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TLS                                                           M. Thomson
Internet-Draft                                                   Mozilla
Intended status: Standards Track                          March 27, 2019
Expires: September 28, 2019


              Suppressing Intermediate Certificates in TLS
                        draft-thomson-tls-sic-00

Abstract

   A TLS client that has access to the complete set of published
   intermediate certificates can inform servers of this fact so that the
   server can avoid sending intermediates, reducing the size of the TLS
   handshake.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 28, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terms and Definitions . . . . . . . . . . . . . . . . . . . .   2
   3.  Got Intermediates Flag  . . . . . . . . . . . . . . . . . . .   2
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   3
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   3
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   In some uses of public key infrastructure (PKI) intermediate
   certificates are used to sign end-entity certificates.  In the web
   PKI, clients require that certificate authorities disclose all
   intermediate certificates that they create.  Though the set of
   intermediate certificates is large, the size is bounded, so it is
   possible to provide a complete set of certificates.

   For a client that has all intermediates, having the server send
   intermediates in the TLS handshake increases the size of the
   handshake unnecessarily.  This document creates a signal that a
   client can send that informs the server that it has a complete set of
   intermediates.  A server that receives this signal can limit the
   certificate chain it sends to just the end-entity certificate, saving
   on handshake size.

   This mechanism is intended to be complementary with certificate
   compression [COMPRESS] in that it reduces the size of the handshake.

2.  Terms and Definitions

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Got Intermediates Flag

   A client that believes that it has a current, complete set of
   intermediate certificates sends the tls_flags extension [TLS-FLAGS]
   with the 0xTBD flag set to 1.  A server can also set the flag in a
   CertificateRequest extension.





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   A server that receives a value of 1 in the 0xTBD flag from a
   ClientHello message SHOULD omit all certificates other than the end-
   entity certificate from its Certificate message.  A client that
   receives a value of 1 in the 0xTBD flag in a CertificateRequest
   message SHOULD omit all certificates other than the end-entity
   certificate from the Certificate message that it sends in response.

   The 0xTBD flag can only be send in a ClientHello or
   CertificateRequest message.  Endpoints that receive a value of 1 in
   any other handshake message MUST generate a fatal illegal_parameter
   alert.

4.  Security Considerations

   This creates an unencrypted signal that might be used to identify
   which clients believe that they have all intermediates.  This might
   allow cilents to be more effectively fingerprinted by peers and any
   elements on the network path.

5.  IANA Considerations

   This document registers the 0xTBD flag in the registry created by
   [TLS-FLAGS].

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [TLS-FLAGS]
              Nir, Y., "A Flags Extension for TLS 1.3", draft-nir-tls-
              tlsflags-00 (work in progress), March 2019.

6.2.  Informative References

   [COMPRESS]
              Ghedini, A. and V. Vasiliev, "TLS Certificate
              Compression", draft-ietf-tls-certificate-compression-04
              (work in progress), October 2018.




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Author's Address

   Martin Thomson
   Mozilla

   Email: mt@lowentropy.net













































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