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rfc:rfc8143

Internet Engineering Task Force (IETF) J. Elie Request for Comments: 8143 April 2017 Updates: 4642 Category: Standards Track ISSN: 2070-1721

                Using Transport Layer Security (TLS)
             with Network News Transfer Protocol (NNTP)

Abstract

 This document provides recommendations for improving the security of
 the Network News Transfer Protocol (NNTP) when using Transport Layer
 Security (TLS).  It modernizes the NNTP usage of TLS to be consistent
 with TLS best current practices.  This document updates RFC 4642.

Status of This Memo

 This is an Internet Standards Track document.
 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
 Internet Standards 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
 http://www.rfc-editor.org/info/rfc8143.

Copyright Notice

 Copyright (c) 2017 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Elie Standards Track [Page 1] RFC 8143 Using TLS with NNTP April 2017

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   1.1.  Conventions Used in This Document . . . . . . . . . . . .   3
 2.  Updates/Changes to RFC 4642 . . . . . . . . . . . . . . . . .   3
 3.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .   4
   3.1.  Compression . . . . . . . . . . . . . . . . . . . . . . .   4
   3.2.  Protocol Versions and Security Preferences  . . . . . . .   4
   3.3.  Server Name Indication  . . . . . . . . . . . . . . . . .   5
   3.4.  Prevention of SSL Stripping . . . . . . . . . . . . . . .   5
   3.5.  Authenticated Connections . . . . . . . . . . . . . . . .   5
   3.6.  Human Factors . . . . . . . . . . . . . . . . . . . . . .   6
 4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
 5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
 6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
   6.2.  Informative References  . . . . . . . . . . . . . . . . .   9
 Appendix A.  Detailed Changes to RFC 4642 . . . . . . . . . . . .  11
   A.1.  Related to TLS-Level Compression  . . . . . . . . . . . .  11
   A.2.  Related to Implicit TLS . . . . . . . . . . . . . . . . .  11
   A.3.  Related to RC4 Cipher Suites  . . . . . . . . . . . . . .  12
   A.4.  Related to Server Name Indication . . . . . . . . . . . .  12
   A.5.  Related to Certificate Verification . . . . . . . . . . .  12
   A.6.  Related to Other Obsolete Wording . . . . . . . . . . . .  13
 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  13
 Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  13

1. Introduction

 The Network News Transfer Protocol (NNTP) [RFC3977] has been using
 Transport Layer Security (TLS) [RFC5246] along with its precursor,
 Secure Sockets Layer (SSL), since at least the year 2000.  The use of
 TLS in NNTP was formalized in [RFC4642], providing implementation
 recommendations at the same time.  In order to address the evolving
 threat model on the Internet today, this document provides stronger
 recommendations regarding that use.
 In particular, this document updates [RFC4642] by specifying that
 NNTP implementations and deployments MUST follow the best current
 practices documented in [BCP195], which currently consists of RFC
 7525 ("Recommendations for Secure Use of Transport Layer Security
 (TLS) and Datagram Transport Layer Security (DTLS)").  This includes
 stronger recommendations regarding SSL/TLS protocol versions,
 fallback to lower versions, TLS negotiation, TLS-level compression,
 TLS session resumption, cipher suites, public key lengths, forward
 secrecy, hostname validation, certificate verification, and other
 aspects of using TLS with NNTP.

Elie Standards Track [Page 2] RFC 8143 Using TLS with NNTP April 2017

1.1. Conventions Used in This Document

 Any term not defined in this document has the same meaning as it does
 in [RFC4642] or the NNTP core specification [RFC3977].
 When this document uses the term "implicit TLS", it refers to TLS
 negotiation immediately upon connection on a separate port.
 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 RFC
 2119 [BCP14].

2. Updates/Changes to RFC 4642

 This document updates [RFC4642] in the following aspects:
 o  NNTP implementations and deployments SHOULD disable TLS-level
    compression (Section 3.3 of RFC 7525 [BCP195]), thus no longer
    using TLS as a means to provide data compression (contrary to the
    Abstract and Section 2.2.2 of [RFC4642]).
 o  NNTP implementations and deployments SHOULD prefer implicit TLS,
    and therefore use strict TLS configuration (Section 3.2 of RFC
    7525 [BCP195]).  That is to say, they SHOULD use a port dedicated
    to NNTP over TLS and begin the TLS negotiation immediately upon
    connection (contrary to a dynamic upgrade from unencrypted to TLS-
    protected traffic via the use of the STARTTLS command, as
    Section 1 of [RFC4642] was encouraging).  Implicit TLS is the
    preferred way of using TLS with NNTP for the same reasons,
    transposed to NNTP, as those given in Appendix A of [MUA-STS].
    (Note that [MUA-STS] and [RFC4642] have one author in common.)
 o  NNTP implementations and deployments MUST NOT negotiate RC4 cipher
    suites ([RFC7465]); this is contrary to Section 5 of [RFC4642],
    which required them to implement the TLS_RSA_WITH_RC4_128_MD5
    cipher suite so as to ensure that any two NNTP-compliant
    implementations can be configured to interoperate.  This document
    removes that requirement, so that NNTP client and server
    implementations follow the recommendations given in Sections 4.2
    and 4.2.1 of RFC 7525 [BCP195] instead.  The mandatory-to-
    implement cipher suite or cipher suites depend on the TLS protocol
    version.  For instance, when TLS 1.2 is used, the
    TLS_RSA_WITH_AES_128_CBC_SHA cipher suite MUST be implemented
    (Section 9 of [RFC5246]).

Elie Standards Track [Page 3] RFC 8143 Using TLS with NNTP April 2017

 o  All NNTP clients and any NNTP server that is known by multiple
    names MUST support the Server Name Indication (SNI) extension
    defined in Section 3 of [RFC6066], in conformance with Section 3.6
    of RFC 7525 [BCP195].  It was only a "SHOULD" in Section 2.2.2 of
    [RFC4642].
 o  NNTP implementations and deployments MUST follow the rules and
    guidelines defined in [RFC6125] and [RFC5280] for hostname
    validation and certificate verification.  Part of Section 5 of
    [RFC4642] is, therefore, rationalized in favor of following those
    two documents.
 Appendix A of this document gives detailed changes with regard to the
 wording of [RFC4642].

3. Recommendations

 The best current practices documented in [BCP195] apply here.
 Therefore, NNTP implementations and deployments compliant with this
 document are REQUIRED to comply with [BCP195] as well.
 Instead of repeating those recommendations here, this document mostly
 provides supplementary information regarding secure implementation
 and deployment of NNTP technologies.

3.1. Compression

 NNTP supports the use of the COMPRESS command, defined in Section 2.2
 of [RFC8054], to compress data between an NNTP client and server.
 Although this NNTP extension might have slightly stronger security
 properties than TLS-level compression [RFC3749] (since NNTP
 compression can be activated after authentication has completed, thus
 reducing the chances that authentication credentials can be leaked
 via, for instance, a Compression Ratio Info-leak Made Easy (CRIME)
 attack, as described in Section 2.6 of [CRIME]), this document
 neither encourages nor discourages the use of the NNTP COMPRESS
 extension.

3.2. Protocol Versions and Security Preferences

 NNTP implementations of news servers are encouraged to support
 options to configure 1) the minimal TLS protocol version to accept
 and 2) which cipher suites, signature algorithms, or groups (like
 elliptic curves) to use for incoming connections.  Additional options
 can naturally also be supported.  The goal is to enable
 administrators of news servers to easily and quickly strengthen
 security, if needed (for instance, by rejecting cipher suites
 considered unsafe with regard to local policy).

Elie Standards Track [Page 4] RFC 8143 Using TLS with NNTP April 2017

 News clients may also support similar options, either configurable by
 the user or enforced by the news reader.

3.3. Server Name Indication

 The TLS extension for Server Name Indication (SNI) defined in
 Section 3 of [RFC6066] MUST be implemented by all news clients.  It
 also MUST be implemented by any news server that is known by multiple
 names.  (Otherwise, it is not possible for a server with several
 hostnames to present the correct certificate to the client.)

3.4. Prevention of SSL Stripping

 In order to help prevent SSL Stripping attacks (Section 2.1 of
 [RFC7457]), NNTP implementations and deployments MUST follow the
 recommendations provided in Section 3.2 of RFC 7525 [BCP195].
 Notably, in case implicit TLS is not used, news clients SHOULD
 attempt to negotiate TLS even if the server does not advertise the
 STARTTLS capability label in response to the CAPABILITIES command
 (Section 2.1 of [RFC4642]).

3.5. Authenticated Connections

 [RFC4642] already provides recommendations and requirements for
 certificate validation in the context of checking the client or the
 server's identity.  Those requirements are strengthened by
 Appendix A.5 of this document.
 Wherever possible, it is best to prefer certificate-based
 authentication (along with Simple Authentication and Security Layer
 (SASL) [RFC4422]), and ensure that:
 o  Clients authenticate servers.
 o  Servers authenticate clients.
 o  Servers authenticate other peer servers.
 This document does not mandate certificate-based authentication,
 although such authentication is strongly preferred.  As mentioned in
 Section 2.2.2 of [RFC4642], the AUTHINFO SASL command (Section 2.4 of
 [RFC4643]) with the EXTERNAL mechanism (Appendix A of [RFC4422]) MAY
 be used to authenticate a client once its TLS credentials have been
 successfully exchanged.
 Given the pervasiveness of eavesdropping [RFC7258], even an encrypted
 but unauthenticated connection might be better than an unencrypted
 connection (this is similar to the "better-than-nothing security"

Elie Standards Track [Page 5] RFC 8143 Using TLS with NNTP April 2017

 approach for IPsec [RFC5386], and in accordance with opportunistic
 security principles [RFC7435]).  Encrypted but unauthenticated
 connections include connections negotiated using anonymous Diffie-
 Hellman mechanisms or using self-signed certificates, among others.
 Note: when an NNTP server receives a Netnews article, it MAY add a
 <diag-match> (Section 3.1.5 of [RFC5536]), which appears as "!!" in
 the Path header field of that article, to indicate that it verified
 the identity of the client or peer server.  This document encourages
 the construction of such Path header fields, as described in
 Section 3.2.1 of [RFC5537].

3.6. Human Factors

 NNTP clients SHOULD provide ways for end users (and NNTP servers
 SHOULD provide ways for administrators) to complete at least the
 following tasks:
 o  Determine if a given incoming or outgoing connection is encrypted
    using a security layer (either using TLS or an SASL mechanism that
    negotiates a security layer).
 o  Be warned if the version of TLS used for encryption of a given
    stream is not secure enough.
 o  If authenticated encryption is used, determine how the connection
    was authenticated or verified.
 o  Be warned if the certificate offered by an NNTP server cannot be
    verified.
 o  Be warned if the cipher suite used to encrypt a connection is not
    secure enough.
 o  Be warned if the certificate changes for a given server.
 o  When a security layer is not already in place, be warned if a
    given server stops advertising the STARTTLS capability label in
    response to the CAPABILITIES command (Section 2.1 of [RFC4642]),
    whereas it advertised the STARTTLS capability label during any
    previous connection within a (possibly configurable) time frame.
    (Otherwise, a human might not see the warning the first time, and
    the warning would disappear immediately after that.)
 o  Be warned if a failure response to the STARTTLS command is
    received from the server, whereas the STARTTLS capability label
    was advertised.

Elie Standards Track [Page 6] RFC 8143 Using TLS with NNTP April 2017

 Note that the last two tasks cannot occur when implicit TLS is used,
 and that the penultimate task helps prevent an attack known as "SSL
 Stripping" (Section 2.1 of [RFC7457]).

4. Security Considerations

 Beyond the security considerations already described in [RFC4642],
 [RFC6125], and [BCP195], the following caveat is worth mentioning
 when not using implicit TLS: NNTP servers need to ensure that they
 are not vulnerable to the STARTTLS command injection vulnerability
 (Section 2.2 of [RFC7457]).  Though this command MUST NOT be
 pipelined, an attacker could pipeline it.  Therefore, NNTP servers
 MUST discard any NNTP command received between the use of STARTTLS
 and the end of TLS negotiation.

5. IANA Considerations

 This document does not change the formal definition of the STARTTLS
 extension (Section 6 of [RFC4642]).  Nonetheless, as implementations
 of the STARTTLS extension should follow this document, IANA has added
 reference to this document to the existing STARTTLS label in the
 "NNTP Capability Labels" registry contained in the "Network News
 Transfer Protocol (NNTP) Parameters" registry:
     +----------+--------------------------+--------------------+
     | Label    | Meaning                  | Reference          |
     +----------+--------------------------+--------------------+
     | STARTTLS | Transport layer security | [RFC4642][RFC8143] |
     +----------+--------------------------+--------------------+

6. References

6.1. Normative References

 [BCP14]    Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997,
            <http://www.rfc-editor.org/info/bcp14>.
 [BCP195]   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, May 2015,
            <https://www.rfc-editor.org/info/bcp195>.
 [RFC3977]  Feather, C., "Network News Transfer Protocol (NNTP)",
            RFC 3977, DOI 10.17487/RFC3977, October 2006,
            <http://www.rfc-editor.org/info/rfc3977>.

Elie Standards Track [Page 7] RFC 8143 Using TLS with NNTP April 2017

 [RFC4422]  Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
            Authentication and Security Layer (SASL)", RFC 4422,
            DOI 10.17487/RFC4422, June 2006,
            <http://www.rfc-editor.org/info/rfc4422>.
 [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, <http://www.rfc-editor.org/info/rfc4642>.
 [RFC4643]  Vinocur, J. and K. Murchison, "Network News Transfer
            Protocol (NNTP) Extension for Authentication", RFC 4643,
            DOI 10.17487/RFC4643, October 2006,
            <http://www.rfc-editor.org/info/rfc4643>.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246,
            DOI 10.17487/RFC5246, August 2008,
            <http://www.rfc-editor.org/info/rfc5246>.
 [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,
            <http://www.rfc-editor.org/info/rfc5280>.
 [RFC5536]  Murchison, K., Ed., Lindsey, C., and D. Kohn, "Netnews
            Article Format", RFC 5536, DOI 10.17487/RFC5536, November
            2009, <http://www.rfc-editor.org/info/rfc5536>.
 [RFC5537]  Allbery, R., Ed. and C. Lindsey, "Netnews Architecture and
            Protocols", RFC 5537, DOI 10.17487/RFC5537, November 2009,
            <http://www.rfc-editor.org/info/rfc5537>.
 [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
            Extensions: Extension Definitions", RFC 6066,
            DOI 10.17487/RFC6066, January 2011,
            <http://www.rfc-editor.org/info/rfc6066>.
 [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
            Verification of Domain-Based Application Service Identity
            within Internet Public Key Infrastructure Using X.509
            (PKIX) Certificates in the Context of Transport Layer
            Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
            2011, <http://www.rfc-editor.org/info/rfc6125>.

Elie Standards Track [Page 8] RFC 8143 Using TLS with NNTP April 2017

6.2. Informative References

 [CRIME]    Rizzo, J. and T. Duong, "The CRIME Attack", Ekoparty
            Security Conference, 2012.
 [MUA-STS]  Moore, K. and C. Newman, "Mail User Agent Strict Transport
            Security (MUA-STS)", Work in Progress,
            draft-ietf-uta-email-deep-06, March 2017.
 [PKI-CERT] Housley, R., Ford, W., Polk, T., and D. Solo, "Internet
            X.509 Public Key Infrastructure Certificate and
            Certificate Revocation List (CRL) Profile", RFC 3280,
            DOI 10.17487/RFC3280, April 2002,
            <http://www.rfc-editor.org/info/rfc3280>.
 [RFC3749]  Hollenbeck, S., "Transport Layer Security Protocol
            Compression Methods", RFC 3749, DOI 10.17487/RFC3749, May
            2004, <http://www.rfc-editor.org/info/rfc3749>.
 [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
            Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
            December 2005, <http://www.rfc-editor.org/info/rfc4301>.
 [RFC5386]  Williams, N. and M. Richardson, "Better-Than-Nothing
            Security: An Unauthenticated Mode of IPsec", RFC 5386,
            DOI 10.17487/RFC5386, November 2008,
            <http://www.rfc-editor.org/info/rfc5386>.
 [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
            Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
            2014, <http://www.rfc-editor.org/info/rfc7258>.
 [RFC7435]  Dukhovni, V., "Opportunistic Security: Some Protection
            Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
            December 2014, <http://www.rfc-editor.org/info/rfc7435>.
 [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, <http://www.rfc-editor.org/info/rfc7457>.
 [RFC7465]  Popov, A., "Prohibiting RC4 Cipher Suites", RFC 7465,
            DOI 10.17487/RFC7465, February 2015,
            <http://www.rfc-editor.org/info/rfc7465>.

Elie Standards Track [Page 9] RFC 8143 Using TLS with NNTP April 2017

 [RFC7590]  Saint-Andre, P. and T. Alkemade, "Use of Transport Layer
            Security (TLS) in the Extensible Messaging and Presence
            Protocol (XMPP)", RFC 7590, DOI 10.17487/RFC7590, June
            2015, <http://www.rfc-editor.org/info/rfc7590>.
 [RFC8054]  Murchison, K. and J. Elie, "Network News Transfer Protocol
            (NNTP) Extension for Compression", RFC 8054,
            DOI 10.17487/RFC8054, January 2017,
            <http://www.rfc-editor.org/info/rfc8054>.

Elie Standards Track [Page 10] RFC 8143 Using TLS with NNTP April 2017

Appendix A. Detailed Changes to RFC 4642

 This section lists the detailed changes that this document applies to
 [RFC4642].

A.1. Related to TLS-Level Compression

 The second sentence in the Abstract in [RFC4642] is replaced with the
 following text:
    The primary goal is to provide encryption for single-link
    confidentiality purposes, but data integrity, and (optional)
    certificate-based peer entity authentication are also possible.
 The second sentence of the first paragraph in Section 2.2.2 of
 [RFC4642] is replaced with the following text:
    The STARTTLS command is usually used to initiate session security,
    although it can also be used for client and/or server certificate
    authentication.

A.2. Related to Implicit TLS

 The third and fourth paragraphs in Section 1 of [RFC4642] are
 replaced with the following text:
    TCP port 563 is dedicated to NNTP over TLS, and registered in the
    IANA Service Name and Transport Protocol Port Number Registry for
    that usage.  NNTP implementations using TCP port 563 begin the TLS
    negotiation immediately upon connection and then continue with the
    initial steps of an NNTP session.  This immediate TLS negotiation
    on a separate port (referred to in this document as "implicit
    TLS") is the preferred way of using TLS with NNTP.
    If a host wishes to offer separate servers for transit and reading
    clients (Section 3.4.1 of [NNTP]), TCP port 563 SHOULD be used for
    implicit TLS with the reading server, and an unused port of its
    choice different than TCP port 433 SHOULD be used for implicit TLS
    with the transit server.  The ports used for implicit TLS should
    be clearly communicated to the clients, and specifically that no
    plaintext communication occurs before the TLS session is
    negotiated.
    As some existing implementations negotiate TLS via a dynamic
    upgrade from unencrypted to TLS-protected traffic during an NNTP
    session on well-known TCP ports 119 or 433, this specification

Elie Standards Track [Page 11] RFC 8143 Using TLS with NNTP April 2017

    formalizes the STARTTLS command in use for that purpose.  However,
    as already mentioned above, implementations SHOULD use implicit
    TLS on a separate port.
    Note: a common alternative to protect NNTP exchanges with transit
    servers that do not implement TLS is the use of IPsec with
    encryption [RFC4301].
 An additional informative reference to [RFC4301] is, therefore, added
 to Section 7.2 of [RFC4642].

A.3. Related to RC4 Cipher Suites

 The third paragraph in Section 5 of [RFC4642] is removed.
 Consequently, NNTP no longer requires the implementation of any
 cipher suites, other than those prescribed by TLS (Section 9 of
 [RFC5246]), and Sections 4.2 and 4.2.1 of RFC 7525 [BCP195].

A.4. Related to Server Name Indication

 The last two sentences of the seventh paragraph in Section 2.2.2 of
 [RFC4642] are removed.  Section 3.6 of RFC 7525 [BCP195] applies.

A.5. Related to Certificate Verification

 The text between "During the TLS negotiation" and "identity
 bindings)." in Section 5 of [RFC4642] is replaced with the following
 text:
    During TLS negotiation, the client MUST verify the server's
    identity in order to prevent man-in-the-middle attacks.  The
    client MUST follow the rules and guidelines defined in [RFC6125],
    where the reference identifier MUST be the server hostname that
    the client used to open the connection, and that is also specified
    in the TLS "server_name" extension [RFC6066].  The following NNTP-
    specific consideration applies: DNS domain names in server
    certificates MAY contain the wildcard character "*" as the
    complete leftmost label within the identifier.
    If the match fails, the client MUST follow the recommendations in
    Section 6.6 of [RFC6125] regarding certificate pinning and
    fallback.
    Beyond server identity checking, clients also MUST apply the
    procedures specified in [RFC5280] for general certificate
    validation (e.g., certificate integrity, signing, and path
    validation).

Elie Standards Track [Page 12] RFC 8143 Using TLS with NNTP April 2017

 Additional normative references to [RFC5280] (replacing [PKI-CERT],
 which it obsoletes), [RFC6066], and [RFC6125] are, therefore, added
 to Section 7.1 of [RFC4642].

A.6. Related to Other Obsolete Wording

 The first two sentences of the seventh paragraph in Section 2.2.2 of
 [RFC4642] are removed.  There is no special requirement for NNTP with
 regard to TLS Client Hello messages.  Section 7.4.1.2 and Appendix E
 of [RFC5246] apply.

Acknowledgments

 This document draws heavily on ideas in [RFC7590] by Peter Saint-
 Andre and Thijs Alkemade; a large portion of this text was borrowed
 from that specification.
 The author would like to thank the following individuals for
 contributing their ideas and support for writing this specification:
 Stephane Bortzmeyer, Ben Campbell, Viktor Dukhovni, Stephen Farrell,
 Sabahattin Gucukoglu, Richard Kettlewell, Jouni Korhonen, Mirja
 Kuehlewind, David Eric Mandelberg, Matija Nalis, Chris Newman, and
 Peter Saint-Andre.
 Special thanks to Michael Baeuerle, for shepherding this document,
 and to the Responsible Area Director, Alexey Melnikov, for sponsoring
 it.  They both significantly helped to increase its quality.

Author's Address

 Julien Elie
 10 allee Clovis
 Noisy-le-Grand  93160
 France
 Email: julien@trigofacile.com
 URI:   http://www.trigofacile.com/

Elie Standards Track [Page 13]

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