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<!-- draft submitted in xml v3 -->

<!DOCTYPE rfc> rfc [
 <!ENTITY nbsp    "&#160;">
 <!ENTITY zwsp   "&#8203;">
 <!ENTITY nbhy   "&#8209;">
 <!ENTITY wj     "&#8288;">
]>

<rfc version='3'
     docName='draft-ietf-babel-mac-relaxed-05'
     ipr='trust200902'
     consensus='true'
     submissionType='IETF'
     category='std'
     updates='8967'
     xml:lang='en'
     xmlns:xi="http://www.w3.org/2001/XInclude"> version="3"
     docName="draft-ietf-babel-mac-relaxed-05"
     number="9467"
     ipr="trust200902"
     submissionType="IETF"
     category="std"
     consensus="true"
     updates="8967"
     obsoletes=""
     xml:lang="en"
     xmlns:xi="http://www.w3.org/2001/XInclude"
     tocInclude="true"
     symRefs="true"
     sortRefs="true">

<front>
<title abbrev='Babel-MAC abbrev='Babel MAC Relaxed PC'>
Relaxed Packet Counter Verification for Babel MAC Authentication
</title>
<seriesInfo name="RFC" value="9467"/>
<author fullname="Juliusz Chroboczek" initials="J." surname="Chroboczek">
<organization>IRIF, University of Paris-Cité</organization>
<address>
<postal>
<street>Case 7014</street>
<city>Paris CEDEX 13</city>
<code>75205</code>
<country>France</country>
</postal>
<email>jch@irif.fr</email>
</address>
</author>

<author fullname='Toke Høiland-Jørgensen' initials='T.'
        surname='Høiland-Jørgensen'>
  <organization>Red Hat</organization>
  <address>
    <email>toke@toke.dk</email>
  </address>
</author>

<date year='2023' month='June' day='12'/>

<abstract>
<t>This month='August'/>
<area>rtg</area>
<workgroup>babel</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>

<!--[rfced] We note that MAC was not expanded in the title of RFC 8967
     due to author preference.  We have left it unexpanded here to
     match that preference.  Please let us know if expansion is
     desired.

Original:
Relaxed Packet Counter Verification for Babel MAC Authentication

-->

<!--[rfced] In the Abstract, we have made a few updates.  Please
     review and confirm or provide alternate suggestions.

a) We have clarified that this document is relaxing the packet
verification rules in RFC 8967.

b) We have attempted to clarify what "it" was referring to.  Please
let us know if further updates are necessary.

Original:
   This document relaxes packet verification rules defined in the Babel
   MAC Authentication protocol in order to make it more robust in the
   presence of packet reordering.

Current:
   This document relaxes packet verification rules defined in "MAC
   Authentication for the Babel Routing Protocol" (RFC 8967) in order to
   make the rules more robust in the presence of packet reordering.
-->
<abstract>
<t>This document relaxes packet verification rules defined in "MAC Authentication for the Babel Routing Protocol" (RFC 8967) in order to make the rules more robust in the
presence of packet reordering.  This document updates RFC 8967 by relaxing
the packet validation rules defined therein.</t>
</abstract>
</front>

<middle>

<section><name>Introduction</name>

<t>The design of the Babel MAC authentication mechanism <xref
target="RFC8967"/> assumes that packet reordering is an exceptional
occurrence, and the protocol drops any packets that arrive out-of-order.
The assumption that packets are not routinely reordered is generally
correct on wired links, but turns out to be incorrect on some kinds of
wireless links.</t>

<t>In particular, IEEE 802.11 (Wi-Fi) <xref target="IEEE80211"/> defines
a number of power-saving modes that allow stations (mobile nodes) to
switch their radio off for extended periods of time, ranging in the
hundreds of milliseconds.  The access point (network switch) buffers all
multicast packets, and it only sends them out after the power-saving interval
ends.  The result is that multicast packets are delayed by up to a few
hundred milliseconds with respect to unicast packets, which, under packets.  Under some
traffic patterns, this causes the Packet Counter (PC) verification procedure in
RFC 8967 to systematically fail for multicast packets.</t>

<t>This

<!--[rfced] FYI - we have reformatted this sentence to appear as a
     bulleted list for the ease of the reader.  Please let us know any
     objections.

Original:
   This document defines two distinct ways to relax the PC validation:
   using two separate receiver-side states, one for unicast and one for
   multicast packets (<xref target="separate-pc"/>), (Section 3.1), which allows arbitrary reordering
   between unicast and multicast packets, and using a window of
   previously received PC values (<xref target="window"/>), (Section 3.2), which allows a bounded
   amount of reordering between arbitrary packets.  We assume that
   reordering between arbitrary packets only happens occasionally, and,
   since Babel is designed to gracefully deal with occasional packet
   loss, usage of the former mechanism is RECOMMENDED, while usage of
   the latter is OPTIONAL.  The two mechanisms MAY be used
   simultaneously (Section 3.3).

Current:

   This document defines two distinct ways to relax the PC validation:

   *  using two separate receiver-side states, one for unicast and one
      for multicast packets (Section 3.1), which allows arbitrary
      reordering between unicast and multicast packets, and

   *  using a window of previously received PC values (Section 3.2),
      which allows a bounded amount of reordering between arbitrary
      packets.

   We assume that reordering between arbitrary packets only happens
   occasionally, and, since Babel is designed to gracefully deal with
   occasional packet loss, usage of the former mechanism is RECOMMENDED,
   while usage of the latter is OPTIONAL.  The two mechanisms MAY be
   used simultaneously (Section 3.3).
-->
<t>This document defines two distinct ways to relax the PC validation:</t>
<ul>
<li>using two separate receiver-side states, one for unicast and one for
multicast packets (<xref target="separate-pc"/>), which allows arbitrary
reordering between unicast and multicast packets, and</li>
<li>using a window of
previously received PC values (<xref target="window"/>), which allows
a bounded amount of reordering between arbitrary packets.</li></ul>
<t>We assume that
reordering between arbitrary packets only happens occasionally, and, since
Babel is designed to gracefully deal with occasional packet loss, usage of
the former mechanism is <bcp14>RECOMMENDED</bcp14>, while usage of the latter is <bcp14>OPTIONAL</bcp14>.
The two mechanisms <bcp14>MAY</bcp14> be used simultaneously (<xref target="combining"/>).</t>

<t>This document updates RFC 8967 by relaxing the packet validation rules
defined therein.  It does not change the security properties of the protocol.</t>

</section>

<section><name>Specification of Requirements</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.</t> here.
        </t>

</section>

<section><name>Relaxing PC validation</name> Validation</name>

<!--[rfced] In the following, might rephrasing "by more than one
     between two packets" help the reader?  If our suggestion is not
     correct, please let us know how we may update to make this
     sentence.

Original:
Notwithstanding the name, the PC does not actually
   count packets: a sender is permitted to increment the PC by more than
   one between two packets.

Perhaps:
Notwithstanding the name, the PC does not actually
   count packets: a sender is permitted to increment the PC by more than
   one between two sequentially received packets.

-->

<t>The Babel MAC authentication mechanism prevents replay by decorating
every sent packet with a strictly increasing value, the Packet Counter
(PC).  Notwithstanding the name, the PC does not actually count packets:
a sender is permitted to increment the PC by more than one between two
packets.</t>

<t>A receiver maintains the highest PC received from each neighbour.  When
a new packet is received, the receiver compares the PC contained in the
packet with the highest received PC; if PC. If the new value is smaller or equal,
the packet is discarded; otherwise, the packet is accepted, and the
highest PC value for that neighbour is updated.</t>

<!--[rfced] In the following, is "single sender state" singular or
     plural?

Original:
The receiver states corresponding to single
   sender state are not necessarily identical, since only a subset of
   receiver states are updated when a packet is sent to a unicast
   address or when a multicast packet is received by a subset of the
   receivers.

Perhaps A:
The receiver states corresponding to single
   sender states are not necessarily identical, since only a subset of
   receiver states are updated when a packet is sent to a unicast
   address or when a multicast packet is received by a subset of the
   receivers.

Perhaps B:
The receiver states corresponding to a single
   sender state are not necessarily identical, since only a subset of
   receiver states are updated when a packet is sent to a unicast
   address or when a multicast packet is received by a subset of the
   receivers.

-->

<t>Note that there does not exist a one-to-one correspondence between
sender states and receiver states: multiple receiver states track a single
sender state.  The receiver states corresponding to single sender state
are not necessarily identical, since only a subset of receiver states are
updated when a packet is sent to a unicast address or when a multicast
packet is received by a subset of the receivers.</t>

<section anchor="separate-pc"><name>Multiple highest Highest PC values</name> Values</name>

<t>Instead of maintaining a single highest PC value maintained for each neighbour, an
implementation of the procedure described in this section uses two values, values:
the highest multicast value PCm and the highest non-multicast (unicast)
value PCu.  More PCu.</t>
<t>More precisely, the (Index, PC) pair contained in the
neighbour table (<relref target="RFC8967" section="3.2"/>) is replaced
by:</t>
<ul>
<li>a
by a triple (Index, PCm, PCu), where Index where:</t>
<ul>
  <li>Index is an arbitrary string of 0 to
  32 octets, and PCm and</li>
  <li>PCm and PCu are 32-bit (4-octet) integers.</li>
</ul>

<t>When a challenge reply Challenge Reply is successful, both highest PC values are updated
to the value contained in the PC TLV from the packet containing the
successful challenge.  More precisely, the last sentence of the fourth
bullet point of <relref target="RFC8967" section="4.3"/> is replaced
by:</t>
<ul>
<li>If
as follows:</t>

<!--[rfced] For the ease of the reader, we have added in the text from
     RFC 8967 that is being updated by adopting an Old/New format that
     we frequently see in RFCs.  Please let us know any
     objections. -->

<t>OLD:</t>
<blockquote>
  <t>The preparse phase above yields two pieces of data: the PC and Index from the first PC TLV, and a bit indicating whether the packet contains a successful Challenge Reply. If the packet does not contain a PC TLV, the packet <bcp14>MUST</bcp14> be dropped, and processing stops at this point. If the packet contains a successful Challenge Reply, then the PC and Index contained in the PC TLV <bcp14>MUST</bcp14> be stored in the neighbour table entry corresponding to the sender (which already exists in this case), and the packet is accepted.</t>

</blockquote>
<t>NEW:</t>
<blockquote>
<t>If the packet contains a successful Challenge Reply, then the Index
contained in the PC TLV MUST <bcp14>MUST</bcp14> be stored in the Index field of the neighbour
table entry corresponding to the sender (which already exists in this
case), the PC contained in the TLV MUST <bcp14>MUST</bcp14> be stored in both the PCm and
PCu fields of the neighbour table entry, and the packet is accepted.</li>
</ul> accepted.</t>
</blockquote>

<t>When a packet that does not contain a successful challenge reply Challenge Reply is
received, the PC value that it contains is compared to either the PCu or
the PCm field of the corresponding neighbour entry, depending on whether
or not the packet was sent to a muticast address or not. multicast address.  If the comparison is
successful, then the same value (PCm or PCu) is updated.  More precisely,
the last bullet point of <relref target="RFC8967" section="4.3"/> is
replaced by:</t>
<ul>
<li>At as follows:</t>
<t>OLD:</t>
<blockquote>
  <t>At this stage, the packet contains no successful Challenge Reply, and the Index contained in the PC TLV is equal to the Index in the neighbour table entry corresponding to the sender. The receiver compares the received PC with the PC contained in the neighbour table; if the received PC is smaller or equal than the PC contained in the neighbour table, the packet <bcp14>MUST</bcp14> be dropped and processing stops (no challenge reply is sent in this case, since the mismatch might be caused by harmless packet reordering on the link). Otherwise, the PC contained in the neighbour table entry is set to the received PC, and the packet is accepted.</t>
</blockquote>
<t>NEW:</t>
<blockquote>
<t>At this stage, the packet contains no successful Challenge Reply and
the Index contained in the PC TLV is equal to the Index in the neighbour
table entry corresponding to the sender.  The receiver compares the
received PC with either the PCm field (if the packet was sent to a multicast
IP address) or the PCu field (otherwise) in the neighbour table; if table. If the
received PC is smaller than or equal than to the value contained in the neighbour
table, the packet MUST <bcp14>MUST</bcp14> be dropped and processing stops (no stops. Note that no challenge is
sent in this case, since the mismatch might be caused by harmless packet
reordering on the link). link.  Otherwise, the PCm (if the packet was sent to
a multicast address) or the PCu (otherwise) field contained in the
neighbour table entry is set to the received PC, and the packet is
accepted.</li>
</ul>
accepted.</t></blockquote>

<section><name>Generalisations</name>

<t>Modern networking hardware tends to maintain more than just two queues,
and it might be tempting to generalise the approach taken to more than
just two the last two PC values.  For example, one might be tempted to use
distinct last PC values for packets received with different values of the
Type of Service (ToS) (TOS) field, or with different IEEE 802.11 <xref
target="IEEE80211"/> access categories.  However, choosing a the highest PC
field by consulting a value that is not protected by the MAC Message Authentication Code (MAC) (<relref
target="RFC8967" section="4.1"/>) would no longer protect against replay.

<!--[rfced] In the following text, are destination address and port
     number combined as one idea or should the list contain 3 items?

Original:
   In effect, this means that only the destination address and port
   number and data stored in the packet body may be used for choosing
   the highest PC
value, since value,...

Perhaps:
   In effect, this means that only the destination address, port
   number, and data stored in the packet body may be used for choosing
   the highest PC value,...
-->
In effect, this means that only the destination address and port number
and data stored in the packet body may be used for choosing the highest PC
value. This is because these are the only fields that are protected by the MAC (in
addition to the source address and port number, which are already used
when choosing the neighbour table entry and therefore provide no
additional information).  Since Babel implementations do not usually send
packets with differing ToS TOS values or IEEE 802.11 access categories, this
is unlikely to be an issue in practice.</t>

<t>The following example shows why it would be unsafe to select the highest
PC depending on the ToS TOS field.  Suppose that a node B were to maintain
distinct highest PC values for different values T1 and T2 of the ToS TOS field,
and that initially that, initially, all of the highest PC fields at B have value 42.  Suppose
now that a node A sends a packet P1 with ToS TOS equal to T1 and PC equal to
43; when B receives the packet, it sets the highest PC value associated with
ToS
TOS T1 to 43.  If an attacker were now to send an exact copy of P1 but
with ToS TOS equal to T2, B would consult the highest PC value associated with
T2, which is still equal to 42, and accept the replayed packet.</t>
</section>

</section>

<section anchor="window"><name>Window-based validation</name> anchor="window"><name>Window-Based Validation</name>

<t>Window-based validation is similar to what is described in <relref
target="RFC4303" section="3.4.3"/>.  When using window-based validation,
in addition to retaining within its neighbour table the highest PC value
PCh seen from every neighbour, an implementation maintains a fixed-size
window of booleans corresponding to PC values directly below PCh.  More
precisely, the (Index, PC) pair contained in the neighbour table (<relref
target="RFC8967" section="3.2"/>) is replaced by:</t>
<ul>
<ul spacing="normal">
<li>a triple (Index, PCh, Window), where Index is an arbitrary string of
0 to 32 octets, PCh is a 32-bit (4-octet) integer, and Window is a vector
of booleans of size S (the default value S=128 is RECOMMENDED).</li> <bcp14>RECOMMENDED</bcp14>).</li>
</ul>

<!--[rfced] Please confirm that the edits to the following sentence
     maintain your intended meaning.

Original:
Shifting the window to the
   left by an integer amount k is defined as moving all values so that
   the value previously at index n is now at index (n - k); k values are
   discarded at the left edge, and k new unset values are inserted at
   the right edge.

Current:
Shifting the window
   to the left by an integer amount k is defined as moving all values:
   the value previously at index n is now at index (n - k), k values are
   discarded at the left edge, and k new unset values are inserted at
   the right edge.
-->

<t>The window is a vector of S boolean values numbered from 0 (the "left
edge" of the window) up to S-1 (the "right edge"); the edge"). The boolean associated
with the index i indicates whether a packet with a PC value of (PCh - (S-1) + i)
has been seen before.  Shifting the window to the left by an integer
amount k is defined as moving all values so that values: the value previously at
index n is now at index (n - k); k), k values are discarded at the left edge,
and k new unset values are inserted at the right edge.</t>

<t>Whenever a packet is received, the receiver computes its <em>index</em>
i = (PC - PCh + S - 1).  It then proceeds as follows:</t>
<ol>
<ol spacing="normal">
  <li>If the index i is negative, the packet is considered too old,
  and MUST it <bcp14>MUST</bcp14> be discarded.</li>

  <li>If the index i is non-negative and strictly less than the
  window size S, the window value at the index is checked; if checked. If this
  value is already set, the received PC has been seen before and the
  packet MUST <bcp14>MUST</bcp14> be discarded.  Otherwise, the corresponding window value is marked as set, and the packet is accepted.</li>

  <li>If the index i is larger or equal to the window size (i.e., PC
  is strictly larger than PCh), the window MUST <bcp14>MUST</bcp14> be shifted to the left by
  (i - S + 1) values (or, equivalently, by the difference PC - PCh) PCh), and
  the highest PC value PCh MUST <bcp14>MUST</bcp14> be set to the received PC.  The value at
  the right of the window (the value with index S - 1) MUST <bcp14>MUST</bcp14> be set, and
  the packet is accepted.</li>
</ol>

<t>When receiving a successful Challenge Reply, the remembered highest PC
value PCh MUST <bcp14>MUST</bcp14> be set to the value received in the challenge reply, Challenge Reply, and
all of the values in the window MUST <bcp14>MUST</bcp14> be reset except the value at index
S - 1, which MUST <bcp14>MUST</bcp14> be set.</t>

</section>

<section anchor="combining"><name>Combining the two techniques</name> Two Techniques</name>

<t>The two techniques described above serve complementary purposes:
splitting purposes:</t>
<ul>
  <li>splitting the state allows multicast packets to be reordered with respect
  to unicast ones by an arbitrary number of PC values, while the and</li>
  <li>the window-based technique allows arbitrary packets to be reordered but only
by a bounded number of PC values. values.</li></ul><t> Thus, they can profitably be combined.</t>

<t>An implementation that uses both techniques MUST <bcp14>MUST</bcp14> maintain, for every
entry of the neighbour table, two distinct windows, windows: one for multicast and
one for unicast packets.  When a successful challenge reply Challenge Reply is received,
both windows MUST <bcp14>MUST</bcp14> be reset.  When a packet that does not contain
a challenge reply Challenge Reply is received, then if the packet's destination address is
a multicast address, the multicast window MUST <bcp14>MUST</bcp14> be consulted and possibly
updated, as described in <xref target="window"/>; otherwise, target="window"/>. Otherwise, the unicast
window MUST <bcp14>MUST</bcp14> be consulted and possibly updated.</t>

</section>

</section>

<section><name>Security considerations</name> Considerations</name>

<t>The procedures described in this document do not change the security
properties described in Section 1.2 of RFC 8967. <xref target="RFC8967" sectionFormat="of"
section="1.2"/>.  In particular, the choice between the multicast and the
unicast packet counter is done made by examining a packet's destination IP address,
which is included in the pseudo-header and therefore participates in MAC computation; hence,
computation. Hence, an attacker cannot change the destination address without
invalidating the
MAC, and therefore MAC; therefore, it cannot replay a unicast packet as a
multicast one or vice versa.</t>

<t>While these procedures do slightly increase the amount of per-neighbour
state maintained by each node, this increase is marginal (between 4 and 36
octets per neighbour, depending on implementation choices), and should not
significantly impact the ability of nodes to survive denial-of-service
attacks.</t>

</section>

<section title="IANA Considerations">

  <t>This document requires has no IANA actions.</t>

</section>

<section title="Acknowledgments">

<t>The authors are greatly indebted to Daniel Gröber, who first identified
the problem that document aims to solve and first suggested the solution
described in <xref target="separate-pc"/>.</t>

</section>

</middle>

<back>
<references><name>Normative references</name>

<reference anchor="RFC8967" target="https://www.rfc-editor.org/info/rfc8967">
<front>
<title>MAC Authentication for the Babel Routing Protocol</title>
<author initials="C." surname="Dô" fullname="C. Dô"/>
<author initials="W." surname="Kolodziejak" fullname="W. Kolodziejak"/>
<author initials="J." surname="Chroboczek" fullname="J. Chroboczek"/>
<date year="2021" month="January"/>
</front>
<seriesInfo name="RFC" value="8967"/>
<seriesInfo name="DOI" value="10.17487/RFC8967"/>
</reference>

<reference anchor="RFC2119"><front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials="S." surname="Bradner" fullname="S. Bradner"/>
<date year="1997" month="March"/>
</front>
<seriesInfo name="BCP" value="14"/>
<seriesInfo name="RFC" value="2119"/>
<seriesInfo name="DOI" value="10.17487/RFC2119"/>
</reference>

<reference anchor="RFC8174"><front>
<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
<author initials="B." surname="Leiba" fullname="B. Leiba"/>
<date year="2017" month="May"/>
</front>
<seriesInfo name="BCP" value="14"/>
<seriesInfo name="RFC" value="8174"/>
<seriesInfo name="DOI" value="10.17487/RFC8174"/>
</reference> References</name>

<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8967.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>

</references>

<references><name>Informative references</name>

<reference anchor="IEEE80211" target="https://ieeexplore.ieee.org/document/9363693">
<front>
<title>IEEE References</name>

<!-- [rfced] FYI, to match past RFCs, we updated the reference [IEEE80211] as
follows. Please let us know if there are any objections.

Original:
   [IEEE80211]
              "IEEE Standard for Information Technology —
              Telecommunications and information exchange between
              systems Local and metropolitan area networks — Specific
              requirements — Part 11: Wireless LAN Medium Access Control
              (MAC) and Physical Layer (PHY) Specifications.</title>
<author/>
</front>
</reference> Specifications.",
              <https://ieeexplore.ieee.org/document/9363693>.

Current:
   [IEEE80211]
              IEEE, "IEEE Standard for Information Technology -
              Telecommunications and Information Exchange between
              Systems - Local and Metropolitan Area Networks - Specific
              requirements - Part 11: Wireless LAN Medium Access Control
              (MAC) and Physical Layer (PHY) Specifications",
              DOI 10.1109/IEEESTD.2021.9363693, IEEE Std 802.11-2020,
              February 2021,
              <https://ieeexplore.ieee.org/document/9363693>.
-->

<reference anchor='RFC4303' target='https://www.rfc-editor.org/info/rfc4303'> anchor="IEEE80211" target="https://ieeexplore.ieee.org/document/9363693">
<front>
<title>IP Encapsulating Security Payload (ESP)</title>
<author initials='S.' surname='Kent' fullname='S. Kent'/>
<title>IEEE Standard for Information Technology--Telecommunications and
Information Exchange between Systems - Local and Metropolitan Area
Networks--Specific requirements - Part 11: Wireless LAN Medium Access
Control (MAC) and Physical Layer (PHY) Specifications</title>
          <author>
            <organization>IEEE</organization>
          </author>
          <date year='2005' month='December' /> month="February" year="2021"/>
        </front>
        <seriesInfo name='RFC' value='4303'/> name="DOI" value="10.1109/IEEESTD.2021.9363693"/>
        <seriesInfo name='DOI' value='10.17487/RFC4303'/> name="IEEE Std" value="802.11-2020"/>
      </reference>

<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4303.xml"/>

</references>

<section title="Acknowledgments" numbered="false">

<!--[rfced] In the following, can we assume "that document" refers to
     RFC 8967?

Original:
   The authors are greatly indebted to Daniel Gröber, who first
   identified the problem that document aims to solve and first
   suggested the solution described in Section 3.1.

Perhaps:
   The authors are greatly indebted to Daniel Gröber, who first
   identified the problem RFC 8967 aims to solve and first
   suggested the solution described in Section 3.1.
-->

<t>The authors are greatly indebted to <contact fullname="Daniel Gröber"/>,
who first identified the problem that document aims to solve and first
suggested the solution described in <xref target="separate-pc"/>.</t>

</section>

<!--[rfced] We had the following questions related to terminology use
     throughout the document:

a) We see both "packet verification rules" and "packet validation
rules".  May we make these consistently "packet verification rules"?
Please see b) below before prior to a decision.

b) Related to a) above, we see the following:

Packet Counter Verification
Packet Counter (PC) verification procedure

Are "packet verification rules" and "packet validation rules" really
"Packet Counter verification" rules?  Should the latter form be used
throughout?  (Or perhaps use "PC verification rules" after the
abbreviation is introduced?)

c) Please note that we have consistently capped "Challenge Reply" to
match its use in RFC 8967.  Please review and confirm.

d) This document uses "index", "Index", and 1 instance of
"<em>index</em>".  Please review and let us know if/how to update
these for uniformity.

-->
<!-- [rfced] Please review the "Inclusive Language" portion of the
     online Style Guide
     <https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
     and let us know if any changes are needed.

Note that our script did not flag any words in particular, but this
should still be reviewed as a best practice.

-->

</back>
</rfc>