< draft-ietf-tls-certificate-compression-07.txt   draft-ietf-tls-certificate-compression-10.txt >
TLS A. Ghedini TLS A. Ghedini
Internet-Draft Cloudflare, Inc. Internet-Draft Cloudflare, Inc.
Intended status: Standards Track V. Vasiliev Intended status: Standards Track V. Vasiliev
Expires: May 24, 2020 Google Expires: July 9, 2020 Google
November 21, 2019 January 06, 2020
TLS Certificate Compression TLS Certificate Compression
draft-ietf-tls-certificate-compression-07 draft-ietf-tls-certificate-compression-10
Abstract Abstract
In TLS handshakes, certificate chains often take up the majority of In TLS handshakes, certificate chains often take up the majority of
the bytes transmitted. the bytes transmitted.
This document describes how certificate chains can be compressed to This document describes how certificate chains can be compressed to
reduce the amount of data transmitted and avoid some round trips. reduce the amount of data transmitted and avoid some round trips.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 24, 2020. This Internet-Draft will expire on July 9, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 2 2. Notational Conventions . . . . . . . . . . . . . . . . . . . 2
3. Negotiating Certificate Compression . . . . . . . . . . . . . 2 3. Negotiating Certificate Compression . . . . . . . . . . . . . 2
4. Compressed Certificate Message . . . . . . . . . . . . . . . 3 4. Compressed Certificate Message . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Middlebox Compatibility . . . . . . . . . . . . . . . . . . . 5 6. Middlebox Compatibility . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7.1. Update of the TLS ExtensionType Registry . . . . . . . . 5 7.1. Update of the TLS ExtensionType Registry . . . . . . . . 5
7.2. Update of the TLS HandshakeType Registry . . . . . . . . 5 7.2. Update of the TLS HandshakeType Registry . . . . . . . . 6
7.3. Registry for Compression Algorithms . . . . . . . . . . . 5 7.3. Registry for Compression Algorithms . . . . . . . . . . . 6
8. Normative References . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
In order to reduce latency and improve performance it can be useful In order to reduce latency and improve performance it can be useful
to reduce the amount of data exchanged during a TLS handshake. to reduce the amount of data exchanged during a TLS handshake.
[RFC7924] describes a mechanism that allows a client and a server to [RFC7924] describes a mechanism that allows a client and a server to
avoid transmitting certificates already shared in an earlier avoid transmitting certificates already shared in an earlier
handshake, but it doesn't help when the client connects to a server handshake, but it doesn't help when the client connects to a server
for the first time and doesn't already have knowledge of the server's for the first time and doesn't already have knowledge of the server's
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2. Notational Conventions 2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Negotiating Certificate Compression 3. Negotiating Certificate Compression
This extension is only supported with TLS 1.3 and newer; if TLS 1.2 This extension is only supported with TLS 1.3 [RFC8446] and newer; if
or earlier is negotiated, the peers MUST ignore this extension. TLS 1.2 [RFC5246] or earlier is negotiated, the peers MUST ignore
this extension.
This document defines a new extension type This document defines a new extension type
(compress_certificate(27)), which can be used to signal the supported (compress_certificate(27)), which can be used to signal the supported
compression formats for the Certificate message to the peer. compression formats for the Certificate message to the peer.
Whenever it is sent by the client as a ClientHello message extension Whenever it is sent by the client as a ClientHello message extension
([RFC8446], Section 4.1.2), it indicates the support for compressed ([RFC8446], Section 4.1.2), it indicates the support for compressed
server certificates. Whenever it is sent by the server as a server certificates. Whenever it is sent by the server as a
CertificateRequest extension ([RFC8446], Section 4.3.2), it indicates CertificateRequest extension ([RFC8446], Section 4.3.2), it indicates
the support for compressed client certificates. the support for compressed client certificates.
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struct { struct {
CertificateCompressionAlgorithm algorithms<2..2^8-2>; CertificateCompressionAlgorithm algorithms<2..2^8-2>;
} CertificateCompressionAlgorithms; } CertificateCompressionAlgorithms;
The compress_certificate extension is a unidirectional indication; no The compress_certificate extension is a unidirectional indication; no
corresponding response extension is needed. corresponding response extension is needed.
4. Compressed Certificate Message 4. Compressed Certificate Message
If the peer has indicated that it supports compression, server and If the peer has indicated that it supports compression, server and
client MAY compress their corresponding Certificate messages and send client MAY compress their corresponding Certificate messages
them in the form of the CompressedCertificate message (replacing the (Section 4.4.2 of [RFC8446]) and send them in the form of the
Certificate message). CompressedCertificate message (replacing the Certificate message).
The CompressedCertificate message is formed as follows: The CompressedCertificate message is formed as follows:
struct { struct {
CertificateCompressionAlgorithm algorithm; CertificateCompressionAlgorithm algorithm;
uint24 uncompressed_length; uint24 uncompressed_length;
opaque compressed_certificate_message<1..2^24-1>; opaque compressed_certificate_message<1..2^24-1>;
} CompressedCertificate; } CompressedCertificate;
algorithm The algorithm used to compress the certificate. The algorithm The algorithm used to compress the certificate. The
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CompressedCertificate message. CompressedCertificate message.
Implementations MUST limit the size of the resulting decompressed Implementations MUST limit the size of the resulting decompressed
chain to the specified uncompressed length, and they MUST abort the chain to the specified uncompressed length, and they MUST abort the
connection if the size of the output of the decompression function connection if the size of the output of the decompression function
exceeds that limit. TLS framing imposes 16777216 byte limit on the exceeds that limit. TLS framing imposes 16777216 byte limit on the
certificate message size, and the implementations MAY impose a limit certificate message size, and the implementations MAY impose a limit
that is lower than that; in both cases, they MUST apply the same that is lower than that; in both cases, they MUST apply the same
limit as if no compression were used. limit as if no compression were used.
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 and
E.3 of [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, or disable it altogether.
6. Middlebox Compatibility 6. Middlebox Compatibility
It's been observed that a significant number of middleboxes intercept It's been observed that a significant number of middleboxes intercept
and try to validate the Certificate message exchanged during a TLS and try to validate the Certificate message exchanged during a TLS
handshake. This means that middleboxes that don't understand the handshake. This means that middleboxes that don't understand the
CompressedCertificate message might misbehave and drop connections CompressedCertificate message might misbehave and drop connections
that adopt certificate compression. Because of that, the extension that adopt certificate compression. Because of that, the extension
is only supported in the versions of TLS where the certificate is only supported in the versions of TLS where the certificate
message is encrypted in a way that prevents middleboxes from message is encrypted in a way that prevents middleboxes from
intercepting it, that is, TLS version 1.3 [RFC8446] and higher. intercepting it, that is, TLS version 1.3 [RFC8446] and higher.
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7.1. Update of the TLS ExtensionType Registry 7.1. Update of the TLS ExtensionType Registry
Create an entry, compress_certificate(27), in the existing registry Create an entry, compress_certificate(27), in the existing registry
for ExtensionType (defined in [RFC8446]), with "TLS 1.3" column for ExtensionType (defined in [RFC8446]), with "TLS 1.3" column
values being set to "CH, CR", and "Recommended" column being set to values being set to "CH, CR", and "Recommended" column being set to
"Yes". "Yes".
7.2. Update of the TLS HandshakeType Registry 7.2. Update of the TLS HandshakeType Registry
Create an entry, compressed_certificate(25), in the existing registry Create an entry, compressed_certificate(25), in the existing registry
for HandshakeType (defined in [RFC8446]). for HandshakeType (defined in [RFC8446]), with "DTLS-OK" column value
being set to "Yes".
7.3. Registry for Compression Algorithms 7.3. Registry for Compression Algorithms
This document establishes a registry of compression algorithms This document establishes a registry of compression algorithms
supported for compressing the Certificate message, titled supported for compressing the Certificate message, titled
"Certificate Compression Algorithm IDs", under the existing "Certificate Compression Algorithm IDs", under the existing
"Transport Layer Security (TLS) Extensions" heading. "Transport Layer Security (TLS) Extensions" heading.
The entries in the registry are: The entries in the registry are:
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+------------------+------------------------------+-----------------+ +------------------+------------------------------+-----------------+
The values in this registry shall be allocated under "IETF Review" The values in this registry shall be allocated under "IETF Review"
policy for values strictly smaller than 256, under "Specification policy for values strictly smaller than 256, under "Specification
Required" policy for values 256-16383, and under "Experimental Use" Required" policy for values 256-16383, and under "Experimental Use"
otherwise (see [RFC8126] for the definition of relevant policies). otherwise (see [RFC8126] for the definition of relevant policies).
Experimental Use extensions can be used both on private networks and Experimental Use extensions can be used both on private networks and
over the open Internet. over the open Internet.
The procedures for requesting values in the Specification Required The procedures for requesting values in the Specification Required
space are specified in [RFC8447]. space are specified in Section 17 of [RFC8447].
8. Normative References 8. References
8.1. Normative References
[I-D.kucherawy-rfc8478bis] [I-D.kucherawy-rfc8478bis]
Collet, Y. and M. Kucherawy, "Zstandard Compression and Collet, Y. and M. Kucherawy, "Zstandard Compression and
the application/zstd Media Type", draft-kucherawy- the application/zstd Media Type", draft-kucherawy-
rfc8478bis-00 (work in progress), October 2019. rfc8478bis-03 (work in progress), December 2019.
[RFC1950] Deutsch, P. and J-L. Gailly, "ZLIB Compressed Data Format [RFC1950] Deutsch, P. and J-L. Gailly, "ZLIB Compressed Data Format
Specification version 3.3", RFC 1950, Specification version 3.3", RFC 1950,
DOI 10.17487/RFC1950, May 1996, DOI 10.17487/RFC1950, May 1996,
<https://www.rfc-editor.org/info/rfc1950>. <https://www.rfc-editor.org/info/rfc1950>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
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May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS [RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS
and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018, and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018,
<https://www.rfc-editor.org/info/rfc8447>. <https://www.rfc-editor.org/info/rfc8447>.
8.2. Informative References
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
Appendix A. Acknowledgements Appendix A. Acknowledgements
Certificate compression was originally introduced in the QUIC Crypto Certificate compression was originally introduced in the QUIC Crypto
protocol, designed by Adam Langley and Wan-Teh Chang. protocol, designed by Adam Langley and Wan-Teh Chang.
This document has benefited from contributions and suggestions from This document has benefited from contributions and suggestions from
David Benjamin, Ryan Hamilton, Ilari Liusvaara, Piotr Sikora, Ian David Benjamin, Ryan Hamilton, Christian Huitema, Benjamin Kaduk,
Swett, Martin Thomson, Sean Turner and many others. Ilari Liusvaara, Piotr Sikora, Ian Swett, Martin Thomson, Sean Turner
and many others.
Authors' Addresses Authors' Addresses
Alessandro Ghedini Alessandro Ghedini
Cloudflare, Inc. Cloudflare, Inc.
Email: alessandro@cloudflare.com Email: alessandro@cloudflare.com
Victor Vasiliev Victor Vasiliev
Google Google
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