wdiff rfc8879xml2.original.xml rfc8879.xml

<?xml version="1.0" encoding="UTF-8"?>
  <?xml-stylesheet type="text/xsl" href="rfc2629.xslt" ?>

<!-- generated updated by https://github.com/cabo/kramdown-rfc2629 version Chris 05/07/20 -->

<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
]>

<?rfc toc="yes"?>
<?rfc sortrefs="yes"?>
<?rfc symrefs="yes"?>
<?rfc docmapping="yes"?> "rfc2629-xhtml.ent">

<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902"
     docName="draft-ietf-tls-certificate-compression-10" category="std"> number="8879"
     obsoletes="" updates="" submissionType="IETF" category="std"
     consensus="true" xml:lang="en" tocInclude="true" sortRefs="true"
     symRefs="true" version="3">

  <!-- xml2rfc v2v3 conversion 2.44.0 -->
  <front>
    <title abbrev="TLS Certificate Compression">TLS Certificate Compression</title>
    <seriesInfo name="RFC" value="8879"/>
    <author initials="A." surname="Ghedini" fullname="Alessandro Ghedini">
      <organization>Cloudflare, Inc.</organization>
      <address>
        <email>alessandro@cloudflare.com</email>
      </address>
    </author>
    <author initials="V." surname="Vasiliev" fullname="Victor Vasiliev">
      <organization>Google</organization>
      <address>
        <email>vasilvv@google.com</email>
      </address>
    </author>
    <date year="2020" month="January" day="06"/> month="August"/>
    <area>Security</area>
    <workgroup>TLS</workgroup>

    <abstract>
      <t>In TLS handshakes, certificate chains often take up
the majority of the bytes transmitted.</t>
      <t>This document describes how certificate chains can be compressed to reduce the
amount of data transmitted and avoid some round trips.</t>
    </abstract>
  </front>
  <middle>
    <section anchor="introduction" title="Introduction"> numbered="true" toc="default">
      <name>Introduction</name>
      <t>In order to reduce latency and improve performance performance, it can be useful to reduce
the amount of data exchanged during a TLS handshake.</t>
      <t><xref target="RFC7924"></xref> target="RFC7924" format="default"/> describes a mechanism that allows a client and a server to avoid
transmitting certificates already shared in an earlier handshake, but it
doesn’t
doesn't help when the client connects to a server for the first time and
doesn’t
doesn't already have knowledge of the server’s server's certificate chain.</t>
      <t>This document describes a mechanism that would allow certificates to be
compressed during all handshakes.</t>
    </section>
    <section anchor="notational-conventions" title="Notational Conventions">

<t>The numbered="true" toc="default">
      <name>Notational Conventions</name>
        <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 anchor="negotiating-certificate-compression" title="Negotiating numbered="true" toc="default">
      <name>Negotiating Certificate Compression"> Compression</name>
      <t>This extension is only supported with TLS 1.3 <xref target="RFC8446"></xref> target="RFC8446" format="default"/> and newer; if TLS 1.2
<xref target="RFC5246"></xref> target="RFC5246" format="default"/> or earlier is negotiated, the peers MUST <bcp14>MUST</bcp14> ignore this extension.</t>
      <t>This document defines a new extension type (compress_certificate(27)), which
can be used to signal the supported compression formats for the Certificate
message to the peer.  Whenever it is sent by the client as a ClientHello message
extension (<xref target="RFC8446"></xref>, Section 4.1.2), target="RFC8446" sectionFormat="comma" section="4.1.2"/>), it indicates the support for
compressed server certificates.  Whenever it is sent by the server as a
CertificateRequest extension (<xref target="RFC8446"></xref>, Section 4.3.2), target="RFC8446" sectionFormat="comma"
section="4.3.2"/>), it indicates
the support for compressed client certificates.</t>
      <t>By sending a compress_certificate extension, the sender indicates to the peer
the certificate compression certificate-compression algorithms it is willing to use for decompression.
The “extension_data” "extension_data" field of this extension SHALL <bcp14>SHALL</bcp14> contain a
      CertificateCompressionAlgorithms value:</t>

<figure><artwork><![CDATA[

<sourcecode type="tls-presentation">
    enum {
        zlib(1),
        brotli(2),
        zstd(3),
        (65535)
    } CertificateCompressionAlgorithm;

    struct {
        CertificateCompressionAlgorithm algorithms<2..2^8-2>; algorithms&lt;2..2^8-2&gt;;
    } CertificateCompressionAlgorithms;
]]></artwork></figure>
</sourcecode>

      <t>The compress_certificate extension is a unidirectional indication; no
corresponding response extension is needed.</t>
    </section>
    <section anchor="compressed-certificate-message" title="Compressed numbered="true" toc="default">
      <name>Compressed Certificate Message"> Message</name>
      <t>If the peer has indicated that it supports compression, server and
      client MAY <bcp14>MAY</bcp14>
compress their corresponding Certificate messages (Section 4.4.2 of <xref target="RFC8446"/>) (<xref
target="RFC8446" sectionFormat="of" section="4.4.2"/>)
and send them in the form of the CompressedCertificate message (replacing the
Certificate message).</t>
      <t>The CompressedCertificate message is formed as follows:</t>

<figure><artwork><![CDATA[
<sourcecode>
    struct {
         CertificateCompressionAlgorithm algorithm;
         uint24 uncompressed_length;
         opaque compressed_certificate_message<1..2^24-1>; compressed_certificate_message&lt;1..2^24-1&gt;;
    } CompressedCertificate;
]]></artwork></figure>

<t><list style="hanging">
  <t hangText='algorithm'>
  The
</sourcecode>
      <dl newline="false" spacing="normal">
        <dt>algorithm:</dt>
        <dd>The algorithm used to compress the certificate.  The algorithm MUST
	<bcp14>MUST</bcp14> be one of
	the algorithms listed in the peer’s peer's compress_certificate extension.</t>
  <t hangText='uncompressed_length'> extension.</dd>
        <dt>uncompressed_length:</dt>
        <dd>
  The length of the Certificate message once it is uncompressed.  If  If, after
decompression
decompression, the specified length does not match the actual length, the
party receiving the invalid message MUST <bcp14>MUST</bcp14> abort the connection with the
“bad_certificate”
"bad_certificate" alert.  The presence of this field allows the receiver to
pre-allocate
preallocate the buffer for the uncompressed Certificate message and to enforce
	limits on the message size before performing decompression.</t>
  <t hangText='compressed_certificate_message'> decompression.</dd>
        <dt>compressed_certificate_message:</dt>
        <dd>
  The result of applying the indicated compression algorithm to the encoded
Certificate message that would have been sent if certificate compression was not
in use. The compression algorithm defines how the
bytes in the compressed_certificate_message field are converted into the
Certificate message.</t>
</list></t> message.</dd>
      </dl>
      <t>If the specified compression algorithm is zlib, then the Certificate message
MUST
<bcp14>MUST</bcp14> be compressed with the ZLIB compression algorithm, as defined in <xref target="RFC1950"></xref>. target="RFC1950" format="default"/>.
If the specified compression algorithm is brotli, the Certificate message MUST <bcp14>MUST</bcp14>
be compressed with the Brotli compression algorithm algorithm, as defined in <xref target="RFC7932"></xref>. target="RFC7932" format="default"/>.  If
the specified compression algorithm is zstd, the Certificate message MUST <bcp14>MUST</bcp14> be
compressed with the Zstandard compression algorithm algorithm, as defined in <xref target="I-D.kucherawy-rfc8478bis"></xref>.</t> target="RFC8878" format="default"/>.</t>
      <t>It is possible to define a certificate compression algorithm that uses a
pre-shared
preshared dictionary to achieve a higher compression ratio.  This document does
not define any such algorithms, but additional codepoints may be allocated for
such use per the policy in <xref target="registry"/>.</t> target="registry" format="default"/>.</t>
      <t>If the received CompressedCertificate message cannot be decompressed, the
connection MUST <bcp14>MUST</bcp14> be terminated with the “bad_certificate” "bad_certificate" alert.</t>
      <t>If the format of the Certificate message is altered using the
server_certificate_type or client_certificate_type extensions <xref target="RFC7250"></xref>, target="RFC7250" format="default"/>, the
resulting altered message is compressed instead.</t>
    </section>
    <section anchor="security-considerations" title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>After decompression, the Certificate message MUST <bcp14>MUST</bcp14> be processed as if it were
encoded without being compressed.  This way, the parsing and the verification
have the same security properties as they would have in TLS normally.</t>
      <t>In order for certificate compression to function correctly, the underlying
compression algorithm MUST <bcp14>MUST</bcp14> output the same data
that was provided as input by the peer.</t>
      <t>Since certificate chains are typically presented on a per-server name per-server-name or
per-user basis, a malicious application does not have control over any individual fragments
in the Certificate message, meaning that they cannot leak information about the
certificate by modifying the plaintext.</t>
      <t>Implementations SHOULD <bcp14>SHOULD</bcp14> bound the memory usage when decompressing the
CompressedCertificate message.</t>
      <t>Implementations MUST <bcp14>MUST</bcp14> limit the size of the resulting decompressed chain to
the specified uncompressed length, and they MUST <bcp14>MUST</bcp14> abort the connection if the
size of the output of the decompression function exceeds that limit.  TLS framing
imposes 16777216 byte a 16777216-byte limit on the certificate message size, and the implementations
MAY
<bcp14>MAY</bcp14> impose a limit that is lower than that; in both cases, they MUST <bcp14>MUST</bcp14> apply the same
limit as if no compression were used.</t>
      <t>While the Certificate message in TLS 1.3 is encrypted, third parties can draw
inferences from the message length observed on the wire.  TLS 1.3 provides a padding
mechanism (discussed in Sections 5.4 <xref target="RFC8446"
sectionFormat="bare" section="5.4"/> and E.3 <xref target="RFC8446"
sectionFormat="bare" section="E.3"/> of <xref target="RFC8446"></xref>) target="RFC8446"/>) to counteract such
analysis.  Certificate compression alters the length of the Certificate message,
and the change in length is dependent on the actual contents of the certificate.
Any padding scheme covering the Certificate message has to address compression
within its design, design or disable it altogether.</t>
    </section>
    <section anchor="middlebox-compatibility" title="Middlebox Compatibility">

<t>It’s numbered="true" toc="default">
      <name>Middlebox Compatibility</name>
      <t>It's been observed that a significant number of middleboxes intercept and try
to validate the Certificate message exchanged during a TLS handshake. This
means that middleboxes that don’t don't understand the CompressedCertificate message
might misbehave and drop connections that adopt certificate compression.
Because of that, the extension is only supported in the versions of TLS where
the certificate message is encrypted in a way that prevents middleboxes from
intercepting it, it -- that is, TLS version 1.3 <xref target="RFC8446"></xref> target="RFC8446" format="default"/> and higher.</t>
    </section>
    <section anchor="iana-considerations" title="IANA Considerations"> numbered="true" toc="default">
      <name>IANA Considerations</name>
      <section anchor="update-of-the-tls-extensiontype-registry" title="Update of the TLS numbered="true" toc="default">
        <name>TLS ExtensionType Registry">

<t>Create Values</name>
        <t>IANA has created an entry, compress_certificate(27), in the existing registry for
	"TLS ExtensionType Values" registry (defined in <xref target="RFC8446"></xref>),
	target="RFC8446" format="default"/>) with “TLS 1.3” column the values
being in the "TLS 1.3" column
set to “CH, CR”, "CH, CR" and “Recommended” the "Recommended" column being entry set to “Yes”.</t> "Yes".</t>
      </section>
      <section anchor="update-of-the-tls-handshaketype-registry" title="Update of the TLS HandshakeType Registry">

<t>Create numbered="true" toc="default">
        <name>TLS HandshakeType</name>
        <t>IANA has created an entry, compressed_certificate(25), in
	the existing "TLS Handshake Type" registry for
HandshakeType (defined in <xref target="RFC8446"></xref>),
	target="RFC8446" format="default"/>), with “DTLS-OK” the "DTLS-OK" column value being set to
“Yes”.</t>
"Yes".</t>
      </section>
      <section anchor="registry" title="Registry for Compression Algorithms"> numbered="true" toc="default">
        <name>Compression Algorithms</name>
        <t>This document establishes a registry of compression algorithms supported for
compressing the Certificate message, titled “Certificate "TLS Certificate Compression Algorithm
IDs”,
IDs", under the existing “Transport "Transport Layer Security (TLS) Extensions” heading.</t> Extensions" registry.</t>
        <t>The entries in the registry are:</t>

<texttable>
      <ttcol align='left'>Algorithm Number</ttcol>
      <ttcol align='left'>Description</ttcol>
      <ttcol align='left'>Reference</ttcol>
      <c>0</c>
      <c>Reserved</c>
      <c>&#160;</c>
      <c>1</c>
      <c>zlib</c>
      <c>[this document]</c>
      <c>2</c>
      <c>brotli</c>
      <c>[this document]</c>
      <c>3</c>
      <c>zstd</c>
      <c>[this document]</c>
      <c>16384 to 65535</c>
      <c>Reserved
        <table align="center">
	  <name>TLS Certificate Compression Algorithm IDs</name>
          <thead>
            <tr>
              <th align="left">Algorithm Number</th>
              <th align="left">Description</th>
              <th align="left">Reference</th>
            </tr>
          </thead>

          <tbody>
            <tr>
              <td align="left">0</td>
              <td align="left">Reserved</td>
              <td align="left">RFC 8879</td>
            </tr>
            <tr>
              <td align="left">1</td>
              <td align="left">zlib</td>
              <td align="left">RFC 8879</td>
            </tr>
            <tr>
              <td align="left">2</td>
              <td align="left">brotli</td>
              <td align="left">RFC 8879</td>
            </tr>
            <tr>
              <td align="left">3</td>
              <td align="left">zstd</td>
              <td align="left">RFC 8879</td>
            </tr>
            <tr>
              <td align="left">16384 to 65535</td>
              <td align="left">Reserved for Experimental Use</c>
      <c>&#160;</c>
</texttable> Use</td>
              <td align="left">&nbsp;</td>
            </tr>
          </tbody>
        </table>
        <t>The values in this registry shall be allocated under “IETF Review” "IETF Review" policy for
values strictly smaller than 256, under “Specification Required” "Specification Required" policy for
values 256-16383, and under “Experimental Use” "Experimental Use" otherwise (see <xref target="RFC8126"></xref> target="RFC8126" format="default"/> for the
definition of relevant policies).  Experimental Use extensions can be used both
on private networks and over the open Internet.</t>
        <t>The procedures for requesting values in the Specification Required space are
specified in Section 17 of <xref target="RFC8447"></xref>.</t> target="RFC8447" sectionFormat="of" section="17"/>.</t>
      </section>
    </section>
  </middle>
  <back>

    <references title='Normative References'>
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.1950.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7250.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7932.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7924.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8446.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8447.xml"/>

<!-- [rfced] [I-D.kucherawy-rfc8478bis]; companion document RFC 8878 -->

<reference  anchor="RFC1950" target='https://www.rfc-editor.org/info/rfc1950'> anchor='RFC8878'>
<front>
<title>ZLIB Compressed Data Format Specification version 3.3</title>
<title>Zstandard Compression and the 'application/zstd' Media Type</title>

<author initials='P.' surname='Deutsch' fullname='P. Deutsch'><organization /></author> initials='Y' surname='Collet' fullname='Yann Collet'>
    <organization />
</author>

<author initials='J-L.' surname='Gailly' fullname='J-L. Gailly'><organization /></author> initials='M' surname='Kucherawy' fullname='Murray Kucherawy' role="editor">
    <organization />
</author>

<date year='1996' month='May' month='August' year='2020' />
<abstract><t>This specification defines a lossless compressed data format.  This memo provides information for the Internet community.  This memo does not specify an Internet standard of any kind.</t></abstract>
</front>
<seriesInfo name='RFC' value='1950'/> name="RFC" value="8878"/>
<seriesInfo name='DOI' value='10.17487/RFC1950'/> name="DOI" value="10.17487/RFC8878"/>
</reference>

<reference  anchor="RFC2119" target='https://www.rfc-editor.org/info/rfc2119'>
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='S. Bradner'><organization /></author>
<date year='1997' month='March' />
<abstract><t>In many standards track documents several words are used to signify the requirements

      </references>
      <references>
        <name>Informative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5246.xml"/>
      </references>
    </references>
    <section anchor="acknowledgements" numbered="false" toc="default">
      <name>Acknowledgements</name>
      <t>Certificate compression was originally introduced in the specification.  These words are often capitalized. This document defines these words as they should be interpreted in IETF documents.  This QUIC Crypto protocol,
designed by <contact fullname="Adam Langley"/> and <contact fullname="Wan-Teh
Chang" />.</t>
      <t>This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion has benefited from contributions 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>

<reference  anchor="RFC7250" target='https://www.rfc-editor.org/info/rfc7250'>
<front>
<title>Using Raw Public Keys in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)</title>
<author initials='P.' surname='Wouters' fullname='P. Wouters' role='editor'><organization /></author>
<author initials='H.' surname='Tschofenig' fullname='H. Tschofenig' role='editor'><organization /></author>
<author initials='J.' surname='Gilmore' fullname='J. Gilmore'><organization /></author>
<author initials='S.' surname='Weiler' fullname='S. Weiler'><organization /></author>
<author initials='T.' surname='Kivinen' fullname='T. Kivinen'><organization /></author>
<date year='2014' month='June' />
<abstract><t>This document specifies a new certificate type and two TLS extensions for exchanging raw public keys in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS).  The new certificate type allows raw public keys to be used for authentication.</t></abstract>
</front>
<seriesInfo name='RFC' value='7250'/>
<seriesInfo name='DOI' value='10.17487/RFC7250'/>
</reference>

<reference  anchor="RFC7932" target='https://www.rfc-editor.org/info/rfc7932'>
<front>
<title>Brotli Compressed Data Format</title>
<author initials='J.' surname='Alakuijala' fullname='J. Alakuijala'><organization /></author>
<author initials='Z.' surname='Szabadka' fullname='Z. Szabadka'><organization /></author>
<date year='2016' month='July' />
<abstract><t>This specification defines a lossless compressed data format that compresses data using a combination of the LZ77 algorithm and Huffman coding, with efficiency comparable to the best currently available general-purpose compression methods.</t></abstract>
</front>
<seriesInfo name='RFC' value='7932'/>
<seriesInfo name='DOI' value='10.17487/RFC7932'/>
</reference>

<reference  anchor="RFC7924" target='https://www.rfc-editor.org/info/rfc7924'>
<front>
<title>Transport Layer Security (TLS) Cached Information Extension</title>
<author initials='S.' surname='Santesson' fullname='S. Santesson'><organization /></author>
<author initials='H.' surname='Tschofenig' fullname='H. Tschofenig'><organization /></author>
<date year='2016' month='July' />
<abstract><t>Transport Layer Security (TLS) handshakes often include fairly static information, such as the server certificate and a list of trusted certification authorities (CAs).  This information can be of considerable size, particularly if the server certificate is bundled with a complete certificate chain (i.e., the certificates of intermediate CAs up to the root CA).</t><t>This document defines an extension that allows a TLS client to inform a server of cached information, thereby enabling the server to omit already available information.</t></abstract>
</front>
<seriesInfo name='RFC' value='7924'/>
<seriesInfo name='DOI' value='10.17487/RFC7924'/>
</reference>

<reference  anchor="RFC8126" target='https://www.rfc-editor.org/info/rfc8126'>
<front>
<title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
<author initials='M.' surname='Cotton' fullname='M. Cotton'><organization /></author>
<author initials='B.' surname='Leiba' fullname='B. Leiba'><organization /></author>
<author initials='T.' surname='Narten' fullname='T. Narten'><organization /></author>
<date year='2017' month='June' />
<abstract><t>Many protocols make use of points of extensibility that use constants to identify various protocol parameters.  To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper.  For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA).</t><t>To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed.  This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry.</t><t>This is the third edition of this document; it obsoletes RFC 5226.</t></abstract>
</front>
<seriesInfo name='BCP' value='26'/>
<seriesInfo name='RFC' value='8126'/>
<seriesInfo name='DOI' value='10.17487/RFC8126'/>
</reference>

<reference  anchor="RFC8174" target='https://www.rfc-editor.org/info/rfc8174'>
<front>
<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
<author initials='B.' surname='Leiba' fullname='B. Leiba'><organization /></author>
<date year='2017' month='May' />
<abstract><t>RFC 2119 specifies common key words that may 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="RFC8446" target='https://www.rfc-editor.org/info/rfc8446'>
<front>
<title>The Transport Layer Security (TLS) Protocol Version 1.3</title>
<author initials='E.' surname='Rescorla' fullname='E. Rescorla'><organization /></author>
<date year='2018' month='August' />
<abstract><t>This document specifies version 1.3 of the Transport Layer Security (TLS) protocol.  TLS allows client/server applications to communicate over the Internet in a way that 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="RFC8447" target='https://www.rfc-editor.org/info/rfc8447'>
<front>
<title>IANA Registry Updates for TLS and DTLS</title>
<author initials='J.' surname='Salowey' fullname='J. Salowey'><organization /></author>
<author initials='S.' surname='Turner' fullname='S. Turner'><organization /></author>
<date year='2018' month='August' />
<abstract><t>This document describes a number of changes to TLS and DTLS IANA registries that range from adding notes to the registry all the way to changing the registration policy.  These changes were mostly motivated by WG review of the TLS- and DTLS-related registries undertaken as part of the TLS 1.3 development process.</t><t>This document updates the following RFCs: 3749, 5077, 4680, 5246, 5705, 5878, 6520, and 7301.</t></abstract>
</front>
<seriesInfo name='RFC' value='8447'/>
<seriesInfo name='DOI' value='10.17487/RFC8447'/>
</reference>

<reference anchor="I-D.kucherawy-rfc8478bis">
<front>
<title>Zstandard Compression and the application/zstd Media Type</title>

<author initials='Y' surname='Collet' fullname='Yann Collet'>
    <organization />
</author>

<author initials='M' surname='Kucherawy' fullname='Murray Kucherawy'>
    <organization />
</author>

<date month='December' day='20' year='2019' />

<abstract><t>Zstandard, or "zstd" (pronounced "zee standard"), is a data compression mechanism.  This document describes the mechanism and registers a media type and content encoding to be used when transporting zstd-compressed content via Multipurpose Internet Mail Extensions (MIME).  Despite use of the word "standard" as part of its name, readers are advised that this document is not an Internet Standards Track specification; it is being published for informational purposes only.  This document replaces and obsoletes RFC 8478.</t></abstract>

</front>

<seriesInfo name='Internet-Draft' value='draft-kucherawy-rfc8478bis-03' />
<format type='TXT'
        target='http://www.ietf.org/internet-drafts/draft-kucherawy-rfc8478bis-03.txt' />
</reference>

    </references>

    <references title='Informative References'>

<reference  anchor="RFC5246" target='https://www.rfc-editor.org/info/rfc5246'>
<front>
<title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
<author initials='T.' surname='Dierks' fullname='T. Dierks'><organization /></author>
<author initials='E.' surname='Rescorla' fullname='E. Rescorla'><organization /></author>
<date year='2008' month='August' />
<abstract><t>This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol.  The TLS protocol provides communications security over the Internet.  The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery.  [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5246'/>
<seriesInfo name='DOI' value='10.17487/RFC5246'/>
</reference>

    </references>

<section anchor="acknowledgements" title="Acknowledgements">

<t>Certificate compression was originally introduced in the QUIC Crypto protocol,
designed by Adam Langley and Wan-Teh Chang.</t>

<t>This document has benefited from contributions and suggestions from David
Benjamin, Ryan Hamilton, Christian Huitema, Benjamin Kaduk, Ilari Liusvaara,
Piotr Sikora, Ian Swett, Martin Thomson, Sean Turner from <contact fullname="David
Benjamin"/>, <contact fullname="Ryan Hamilton"/>, <contact fullname="Christian
Huitema"/>, <contact fullname="Benjamin Kaduk"/>, <contact fullname="Ilari
Liusvaara"/>, <contact fullname="Piotr Sikora"/>, <contact fullname="Ian Swett"/>, <contact fullname="Martin Thomson"/>, <contact fullname="Sean Turner"/>, and many others.</t>
    </section>
  </back>

<!-- ##markdown-source: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-->

</rfc>