [RFC5024], [RFC4540],
   and [RFC3656] will be updated with permission of the Independent
   Submissions Editor.

   In addition, these RFCs normatively refer to TLS 1.0 or TLS 1.1 and
   have already been obsoleted; they are still listed here and marked as
   updated by this document in order to reiterate that any usage of the
   obsolete protocol should use modern TLS: [RFC3316], [RFC3489],
   [RFC3546], [RFC3588], [RFC3734], [RFC3920], [RFC4132], [RFC4244],
   [RFC4347], [RFC4366], [RFC4492], [RFC4507], [RFC4572], [RFC4582],
   [RFC4934], [RFC5077], [RFC5081], [RFC5101], and [RFC5953].

   Note that [RFC4642] has already been updated by [RFC8143], which
   makes an overlapping, but not quite identical, update as this
   document.

   [RFC6614] has a requirement for TLS 1.1 or later, although it only
   makes an informative reference to [RFC4346].  This requirement is
   updated to be for TLS 1.2 or later.

   [RFC6460], [RFC4744], and [RFC4743] are already Historic; they are
   still listed here and marked as updated by this document in order to
   reiterate that any usage of the obsolete protocol should use modern
   TLS.

   This document updates DTLS [RFC6347].  [RFC6347] had allowed for
   negotiating the use of DTLS 1.0, which is now forbidden.

   The DES and International Data Encryption Algorithm (IDEA) cipher
   suites specified in [RFC5469] were specifically removed from TLS 1.2
   by [RFC5246]; since the only versions of TLS for which their usage is
   defined are now Historic, [RFC5469] has been moved to Historic as
   well.

   The version-fallback Signaling Cipher Suite Value specified in
   [RFC7507] was defined to detect when a given client and server
   negotiate a lower version of (D)TLS than their highest shared
   version.  TLS 1.3 ([RFC8446]) incorporates a different mechanism that
   achieves this purpose, via sentinel values in the ServerHello.Random
   field.  With (D)TLS versions prior to 1.2 fully deprecated, the only
   way for (D)TLS implementations to negotiate a lower version than
   their highest shared version would be to negotiate (D)TLS 1.2 while
   supporting (D)TLS 1.3; supporting (D)TLS 1.3 implies support for the
   ServerHello.Random mechanism.  Accordingly, the functionality from
   [RFC7507] has been superseded, and this document marks it as
   Obsolete.

1.2.  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.

2.  Support for Deprecation

   Specific details on attacks against TLS 1.0 and TLS 1.1, as well as
   their mitigations, are provided in [NIST800-52r2], [RFC7457], and
   other RFCs referenced therein.  Although mitigations for the current
   known vulnerabilities have been developed, any future issues
   discovered in old protocol versions might not be mitigated in older
   library versions when newer library versions do not support those old
   protocols.

   For example, NIST has provided the following rationale, copied with
   permission from Section 1.1, "History of TLS", of [NIST800-52r2]:

   |  TLS 1.1, specified in RFC 4346 [24], was developed to address
   |  weaknesses discovered in TLS 1.0, primarily in the areas of
   |  initialization vector selection and padding error processing.
   |  Initialization vectors were made explicit to prevent a certain
   |  class of attacks on the Cipher Block Chaining (CBC) mode of
   |  operation used by TLS.  The handling of padding errors was altered
   |  to treat a padding error as a bad message authentication code
   |  rather than a decryption failure.  In addition, the TLS 1.1 RFC
   |  acknowledges attacks on CBC mode that rely on the time to compute
   |  the message authentication code (MAC).  The TLS 1.1 specification
   |  states that to defend against such attacks, an implementation must
   |  process records in the same manner regardless of whether padding
   |  errors exist.  Further implementation considerations for CBC modes
   |  (which were not included in RFC 4346 [24]) are discussed in
   |  Section 3.3.2.
   |  
   |  TLS 1.2, specified in RFC 5246 [25], made several cryptographic
   |  enhancements, particularly in the area of hash functions, with the
   |  ability to use or specify the SHA-2 family of algorithms for hash,
   |  MAC, and Pseudorandom Function (PRF) computations.  TLS 1.2 also
   |  adds authenticated encryption with associated data (AEAD) cipher
   |  suites.
   |  
   |  TLS 1.3, specified in RFC 8446 [57], represents a significant
   |  change to TLS that aims to address threats that have arisen over
   |  the years.  Among the changes are a new handshake protocol, a new
   |  key derivation process that uses the HMAC-based Extract-and-Expand
   |  Key Derivation Function (HKDF) [37], and the removal of cipher
   |  suites that use RSA key transport or static Diffie-Hellman ( DH)
   |  [sic] key exchanges, the CBC mode of operation, or SHA-1.  Many
   |  extensions defined for use with TLS 1.2 and previous versions
   |  cannot be used with TLS 1.3.

3.  SHA-1 Usage Problematic in TLS 1.0 and TLS 1.1

   The integrity of both TLS 1.0 and TLS 1.1 depends on a running SHA-1
   hash of the exchanged messages.  This makes it possible to perform a
   downgrade attack on the handshake by an attacker able to perform 2^77
   operations, well below the acceptable modern security margin.

   Similarly, the authentication of the handshake depends on signatures
   made using a SHA-1 hash or a concatenation of MD5 and SHA-1 hashes
   that is not appreciably stronger than a SHA-1 hash, allowing the
   attacker to impersonate a server when it is able to break the
   severely weakened SHA-1 hash.

   Neither TLS 1.0 nor TLS 1.1 allows the peers to select a stronger
   hash for signatures in the ServerKeyExchange or CertificateVerify
   messages, making the only upgrade path the use of a newer protocol
   version.

   See [Bhargavan2016] for additional details.

4.  Do Not Use TLS 1.0

   TLS 1.0 MUST NOT be used.  Negotiation of TLS 1.0 from any version of
   TLS MUST NOT be permitted.

   Any other version of TLS is more secure than TLS 1.0.  While TLS 1.0
   can be configured to prevent some types of interception, using the
   highest version available is preferred.

   Pragmatically, clients MUST NOT send a ClientHello with
   ClientHello.client_version set to {03,01}.  Similarly, servers MUST
   NOT send a ServerHello with ServerHello.server_version set to
   {03,01}.  Any party receiving a Hello message with the protocol
   version set to {03,01} MUST respond with a "protocol_version" alert
   message and close the connection.

   Historically, TLS specifications were not clear on what the record
   layer version number (TLSPlaintext.version) could contain when
   sending a ClientHello message.  Appendix E of [RFC5246] notes that
   TLSPlaintext.version could be selected to maximize interoperability,
   though no definitive value is identified as ideal.  That guidance is
   still applicable; therefore, TLS servers MUST accept any value
   {03,XX} (including {03,00}) as the record layer version number for
   ClientHello, but they MUST NOT negotiate TLS 1.0.

5.  Do Not Use TLS 1.1

   TLS 1.1 MUST NOT be used.  Negotiation of TLS 1.1 from any version of
   TLS MUST NOT be permitted.

   Pragmatically, clients MUST NOT send a ClientHello with
   ClientHello.client_version set to {03,02}.  Similarly, servers MUST
   NOT send a ServerHello with ServerHello.server_version set to
   {03,02}.  Any party receiving a Hello message with the protocol
   version set to {03,02} MUST respond with a "protocol_version" alert
   message and close the connection.

   Any newer version of TLS is more secure than TLS 1.1.  While TLS 1.1
   can be configured to prevent some types of interception, using the
   highest version available is preferred.  Support for TLS 1.1 is
   dwindling in libraries and will impact security going forward if
   mitigations for attacks cannot be easily addressed and supported in
   older libraries.

   Historically, TLS specifications were not clear on what the record
   layer version number (TLSPlaintext.version) could contain when
   sending a ClientHello message.  Appendix E of [RFC5246] notes that
   TLSPlaintext.version could be selected to maximize interoperability,
   though no definitive value is identified as ideal.  That guidance is
   still applicable; therefore, TLS servers MUST accept any value
   {03,XX} (including {03,00}) as the record layer version number for
   ClientHello, but they MUST NOT negotiate TLS 1.1.

6.  Updates to RFC 7525

   "Recommendations for Secure Use of Transport Layer Security (TLS) and
   Datagram Transport Layer Security (DTLS)" [RFC7525] is BCP 195, which
   is the most recent Best Current Practice for implementing TLS and was
   based on TLS 1.2.  At the time of publication, TLS 1.0 and TLS 1.1
   had not yet been deprecated.  As such, BCP 195 is called out
   specifically to update text implementing the deprecation
   recommendations of this document.

   This document updates Section 3.1.1 of [RFC7525] by changing SHOULD
   NOT to MUST NOT as follows:

   *  Implementations MUST NOT negotiate TLS version 1.0 [RFC2246].

      Rationale: TLS 1.0 (published in 1999) does not support many
      modern, strong cipher suites.  In addition, TLS 1.0 lacks a per-
      record Initialization Vector (IV) for CBC-based cipher suites and
      does not warn against common padding errors.

   *  Implementations MUST NOT negotiate TLS version 1.1 [RFC4346].

      Rationale: TLS 1.1 (published in 2006) is a security improvement
      over TLS 1.0 but still does not support certain stronger cipher
      suites.

   This document updates Section 3.1.2 of [RFC7525] by changing SHOULD
   NOT to MUST NOT and adding a reference to RFC 6347 as follows:

   *  Implementations MUST NOT negotiate DTLS version 1.0 [RFC4347]
      [RFC6347].

      Version 1.0 of DTLS correlates to version 1.1 of TLS (see above).

7.  Operational Considerations

   This document is part of BCP 195 and, as such, reflects the
   understanding of the IETF (at the time of this document's
   publication) as to the best practices for TLS and DTLS usage.

   Though TLS 1.1 has been obsolete since the publication of [RFC5246]
   in 2008, and DTLS 1.0 has been obsolete since the publication of
   [RFC6347] in 2012, there may remain some systems in operation that do
   not support (D)TLS 1.2 or higher.  Adopting the practices recommended
   by this document for any systems that need to communicate with the
   aforementioned class of systems will cause failure to interoperate.
   However, disregarding the recommendations of this document in order
   to continue to interoperate with the aforementioned class of systems
   incurs some amount of risk.  The nature of the risks incurred by
   operating in contravention to the recommendations of this document
   are discussed in Sections 2 and 3, and knowledge of those risks
   should be used along with any potential mitigating factors and the
   risks inherent to updating the systems in question when deciding how
   quickly to adopt the recommendations specified in this document.

8.  Security Considerations

   This document deprecates two older TLS protocol versions and one
   older DTLS protocol version for security reasons already described.
   The attack surface is reduced when there are a smaller number of
   supported protocols and fallback options are removed.

9.  IANA Considerations

   This document has no IANA actions.

10.  References

10.1.  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>.

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, DOI 10.17487/RFC2246, January 1999,
              <https://www.rfc-editor.org/info/rfc2246>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC3329]  Arkko, J., Torvinen, V., Camarillo, G., Niemi, A., and T.
              Haukka, "Security Mechanism Agreement for the Session
              Initiation Protocol (SIP)", RFC 3329,
              DOI 10.17487/RFC3329, January 2003,
              <https://www.rfc-editor.org/info/rfc3329>.

   [RFC3436]  Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport
              Layer Security over Stream Control Transmission Protocol",
              RFC 3436, DOI 10.17487/RFC3436, December 2002,
              <https://www.rfc-editor.org/info/rfc3436>.

   [RFC3470]  Hollenbeck, S., Rose, M., and L. Masinter, "Guidelines for
              the Use of Extensible Markup Language (XML) within IETF
              Protocols", BCP 70, RFC 3470, DOI 10.17487/RFC3470,
              January 2003, <https://www.rfc-editor.org/info/rfc3470>.

   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
              <https://www.rfc-editor.org/info/rfc3501>.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              DOI 10.17487/RFC3552, July 2003,
              <https://www.rfc-editor.org/info/rfc3552>.

   [RFC3568]  Barbir, A., Cain, B., Nair, R., and O. Spatscheck, "Known
              Content Network (CN) Request-Routing Mechanisms",
              RFC 3568, DOI 10.17487/RFC3568, July 2003,
              <https://www.rfc-editor.org/info/rfc3568>.

   [RFC3656]  Siemborski, R., "The Mailbox Update (MUPDATE) Distributed
              Mailbox Database Protocol", RFC 3656,
              DOI 10.17487/RFC3656, December 2003,
              <https://www.rfc-editor.org/info/rfc3656>.

   [RFC3749]  Hollenbeck, S., "Transport Layer Security Protocol
              Compression Methods", RFC 3749, DOI 10.17487/RFC3749, May
              2004, <https://www.rfc-editor.org/info/rfc3749>.

   [RFC3767]  Farrell, S., Ed., "Securely Available Credentials
              Protocol", RFC 3767, DOI 10.17487/RFC3767, June 2004,
              <https://www.rfc-editor.org/info/rfc3767>.

   [RFC3856]  Rosenberg, J., "A Presence Event Package for the Session
              Initiation Protocol (SIP)", RFC 3856,
              DOI 10.17487/RFC3856, August 2004,
              <https://www.rfc-editor.org/info/rfc3856>.

   [RFC3871]  Jones, G., Ed., "Operational Security Requirements for
              Large Internet Service Provider (ISP) IP Network
              Infrastructure", RFC 3871, DOI 10.17487/RFC3871, September
              2004, <https://www.rfc-editor.org/info/rfc3871>.

   [RFC3887]  Hansen, T., "Message Tracking Query Protocol", RFC 3887,
              DOI 10.17487/RFC3887, September 2004,
              <https://www.rfc-editor.org/info/rfc3887>.

   [RFC3903]  Niemi, A., Ed., "Session Initiation Protocol (SIP)
              Extension for Event State Publication", RFC 3903,
              DOI 10.17487/RFC3903, October 2004,
              <https://www.rfc-editor.org/info/rfc3903>.

   [RFC3943]  Friend, R., "Transport Layer Security (TLS) Protocol
              Compression Using Lempel-Ziv-Stac (LZS)", RFC 3943,
              DOI 10.17487/RFC3943, November 2004,
              <https://www.rfc-editor.org/info/rfc3943>.

   [RFC3983]  Newton, A. and M. Sanz, "Using the Internet Registry
              Information Service (IRIS) over the Blocks Extensible
              Exchange Protocol (BEEP)", RFC 3983, DOI 10.17487/RFC3983,
              January 2005, <https://www.rfc-editor.org/info/rfc3983>.

   [RFC4097]  Barnes, M., Ed., "Middlebox Communications (MIDCOM)
              Protocol Evaluation", RFC 4097, DOI 10.17487/RFC4097, June
              2005, <https://www.rfc-editor.org/info/rfc4097>.

   [RFC4111]  Fang, L., Ed., "Security Framework for Provider-
              Provisioned Virtual Private Networks (PPVPNs)", RFC 4111,
              DOI 10.17487/RFC4111, July 2005,
              <https://www.rfc-editor.org/info/rfc4111>.

   [RFC4162]  Lee, H.J., Yoon, J.H., and J.I. Lee, "Addition of SEED
              Cipher Suites to Transport Layer Security (TLS)",
              RFC 4162, DOI 10.17487/RFC4162, August 2005,
              <https://www.rfc-editor.org/info/rfc4162>.

   [RFC4168]  Rosenberg, J., Schulzrinne, H., and G. Camarillo, "The
              Stream Control Transmission Protocol (SCTP) as a Transport
              for the Session Initiation Protocol (SIP)", RFC 4168,
              DOI 10.17487/RFC4168, October 2005,
              <https://www.rfc-editor.org/info/rfc4168>.

   [RFC4217]  Ford-Hutchinson, P., "Securing FTP with TLS", RFC 4217,
              DOI 10.17487/RFC4217, October 2005,
              <https://www.rfc-editor.org/info/rfc4217>.

   [RFC4235]  Rosenberg, J., Schulzrinne, H., and R. Mahy, Ed., "An
              INVITE-Initiated Dialog Event Package for the Session
              Initiation Protocol (SIP)", RFC 4235,
              DOI 10.17487/RFC4235, November 2005,
              <https://www.rfc-editor.org/info/rfc4235>.

   [RFC4261]  Walker, J. and A. Kulkarni, Ed., "Common Open Policy
              Service (COPS) Over Transport Layer Security (TLS)",
              RFC 4261, DOI 10.17487/RFC4261, December 2005,
              <https://www.rfc-editor.org/info/rfc4261>.

   [RFC4279]  Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
              Ciphersuites for Transport Layer Security (TLS)",
              RFC 4279, DOI 10.17487/RFC4279, December 2005,
              <https://www.rfc-editor.org/info/rfc4279>.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346,
              DOI 10.17487/RFC4346, April 2006,
              <https://www.rfc-editor.org/info/rfc4346>.

   [RFC4497]  Elwell, J., Derks, F., Mourot, P., and O. Rousseau,
              "Interworking between the Session Initiation Protocol
              (SIP) and QSIG", BCP 117, RFC 4497, DOI 10.17487/RFC4497,
              May 2006, <https://www.rfc-editor.org/info/rfc4497>.

   [RFC4513]  Harrison, R., Ed., "Lightweight Directory Access Protocol
              (LDAP): Authentication Methods and Security Mechanisms",
              RFC 4513, DOI 10.17487/RFC4513, June 2006,
              <https://www.rfc-editor.org/info/rfc4513>.

   [RFC4531]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP) Turn Operation", RFC 4531, DOI 10.17487/RFC4531,
              June 2006, <https://www.rfc-editor.org/info/rfc4531>.

   [RFC4540]  Stiemerling, M., Quittek, J., and C. Cadar, "NEC's Simple
              Middlebox Configuration (SIMCO) Protocol Version 3.0",
              RFC 4540, DOI 10.17487/RFC4540, May 2006,
              <https://www.rfc-editor.org/info/rfc4540>.

   [RFC4582]  Camarillo, G., Ott, J., and K. Drage, "The Binary Floor
              Control Protocol (BFCP)", RFC 4582, DOI 10.17487/RFC4582,
              November 2006, <https://www.rfc-editor.org/info/rfc4582>.

   [RFC4616]  Zeilenga, K., Ed., "The PLAIN Simple Authentication and
              Security Layer (SASL) Mechanism", RFC 4616,
              DOI 10.17487/RFC4616, August 2006,
              <https://www.rfc-editor.org/info/rfc4616>.

   [RFC4642]  Murchison, K., Vinocur, J., and C. Newman, "Using
              Transport Layer Security (TLS) with Network News Transfer
              Protocol (NNTP)", RFC 4642, DOI 10.17487/RFC4642, October
              2006, <https://www.rfc-editor.org/info/rfc4642>.

   [RFC4680]  Santesson, S., "TLS Handshake Message for Supplemental
              Data", RFC 4680, DOI 10.17487/RFC4680, October 2006,
              <https://www.rfc-editor.org/info/rfc4680>.

   [RFC4681]  Santesson, S., Medvinsky, A., and J. Ball, "TLS User
              Mapping Extension", RFC 4681, DOI 10.17487/RFC4681,
              October 2006, <https://www.rfc-editor.org/info/rfc4681>.

   [RFC4712]  Siddiqui, A., Romascanu, D., Golovinsky, E., Rahman, M.,
              and Y. Kim, "Transport Mappings for Real-time Application
              Quality-of-Service Monitoring (RAQMON) Protocol Data Unit
              (PDU)", RFC 4712, DOI 10.17487/RFC4712, October 2006,
              <https://www.rfc-editor.org/info/rfc4712>.

   [RFC4732]  Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
              Denial-of-Service Considerations", RFC 4732,
              DOI 10.17487/RFC4732, December 2006,
              <https://www.rfc-editor.org/info/rfc4732>.

   [RFC4743]  Goddard, T., "Using NETCONF over the Simple Object Access
              Protocol (SOAP)", RFC 4743, DOI 10.17487/RFC4743, December
              2006, <https://www.rfc-editor.org/info/rfc4743>.

   [RFC4744]  Lear, E. and K. Crozier, "Using the NETCONF Protocol over
              the Blocks Extensible Exchange Protocol (BEEP)", RFC 4744,
              DOI 10.17487/RFC4744, December 2006,
              <https://www.rfc-editor.org/info/rfc4744>.

   [RFC4785]  Blumenthal, U. and P. Goel, "Pre-Shared Key (PSK)
              Ciphersuites with NULL Encryption for Transport Layer
              Security (TLS)", RFC 4785, DOI 10.17487/RFC4785, January
              2007, <https://www.rfc-editor.org/info/rfc4785>.

   [RFC4791]  Daboo, C., Desruisseaux, B., and L. Dusseault,
              "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
              DOI 10.17487/RFC4791, March 2007,
              <https://www.rfc-editor.org/info/rfc4791>.

   [RFC4823]  Harding, T. and R. Scott, "FTP Transport for Secure Peer-
              to-Peer Business Data Interchange over the Internet",
              RFC 4823, DOI 10.17487/RFC4823, April 2007,
              <https://www.rfc-editor.org/info/rfc4823>.

   [RFC4851]  Cam-Winget, N., McGrew, D., Salowey, J., and H. Zhou, "The
              Flexible Authentication via Secure Tunneling Extensible
              Authentication Protocol Method (EAP-FAST)", RFC 4851,
              DOI 10.17487/RFC4851, May 2007,
              <https://www.rfc-editor.org/info/rfc4851>.

   [RFC4964]  Allen, A., Ed., Holm, J., and T. Hallin, "The P-Answer-
              State Header Extension to the Session Initiation Protocol
              for the Open Mobile Alliance Push to Talk over Cellular",
              RFC 4964, DOI 10.17487/RFC4964, September 2007,
              <https://www.rfc-editor.org/info/rfc4964>.

   [RFC4975]  Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed.,
              "The Message Session Relay Protocol (MSRP)", RFC 4975,
              DOI 10.17487/RFC4975, September 2007,
              <https://www.rfc-editor.org/info/rfc4975>.

   [RFC4976]  Jennings, C., Mahy, R., and A. B. Roach, "Relay Extensions
              for the Message Sessions Relay Protocol (MSRP)", RFC 4976,
              DOI 10.17487/RFC4976, September 2007,
              <https://www.rfc-editor.org/info/rfc4976>.

   [RFC4992]  Newton, A., "XML Pipelining with Chunks for the Internet
              Registry Information Service", RFC 4992,
              DOI 10.17487/RFC4992, August 2007,
              <https://www.rfc-editor.org/info/rfc4992>.

   [RFC5018]  Camarillo, G., "Connection Establishment in the Binary
              Floor Control Protocol (BFCP)", RFC 5018,
              DOI 10.17487/RFC5018, September 2007,
              <https://www.rfc-editor.org/info/rfc5018>.

   [RFC5019]  Deacon, A. and R. Hurst, "The Lightweight Online
              Certificate Status Protocol (OCSP) Profile for High-Volume
              Environments", RFC 5019, DOI 10.17487/RFC5019, September
              2007, <https://www.rfc-editor.org/info/rfc5019>.

   [RFC5023]  Gregorio, J., Ed. and B. de hOra, Ed., "The Atom
              Publishing Protocol", RFC 5023, DOI 10.17487/RFC5023,
              October 2007, <https://www.rfc-editor.org/info/rfc5023>.

   [RFC5024]  Friend, I., "ODETTE File Transfer Protocol 2.0", RFC 5024,
              DOI 10.17487/RFC5024, November 2007,
              <https://www.rfc-editor.org/info/rfc5024>.

   [RFC5049]  Bormann, C., Liu, Z., Price, R., and G. Camarillo, Ed.,
              "Applying Signaling Compression (SigComp) to the Session
              Initiation Protocol (SIP)", RFC 5049,
              DOI 10.17487/RFC5049, December 2007,
              <https://www.rfc-editor.org/info/rfc5049>.

   [RFC5054]  Taylor, D., Wu, T., Mavrogiannopoulos, N., and T. Perrin,
              "Using the Secure Remote Password (SRP) Protocol for TLS
              Authentication", RFC 5054, DOI 10.17487/RFC5054, November
              2007, <https://www.rfc-editor.org/info/rfc5054>.

   [RFC5091]  Boyen, X. and L. Martin, "Identity-Based Cryptography
              Standard (IBCS) #1: Supersingular Curve Implementations of
              the BF and BB1 Cryptosystems", RFC 5091,
              DOI 10.17487/RFC5091, December 2007,
              <https://www.rfc-editor.org/info/rfc5091>.

   [RFC5158]  Huston, G., "6to4 Reverse DNS Delegation Specification",
              RFC 5158, DOI 10.17487/RFC5158, March 2008,
              <https://www.rfc-editor.org/info/rfc5158>.

   [RFC5216]  Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
              Authentication Protocol", RFC 5216, DOI 10.17487/RFC5216,
              March 2008, <https://www.rfc-editor.org/info/rfc5216>.

   [RFC5238]  Phelan, T., "Datagram Transport Layer Security (DTLS) over
              the Datagram Congestion Control Protocol (DCCP)",
              RFC 5238, DOI 10.17487/RFC5238, May 2008,
              <https://www.rfc-editor.org/info/rfc5238>.

   [RFC5263]  Lonnfors, M., Costa-Requena, J., Leppanen, E., and H.
              Khartabil, "Session Initiation Protocol (SIP) Extension
              for Partial Notification of Presence Information",
              RFC 5263, DOI 10.17487/RFC5263, September 2008,
              <https://www.rfc-editor.org/info/rfc5263>.

   [RFC5281]  Funk, P. and S. Blake-Wilson, "Extensible Authentication
              Protocol Tunneled Transport Layer Security Authenticated
              Protocol Version 0 (EAP-TTLSv0)", RFC 5281,
              DOI 10.17487/RFC5281, August 2008,
              <https://www.rfc-editor.org/info/rfc5281>.

   [RFC5364]  Garcia-Martin, M. and G. Camarillo, "Extensible Markup
              Language (XML) Format Extension for Representing Copy
              Control Attributes in Resource Lists", RFC 5364,
              DOI 10.17487/RFC5364, October 2008,
              <https://www.rfc-editor.org/info/rfc5364>.

   [RFC5422]  Cam-Winget, N., McGrew, D., Salowey, J., and H. Zhou,
              "Dynamic Provisioning Using Flexible Authentication via
              Secure Tunneling Extensible Authentication Protocol (EAP-
              FAST)", RFC 5422, DOI 10.17487/RFC5422, March 2009,
              <https://www.rfc-editor.org/info/rfc5422>.

   [RFC5469]  Eronen, P., Ed., "DES and IDEA Cipher Suites for Transport
              Layer Security (TLS)", RFC 5469, DOI 10.17487/RFC5469,
              February 2009, <https://www.rfc-editor.org/info/rfc5469>.

   [RFC5734]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Transport over TCP", STD 69, RFC 5734,
              DOI 10.17487/RFC5734, August 2009,
              <https://www.rfc-editor.org/info/rfc5734>.

   [RFC5878]  Brown, M. and R. Housley, "Transport Layer Security (TLS)
              Authorization Extensions", RFC 5878, DOI 10.17487/RFC5878,
              May 2010, <https://www.rfc-editor.org/info/rfc5878>.

   [RFC5953]  Hardaker, W., "Transport Layer Security (TLS) Transport
              Model for the Simple Network Management Protocol (SNMP)",
              RFC 5953, DOI 10.17487/RFC5953, August 2010,
              <https://www.rfc-editor.org/info/rfc5953>.

   [RFC6042]  Keromytis, A., "Transport Layer Security (TLS)
              Authorization Using KeyNote", RFC 6042,
              DOI 10.17487/RFC6042, October 2010,
              <https://www.rfc-editor.org/info/rfc6042>.

   [RFC6176]  Turner, S. and T. Polk, "Prohibiting Secure Sockets Layer
              (SSL) Version 2.0", RFC 6176, DOI 10.17487/RFC6176, March
              2011, <https://www.rfc-editor.org/info/rfc6176>.

   [RFC6353]  Hardaker, W., "Transport Layer Security (TLS) Transport
              Model for the Simple Network Management Protocol (SNMP)",
              STD 78, RFC 6353, DOI 10.17487/RFC6353, July 2011,
              <https://www.rfc-editor.org/info/rfc6353>.

   [RFC6367]  Kanno, S. and M. Kanda, "Addition of the Camellia Cipher
              Suites to Transport Layer Security (TLS)", RFC 6367,
              DOI 10.17487/RFC6367, September 2011,
              <https://www.rfc-editor.org/info/rfc6367>.

   [RFC6739]  Schulzrinne, H. and H. Tschofenig, "Synchronizing Service
              Boundaries and <mapping> Elements Based on the Location-
              to-Service Translation (LoST) Protocol", RFC 6739,
              DOI 10.17487/RFC6739, October 2012,
              <https://www.rfc-editor.org/info/rfc6739>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <https://www.rfc-editor.org/info/rfc6749>.

   [RFC6750]  Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage", RFC 6750,
              DOI 10.17487/RFC6750, October 2012,
              <https://www.rfc-editor.org/info/rfc6750>.

   [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>.

   [RFC7465]  Popov, A., "Prohibiting RC4 Cipher Suites", RFC 7465,
              DOI 10.17487/RFC7465, February 2015,
              <https://www.rfc-editor.org/info/rfc7465>.

   [RFC7507]  Moeller, B. and A. Langley, "TLS Fallback Signaling Cipher
              Suite Value (SCSV) for Preventing Protocol Downgrade
              Attacks", RFC 7507, DOI 10.17487/RFC7507, April 2015,
              <https://www.rfc-editor.org/info/rfc7507>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC7562]  Thakore, D., "Transport Layer Security (TLS) Authorization
              Using Digital Transmission Content Protection (DTCP)
              Certificates", RFC 7562, DOI 10.17487/RFC7562, July 2015,
              <https://www.rfc-editor.org/info/rfc7562>.

   [RFC7568]  Barnes, R., Thomson, M., Pironti, A., and A. Langley,
              "Deprecating Secure Sockets Layer Version 3.0", RFC 7568,
              DOI 10.17487/RFC7568, June 2015,
              <https://www.rfc-editor.org/info/rfc7568>.

   [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>.

   [RFC8422]  Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
              Curve Cryptography (ECC) Cipher Suites for Transport Layer
              Security (TLS) Versions 1.2 and Earlier", RFC 8422,
              DOI 10.17487/RFC8422, August 2018,
              <https://www.rfc-editor.org/info/rfc8422>.

10.2.  Informative References

   [Bhargavan2016]
              Bhargavan, K. and G. Leuren, "Transcript Collision
              Attacks: Breaking Authentication in TLS, IKE, and SSH",
              DOI 10.14722/ndss.2016.23418, February 2016,
              <https://www.mitls.org/downloads/transcript-
              collisions.pdf>.

   [NIST800-52r2]
              National Institute of Standards and Technology,
              "Guidelines for the Selection, Configuration, and Use of
              Transport Layer Security (TLS) Implementations NIST
              SP800-52r2", DOI 10.6028/NIST.SP.800-52r2, August 2019,
              <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
              NIST.SP.800-52r2.pdf>.

   [RFC3316]  Arkko, J., Kuijpers, G., Soliman, H., Loughney, J., and J.
              Wiljakka, "Internet Protocol Version 6 (IPv6) for Some
              Second and Third Generation Cellular Hosts", RFC 3316,
              DOI 10.17487/RFC3316, April 2003,
              <https://www.rfc-editor.org/info/rfc3316>.

   [RFC3489]  Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy,
              "STUN - Simple Traversal of User Datagram Protocol (UDP)
              Through Network Address Translators (NATs)", RFC 3489,
              DOI 10.17487/RFC3489, March 2003,
              <https://www.rfc-editor.org/info/rfc3489>.

   [RFC3546]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
              and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 3546, DOI 10.17487/RFC3546, June 2003,
              <https://www.rfc-editor.org/info/rfc3546>.

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
              Arkko, "Diameter Base Protocol", RFC 3588,
              DOI 10.17487/RFC3588, September 2003,
              <https://www.rfc-editor.org/info/rfc3588>.

   [RFC3734]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Transport Over TCP", RFC 3734, DOI 10.17487/RFC3734, March
              2004, <https://www.rfc-editor.org/info/rfc3734>.

   [RFC3920]  Saint-Andre, P., Ed., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 3920, DOI 10.17487/RFC3920,
              October 2004, <https://www.rfc-editor.org/info/rfc3920>.

   [RFC4132]  Moriai, S., Kato, A., and M. Kanda, "Addition of Camellia
              Cipher Suites to Transport Layer Security (TLS)",
              RFC 4132, DOI 10.17487/RFC4132, July 2005,
              <https://www.rfc-editor.org/info/rfc4132>.

   [RFC4244]  Barnes, M., Ed., "An Extension to the Session Initiation
              Protocol (SIP) for Request History Information", RFC 4244,
              DOI 10.17487/RFC4244, November 2005,
              <https://www.rfc-editor.org/info/rfc4244>.

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, DOI 10.17487/RFC4347, April 2006,
              <https://www.rfc-editor.org/info/rfc4347>.

   [RFC4366]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
              and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 4366, DOI 10.17487/RFC4366, April 2006,
              <https://www.rfc-editor.org/info/rfc4366>.

   [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
              Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
              for Transport Layer Security (TLS)", RFC 4492,
              DOI 10.17487/RFC4492, May 2006,
              <https://www.rfc-editor.org/info/rfc4492>.

   [RFC4507]  Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
              "Transport Layer Security (TLS) Session Resumption without
              Server-Side State", RFC 4507, DOI 10.17487/RFC4507, May
              2006, <https://www.rfc-editor.org/info/rfc4507>.

   [RFC4572]  Lennox, J., "Connection-Oriented Media Transport over the
              Transport Layer Security (TLS) Protocol in the Session
              Description Protocol (SDP)", RFC 4572,
              DOI 10.17487/RFC4572, July 2006,
              <https://www.rfc-editor.org/info/rfc4572>.

   [RFC4934]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Transport Over TCP", RFC 4934, DOI 10.17487/RFC4934, May
              2007, <https://www.rfc-editor.org/info/rfc4934>.

   [RFC5077]  Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
              "Transport Layer Security (TLS) Session Resumption without
              Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
              January 2008, <https://www.rfc-editor.org/info/rfc5077>.

   [RFC5081]  Mavrogiannopoulos, N., "Using OpenPGP Keys for Transport
              Layer Security (TLS) Authentication", RFC 5081,
              DOI 10.17487/RFC5081, November 2007,
              <https://www.rfc-editor.org/info/rfc5081>.

   [RFC5101]  Claise, B., Ed., "Specification of the IP Flow Information
              Export (IPFIX) Protocol for the Exchange of IP Traffic
              Flow Information", RFC 5101, DOI 10.17487/RFC5101, January
              2008, <https://www.rfc-editor.org/info/rfc5101>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5415]  Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
              Ed., "Control And Provisioning of Wireless Access Points
              (CAPWAP) Protocol Specification", RFC 5415,
              DOI 10.17487/RFC5415, March 2009,
              <https://www.rfc-editor.org/info/rfc5415>.

   [RFC5456]  Spencer, M., Capouch, B., Guy, E., Ed., Miller, F., and K.
              Shumard, "IAX: Inter-Asterisk eXchange Version 2",
              RFC 5456, DOI 10.17487/RFC5456, February 2010,
              <https://www.rfc-editor.org/info/rfc5456>.

   [RFC6012]  Salowey, J., Petch, T., Gerhards, R., and H. Feng,
              "Datagram Transport Layer Security (DTLS) Transport
              Mapping for Syslog", RFC 6012, DOI 10.17487/RFC6012,
              October 2010, <https://www.rfc-editor.org/info/rfc6012>.

   [RFC6083]  Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
              Transport Layer Security (DTLS) for Stream Control
              Transmission Protocol (SCTP)", RFC 6083,
              DOI 10.17487/RFC6083, January 2011,
              <https://www.rfc-editor.org/info/rfc6083>.

   [RFC6084]  Fu, X., Dickmann, C., and J. Crowcroft, "General Internet
              Signaling Transport (GIST) over Stream Control
              Transmission Protocol (SCTP) and Datagram Transport Layer
              Security (DTLS)", RFC 6084, DOI 10.17487/RFC6084, January
              2011, <https://www.rfc-editor.org/info/rfc6084>.

   [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>.

   [RFC6460]  Salter, M. and R. Housley, "Suite B Profile for Transport
              Layer Security (TLS)", RFC 6460, DOI 10.17487/RFC6460,
              January 2012, <https://www.rfc-editor.org/info/rfc6460>.

   [RFC6614]  Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
              "Transport Layer Security (TLS) Encryption for RADIUS",
              RFC 6614, DOI 10.17487/RFC6614, May 2012,
              <https://www.rfc-editor.org/info/rfc6614>.

   [RFC7457]  Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
              Known Attacks on Transport Layer Security (TLS) and
              Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457,
              February 2015, <https://www.rfc-editor.org/info/rfc7457>.

   [RFC8143]  Elie, J., "Using Transport Layer Security (TLS) with
              Network News Transfer Protocol (NNTP)", RFC 8143,
              DOI 10.17487/RFC8143, April 2017,
              <https://www.rfc-editor.org/info/rfc8143>.

   [RFC8261]  Tuexen, M., Stewart, R., Jesup, R., and S. Loreto,
              "Datagram Transport Layer Security (DTLS) Encapsulation of
              SCTP Packets", RFC 8261, DOI 10.17487/RFC8261, November
              2017, <https://www.rfc-editor.org/info/rfc8261>.

   [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>.

   [RFC8447]  Salowey, J. and S. Turner, "IANA Registry Updates for TLS
              and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018,
              <https://www.rfc-editor.org/info/rfc8447>.

Acknowledgements

   Thanks to those that provided usage data and reviewed and/or improved
   this document, including: Michael Ackermann, David Benjamin, David
   Black, Deborah Brungard, Alan DeKok, Viktor Dukhovni, Julien Élie,
   Adrian Farrelll, Gary Gapinski, Alessandro Ghedini, Peter Gutmann,
   Jeremy Harris, Nick Hilliard, James Hodgkinson, Russ Housley, Hubert
   Kario, Benjamin Kaduk, John Klensin, Watson Ladd, Eliot Lear, Ted
   Lemon, John Mattsson, Keith Moore, Tom Petch, Eric Mill, Yoav Nir,
   Andrei Popov, Michael Richardson, Eric Rescorla, Rich Salz, Mohit
   Sethi, Yaron Sheffer, Rob Sayre, Robert Sparks, Barbara Stark, Martin
   Thomson, Sean Turner, Loganaden Velvindron, Jakub Wilk, and
   Christopher Wood.

Authors' Addresses

   Kathleen Moriarty
   Center for Internet Security (CIS)
   East Greenbush, NY
   United States of America

   Email: Kathleen.Moriarty.ietf@gmail.com


   Stephen Farrell
   Trinity College Dublin
   Dublin
   2
   Ireland

   Phone: +353-1-896-2354
   Email: stephen.farrell@cs.tcd.ie
