[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

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

TLS                                                           P. Wouters
Internet-Draft                                       No Hats Corporation
Intended status: Standards Track                              J. Gilmore
Expires: September 12, 2012
                                                               S. Weiler
                                                            SPARTA, Inc.
                                                              T. Kivinen
                                                               AuthenTec
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                          March 11, 2012


                 TLS Out-of-Band Public Key Validation
                    draft-ietf-tls-oob-pubkey-02.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 public key validation.
   Currently, TLS authentication can only occur via X.509-based Public
   Key Infrastructure (PKI) or OpenPGP certificates.  By specifying a
   minimum resource for raw public key exchange, implementations can use
   alternative public key validation methods.

   One such alternative public key valiation method is offered by the
   DNS-Based Authentication of Named Entities (DANE) together with DNS
   Security.  Another alternative is to utilize pre-configured keys, as
   is the case with sensors and other embedded devices.  The usage of
   raw public keys, instead of X.509-based certificates, leads to a
   smaller code footprint.

   The support for raw public keys is introduced into TLS via a new non-
   PKIX certificate type.

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
   and may be updated, replaced, or obsoleted by other documents at any



Wouters, et al.        Expires September 12, 2012               [Page 1]

Internet-Draft        TLS OOB Public Key Validation           March 2012


   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 12, 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   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.
































Wouters, et al.        Expires September 12, 2012               [Page 2]

Internet-Draft        TLS OOB Public Key Validation           March 2012


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.  TLS Handshake Extension . . . . . . . . . . . . . . . . . . . . 5
     3.1.  Client Hello  . . . . . . . . . . . . . . . . . . . . . . . 5
     3.2.  Server Hello  . . . . . . . . . . . . . . . . . . . . . . . 6
     3.3.  Certificate Request . . . . . . . . . . . . . . . . . . . . 7
     3.4.  Other Handshake Messages  . . . . . . . . . . . . . . . . . 7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . 8
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9


































Wouters, et al.        Expires September 12, 2012               [Page 3]

Internet-Draft        TLS OOB Public Key Validation           March 2012


1.  Introduction

   Traditionally, TLS server public keys are obtained in PKIX containers
   in-band using the TLS handshake 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
      resource records using DANE [I-D.ietf-dane-protocol].

   o  The TLS server public key is obtained from a [PKIX] certificate
      chain from an Lightweight Directory Access Protocol (LDAP) [LDAP]
      server.

   o  The TLS client and server public key is provisioned into the
      operating system firmware image, and updated via software updates.

   Some smart objects use the UDP-based Constrained Application Protocol
   (CoAP) [I-D.ietf-core-coap] to interact with a Web server to upload
   sensor data at a regular intervals, such as temperature readings.
   CoAP [I-D.ietf-core-coap] can utilize DTLS for securing the client-
   to-server communication.  As part of the manufacturing process, the
   embeded device may be configured with the address and the public key
   of a dedicated CoAP server, as well as a public key for the client
   itself.  The usage of X.509-based PKIX certificates [PKIX] may not
   suit all smart object deployments and would therefore be an
   unneccesarry burden.

   The Transport Layer Security (TLS) Protocol Version 1.2 [RFC5246]
   provides a framework for extensions to TLS as well as guidelines for
   designing such extensions.  This document uses the TLS Certificate
   Type extension point to define a new non-X.509 certificate type for
   carrying raw public keys.


2.  Terminology

   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].







Wouters, et al.        Expires September 12, 2012               [Page 4]

Internet-Draft        TLS OOB Public Key Validation           March 2012


3.  TLS Handshake Extension

   This section describes the changes to the TLS handshake message
   contents when raw public key certificates are to be used.  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.  Note that
   the certificate payloads only contain the SubjectPublicKeyInfo
   structure instead of the entire certificate.



    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

3.1.  Client Hello

   In order to indicate the support of out-of-band 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].




Wouters, et al.        Expires September 12, 2012               [Page 5]

Internet-Draft        TLS OOB Public Key Validation           March 2012


   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:


   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.

3.2.  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
   CertificateType 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



Wouters, et al.        Expires September 12, 2012               [Page 6]

Internet-Draft        TLS OOB Public Key Validation           March 2012


   MUST place the SubjectPublicKeyInfo structure into the Certificate
   payload.  The public key MUST match the selected key exchange
   algorithm.

3.3.  Certificate Request

   The semantics of this message remain the same as in the TLS
   specification.

3.4.  Other Handshake Messages

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


4.  Security Considerations

   The transmission of raw public keys, as described in this document,
   provides benefits by lowering the over-the-air transmission overhead
   since raw public keys are quite naturally smaller than an entire
   certificate.  There are also advantages from a codesize point of view
   for parsing and processing these keys.  The crytographic procedures
   for assocating the public key with the possession of a private key
   also follows standard procedures.

   The main security challenge is, however, how to associate the public
   key with a specific entity.  This information will be needed to make
   authorization decisions.  Without a secure binding, man-in-the-middle
   attacks may be the consequence.  This document assumes that such
   binding can be made out-of-band and we list a few examples in
   Section 1.  DANE [I-D.ietf-dane-protocol] offers one such approach.
   If public keys are obtained using DANE, these public keys are
   authenticated via DNSSEC.  Pre-configured keys is another out of band
   method for authenticating raw public keys.  While pre-configured keys
   are not suitable for a generic Web-based e-commerce environment such
   keys are a reasonable approach for many smart object deployments
   where there is a close relationship between the software running on
   the device and the server-side communication endpoint.  Regardless of
   the chosen mechanism for out-of-band public key validation an
   assessment of the most suitable approach has to be made prior to the
   start of a deployment to ensure the security of the system.


5.  IANA Considerations

   This document requests IANA to assign a TLS cert_type value for
   RawPublicKey.  The cert_type registry is established with [RFC6091].




Wouters, et al.        Expires September 12, 2012               [Page 7]

Internet-Draft        TLS OOB Public Key Validation           March 2012


6.  Contributors

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


7.  Acknowledgements

   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 moved to [I-D.ietf-tls-cached-info] after the
   discussions at the IETF#82 meeting and the feedback from Eric
   Rescorla.

   We would like to thank Martin Rex, Bill Frantz, Zach Shelby, Carsten
   Bormann, Cullen Jennings, Rene Struik, Alper Yegin, and Jim Schaad.


8.  References

8.1.  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.

8.2.  Informative References

   [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>.

   [I-D.ietf-core-coap]
              Frank, B., Bormann, C., Hartke, K., and Z. Shelby,
              "Constrained Application Protocol (CoAP)",
              draft-ietf-core-coap-08 (work in progress), October 2011.

   [I-D.ietf-dane-protocol]



Wouters, et al.        Expires September 12, 2012               [Page 8]

Internet-Draft        TLS OOB Public Key Validation           March 2012


              Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Protocol for Transport Layer
              Security (TLS)", draft-ietf-dane-protocol-18 (work in
              progress), March 2012.

   [I-D.ietf-tls-cached-info]
              Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension",
              draft-ietf-tls-cached-info-11 (work in progress),
              December 2011.

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

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


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






Wouters, et al.        Expires September 12, 2012               [Page 9]

Internet-Draft        TLS OOB Public Key Validation           March 2012


   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

































Wouters, et al.        Expires September 12, 2012              [Page 10]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/