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  <!ENTITY nbsp    "&#160;">
  <!ENTITY zwsp   "&#8203;">
  <!ENTITY nbhy   "&#8209;">
  <!ENTITY wj     "&#8288;">
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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-radext-tls-psk-12" number="9813" category="bcp" consensus="true" submissionType="IETF" tocInclude="true" sortRefs="true" symRefs="true" version="3"> version="3" xml:lang="en" updates="" obsoletes="">

<!-- xml2rfc v2v3 conversion 3.24.0 [rfced] The title of the document has been updated as follows.
"TLS-PSK" has been expanded as "TLS Pre-Shared Key"; however, please
let us know if it should be expanded otherwise both here and in the rest
of the document.

Original:
   Operational Considerations for RADIUS and TLS-PSK

Option A (current title):
   Operational Considerations for RADIUS and TLS Pre-Shared Key (TLS-PSK)

Option B (using the phrase from the abstract):
   Operational Considerations for Using TLS Pre-Shared Keys (TLS-PSKs) with RADIUS

Option C (more similar to the title of RFC 4279):
   Operational Considerations for RADIUS and TLS Pre-Shared Key (TLS-PSK) Cipher Suites

[Note: RFC 4279 has been cited for "TLS-PSK" in RFCs 6614, 6940, and 7593.]
-->

<!--[rfced] This document has been assigned a new BCP number. Please let us know
if this is not correct (i.e., it should be part of an existing BCP).

See the complete list of BCPs here: https://www.rfc-editor.org/bcps
-->

  <front>
    <title abbrev="RADIUS and TLS-PSK">Operational Considerations for RADIUS and TLS-PSK</title> TLS Pre-Shared Key (TLS-PSK)</title>
    <seriesInfo name="RFC" value="9813"/>
    <seriesInfo name="Internet-Draft" value="draft-ietf-radext-tls-psk-12"/> name="BCP" value="243"/>
    <author initials="A." surname="DeKok" fullname="Alan DeKok">
      <organization>InkBridge Networks</organization>
      <address>
        <email>alan.dekok@inkbridge.io</email>
      </address>
    </author>
    <date year="2025" month="January" day="21"/>
    <area>Internet</area>
    <workgroup>RADEXT Working Group</workgroup>
    <keyword>Internet-Draft</keyword> month="June"/>
    <area>SEC</area>
    <workgroup>radext</workgroup>

<!-- [rfced] Please insert any keywords (beyond those that appear in
the title) for use on https://www.rfc-editor.org/search. -->

<keyword>example</keyword>

    <abstract>
      <?line 49?>
      <t>This document provides implementation and operational considerations
      for using TLS-PSK TLS Pre-Shared Keys (TLS-PSKs) with RADIUS/TLS (RFC6614) (RFC 6614) and RADIUS/DTLS (RFC7360). (RFC 7360).
      The purpose of the document is to help smooth the operational transition
      from the use of the RADIUS/UDP to RADIUS/TLS.</t>
    </abstract>
    <note removeInRFC="true">
      <name>About This Document</name>
      <t>
        Status information for this document may be found at <eref target="https://datatracker.ietf.org/doc/draft-ietf-radext-tls-psk/"/>.
      </t>
      <t>
        Discussion of this document takes place on the
        RADEXT Working Group mailing list (<eref target="mailto:radext@ietf.org"/>),
        which is archived at <eref target="https://mailarchive.ietf.org/arch/browse/radext/"/>.
        Subscribe at <eref target="https://www.ietf.org/mailman/listinfo/radext/"/>.
      </t>
      <t>Source for this draft and an issue tracker can be found at
        <eref target="https://github.com/radext-wg/radext-tls-psk.git"/>.</t>
    </note>
  </front>
  <middle>
    <?line 53?>

<section anchor="introduction">
      <name>Introduction</name>

      <t>The previous specifications "Transport Layer Security (TLS)
      Encryption for RADIUS" <xref target="RFC6614"/> and "Datagram Transport
      Layer Security (DTLS) as a Transport Layer for RADIUS" <xref
      target="RFC7360"/> defined how (D)TLS can be used as a transport
      protocol for RADIUS.  However, those documents do not provide guidance
      for using TLS-PSK TLS Pre-Shared Keys (TLS-PSKs) with RADIUS.  This document provides that missing
      guidance, and gives implementation and operational considerations.</t>

      <t>To clearly distinguish the various secrets and keys, this document
      uses "shared secret" to mean "RADIUS shared secret", and Pre-Shared "Pre-Shared Key (PSK)
      (PSK)" to mean secret "secret keys which that are used with TLS-PSK.</t> TLS-PSK".</t>
      <t>The purpose of the document is to help smooth the operational
      transition from the use of the insecure RADIUS/UDP to the use of the
      much more secure RADIUS/TLS.  While using PSKs is often less preferable
      to using public / or private keys, the operational model of PSKs follows
      the legacy RADIUS "shared secret" model.  As such, it can be easier for
      implementers and operators to transition to TLS when that transition is
      offered as a series of small changes.</t>
      <t>The intent for TLS-PSK
      <t>TLS-PSK is intended to be used in networks where the
      addresses of client clients and server servers are known, as with RADIUS/UDP.  This
      situation is similar to the use-case use case of RADIUS/UDP with shared secrets.
      TLS-PSK is not suitable for situations where clients dynamically
      discover servers, as there is no way for the client to dynamically
      determine which PSK should be used with a new server (or vice versa).
      In contrast, <xref target="RFC7585"/> dynamic discovery <xref target="RFC7585"/> allows for
      a client or server to authenticate a previously unknown server or client,
      as the parties can be issued a certificate by a known Certification
      Authority (CA).</t>
      <t>TLS-PSKs have the same issue of symmetric information between client
      and server: both parties know the secret key.  A client could, in
      theory, pretend to be a server.  In contrast, certificates are
      asymmetric, where it is impossible for the parties to assume the others other's
      identity.  Further discussion of this topic is contained in []{#sharing}.</t> <xref target="sharing"/>.</t>
      <t>Unless it is explicitly called out that a recommendation applies to
      TLS alone or to DTLS alone, each recommendation applies to both TLS and
      DTLS.</t>
    </section>
    <section anchor="terminology">
      <name>Terminology</name>
      <t>The
        <t>
    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
    "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>",
    "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
    "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and "OPTIONAL" "<bcp14>OPTIONAL</bcp14>" in this document are to be
    interpreted as described in BCP 14 BCP&nbsp;14 <xref target="RFC2119"/> <xref
    target="RFC8174"/> when, and only when, they appear in all capitals, as
    shown here.
<?line -6?>
        </t>
      <ul spacing="normal">
        <li>
          <t>External PSK</t>
        </li>
      </ul>
      <ul empty="true">
        <li>
          <t>A
	<dl spacing="normal" newline="true">
          <dt>External PSK</dt><dd>A PSK (along with a related PSK Identity) which
          that is administratively configured.  That is, one which that is
          external to TLS, TLS and is not created by the TLS subsystem.</t>
        </li>
      </ul>
      <ul spacing="normal">
        <li>
          <t>Resumption PSK</t>
        </li>
      </ul>
      <ul empty="true">
        <li>
          <t>A subsystem.</dd>
          <dt>Resumption PSK</dt><dd>A PSK (along with a related PSK Identity) which
          that is created by the TLS subsystem and/or application, for use
          with resumption.</t>
        </li>
      </ul> resumption.</dd>
	</dl>
    </section>
    <section anchor="justification-of-psk">
      <name>Justification of PSK.</name> PSK</name>
      <t>TLS deployments usually rely on certificates in most common
      uses. However, we recognize that it may be difficult to fully upgrade
      client implementations to allow for certificates to be used with
      RADIUS/TLS and RADIUS/DTLS.  These upgrades involve not only
      implementing TLS, but can also require significant changes to
      administration interfaces and application programming interfaces (APIs)
      in order to fully support certificates.</t>
      <t>For example, unlike shared secrets, certificates expire.  This
      expiration means that a working system using TLS can suddenly stop
      working.  Managing this expiration can require additional notification
      APIs on RADIUS clients and servers which that were previously not required
      when shared secrets were used.</t>
      <t>Certificates also require the use of certification authorities (CAs), (CAs)
      and chains of certificates.  RADIUS implementations using TLS therefore
      have to track not just a small shared secret, but also potentially many
      large certificates.  The use of TLS-PSK can therefore provide a simpler
      upgrade path for implementations to transition from RADIUS shared
      secrets to TLS.</t>
      <t>In terms of ongoing maintenance, it is generally simpler to maintain
      servers than clients.  For one, there are many fewer servers than
      clients.  Servers are also typically less resource constrained, and
      often run on general-purpose operating systems, where maintenance can be
      automated using widely-available widely available tools.</t>
      <t>In contrast, clients are often numerous, resource constrained, and are more
      likely to be closed or proprietary systems with limited interfaces.  As
      a result, it can be difficult to update these clients when a root CA
      expires.  The use of TLS-PSK in such an environment may therefore offer
      management efficiencies.</t>
    </section>
    <section anchor="general-discussion-of-psks-and-psk-identities">
      <name>General Discussion of PSKs and PSK Identities</name>
      <t>Before we define any RADIUS-specific use of PSKs, we must first
      review the current standards for PSKs, and give general advice on PSKs
      and PSK Identities.</t>
      <t>The requirements in this section apply to both client and server
      implementations which that use TLS-PSK.  Client-specific and server-specific
      issues are discussed in more detail later in this document.</t>
      <section anchor="guidance-for-psks">
        <name>Guidance for PSKs</name>
        <t>We first give requirements for creating and managing PSKs, followed
        by usability guidance, and then a discussion of RADIUS shared secrets
        and their interaction with PSKs.</t>
        <section anchor="psk-requirements">
          <name>PSK Requirements</name>
          <t>Reuse of a PSK in multiple versions of TLS (e.g., TLS 1.2 and TLS
          1.3) is considered unsafe (<xref (see <xref section="E.7" sectionFormat="comma"
          target="RFC8446"/>).  Where TLS 1.3 binds the PSK to a particular
          key derivation function, function (KDF), TLS 1.2 does not.  This binding means that
          it is possible to use the same PSK in different hashes, leading to
          the potential for attacking the PSK by comparing the hash outputs.
          While there are no known insecurities, these uses are not known to
          be secure, and should therefore be avoided.  For this reason, an
          implementation MUST NOT <bcp14>MUST NOT</bcp14> use the same PSK for TLS 1.3
          and for earlier versions of TLS. The exact manner in which this
          requirement is enforced is implementation-specific. One possibility
          is to have two different PSKs. Another possibility is to forbid the
          use of TLS versions less than TLS 1.3</t>
          <t><xref target="RFC9258"/> adds a key derivation function (KDF) KDF to the import interface of
          (D)TLS 1.3, which binds the externally provided PSK to the protocol
          version.  That process is preferred to any TOFU trust-on-first-use (TOFU) mechanism.  In
          particular, that document:</t>
          <ul empty="true">
            <li>

<!-- DNE: blockquote from Section 1 of [RFC9258]. -->

            <blockquote>
              <t>... describes a mechanism for importing PSKs derived from
              external PSKs by including the target KDF, (D)TLS protocol
              version, and an optional context string to ensure
              uniqueness. This process yields a set of candidate PSKs, each of
              which are bound to a target KDF and protocol, that are separate
              from those used in (D)TLS 1.2 and prior versions. This expands
              what would normally have been a single PSK and identity into a
              set of PSKs and identities.</t>
            </li>
          </ul>
            </blockquote>

          <t>An implementation MUST NOT <bcp14>MUST NOT</bcp14> use the same PSK for
          TLS 1.3 and for earlier versions of TLS.  This requirement prevents
          reuse of a PSK with multiple TLS versions, which prevents the
          attacks discussed in <xref section="E.7" sectionFormat="comma"
          target="RFC8446"/>.  The exact manner in which this requirement is
          enforced is implementation-specific.  One possibility is to have two
          different PSKs.  Another possibility is to forbid the use of TLS
          versions less than TLS 1.3.</t>
          <t>Implementations MUST <bcp14>MUST</bcp14> follow the directions of
          <xref section="6" sectionFormat="comma" target="RFC9257"/> for the
          use of external PSKs in TLS.  That document provides extremely
          useful guidance on generating and using PSKs.</t>

<!-- [rfced] What specific text does "base32 in the example below" refer to?
May we update to provide a more clear pointer for the reader?

Original:
   That is, a PSK with high entropy may be expanded via some construct
   (e.g., base32 as in the example below) in order to make it easier for
   people to interact with.
-->

          <t>Implementations MUST <bcp14>MUST</bcp14> support PSKs of at least 32
          octets in length, and SHOULD <bcp14>SHOULD</bcp14> support PSKs of 64
          octets or more.  As the PSKs are generally hashed before being used
          in TLS, the useful entropy of a PSK is limited by the size of the
          hash output.  This output may be 256, 384, or 512 bits in length.
          Nevertheless, it is good practice for implementations to allow entry
          of PSKs of more than 64 octets, as the PSK may be in a form other
          than bare binary data.  Implementations which that limit the PSK to a
          maximum of 64 octets are likely to use PSKs which that have much less
          than 512 bits of entropy.  That is, a PSK with high entropy may be
          expanded via some construct (e.g., base32 as in the example below)
          in order to make it easier for people to interact with.  Where 512
          bits of entropy are input to an encoding construct, the output may
          be larger than 64 octets.</t>
          <t>Implementations MUST <bcp14>MUST</bcp14> require that PSKs be at least
          16 octets in length.  That is, short PSKs MUST NOT <bcp14>MUST NOT</bcp14> be
          permitted to be used, and PSKs MUST <bcp14>MUST</bcp14> be random.  The
          strength of the PSK is not determined by the length of the PSK, but
          instead by the number of bits of entropy which that it contains.  People
          are not good at creating data with high entropy, so a source of
          cryptographically secure random numbers MUST <bcp14>MUST</bcp14> be
          used.</t>
          <t>Where user passwords are generally intended to be remembered and
          entered by people on a regular basis, PSKs are intended to be
          entered once, and then automatically saved in a system
          configuration.  As such, due to the limited entropy of passwords,
          they are not acceptable for use with TLS-PSK, and would only be
          acceptable for use with a password-authenticated key exchange (PAKE)
          TLS method <xref target="RFC8492"/>.  Implementations MUST
          <bcp14>MUST</bcp14> therefore support entry and storage of PSKs as
          undistinguished octets.</t>

	  <t>We also incorporate by reference the requirements of <xref
          section="10.2" sectionFormat="comma" target="RFC7360"/> when using
          PSKs.</t>
          <t>It may be tempting for servers to implement a "trust on first use" (TOFU) TOFU policy with
          respect to clients.  Such behavior is NOT RECOMMENDED. <bcp14>NOT RECOMMENDED</bcp14>.  When servers receive a connection from an
          unknown client, they SHOULD <bcp14>SHOULD</bcp14> log the PSK Identity,
          source IP address, and any other information which that may be relevant.
          An administrator can then later look at the logs and determine the
          appropriate action to take.</t>
        </section>

        <section anchor="usability-guidance">
          <name>Usability Guidance</name>
          <t>PSKs are in their purest form are opaque tokens, represented as
          an undistinguished series of octets.  Where PSKs are expected to be
          managed automatically by scripted methods, this format is
          acceptable.  However, in some cases it is necessary for
          administrators to share PSKs, in which case humanly readable human-readable formats
          may be useful.  Implementations SHOULD <bcp14>SHOULD</bcp14> support
          entering PSKs as both binary data, data and via a humanly readable human-readable form
          such as hex encoding.</t>
          <t>Implementations SHOULD <bcp14>SHOULD</bcp14> use a humanly readable human-readable form
          of PKSs PSKs for interfaces which that are intended to be used by people, and SHOULD
          <bcp14>SHOULD</bcp14> allow for binary data to be entered via an
          application programming interface (API).  Implementations SHOULD
          <bcp14>SHOULD</bcp14> also allow for PSKs to be displayed in the above-mentioned hex encoding,
          encoding mentioned above, so that administrators can manually verify
          that a particular PSK is being used.</t>
          <t>When using PSKs, administrators SHOULD <bcp14>SHOULD</bcp14> use PSKs of
          at least 24 octets, octets that are generated using a source of cryptographically
          secure random numbers.  Implementers needing a secure random number
          generator should see <xref target="RFC8937"/> for for further
          guidance.  PSKs are not passwords, and administrators should not try
          to manually create PSKs.</t>
          <t>In order to guide implementers and administrators, we give
          example commands below which that generate random PSKs from a locally
          secure source.  While some commands may not work on some systems systems, one
          of the commands should succeed.  The intent here is to document a
          concise and simple example of creating PSKs which that are both secure, secure
          and humanly manageable. human-manageable.  This document does not mandate that the
          PSKs follow this format, format or any other format.</t>
          <artwork><![CDATA[

          <sourcecode type=""><![CDATA[
openssl rand -base64 16

dd if=/dev/urandom bs=1 count=16 | base64

dd if=/dev/urandom bs=1 count=16 | base32

dd if=/dev/urandom bs=1 count=16 | (hexdump -ve '/1 "%02x"' && echo)
]]></artwork>
]]></sourcecode>

          <t>Only one of the above commands should be run, run; there is no need to
          run all of them.  Each command reads 128 bits (16 octets) of random
          data from a secure source, and encodes it as printable / and readable
          ASCII.  This form of PSK will be accepted by any implementation which
          that supports at least 32 octets for PSKs.  Larger PSKs can be
          generated by changing the "16" number to a larger value.  The above
          derivation assumes that the random source returns one bit of entropy
          for every bit of randomness which that is returned.  Sources failing that
          assumption are NOT RECOMMENDED.</t> <bcp14>NOT RECOMMENDED</bcp14>.</t>
        </section>

        <section anchor="interaction-between-psks-and-radius-shared-secrets">
          <name>Interaction between Between PSKs and RADIUS Shared Secrets</name>

          <t>Any shared secret used for RADIUS/UDP or RADIUS/TLS MUST NOT <bcp14>MUST
          NOT</bcp14> be used for TLS-PSK.</t>
          <t>It is RECOMMENDED <bcp14>RECOMMENDED</bcp14> that RADIUS clients and servers
          track all used shared secrets and PSKs, and then verify that the
          following requirements all hold true:</t>
          <ul spacing="normal">
            <li>
              <t>no shared secret is used for more than one RADIUS client</t>
            </li>
            <li>
              <t>no PSK is used for more than one RADIUS client</t>
            </li>
            <li>
              <t>no shared secret is used as a PSK</t>
            </li>
          </ul>
          <t>Note that the shared secret of "radsec" given in <xref
          target="RFC6614"/> can be used across multiple clients, as that
          value is mandated by the specification.  The intention here is to
          recommend best practices for administrators who enter site-local
          shared secrets.</t>
          <t>There may be use-cases use cases for using one shared secret across
          multiple RADIUS clients.  There may similarly be use-cases use cases for
          sharing a PSK across multiple RADIUS clients.  Details of the
          possible attacks on reused PSKs are given in <xref section="4.1"
          sectionFormat="comma" target="RFC9257"/>.</t>
          <t>There are no known use-cases use cases for using a PSK as a shared secret,
          or vice-versa.</t> vice versa.</t>
          <t>Implementations MUST <bcp14>MUST</bcp14> reject configuration attempts
          that try to use the same value for the PSK and shared secret.  To
          prevent administrative errors, implementations should not have
          interfaces which that confuse PSKs and shared secrets, secrets or which that allow
          both PSKs and shared secrets to be entered at the same time.  There
          is too much of a temptation for administrators to enter the same
          value in both fields, which would violate the limitations given
          above.  Similarly, using a "shared secret" field as a way for
          administrators to enter PSKs is bad practice.  The PSK entry fields
          need to be labeled as being related to PSKs, and not to shared
          secrets.</t>
        </section>
      </section>
      <section anchor="psk-identities">
        <name>PSK Identities</name>
        <t><xref section="5.1" sectionFormat="comma" target="RFC4279"/>
        requires that PSK Identities be encoded in UTF-8 format.  However,
        <xref section="4.2.11" sectionFormat="comma" target="RFC8446"/>
        describes the "Pre-Shared Key Extension" and defines the ticket as an
        opaque string: "opaque identity&lt;1..2^16-1&gt;;". identity&lt;1..2<sup>16</sup>-1&gt;;".  This PSK is then
        used in <xref section="4.6.1" sectionFormat="comma" target="RFC8446"/>
        for resumption.</t>
        <t>These definitions appear to be in conflict.  This conflict is
        addressed in <xref section="6.1.1" sectionFormat="comma"
        target="RFC9257"/>, which discusses requirements for encoding and
        comparison of PSK Identities.  Systems MUST <bcp14>MUST</bcp14> follow the
        directions of <xref section="6.1.1" sectionFormat="comma"
        target="RFC9257"/> when using or comparing PSK Identities for
        RADIUS/TLS.  Implementations MUST <bcp14>MUST</bcp14> follow the
        recommendations of <xref target="RFC8265"/> for handling PSK Identity
        strings.</t>
        <t>In general, implementers should allow for external PSK Identities
        to follow <xref target="RFC4279"/> and be UTF-8, while PSK Identities
        provisioned as part of resumption are automatically provisioned, and
        therefore follow <xref target="RFC8446"/>.</t>
        <t>Note that the PSK Identity is sent in the clear, and is therefore
        visible to attackers.  Where privacy is desired, the PSK Identity
        could be either an opaque token generated cryptographically, or
        perhaps in the form of a Network Access Identifier (NAI) <xref
        target="RFC7542"/>, where the "user" portion is an opaque token.  For
        example, an NAI could be "68092112@example.com".  If the attacker
        already knows that the client is associated with "example.com", then
        using that domain name in the PSK Identity offers no additional
        information.  In contrast, the "user" portion needs to be both unique
        to the client and private, so using an opaque token there is a more
        secure approach.</t>
        <t>Implementations MUST <bcp14>MUST</bcp14> support PSK Identities of 128
        octets, and SHOULD <bcp14>SHOULD</bcp14> support longer PSK Identities.  We
        note that while TLS provides for PSK Identities of up to 2^16-1 2<sup>16</sup>-1 octets
        in length, there are few practical uses for extremely long PSK
        Identities.</t>
        <t>It is up to administrators and implementations as to how they
        differentiate external PSK Identities from session resumption PSK
        Identities used in TLS 1.3 session tickets.  While <xref
        section="6.1.2" sectionFormat="comma" target="RFC9257"/> suggests the
        identities should be unique, it offers no concrete steps for how this
        differentiation may be done.</t>
        <t>One approach could be to have externally provisioned PSK Identities
        contain an NAI such as what is described above, while session resumption PSK
        Identities contain large blobs of opaque, encrypted, and authenticated
        text.  It should then be relatively straightforward to differentiate
        the two types of identities.  One is UTF-8, the other is not.  One is
        unauthenticated, the other is authenticated.</t>
        <t>Servers MUST <bcp14>MUST</bcp14> assign and/or track session resumption
        PSK Identities in a way which that facilities the ability to distinguish
        those identities from externally configured PSK Identities, and which that
        enables them to both find and validate the session resumption PSK.
        See {}(#resumption) <xref target="resumption"/> below for more discussion of issues around
        resumption.</t>
        <t>A sample validation flow for TLS-PSK Identities could be performed
        via the following steps:</t>
        <ul empty="true">
          <li>

<!-- [rfced] Section 4.2: We have made some updates to the numbered list
at the end of this section, in order to make the list items more
parallel. Please review and let us know any further updates. -->

        <ol spacing="normal" type="1"><li>
                <t>PSK type="1">
          <li>PSK Identities provided via an administration interface are
          enforced to be only UTF-8 on both client and server.</t>
              </li>
              <li>
                <t>The server.</li>
          <li>The client treats session tickets received from the server as
          opaque blobs.</t>
              </li>
              <li>
                <t>When blobs.</li>
          <li>When the server issues session tickets for resumption, the
          server ensures that they are not valid UTF-8.</t>
              </li>
              <li>
                <t>One UTF-8.</li>
          <li>One way to do this is to use stateless resumption with a forced
          non-UTF-8 key_name per <xref section="4" sectionFormat="comma"
          target="RFC5077"/>, such as by setting one octet to 0x00.</t>
              </li>
            </ol>
            <t>5 When 0x00.</li>
          <li>
	    <t>When receiving TLS, the server receives a Client-Hello containing
	    a PSK, and checks if the identity is valid UTF-8.</t>
            <ul empty="true"> UTF-8:</t>

            <ol type="%p%d.">
              <li>
                <t>5.1. If
		<t>If yes, it searches for a pre-configured preconfigured client which that matches that identity.</t>
                <ul empty="true">
                  <li>
                    <t>5.1.1. If
		<ol type="5.1.%d.">
                  <li>If the identity is found, it authenticates the client via PSK.</t>
                    <t>5.1.2. else PSK.</li>
                  <li>Else, the identity is invalid, and the server closes the connection.</t> connection.</li>
		</ol>
	      </li>
                </ul>
                <t>5.2 If the identity is not UTF-8,
              <li>
		<t>If not, try resumption, which is usually be handled by a TLS library.</t>
                <ul empty="true">
                  <li>
                    <t>5.2.1 If
		<ol type="5.2.%d.">
                  <li>If the TLS library verifies the session ticket, then resumption has happened, and the connection is established.</t>
                    <t>5.2.2. else established.</li>
                  <li>Else, the server ignores the session ticket, and performs a normal TLS handshake with a certificate.</t>
                  </li>
                </ul> certificate.</li>
		</ol>
	      </li>
            </ul>
            </ol>
	  </li>
        </ul>
	</ol>

        <t>This validation flow is only suggested.  Other validation methods are possible.</t>
        <section anchor="security-of-psk-identities">
          <name>Security of PSK Identities</name>
          <t>We note that the PSK Identity is a field created by the
          connecting client.  Since the client is untrusted until both the
          identity and PSK have been verified, both of those fields MUST
          <bcp14>MUST</bcp14> be treated as untrusted.  That is, a well-formed
          PSK Identity is likely to be in UTF-8 format, due to the
          requirements of <xref section="5.1" sectionFormat="comma"
          target="RFC4279"/>.  However, implementations MUST <bcp14>MUST</bcp14>
          support managing PSK Identities as a set of undistinguished
          octets.</t>

<!-- [rfced] For readability, may we format this sentence as a list?

Original:
   For example, the identity may have incorrect UTF-8 format; or it may
   contain data which forms an injection attack for SQL, LDAP, REST or shell
   meta characters; or it may contain embedded NUL octets which are
   incompatible with APIs which expect NUL terminated strings.

Perhaps:
   For example, the identity may:

   *  have an incorrect UTF-8 format,

   *  contain data that forms an injection attack for SQL, the Lightweight
      Directory Access Protocol (LDAP), Representational State Transfer
      (REST), or shell meta characters, or

   *  contain embedded NUL octets that are incompatible with APIs that
      expect NUL terminated strings.
-->

          <t>It is not safe to use a raw PSK Identity to look up a
          corresponding PSK.  The PSK may come from an untrusted source, source and
          may contain invalid or malicious data.  For example, the identity
          may have incorrect UTF-8 format; or it may contain data which that forms
          an injection attack for SQL, LDAP, REST Lightweight Directory Access
          Protocol (LDAP), Representational State Transfer (REST), or shell
          meta characters; or it may contain embedded NUL octets which that are
          incompatible with APIs which that expect NUL terminated strings.  The
          identity may also be up to 65535 octets long.</t>
          <t>As such, implementations MUST <bcp14>MUST</bcp14> validate the
          identity prior to it being used as a lookup key.  When the identity
          is passed to an external API (e.g., database lookup),
          implementations MUST <bcp14>MUST</bcp14> either escape any characters in
          the identity which that are invalid for that API, or else reject the
          identity entirely.  The exact form of any escaping depends on the
          API, and we cannot document all possible methods here.  However, a
          few basic validation rules are suggested, as outlined below.  Any
          identity which that is rejected by these validation rules MUST
          <bcp14>MUST</bcp14> cause the server to close the TLS
          connection.</t>
          <t>The suggested validation rules for identities used outside of resumption are as follows:</t>
          <ul spacing="normal">
            <li>
              <t>Identities MUST <bcp14>MUST</bcp14> be checked to see if they have
              been provisioned as a resumption PSK.  If so, then the session
              can be resumed, subject to any policies around resumption.</t>
            </li>
            <li>
              <t>Identities longer than a fixed maximum SHOULD <bcp14>SHOULD</bcp14>
              be rejected.  The limit is implementation dependent, but SHOULD NOT
              <bcp14>SHOULD NOT</bcp14> be less than 128, and SHOULD NOT <bcp14>SHOULD
              NOT</bcp14> be more than 1024.  There is no purpose to allowing
              extremely long identities, and allowing them does little more
              than complicate implementations.</t>
            </li>
            <li>
              <t>Identities configured by administrators SHOULD <bcp14>SHOULD</bcp14>
              be in UTF-8 format, and SHOULD <bcp14>SHOULD</bcp14> be in the <xref target="RFC7542"/> NAI format.
              format from <xref target="RFC7542"/>.  While <xref
              section="4.2.11" sectionFormat="comma" target="RFC8446"/>
              defines the PSK Identity as "opaque identity&lt;1..2^16-1&gt;", identity&lt;1..2<sup>16</sup>-1&gt;",
              it is useful for administrators to manage humanly-readable human-readable
              identities in a recognizable format.
<br/><br/>
This format.</t>
	      <t>This suggestion makes it easier to distinguish TLS-PSK
	      Identities from TLS 1.3 resumption identities.  It also allows
	      implementations to more easily filter out unexpected or bad
	      identities, and then to close inappropriate TLS connections.</t>
            </li>
          </ul>
          <t>It is RECOMMENDED <bcp14>RECOMMENDED</bcp14> that implementations extend
          these rules with any additional validation which are that is found to be
          useful.  For example, implementations and/or deployments could both
          generate PSK Identities in a particular format for passing to client
          systems, and then also verify that any received identity matches
          that format.  For example, a site could generate PSK Identities which
          that are composed of characters in the local language.  The site
          could then reject identities which that contain characters from other
          languages, even if those characters are valid UTF-8.</t>
          <t>The purpose of these rules is to help administrators and
          implementers more easily manage systems using TLS-PSK, while also
          minimizing complexity and protecting from potential attackers attackers'
          traffic.  The rules follow a principle of "discard bad traffic
          quickly", which helps to improve system stability and
          performance.</t>
        </section>
      </section>

      <section anchor="sharing">
        <name>PSK and PSK Identity Sharing</name>
        <t>While administrators may desire to share PSKs and/or PSK Identities
        across multiple systems, such usage is NOT RECOMMENDED. <bcp14>NOT RECOMMENDED</bcp14>.
        Details of the possible attacks on reused PSKs are given in <xref
        section="4.1" sectionFormat="comma" target="RFC9257"/>.</t>
        <t>Implementations MUST <bcp14>MUST</bcp14> support the ability to
        configure a unique PSK and PSK Identity for each possible
        client-server relationship.  This configuration allows administrators
        desiring security to use unique PSKs for each such relationship.  This
        configuration is also compatible with the practice of administrators
        who wish to re-use reuse PSKs and PSK Identities where local policies
        permit.</t>
        <t>Implementations SHOULD <bcp14>SHOULD</bcp14> warn administrators if the
        same PSK Identity and/or PSK is used for multiple client-server
        relationships.</t>
      </section>

      <section anchor="psk-lifetimes">
        <name>PSK Lifetimes</name>
        <t>Unfortunately, <xref target="RFC9257"/> offers no guidance on PSK
        lifetimes other than to note in Section 4.2 <xref target="RFC9257" sectionFormat="bare" section="4.2"/> that:</t>
        <ul empty="true">
          <li>
<!-- Note to PE: Quote from [RFC9257] is correct. -->
	<blockquote>
            <t>Forward security may be achieved by using a PSK-DH mode or by
            using PSKs with short lifetimes.</t>
          </li>
        </ul>
	</blockquote>
        <t>It is RECOMMENDED <bcp14>RECOMMENDED</bcp14> that PSKs be rotated regularly.
        We offer no additional guidance on how often this process should
        occur.  Changing PSKs has a non-zero cost.  It is therefore up to
        administrators to determine how best to balance the cost of changing
        the PSK against the cost of a potential PSK compromise.</t>
        <t>TLS-PSK MUST <bcp14>MUST</bcp14> use modes such as PSK-DH or ECDHE_PSK
        <xref target="RFC5489"/> which that provide forward secrecy.  Failure to
        use such modes would mean that compromise of a PSK would allow an
        attacker to decrypt all sessions which that had used that PSK.</t>
        <t>As the PSKs are looked up by identity, the PSK Identity MUST
        <bcp14>MUST</bcp14> also be changed when the PSK changes.</t>
        <t>Servers SHOULD <bcp14>SHOULD</bcp14> track when a connection was last
        received for a particular PSK Identity, and SHOULD <bcp14>SHOULD</bcp14>
        automatically invalidate credentials when a client has not connected
        for an extended period of time.  This process helps to mitigate the
        issue of credentials being leaked when a device is stolen or
        discarded.</t>
      </section>
    </section>
    <section anchor="guidance-for-radius-clients">
      <name>Guidance for RADIUS Clients</name>
      <t>Client

<!-- [rfced] For clarity, may we update the second part of this sentence
to repeat "expose"? This helps to avoid misreading "fields" as a verb.

Original:
   The client implementation can then expose a user interface flag which is
   "TLS yes / no", and then also fields which ask for the PSK Identity and PSK
   itself.

Perhaps:
   The client implementation can then expose a user interface flag that is
   "TLS yes / no", and also expose fields that ask for the PSK Identity and PSK
   itself.
-->

<!-- [rfced] Regarding this text in Section 5:
a) May we update the first sentence to avoid repetition of "TLS 1.3"?
b) This exact text appears again in Section 6 (i.e., for clients
and servers). Please review and confirm it is correct for this text
to appear twice in this document.

Original:
   For TLS 1.3, Implementations MUST support "psk_dhe_ke" Pre-Shared Key
   Exchange Mode in TLS 1.3 as discussed in [RFC8446], Section 4.2.9 and
   in [RFC9257], Section 6.  Implementations MUST implement the
   recommended cipher suites in [RFC9325], Section 4.2 for TLS 1.2, and
   in [RFC8446], Section 9.1 for TLS 1.3.  In order to future-proof
   these recommendations, we give the following recommendations:

   *  Implementations SHOULD use the "Recommended" cipher suites listed
      in the IANA "TLS Cipher Suites" registry,

      -  for TLS 1.3, the use "psk_dhe_ke" PSK key exchange mode,

      -  for TLS 1.2 and earlier, use cipher suites which require
         ephemeral keying.

Perhaps:
   For TLS 1.3, implementations MUST support the "psk_dhe_ke" Pre-Shared
   Key Exchange Mode as discussed in [RFC8446], Section 4.2.9
   and in [RFC9257], Section 6.  Implementations MUST implement the
   recommended cipher suites in [RFC9325], Section 4.2 for TLS 1.2 and
   in [RFC8446], Section 9.1 for TLS 1.3.  In order to future-proof
   these recommendations, we give the following recommendations.

   *  Implementations SHOULD use the "Recommended" cipher suites listed
      in the IANA "TLS Cipher Suites" registry:

      -  For TLS 1.3, use the "psk_dhe_ke" PSK key exchange mode.

      -  For TLS 1.2 and earlier, use cipher suites that require
         ephemeral keying.
-->

      <t>Client implementations <bcp14>MUST</bcp14> allow the use of a
      pre-shared key (PSK) for RADIUS/TLS.  The client implementation can then
      expose a user interface flag which is "TLS yes / no", and then also
      fields which that ask for the PSK Identity and PSK itself.</t>
      <t>For TLS 1.3, Implementations MUST implementations <bcp14>MUST</bcp14> support the "psk_dhe_ke"
      Pre-Shared Key Exchange Mode in TLS 1.3 as discussed in <xref
      section="4.2.9" sectionFormat="comma" target="RFC8446"/> and in <xref
      section="6" sectionFormat="comma" target="RFC9257"/>.  Implementations MUST
      <bcp14>MUST</bcp14> implement the recommended cipher suites in <xref
      section="4.2" sectionFormat="comma" target="RFC9325"/> for TLS 1.2, 1.2 and
      in <xref section="9.1" sectionFormat="comma" target="RFC8446"/> for TLS
      1.3.  In order to future-proof these recommendations, we give the
      following recommendations:</t> recommendations.</t>
      <ul spacing="normal">
        <li>
          <t>Implementations SHOULD <bcp14>SHOULD</bcp14> use the "Recommended"
          cipher suites listed in the IANA "TLS Cipher Suites" registry, registry:
          </t>
          <ul spacing="normal">
            <li>
              <t>for
              <t>For TLS 1.3, the use the "psk_dhe_ke" PSK key exchange mode,</t> mode.</t>
            </li>
            <li>
              <t>for
              <t>For TLS 1.2 and earlier, use cipher suites which that require ephemeral keying.</t>
            </li>
          </ul>
        </li>
      </ul>
      <t>If a client initiated a connection using a PSK with TLS 1.3 by
      including the pre-shared key extension, it MUST <bcp14>MUST</bcp14> close the
      connection if the server did not also select the pre-shared key to
      continue the handshake.</t>

      <section anchor="psk-identities-1">
        <name>PSK Identities</name>
        <t>This section offers advice on both requirements for PSK Identities, Identities and on usability.</t>
        <section anchor="psk-identity-requirements">
          <name>PSK Identity Requirements</name>
          <t><xref target="RFC6614"/> is silent on the subject of PSK
          Identities, which is an issue that we correct here.  Guidance is
          required on the use of PSK Identities, as the need to manage
          identities associated with PSK PSKs is a new requirement for NAS both Network Access Server (NAS)
          management interfaces, interfaces and is a new requirement for RADIUS
          servers.</t>
          <t>RADIUS systems implementing TLS-PSK MUST <bcp14>MUST</bcp14> support
          identities as per <xref section="5.3" sectionFormat="comma" target="RFC4279"/>,
          target="RFC4279"/> and MUST <bcp14>MUST</bcp14> enable configuring
          TLS-PSK Identities in management interfaces as per <xref
          section="5.4" sectionFormat="comma" target="RFC4279"/>.</t>
          <t>The historic methods of signing RADIUS packets have not yet been
          broken, but they are believed to be much less secure than modern
          TLS.  Therefore, when a RADIUS shared secret is used to sign
          RADIUS/UDP or RADIUS/TCP packets, that shared secret MUST NOT <bcp14>MUST
          NOT</bcp14> be used with TLS-PSK.  If the secrets were to be reused,
          then an attack on historic RADIUS cryptography could be trivially
          leveraged to decrypt TLS-PSK sessions.</t>
          <t>With TLS-PSK, RADIUS/TLS clients MUST <bcp14>MUST</bcp14> permit the
          configuration of a RADIUS server IP address or host name, because
          dynamic server lookups <xref target="RFC7585"/> can only be used if
          servers use certificates.</t>
        </section>

        <section anchor="usability-guidance-1">
          <name>Usability Guidance</name>
          <t>In order to prevent confusion between shared secrets and
          TLS-PSKs, management interfaces and APIs need to label PSK fields as
          "PSK" or "TLS-PSK", rather than as "shared secret".</t>
        </section>
      </section>
    </section>

    <section anchor="guidance-for-radius-servers">
      <name>Guidance for RADIUS Servers</name>
      <t>In order to support clients with TLS-PSK, server implementations MUST
      <bcp14>MUST</bcp14> allow the use of a pre-shared key (TLS-PSK) for
      RADIUS/TLS.</t>
      <t>Systems which that act as both client and server at the same time MUST NOT
      <bcp14>MUST NOT</bcp14> share or reuse PSK Identities between incoming
      and outgoing connections.  Doing so would open up the systems to attack,
      as discussed in <xref section="4.1" sectionFormat="comma"
      target="RFC9257"/>.</t>
      <t>For TLS 1.3, Implementations MUST implementations <bcp14>MUST</bcp14> support the "psk_dhe_ke"
      Pre-Shared Key Exchange Mode in TLS 1.3 as discussed in <xref
      section="4.2.9" sectionFormat="comma" target="RFC8446"/> and in <xref
      section="6" sectionFormat="comma" target="RFC9257"/>.  Implementations MUST
      <bcp14>MUST</bcp14> implement the recommended cipher suites in <xref
      section="4.2" sectionFormat="comma" target="RFC9325"/> for TLS 1.2, 1.2 and
      in <xref section="9.1" sectionFormat="comma" target="RFC8446"/> for TLS
      1.3.  In order to future-proof these recommendations, we give the
      following recommendations:</t> recommendations.</t>
      <ul spacing="normal">
        <li>
          <t>Implementations SHOULD <bcp14>SHOULD</bcp14> use the "Recommended"
          cipher suites listed in the IANA "TLS Cipher Suites" registry, registry:
          </t>
          <ul spacing="normal">
            <li>
              <t>for
              <t>For TLS 1.3, use the "psk_dhe_ke" PSK key exchange mode,</t> mode.</t>
            </li>
            <li>
              <t>for
              <t>For TLS 1.2 and earlier, use cipher suites which that require ephemeral keying.</t>
            </li>
          </ul>
        </li>
      </ul>
      <t>The following section(s) describe guidance for RADIUS server
      implementations and deployments.  We first give an overview of current
      practices, and then extend and/or replace those practices for
      TLS-PSK.</t>

      <section anchor="current-practices">
        <name>Current Practices</name>
        <t>RADIUS identifies clients by source IP address (<xref (see <xref
        target="RFC2865"/> and <xref target="RFC6613"/>) or by client
        certificate (<xref (see <xref target="RFC6614"/> and <xref target="RFC7585"/>).
        Neither of these approaches work for TLS-PSK.  This section describes
        current practices and mandates behavior for servers which that use
        TLS-PSK.</t>
        <t>A RADIUS/UDP server is typically configured with a set of
        information per client, which includes at least the source IP address
        and shared secret.  When the server receives a RADIUS/UDP packet, it
        looks up the source IP address, finds a client definition, and
        therefore the shared secret.  The packet is then authenticated (or
        not) using that shared secret.</t>
        <t>That

<!-- [rfced] Is "clients" meant to be singular possessive or
plural possessive in the text below?

Original:
   That is, the IP address is treated as the clients identity, and the
   shared secret is used to prove the clients authenticity and shared
   trust.  The set of clients forms a logical database "client table",
   with the IP address as the key.

Perhaps (singular possessive):
   That is, the IP address is treated as the client's identity, and the
   shared secret is used to prove the client's authenticity and shared
   trust.  The set of clients forms a logical database "client table"
   with the IP address as the key.
-->

        <t>That is, the IP address is treated as the clients identity, and the
        shared secret is used to prove the clients authenticity and shared
        trust.  The set of clients forms a logical database "client table"
        with the IP address as the key.</t>
        <t>A server may be configured with additional site-local policies
        associated with that client.  For example, a client may be marked up
        as being a WiFi Wi-Fi Access Point, or a VPN concentrator, etc.  Different
        clients may be permitted to send different kinds of requests, where
        some may send Accounting-Request packets, and other clients may not
        send accounting packets.</t>
      </section>
      <section anchor="practices-for-tls-psk">
        <name>Practices for TLS-PSK</name>
        <t>We define practices for TLS-PSK by analogy with the RADIUS/UDP use-case,
        use case and by extending the additional policies associated with the
        client.  The PSK Identity replaces the source IP address as the client
        identifier.  The PSK replaces the shared secret as proof of client
        authenticity and shared trust.  However, systems implementing
        RADIUS/TLS <xref target="RFC6614"/> and RADIUS/DTLS <xref
        target="RFC7360"/> MUST <bcp14>MUST</bcp14> still use the shared secret as
        discussed in those specifications.  Any PSK is only used by the TLS layer,
        layer and has no effect on the RADIUS data which that is being
        transported.  That is, the RADIUS data transported in a TLS tunnel is
        the same no matter if client authentication is done via PSK or by
        client certificates.  The encoding of the RADIUS data is entirely
        unaffected by the use (or not) of PSKs and client certificates.</t>
        <t>In order to securely support dynamic source IP addresses for
        clients, we also require that servers limit clients based on a network
        range.  The alternative would be to suggest that RADIUS servers allow
        any source IP address to connect and try TLS-PSK, which could be a
        security risk.  When RADIUS servers do no source IP address filtering,
        it is easier for attackers to send malicious traffic to the server.
        An issue with a TLS library or even a TCP/IP stack could permit the
        attacker to gain unwarranted access.  In contrast, when IP address
        filtering is done, attackers generally must first gain access to a
        secure network before attacking the RADIUS server.</t>
        <t>Even where <xref target="RFC7585"/> dynamic discovery <xref target="RFC7585"/> is not used,
        the use of TLS-PSK across unrelated organizations requires that those
        organizations share PSKs.  Such sharing makes it easier for a client
        to impersonate a server, and vice versa.  In contrast, when
        certificates are used, such impersonations are impossible. It is
        therefore NOT RECOMMENDED <bcp14>NOT RECOMMENDED</bcp14> to use TLS-PSK across
        organizational boundaries.</t>
        <t>When TLS-PSK is used in an environment where both client and server
        are part of the same organization, then impersonations only affect
        that organization.  As TLS offers significant advantages over
        RADIUS/UDP, it is RECOMMENDED <bcp14>RECOMMENDED</bcp14> that organizations use
        RADIUS/TLS with TLS-PSK to replace RADIUS/UDP for all systems managed
        within the same organization.  While such systems are generally
        located inside of private networks, there are no known security issues
        with using TLS-PSK for RADIUS/TLS connections across the public
        Internet.</t>
        <t>If a client system is compromised, its complete configuration is
        exposed to the attacker.  Exposing a client certificate means that the
        attacker can pretend to be the client.  In contrast, exposing a PSK
        means that the attacker can not cannot only pretend to be the client, but can
        also pretend to be the server.</t>
        <t>The main benefit of TLS-PSK, therefore, is that its operational
        processes are similar to that used for managing RADIUS/UDP, while
        gaining the increased security of TLS.  However, it is still
        beneficial for servers to perform IP address filtering, in order to
        further limit their exposure to attacks.</t>

        <section anchor="ip-filtering">
          <name>IP Filtering</name>
          <t>A server supporting this specification MUST <bcp14>MUST</bcp14>
          perform IP address filtering on incoming connections.  There are few
          reasons for a server to have a default configuration which that allows
          connections from any source IP address.</t>
          <t>A TLS-PSK server MUST <bcp14>MUST</bcp14> be configurable with a set
          of "allowed" network ranges from which clients are permitted to
          connect.  Any connection from outside of the allowed range(s) MUST
          <bcp14>MUST</bcp14> be rejected before any PSK Identity is checked.
          It is RECOMMENDED <bcp14>RECOMMENDED</bcp14> that servers support IP address
          filtering even when TLS-PSK is not used.</t>
          <t>The "allowed" network ranges could be implemented as a global
          list, or one or more network ranges could be tied to a client or
          clients.  The intent here is to allow connections to be filtered by
          source IP address, address and to allow clients to be limited to a subset of
          network addresses.  The exact method and representation of that
          filtering is up to an implementation.</t>
          <t>Conceptually, the set of IP addresses and ranges, along with
          permitted clients and their credentials forms credentials, form a logical "client
          table" which that the server uses to both filter and authenticate
          clients.  The client table should contain information such as
          allowed network ranges, PSK Identity and associated PSK, credentials
          for another TLS authentication method, or flags which that indicate that
          the server should require a client certificate.</t>
          <t>Once a server receives a connection, it checks the source IP
          address against the list of all allowed IP addresses or ranges in
          the client table.  If none match, the connection MUST <bcp14>MUST</bcp14>
          be rejected.  That is, the connection MUST <bcp14>MUST</bcp14> be from an
          authorized source IP address.</t>
          <t>Once a connection has been established, the server MUST NOT <bcp14>MUST
          NOT</bcp14> process any application data inside of the TLS tunnel
          until the client has been authenticated.  Instead, the server
          normally receives a TLS-PSK Identity from the client.  The server
          then uses this identity to look up the client in the client table.
          If there is no matching client, the server MUST <bcp14>MUST</bcp14> close
          the connection.  The server then also checks if this client
          definition allows this particular source IP address.  If the source
          IP address is not allowed, the server MUST <bcp14>MUST</bcp14> close the
          connection.</t>
          <t>Where the server does not receive TLS-PSK from the client, it
          proceeds with another authentication method such as client
          certificates.  Such requirements are discussed elsewhere, most
          notably in <xref target="RFC6614"/> and <xref
          target="RFC7360"/>.</t>
          <t>An implementation may perform two independent IP address lookups.  First, lookups:
          first to check if the connection is allowed at all, and second to
          check if the connection is authorized for this particular client.
          One or both checks may be used by a particular implementation.  The
          two sets of IP addresses can overlap, and implementations SHOULD
          <bcp14>SHOULD</bcp14> support that capability.</t>
          <t>Depending on the implementation, one or more clients may share a
          list of allowed network ranges.  Alternately, the allowed network
          ranges for two clients can overlap only partially, or not at all.
          All of these possibilities MUST <bcp14>MUST</bcp14> be supported by the
          server implementation.</t>
          <t>For example, a RADIUS server could be configured to be accept
          connections from a source network of 192.0.2.0/24 or 2001:DB8::/32.
          The server could therefore discard any TLS connection request which that
          comes from a source IP address outside of that network.  In that
          case, there is no need to examine the PSK Identity or to find the
          client definition.  Instead, the IP source filtering policy would
          deny the connection before any TLS communication had been
          performed.</t>
          <t>As some clients may have dynamic IP addresses, it is possible for a
          one PSK Identity to appear at different source IP addresses over
          time.  In addition, as there may be many clients behind one NAT
          gateway, there may be multiple RADIUS clients using one public IP
          address.  RADIUS servers MUST <bcp14>MUST</bcp14> support multiple PSK
          Identifiers at one source IP address.</t>
          <t>That is, a server needs to support multiple different clients
          within one network range, multiple clients behind a NAT, and one
          client having different IP addresses over time.  All of those use-cases
          use cases are common and necessary.</t>
          <t>The following section describes these requirements in more detail.</t>
        </section>

        <section anchor="psk-authentication">
          <name>PSK Authentication</name>
          <t>Once the source IP address has been verified to be allowed for
          this particular client, the server authenticates the TLS connection
          via the PSK taken from the client definition.  If the PSK is
          verified, the server then accepts the connection, connection and proceeds with
          RADIUS/TLS as per <xref target="RFC6614"/>.</t>
          <t>If the PSK is not verified, then the server MUST <bcp14>MUST</bcp14>
          close the connection.  While TLS provides for fallback to other
          authentication methods such as client certificates, there is no
          reason for a client to be configured simultaneously with multiple
          authentication methods.</t>
          <t>A client MUST <bcp14>MUST</bcp14> use only one authentication method
          for TLS.  An authentication method is either TLS-PSK, client
          certificates, or some other method supported by TLS.</t>
          <t>That is, client configuration is relatively simple: use a
          particular set of credentials to authenticate to a particular
          server.  While clients may support multiple servers and fail-over or
          load-balancing, that configuration is generally orthogonal to the
          choice of which credentials to use.</t>
        </section>
        <section anchor="resumption">
          <name>Resumption</name>
          <t>It is NOT RECOMMENDED <bcp14>NOT RECOMMENDED</bcp14> that servers enable
          resumption for sessions which that use TLS-PSK.  There are few practical
          benefits to supporting resumption, resumption and many complexities.</t>
          <t>However, some systems will need to support both TLS-PSK, TLS-PSK and
          other TLS-based authentication methods such as certificates, while
          also supporting session resumption.  It is therefore vital for
          servers to be able to distinguish the use-case use case of TLS-PSK with pre-configured
          preconfigured identities from TLS-PSK which that is being used for
          resumptions.</t>
          <t>The above discussion of PSK Identities is complicated by the use
          of PSKs for resumption in TLS 1.3.  A server which that receives a PSK
          Identity via TLS typically cannot query the TLS layer to see if this
          identity is for a resumed session (which is possibly for another TLS
          authentication method), or is instead a static pre-provisioned
          identity.  This confusion complicates server implementations.</t>
          <t>One way for a server to tell the difference between the two kinds
          of identities is via construction.  Identities used for resumption
          can be constructed via a fixed format, such as what is recommended by <xref
          section="4" sectionFormat="comma" target="RFC5077"/>.  A static
          pre-provisioned identity could be in the format of an NAI, as given in
          <xref target="RFC7542"/>.  An implementation could therefore examine
          the incoming identity, identity and determine from the identity alone what
          kind of authentication was being performed.</t>
          <t>An alternative way for a server to distinguish the two kinds of
          identities is to maintain two tables.  One table would contain
          static identities, as the logical client table described above.
          Another table could be the table of identities handed out for
          resumption.  The server would then look up any PSK Identity in one
          table, and if it is not found, query the other one.  An  Either an identity would be
          found in a table, in which case it can be authenticated.  Or, authenticated, or the
          identity would not be found in either table, in which case it is
          unknown, and the server MUST <bcp14>MUST</bcp14> close the
          connection.</t>
          <t>As suggested in <xref target="RFC8446"/>, TLS-PSK peers MUST NOT
          <bcp14>MUST NOT</bcp14> store resumption PSKs or tickets (and
          associated cached data) for longer than 604800 seconds (7 days) days),
          regardless of the PSK or ticket lifetime.</t>
          <t>Since resumption in TLS 1.3 uses PSK Identies Identities and keys, it is NOT RECOMMENDED
          <bcp14>NOT RECOMMENDED</bcp14> to permit resumption of sessions when
          TLS-PSK is used.  The use of resumption offers additional complexity
          with minimal addition benefit.</t> additional benefits.</t>
          <t>Where resumption is allowed with TLS-PSK, systems MUST
          <bcp14>MUST</bcp14> cache data during the initial full handshake sufficient
          sufficiently enough to allow authorization decisions to be made during
          resumption. If the cached data cannot be retrieved securely,
          resumption MUST NOT <bcp14>MUST NOT</bcp14> be done.  Instead, the system MUST
          <bcp14>MUST</bcp14> perform a full handshake.</t>
          <t>The data which that needs to be cached is typically information such
          as the original PSK Identity, along with any policies associated
          with that identity.</t>
          <t>Information from the original TLS exchange (e.g., the original
          PSK Identity) as well as related information (e.g., source IP
          addresses) may change between the initial full handshake and
          resumption. This change creates a "time-of-check time-of-use"
          (TOCTOU) security vulnerability. A malicious or compromised client
          could supply one set of data during the initial authentication, authentication and
          a different set of data during resumption, potentially allowing them
          to obtain access that they should not have.</t>
          <t>If any authorization or policy decisions were made with
          information that has changed between the initial full handshake and
          resumption, and if change changes may lead to a different decision, such
          decisions MUST <bcp14>MUST</bcp14> be reevaluated.  Systems MUST
          <bcp14>MUST</bcp14> also reevaluate authorization and policy
          decisions during resumption, based on the information given in the
          new connection.  Servers MAY <bcp14>MAY</bcp14> refuse to perform
          resumption where the information supplied during resumption does not
          match the information supplied during the original authentication.
          If a safe decision is not possible, servers MUST <bcp14>MUST</bcp14>
          instead continue with a full handshake.</t>
        </section>

        <section anchor="interaction-with-other-tls-authentication-methods">
          <name>Interaction with other Other TLS authentication methods</name> Authentication Methods</name>
          <t>When a server supports both TLS-PSK and client certificates, it MUST
          <bcp14>MUST</bcp14> be able to accept authenticated connections from
          clients which that may use either type of credentials, perhaps even from
          the same source IP address and at the same time.  That is, servers
          are required to both authenticate the client, client and also to filter
          clients by source IP address.  These checks both have to match in
          order for a client to be accepted.</t>
        </section>
      </section>
    </section>
    <section anchor="privacy-considerations">
      <name>Privacy Considerations</name>
      <t>We make no changes over to <xref target="RFC6614"/> and <xref target="RFC7360"/>.</t>
    </section>
    <section anchor="security-considerations">
      <name>Security Considerations</name>
      <t>The primary focus of this document is addressing security considerations for RADIUS.</t>
      <t>Previous specifications discuss security considerations for TLS-PSK
      in detail.  We refer the reader to <xref section="E.7" sectionFormat="comma"
      sectionFormat="of" target="RFC8446"/>, <xref target="RFC9257"/>, and
      <xref target="RFC9258"/>.  Those documents are newer than <xref
      target="RFC6614"/> and <xref target="RFC7360"/>, andtherefore and therefore raise
      issues which that were not considered during the initial design of RADIUS/TLS
      and RADIUS/DTLS.</t>
      <t>Using TLS-PSK across the wider Internet for RADIUS can have different
      security considerations than for other protocols.  For example, if
      TLS-PSK was for client/server communication with HTTPS, then having a
      PSK be exposed or broken could affect one users user's traffic.  In contrast,
      RADIUS contains credentials and personally identifiable information
      (PII) for many users.  As a result, an attacker being able to see inside
      of a TLS-PSK connection for RADIUS would result in substantial amounts
      of PII being leaked, possibly including passwords.</t>

      <t>When modes providing forward secrecy are used (e.g. (e.g., ECDHE_PSK as seen in <xref
      target="RFC5489"/> and <xref target="RFC8442"/>), such attacks are
      limited to future sessions, and historical sessions are still
      secure.</t>
    </section>
    <section anchor="iana-considerations">
      <name>IANA Considerations</name>
      <t>There are
      <t>This document has no IANA considerations in this document.</t>
      <t>RFC Editor: This section may be removed before final publication.</t> actions.</t>
    </section>

  </middle>
  <back>

<!-- [rfced] Informative reference RFC 5077 has been obsoleted by
RFC 8446.  We recommend replacing RFC 5077 with RFC 8446.  However, if RFC
5077 must be referenced, we suggest mentioning RFC 8446 (e.g., "RFC 5077 has
been obsoleted by RFC 8446.")  See Section 4.8.6 in the RFC Style Guide
(RFC 7322). -->

    <references anchor="sec-combined-references">
      <name>References</name>
      <references anchor="sec-normative-references">
        <name>Normative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6614.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7360.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2865.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4279.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8265.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9257.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9325.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
      </references>
      <references anchor="sec-informative-references">
        <name>Informative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5077.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6613.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7585.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8446.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8937.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9258.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8492.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7542.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5489.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8442.xml"/>
      </references>
    </references>
    <section anchor="acknowledgments"> anchor="acknowledgments" numbered="false">
      <name>Acknowledgments</name>
      <t>Thanks to the many reviewers in the RADEXT working group Working Group for positive
      feedback.</t>
    </section>
    <section anchor="changelog">
      <name>Changelog</name>
      <ul spacing="normal">
        <li>
          <t>00 - initial version</t>
        </li>
        <li>
          <t>01 - update examples</t>
        </li>
      </ul>
    </section>
  </middle>
  <back>
    <references anchor="sec-combined-references">
      <name>References</name>
      <references anchor="sec-normative-references">
        <name>Normative References</name>
        <reference anchor="RFC6614">
          <front>
            <title>Transport Layer Security (TLS) Encryption for RADIUS</title>
            <author fullname="S. Winter" initials="S." surname="Winter"/>
            <author fullname="M. McCauley" initials="M." surname="McCauley"/>
            <author fullname="S. Venaas" initials="S." surname="Venaas"/>
            <author fullname="K. Wierenga" initials="K." surname="Wierenga"/>
            <date month="May" year="2012"/>
            <abstract>
              <t>This document specifies a transport profile for RADIUS using Transport Layer Security (TLS) over TCP as the transport protocol. This enables dynamic trust relationships between RADIUS servers. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="6614"/>
          <seriesInfo name="DOI" value="10.17487/RFC6614"/>
        </reference>
        <reference anchor="RFC7360">
          <front>
            <title>Datagram Transport Layer Security (DTLS) as a Transport Layer for RADIUS</title>
            <author fullname="A. DeKok" initials="A." surname="DeKok"/>
            <date month="September" year="2014"/>
            <abstract>
              <t>The RADIUS protocol defined in RFC 2865 has limited support for authentication
  </back>
</rfc>

<!-- [rfced] Abbreviations and encryption of RADIUS packets. The protocol transports data in the clear, although some parts of Terminology:

a) We note "pre-shared key" appears frequently after the packets can have obfuscated content. Packets may be replayed verbatim by an attacker, and client-server authentication abbreviation "PSK"
is based on fixed shared secrets. This document specifies how the Datagram Transport Layer Security (DTLS) protocol may be used as a fix for these problems. It also describes how implementations introduced. May we update instances of this proposal can coexist with current RADIUS systems.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7360"/>
          <seriesInfo name="DOI" value="10.17487/RFC7360"/>
        </reference>
        <reference anchor="RFC2865">
          <front>
            <title>Remote Authentication Dial In User Service (RADIUS)</title>
            <author fullname="C. Rigney" initials="C." surname="Rigney"/>
            <author fullname="S. Willens" initials="S." surname="Willens"/>
            <author fullname="A. Rubens" initials="A." surname="Rubens"/>
            <author fullname="W. Simpson" initials="W." surname="Simpson"/>
            <date month="June" year="2000"/>
            <abstract>
              <t>This document describes a protocol for carrying authentication, authorization, and configuration information between a Network Access Server which desires "pre-shared key" to authenticate its links and a shared Authentication Server. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="2865"/>
          <seriesInfo name="DOI" value="10.17487/RFC2865"/>
        </reference>
        <reference anchor="RFC4279">
          <front>
            <title>Pre-Shared Key Ciphersuites for Transport Layer Security (TLS)</title>
            <author fullname="P. Eronen" initials="P." role="editor" surname="Eronen"/>
            <author fullname="H. Tschofenig" initials="H." role="editor" surname="Tschofenig"/>
            <date month="December" year="2005"/>
            <abstract>
              <t>This document specifies three sets of new ciphersuites for the Transport Layer Security (TLS) protocol abbreviation
after it is first expanded?

b) FYI, we changed "PKSs" to support authentication based on pre-shared keys (PSKs). These pre-shared keys are symmetric keys, shared "PSKs" in advance among the communicating parties. The first set of ciphersuites uses only symmetric key operations for authentication. The second set uses a Diffie-Hellman exchange authenticated with text below. Please review
whether this is correct.

Original:
   Implementations SHOULD use a pre-shared key, and the third set combines public key authentication of the server with pre-shared key authentication humanly readable form of the client. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="4279"/>
          <seriesInfo name="DOI" value="10.17487/RFC4279"/>
        </reference>
        <reference anchor="RFC8174">
          <front>
            <title>Ambiguity PKSs...

c) Per Section 3.6 of Uppercase vs Lowercase in RFC 2119 Key Words</title>
            <author fullname="B. Leiba" initials="B." surname="Leiba"/>
            <date month="May" year="2017"/>
            <abstract>
              <t>RFC 2119 specifies common key words that may 7322 ("RFC Style Guide"), abbreviations should be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="8174"/>
          <seriesInfo name="DOI" value="10.17487/RFC8174"/>
        </reference>
        <reference anchor="RFC8265">
          <front>
            <title>Preparation, Enforcement, and Comparison of Internationalized Strings Representing Usernames and Passwords</title>
            <author fullname="P. Saint-Andre" initials="P." surname="Saint-Andre"/>
            <author fullname="A. Melnikov" initials="A." surname="Melnikov"/>
            <date month="October" year="2017"/>
            <abstract>
              <t>This document describes updated methods for handling Unicode strings representing usernames
expanded upon first use. How should "PSK-DH" and passwords. The previous approach was known "ECDHE_PSK" be expanded
below?

Original:
   TLS-PSK MUST use modes such as SASLprep (RFC 4013) and was based on Stringprep (RFC 3454). The methods specified in this document PSK-DH or ECDHE_PSK [RFC5489] which
   provide a more sustainable approach to the handling of internationalized usernames and passwords. This document obsoletes RFC 7613.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8265"/>
          <seriesInfo name="DOI" value="10.17487/RFC8265"/>
        </reference>
        <reference anchor="RFC9257">
          <front>
            <title>Guidance for External Pre-Shared Key (PSK) Usage in TLS</title>
            <author fullname="R. Housley" initials="R." surname="Housley"/>
            <author fullname="J. Hoyland" initials="J." surname="Hoyland"/>
            <author fullname="M. Sethi" initials="M." surname="Sethi"/>
            <author fullname="C. A. Wood" initials="C. A." surname="Wood"/>
            <date month="July" year="2022"/>
            <abstract>
              <t>This document provides usage guidance for external Pre-Shared Keys (PSKs) in Transport Layer Security (TLS) 1.3 forward secrecy.

Perhaps:
   TLS-PSK MUST use modes such as defined in RFC 8446. It lists TLS security properties provided by PSKs under certain assumptions, then it demonstrates how violations of these assumptions lead to attacks. Advice for applications to help meet these assumptions is provided. This document also discusses PSK use cases and provisioning processes. Finally, it lists the privacy and security properties Diffie-Hellman (PSK-DH) or Elliptic Curve
   Diffie-Hellman Exchange with PSK (ECDHE_PSK) [RFC5489] that are not provided by TLS 1.3 when external PSKs are used.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="9257"/>
          <seriesInfo name="DOI" value="10.17487/RFC9257"/>
        </reference>
        <reference anchor="RFC9325">
          <front>
            <title>Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)</title>
            <author fullname="Y. Sheffer" initials="Y." surname="Sheffer"/>
            <author fullname="P. Saint-Andre" initials="P." surname="Saint-Andre"/>
            <author fullname="T. Fossati" initials="T." surname="Fossati"/>
            <date month="November" year="2022"/>
            <abstract>
              <t>Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) are used to protect data exchanged over a wide range of application protocols and can also form the basis provide forward
   secrecy.

d) FYI, we added expansions upon first use for secure transport protocols. Over the years, the industry has witnessed several serious attacks on TLS and DTLS, including attacks on abbreviations below. Please
review each expansion in the most commonly used cipher suites and their modes of operation. This document provides the latest recommendations for ensuring the security of deployed services that use TLS and DTLS. These recommendations are applicable carefully to ensure correctness.

   Lightweight Directory Access Protocol (LDAP)
   Representational State Transfer (REST)
   Network Access Server (NAS)
-->

<!-- [rfced] FYI, we fixed the majority of use cases.</t>
              <t>RFC 7525, an earlier version of the TLS recommendations, was published when the industry was transitioning links to TLS 1.2. Years later, this transition is largely complete, and TLS 1.3 is widely available. This document updates the guidance given the new environment and obsoletes RFC 7525. In addition, this document updates RFCs 5288 and 6066 in view of recent attacks.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="195"/>
          <seriesInfo name="RFC" value="9325"/>
          <seriesInfo name="DOI" value="10.17487/RFC9325"/>
        </reference>
        <reference anchor="RFC2119">
          <front>
            <title>Key words for use in RFCs to Indicate Requirement Levels</title>
            <author fullname="S. Bradner" initials="S." surname="Bradner"/>
            <date month="March" year="1997"/>
            <abstract>
              <t>In many standards track documents several words are used sections as follows.
Please review to signify the requirements in the specification. These words are often capitalized. This document defines ensure these words as they should be interpreted updates are correct.

Original:
   Further discussion of this topic is contained in IETF documents. This document specifies an Internet Best Current Practices []{#sharing}.

   See {}(#resumption) below for the Internet Community, and requests more discussion and suggestions for improvements.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="2119"/>
          <seriesInfo name="DOI" value="10.17487/RFC2119"/>
        </reference>
      </references>
      <references anchor="sec-informative-references">
        <name>Informative References</name>
        <reference anchor="RFC5077">
          <front>
            <title>Transport Layer Security (TLS) Session Resumption without Server-Side State</title>
            <author fullname="J. Salowey" initials="J." surname="Salowey"/>
            <author fullname="H. Zhou" initials="H." surname="Zhou"/>
            <author fullname="P. Eronen" initials="P." surname="Eronen"/>
            <author fullname="H. Tschofenig" initials="H." surname="Tschofenig"/>
            <date month="January" year="2008"/>
            <abstract>
              <t>This document describes a mechanism that enables the Transport Layer Security (TLS) server to resume sessions and avoid keeping per-client session state. The TLS server encapsulates the session state into a ticket and forwards it to the client. The client can subsequently resume a session using the obtained ticket. This document obsoletes RFC 4507. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5077"/>
          <seriesInfo name="DOI" value="10.17487/RFC5077"/>
        </reference>
        <reference anchor="RFC6613">
          <front>
            <title>RADIUS over TCP</title>
            <author fullname="A. DeKok" initials="A." surname="DeKok"/>
            <date month="May" year="2012"/>
            <abstract>
              <t>The Remote Authentication Dial-In User Server (RADIUS) protocol has, until now, required the User Datagram Protocol (UDP) as the underlying transport layer. This document defines RADIUS over the Transmission Control Protocol (RADIUS/TCP), in order to address handling of issues related to RADIUS over Transport Layer Security (RADIUS/TLS). It permits TCP to be used as a transport protocol for RADIUS only when a transport layer such as TLS or IPsec provides confidentiality and security. This document defines an Experimental Protocol for the Internet community.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="6613"/>
          <seriesInfo name="DOI" value="10.17487/RFC6613"/>
        </reference>
        <reference anchor="RFC7585">
          <front>
            <title>Dynamic Peer Discovery for RADIUS/TLS and RADIUS/DTLS Based on the Network Access Identifier (NAI)</title>
            <author fullname="S. Winter" initials="S." surname="Winter"/>
            <author fullname="M. McCauley" initials="M." surname="McCauley"/>
            <date month="October" year="2015"/>
            <abstract>
              <t>This document specifies a means to find authoritative RADIUS servers for a given realm. It around resumption.

Current:
   Further discussion of this topic is used contained in conjunction with either RADIUS over Transport Layer Security (RADIUS/TLS) or RADIUS over Datagram Transport Layer Security (RADIUS/DTLS).</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7585"/>
          <seriesInfo name="DOI" value="10.17487/RFC7585"/>
        </reference>
        <reference anchor="RFC8446">
          <front>
            <title>The Transport Layer Security (TLS) Protocol Version 1.3</title>
            <author fullname="E. Rescorla" initials="E." surname="Rescorla"/>
            <date month="August" year="2018"/>
            <abstract>
              <t>This document specifies version 1.3 Section 4.3.

   See Section 6.2.3 below for more discussion of the Transport Layer Security (TLS) protocol. TLS allows client/server applications issues around resumption.
-->

<!-- [rfced] We updated artwork to communicate over the Internet sourcecode in a way Section 4.1.2. Please confirm
that this is designed to prevent eavesdropping, tampering, and message forgery.</t>
              <t>This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8446"/>
          <seriesInfo name="DOI" value="10.17487/RFC8446"/>
        </reference>
        <reference anchor="RFC8937">
          <front>
            <title>Randomness Improvements for Security Protocols</title>
            <author fullname="C. Cremers" initials="C." surname="Cremers"/>
            <author fullname="L. Garratt" initials="L." surname="Garratt"/>
            <author fullname="S. Smyshlyaev" initials="S." surname="Smyshlyaev"/>
            <author fullname="N. Sullivan" initials="N." surname="Sullivan"/>
            <author fullname="C. Wood" initials="C." surname="Wood"/>
            <date month="October" year="2020"/>
            <abstract>
              <t>Randomness is a crucial ingredient for Transport Layer Security (TLS) and related security protocols. Weak or predictable "cryptographically secure" pseudorandom number generators (CSPRNGs) can be abused or exploited for malicious purposes. An initial entropy source that seeds a CSPRNG might correct.

In addition, please consider whether the "type" attribute of any sourcecode
element should be weak or broken as well, which can also lead to critical and systemic security problems. This document describes a way set and/or has been set correctly. The current list of
preferred values for security protocol implementations to augment their CSPRNGs using long-term private keys. This improves randomness from broken or otherwise subverted CSPRNGs.</t>
              <t>This document "type" is a product of the Crypto Forum Research Group (CFRG) in available at
<https://www.rfc-editor.org/rpc/wiki/doku.php?id=sourcecode-types>.  If the IRTF.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8937"/>
          <seriesInfo name="DOI" value="10.17487/RFC8937"/>
        </reference>
        <reference anchor="RFC9258">
          <front>
            <title>Importing External Pre-Shared Keys (PSKs) for TLS 1.3</title>
            <author fullname="D. Benjamin" initials="D." surname="Benjamin"/>
            <author fullname="C. A. Wood" initials="C. A." surname="Wood"/>
            <date month="July" year="2022"/>
            <abstract>
              <t>This document describes
current list does not contain an interface for importing external Pre-Shared Keys (PSKs) into TLS 1.3.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="9258"/>
          <seriesInfo name="DOI" value="10.17487/RFC9258"/>
        </reference>
        <reference anchor="RFC8492">
          <front>
            <title>Secure Password Ciphersuites for Transport Layer Security (TLS)</title>
            <author fullname="D. Harkins" initials="D." role="editor" surname="Harkins"/>
            <date month="February" year="2019"/>
            <abstract>
              <t>This memo defines several new ciphersuites for the Transport Layer Security (TLS) protocol applicable type, feel free to support certificateless, secure authentication using only a simple, low-entropy password. The exchange is called "TLS-PWD". The ciphersuites are all based on an authentication and key exchange protocol, named "dragonfly", suggest
additions for consideration. Note that is resistant to offline dictionary attacks.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8492"/>
          <seriesInfo name="DOI" value="10.17487/RFC8492"/>
        </reference>
        <reference anchor="RFC7542">
          <front>
            <title>The Network Access Identifier</title>
            <author fullname="A. DeKok" initials="A." surname="DeKok"/>
            <date month="May" year="2015"/>
            <abstract>
              <t>In order to provide inter-domain authentication services, it is necessary to have a standardized method that domains can use also acceptable to identify each other's users. This document defines the syntax for leave the Network Access Identifier (NAI), the user identifier submitted by
"type" attribute not set.
-->

<!-- [rfced] Please review the client prior to accessing resources. This document is a revised version "Inclusive Language" portion of RFC 4282. It addresses issues with international character sets the online
Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
and makes a number let us know if any changes are needed.  Updates of other corrections to RFC 4282.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7542"/>
          <seriesInfo name="DOI" value="10.17487/RFC7542"/>
        </reference>
        <reference anchor="RFC5489">
          <front>
            <title>ECDHE_PSK Cipher Suites this nature typically
result in more precise language, which is helpful for Transport Layer Security (TLS)</title>
            <author fullname="M. Badra" initials="M." surname="Badra"/>
            <author fullname="I. Hajjeh" initials="I." surname="Hajjeh"/>
            <date month="March" year="2009"/>
            <abstract>
              <t>This document extends RFC 4279, RFC 4492, and RFC 4785 and specifies a set of cipher suites readers.

Note that use our script did not flag any words in particular, but this should
still be reviewed as a pre-shared key (PSK) to authenticate an Elliptic Curve Diffie-Hellman exchange with Ephemeral keys (ECDHE). These cipher suites provide Perfect Forward Secrecy (PFS). This memo provides information for the Internet community.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5489"/>
          <seriesInfo name="DOI" value="10.17487/RFC5489"/>
        </reference>
        <reference anchor="RFC8442">
          <front>
            <title>ECDHE_PSK with AES-GCM and AES-CCM Cipher Suites for TLS 1.2 and DTLS 1.2</title>
            <author fullname="J. Mattsson" initials="J." surname="Mattsson"/>
            <author fullname="D. Migault" initials="D." surname="Migault"/>
            <date month="September" year="2018"/>
            <abstract>
              <t>This document defines several new cipher suites for version 1.2 of the Transport Layer Security (TLS) protocol and version 1.2 of the Datagram Transport Layer Security (DTLS) protocol. These cipher suites are based on the Ephemeral Elliptic Curve Diffie-Hellman with Pre-Shared Key (ECDHE_PSK) key exchange together with the Authenticated Encryption with Associated Data (AEAD) algorithms AES-GCM and AES-CCM. PSK provides light and efficient authentication, ECDHE provides forward secrecy, and AES-GCM and AES-CCM provide encryption and integrity protection.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8442"/>
          <seriesInfo name="DOI" value="10.17487/RFC8442"/>
        </reference>
      </references>
    </references>
  </back>
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