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Versions: (draft-wouters-tls-oob-pubkey) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 7250

IETF                                                          P. Wouters
Internet-Draft                                       No Hats Corporation
Intended status: Standards Track                              J. Gilmore
Expires: July 10, 2012
                                                               S. Weiler
                                                            SPARTA, Inc.
                                                              T. Kivinen
                                                               AuthenTec
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                         January 7, 2012


                 TLS Out-of-Band Public Key Validation
                    draft-ietf-tls-oob-pubkey-00.txt

Abstract

   This document specifies a new TLS certificate type for exchanging raw
   public keys in Transport Layer Security (TLS) and Datagram Transport
   Layer Security (DTLS) for use with out-of-band authentication.
   Currently, TLS authentication can only occur via PKIX or OpenPGP
   certificates.  By specifying a minimum resource for raw public key
   exchange, implementations can use alternative authentication methods.

   One such method is using DANE Resource Records secured by DNSSEC,
   Another use case is to provide authentication functionality when used
   with devices in a constrained environment that use whitelists and
   blacklists, as is the case with sensors and other embedded devices
   that are constrained by memory, computational, and communication
   limitations where the usage of PKIX is not feasible.

   The new certificate type specified can also be used to reduce the
   latency of a TLS client that is already in possession of a validated
   public key of the TLS server before it starts a (non-resumed) 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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months



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   and may be updated, replaced, or obsoleted by other documents at any
   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 July 10, 2012.

Copyright Notice

   Copyright (c) 2012 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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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Motivation . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.2.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  5
     1.3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Changes to the Handshake Message Contents  . . . . . . . . . .  5
     2.1.  Client Hello . . . . . . . . . . . . . . . . . . . . . . .  6
     2.2.  Server Hello . . . . . . . . . . . . . . . . . . . . . . .  7
     2.3.  Certificate Request  . . . . . . . . . . . . . . . . . . .  7
     2.4.  Other Handshake Messages . . . . . . . . . . . . . . . . .  8
   3.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   5.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     7.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
































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1.  Introduction

1.1.  Motivation

   Traditionally, TLS server public keys are obtained in PKIX containers
   in-band using the TLS connection and validated using trust anchors
   based on a [PKIX] certification authority (CA).  This method can add
   a complicated trust relationship that is difficult to validate.
   Examples of such complexity can be seen in [Defeating-SSL].

   Alternative methods are available that allow a TLS client to obtain
   the TLS server public key:

   o  The TLS server public key is obtained from a DNSSEC secured RRset
      using [DANE]

   o  The TLS server public key is obtained from a [PKIX] certificate
      chain from an [LDAP] server

   o  The TLS server public key is provisioned by the operating system
      and updated via software updates

   o  A TLS client has connected to the TLS server before and has cached
      the TLS server certificate chain or TLS server public key for re-
      use

   [RFC5246] does not provide a mechanism for a TLS client to tell the
   TLS server it is already in possession of the authenticated public
   key.  Therefore, a TLS server must always send a list of trusted CA
   keys and its EE certificate containing its public key, even when the
   TLS client does not require or desire that data for authentication.

   [RFC6066] allows suppression of the certificate trust anchor chain,
   but not suppression of the PKIX EE certificate container.  These
   certificate chains are large opaque blocks of data containing much
   more than the public key of the TLS server.  Since the TLS client
   might only be able to validate the PKIX SubjectPublicKeyInfo via an
   out-of-band method such as [DANE], it has to ignore any additional
   information received that was sent by the server that it could not
   validate.  Furthermore, information that comes in via these
   certificate chains could contain contradicting or additional
   information that the TLS client cannot validate or trust, such as an
   expiry date that conflicts with information obtained from DNS or
   LDAP.  This document specifies a method to suppress sending this
   additional information.

   Some small embedded devices use the UDP based [CoAP], a specialized
   constrained networks and nodes for machine-to-machine applications.



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   These devices interact with a Web server to upload data such as
   temperature sensor readings at a regular intervals.  Constrained
   Application Protocol (CoAP) [CoAP] can utilize DTLS for its
   communication security.  As part of the provisioning procedure, the
   embeded device is configured with the address and public key of a
   dedicated CoAP server to upload sensor data.  Receiving PKIX
   information [PKIX] from a webserver would be an unneccesarry burden
   on a sensor networking deployment environment that requires pre-
   configured client-server public keys.  These devices often also lack
   a real-time clock to perform any PKIX epixry checks.

1.2.  Applicability

   The Transport Layer Security (TLS) Protocol Version 1.2 is specified
   in [RFC5246] and provides a framework for extensions to TLS as well
   as considerations for designing such extensions.  [RFC6066] defines
   several new TLS extensions.  This document extends the specifications
   of those RFCs with one new TLS Certificate Type to facilitate
   suppressing unneeded [PKIX] information from being sent during the
   TLS handshake when this information is not required to authenticate
   the TLS server.

1.3.  Terminology

   Most security-related terms in this document are to be understood in
   the sense defined in [SECTERMS]; such terms include, but are not
   limited to, "attack", "authentication", "authorization",
   "certification authority", "certification path", "certificate",
   "credential", "identity", "self-signed certificate", "trust", "trust
   anchor", "trust chain", "validate", and "verify".

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].


2.  Changes to the Handshake Message Contents

   This section describes the changes to the TLS handshake message
   contents when raw public keys are to be used for authentication.
   Figure 1 illustrates the exchange of messages as described in the
   sub-sections below.  The new "RawPublicKey" value in the cert_type
   extension indicates the ability and desire to exchange raw public
   keys, which are then exchanged as part of the certificate payloads.







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    client_hello,
    cert_type="RawPublicKey" ->

                              <-  server_hello,
                                  cert_type="RawPublicKey",
                                  certificate,
                                  server_key_exchange,
                                  certificate_request,
                                  server_hello_done

    certificate,
    client_key_exchange,
    certificate_verify,
    change_cipher_spec,
    finished                  ->

                              <- change_cipher_spec,
                                 finished

   Application Data        <------->     Application Data


                      Figure 1: Example Message Flow

2.1.  Client Hello

   In order to indicate the support of out-of-bound raw public keys,
   clients MUST include an extension of type "cert_type" to the extended
   client hello message.  The "cert_type" TLS extension, which is
   defined in [RFC6091], is assigned the value of 9 from the TLS
   ExtensionType registry.  This value is used as the extension number
   for the extensions in both the client hello message and the server
   hello message.  The hello extension mechanism is described in
   [RFC5246].

   The "cert_type" TLS extension carries a list of supported certificate
   types the client can use, sorted by client preference.  This
   extension MUST be omitted if the client only supports X.509
   certificates.  The "extension_data" field of this extension contains
   a CertificateTypeExtension structure.  Note that the
   CertificateTypeExtension structure is being used both by the client
   and the server, even though the structure is only specified once in
   this document.

   The [RFC6091] defined CertificateTypeExtension is extended as
   follows:





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   enum { client, server } ClientOrServerExtension;

   enum { X.509(0), OpenPGP(1),
      RawPublicKey([TBD]),
      (255) } CertificateType;

   struct {
      select(ClientOrServerExtension)
          case client:
            CertificateType certificate_types<1..2^8-1>;
          case server:
            CertificateType certificate_type;
      }
   } CertificateTypeExtension;


   No new cipher suites are required to use raw public keys.  All
   existing cipher suites that support a key exchange method compatible
   with the defined extension can be used.

2.2.  Server Hello

   If the server receives a client hello that contains the "cert_type"
   extension and chooses a cipher suite then two outcomes are possible.
   The server MUST either select a certificate type from the
   certificate_types field in the extended client hello or terminate the
   session with a fatal alert of type "unsupported_certificate".

   The certificate type selected by the server is encoded in a
   CertificateTypeExtension structure, which is included in the extended
   server hello message using an extension of type "cert_type".  Servers
   that only support X.509 certificates MAY omit including the
   "cert_type" extension in the extended server hello.

   If the negotiated certificate type is RawPublicKey the TLS server
   MUST send a CertificateTypeExtension structure with a PKIX [PKIX]
   certificate containing ONLY the SubjectPublicKeyInfo.  The public key
   MUST match the selected key exchange algorithm.

2.3.  Certificate Request

   The semantics of this message remain the same as in the TLS
   specification.  However, if this message is sent, and the negotiated
   certificate type is RawPublicKey, the "certificate_authorities" list
   MUST be empty.






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2.4.  Other Handshake Messages

   All the other handshake messages are identical to the TLS
   specification.


3.  Security Considerations

   The TLS cert_type extension defined here lets a TLS client attempt to
   supress the sending of server certificate as well as the
   certification chain for that certificate.

   A client using this cert_type needs to be confident in the
   authenticity of the public key it is using.  Since those public keys
   were obtained out-of-band extension), the authentication must also be
   out-of-band.

   Depending on exactly how the public keys were obtained, it may be
   appropriate to use authentication mechanisms tied to the public key
   transport.  For example, if public keys were obtained using [DANE] it
   is appropriate to use DNSSEC to authenticate the public keys.


4.  IANA Considerations

   We request that IANA assign a TLS cert_type value for RawPublicKey.


5.  Contributors

   The following individuals made important contributions to this
   document: Paul Hoffman.


6.  Acknowledgements

   This document is based on material from RFC 6066 for which the author
   is Donald Eastlake 3rd.  Contributions to that document also include
   Joseph Salowey, Alexey Melnikov, Peter Saint-Andre, and Adrian
   Farrel.

   The feedback from the TLS working group meeting at IETF#81 has
   substantially shaped the document and we would like to thank the
   meeting participants for their input.  The support for hashes of
   public keys has been removed after the discussions at the IETF#82
   meeting and the feedback from Eric Rescorla.





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7.  References

7.1.  Normative References

   [PKIX]     Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [SECTERMS]
              Shirey, R., "Internet Security Glossary, Version 2",
              RFC 4949, August 2007.

7.2.  Informative References

   [CoAP]     Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
              "Constrained Application Protocol",
              draft-ietf-core-coap-07 (work in progress), July 2011.

   [DANE]     Hoffman, P. and J. Schlyter, "Using Secure DNS to
              Associate Certificates with Domain Names For TLS",
              draft-ietf-dane-protocol-12 (work in progress),
              September 2011.

   [Defeating-SSL]
              Marlinspike, M., "New Tricks for Defeating SSL in
              Practice", February 2009, <http://www.blackhat.com/
              presentations/bh-dc-09/Marlinspike/
              BlackHat-DC-09-Marlinspike-Defeating-SSL.pdf>.

   [LDAP]     Sermersheim, J., "Lightweight Directory Access Protocol
              (LDAP): The Protocol", RFC 4511, June 2006.

   [RFC6066]  Eastlake, D., "Transport Layer Security (TLS) Extensions:
              Extension Definitions", RFC 6066, January 2011.

   [RFC6091]  Mavrogiannopoulos, N. and D. Gillmor, "Using OpenPGP Keys
              for Transport Layer Security (TLS) Authentication",
              RFC 6091, February 2011.






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Authors' Addresses

   Paul Wouters
   No Hats Corporation


   Email: paul@nohats.ca


   John Gilmore
   PO Box 170608
   San Francisco, California  94117
   USA

   Phone: +1 415 221 6524
   Email: gnu@toad.com
   URI:   https://www.toad.com/


   Samuel Weiler
   SPARTA, Inc.
   7110 Samuel Morse Drive
   Columbia, Maryland  21046
   US

   Email: weiler@tislabs.com


   Tero Kivinen
   AuthenTec
   Eerikinkatu 28
   HELSINKI  FI-00180
   FI

   Email: kivinen@iki.fi


   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600
   Finland

   Phone: +358 (50) 4871445
   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at





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