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

TLS                                                      P. Wouters, Ed.
Internet-Draft                                                   Red Hat
Intended status: Standards Track                      H. Tschofenig, Ed.
Expires: July 22, 2014
                                                              J. Gilmore

                                                               S. Weiler
                                                            SPARTA, Inc.
                                                              T. Kivinen
                                                               AuthenTec
                                                        January 18, 2014


  Using Raw Public Keys in Transport Layer Security (TLS) and Datagram
                    Transport Layer Security (DTLS)
                    draft-ietf-tls-oob-pubkey-11.txt

Abstract

   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.

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
   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 22, 2014.

Copyright Notice

   Copyright (c) 2014 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



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   (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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Structure of the Raw Public Key Extension . . . . . . . . . .   4
   4.  TLS Client and Server Handshake Behavior  . . . . . . . . . .   6
     4.1.  Client Hello  . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Server Hello  . . . . . . . . . . . . . . . . . . . . . .   8
     4.3.  Client Authentication . . . . . . . . . . . . . . . . . .   9
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  TLS Server uses Raw Public Key  . . . . . . . . . . . . .   9
     5.2.  TLS Client and Server use Raw Public Keys . . . . . . . .  10
     5.3.  Combined Usage of Raw Public Keys and X.509 Certificate .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Appendix A.  Example Encoding . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   Traditionally, TLS client and server public keys are obtained in PKIX
   containers in-band as part of the TLS handshake procedure and are
   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].  TLS is, however, also commonly used with
   self-signed certificates in smaller deployments where the self-signed
   certificates are distributed to all involved protocol end points out-
   of-band.  This practice does, however, still requires the overhead of
   the certificate generation even though none of the information found
   in the certificate is actually used.

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





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   o  The TLS client can obtain the TLS server public key from a DNSSEC
      secured resource records using DANE [RFC6698].

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

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

      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 can utilize DTLS for securing the client-to-server
      communication.  As part of the manufacturing process, the embedded
      device may be configured with the address and the public key of a
      dedicated CoAP server, as well as a public/private key pair for
      the client itself.

   This document introduces the use of raw public keys in TLS/DTLS.
   With raw public keys, only a subset of the information found in
   typical certificates is utilized: namely, the SubjectPublicKeyInfo
   structure of a PKIX certificates that carries the parameters
   necessary to describe the public key.  Other parameters found in PKIX
   certificates are omitted.  By omitting various certificate-related
   structures, the resulting raw public key is kept fairly small in
   comparison to the original certificate, and the code to process the
   keys requires only a minimalistic ASN.1 parser, no code for
   certificate path validation, and other PKIX related processing tasks
   are also omitted.  Note, however, the SubjectPublicKeyInfo structure
   is still in an ASN.1 format.  To further reduce the size of the
   exchanged information this specification can be combined with the TLS
   Cached Info extension [I-D.ietf-tls-cached-info], which enables TLS
   peers to just exchange fingerprints of their public keys.

   The mechanism defined herein only provides authentication when an
   out-of-band mechanism is also used to bind the public key to the
   entity presenting the key.

   Section 3 defines the structure of the two new TLS extensions
   "client_certificate_type" and "server_certificate_type", which can be
   used as part of an extended TLS handshake when raw public keys are to
   be used.  Section 4 defines the behavior of the TLS client and the
   TLS server.  Example exchanges are described in Section 5.  Section 6
   describes security considerations with this approach.  Finally, in
   Section 7 this document also registers a new value to the IANA
   certificate types registry for the support of raw public keys.



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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].

   We use the terms 'TLS server' and 'server' as well as 'TLS client'
   and 'client' interchangable.

3.  Structure of the Raw Public Key Extension

   This section defines the two TLS extensions 'client_certificate_type'
   and 'server_certificate_type', which can be used as part of an
   extended TLS handshake when raw public keys are used.  Section 4
   defines the behavior of the TLS client and the TLS server using this
   extension.

   This specification uses raw public keys whereby the already available
   encoding used in a PKIX certificate in the form of a
   SubjectPublicKeyInfo structure is reused.  To carry the raw public
   key within the TLS handshake the Certificate payload is used as a
   container, as shown in Figure 1.  The shown Certificate structure is
   an adaptation of its original form [RFC5246].


   opaque ASN.1Cert<1..2^24-1>;

   struct {
       select(certificate_type){

           // certificate type defined in this document.
           case RawPublicKey:
             opaque ASN.1_subjectPublicKeyInfo<1..2^24-1>;

           // X.509 certificate defined in RFC 5246
           case X.509:
             ASN.1Cert certificate_list<0..2^24-1>;

           // Additional certificate type based on TLS
           // Certificate Type Registry
       };
   } Certificate;


   Figure 1: Certificate Payload as a Container for the Raw Public Key.

   The SubjectPublicKeyInfo structure is defined in Section 4.1 of RFC
   5280 [PKIX] and does not only contain the raw keys, such as the



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   public exponent and the modulus of an RSA public key, but also an
   algorithm identifier.  The algorithm identifier can also include
   parameters.  The SubjectPublicKeyInfo value in the Certificate
   payload MUST contain the DER encoding [X.690] of the
   SubjectPublicKeyInfo.  The structure, as shown in Figure 2, therefore
   also contains length information as well.  An example is provided in
   Appendix A.


      SubjectPublicKeyInfo  ::=  SEQUENCE  {
           algorithm               AlgorithmIdentifier,
           subjectPublicKey        BIT STRING  }

      AlgorithmIdentifier   ::=  SEQUENCE  {
           algorithm               OBJECT IDENTIFIER,
           parameters              ANY DEFINED BY algorithm OPTIONAL  }


              Figure 2: SubjectPublicKeyInfo ASN.1 Structure.

   The algorithm identifiers are Object Identifiers (OIDs).  RFC 3279
   [RFC3279] and [RFC5480], for example, define the following OIDs shown
   in Figure 3.  Note that this list is not exhaustive and more OIDs may
   be defined in future RFCs.  RFC 5480 also defines a number of OIDs.


Key Type               | Document                   | OID
-----------------------+----------------------------+-------------------
RSA                    | Section 2.3.1 of RFC 3279  | 1.2.840.113549.1.1
.......................|............................|...................
Digital Signature      |                            |
Algorithm (DSA)        | Section 2.3.2 of RFC 3279  | 1.2.840.10040.4.1
.......................|............................|...................
Elliptic Curve         |                            |
Digital Signature      |                            |
Algorithm (ECDSA)      | Section 2 of RFC 5480      | 1.2.840.10045.2.1
-----------------------+----------------------------+-------------------


              Figure 3: Example Algorithm Object Identifiers.

   The extension format for extended client and server hellos, which
   uses the "extension_data" field, is used to carry the
   ClientCertTypeExtension and the ServerCertTypeExtension structures.
   These two structures are shown in Figure 4.  The CertificateType
   structure is an enum with values taken from the 'TLS Certificate
   Type' registry [TLS-Certificate-Types-Registry].




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   struct {
           select(ClientOrServerExtension) {
               case client:
                 CertificateType client_certificate_types<1..2^8-1>;
               case server:
                 CertificateType client_certificate_type;
           }
   } ClientCertTypeExtension;

   struct {
           select(ClientOrServerExtension) {
               case client:
                 CertificateType server_certificate_types<1..2^8-1>;
               case server:
                 CertificateType server_certificate_type;
           }
   } ServerCertTypeExtension;


                  Figure 4: CertTypeExtension Structure.

4.  TLS Client and Server Handshake Behavior

   This specification extends the ClientHello and the ServerHello
   messages, according to the extension procedures defined in [RFC5246].
   It does not extend or modify any other TLS message.

   Note: 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.

   The high-level message exchange in Figure 5 shows the
   'client_certificate_type' and 'server_certificate_type' extensions
   added to the client and server hello messages.

















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    client_hello,
    client_certificate_type,
    server_certificate_type   ->

                              <-  server_hello,
                                  client_certificate_type,
                                  server_certificate_type,
                                  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 5: Basic Raw Public Key TLS Exchange.

4.1.  Client Hello

   In order to indicate the support of raw public keys, clients include
   the 'client_certificate_type' and/or the 'server_certificate_type'
   extensions in an extended client hello message.  The hello extension
   mechanism is described in Section 7.4.1.4 of TLS 1.2 [RFC5246].

   The 'client_certificate_type' in the client hello indicates the
   certificate types the client is able to provide to the server, when
   requested using a certificate_request message.

   The 'server_certificate_type' in the client hello indicates the types
   of certificates the client is able to process when provided by the
   server in a subsequent certificate payload.

   The 'client_certificate_type' and 'server_certificate_type' sent in
   the client hello may carry a list of supported certificate types,
   sorted by client preference.  It is a list in the case where the
   client supports multiple certificate types.

   The TLS client MUST omit the 'client_certificate_type' extension in
   the client hello if it does not possess a raw public key/certificate
   that it can provide to the server when requested using a



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   certificate_request message or is not configured to use one with the
   given TLS server.  The TLS client MUST omit the
   'server_certificate_type' extension in the client hello if it is
   unable to process raw public keys or other certificate types
   introduced via this extension.

4.2.  Server Hello

   If the server receives a client hello that contains the
   'client_certificate_type' extension and/or the
   'server_certificate_type' extension then three outcomes are possible:

   1.  The server does not support the extension defined in this
       document.  In this case the server returns the server hello
       without the extensions defined in this document.

   2.  The server supports the extension defined in this document but it
       does not have any certificate type in common with the client.
       Then, the server terminates the session with a fatal alert of
       type "unsupported_certificate".

   3.  The server supports the extensions defined in this document and
       has at least one certificate type in common with the client.  In
       this case the processing rules described below are followed.

   The 'client_certificate_type' in the client hello indicates the
   certificate types the client is able to provide to the server, when
   requested using a certificate_request message.  If the TLS server
   wants to request a certificate from the client (via the
   certificate_request message) it MUST include the
   'client_certificate_type' extension in the server hello.  This
   'client_certificate_type' in the server hello then indicates the type
   of certificates the client is requested to provide in a subsequent
   certificate payload.  The value conveyed in the
   'client_certificate_type' MUST be selected from one of the values
   provided in the 'client_certificate_type' extension sent in the
   client hello.  The server MUST also include a certificate_request
   payload in the server hello message.

   If the server does not send a certificate_request payload (for
   example, because client authentication happens at the application
   layer or no client authentication is required) or none of the
   certificates supported by the client (as indicated in the
   'client_certificate_type' in the client hello) match the server-
   supported certificate types then the 'client_certificate_type'
   payload in the server hello MUST be omitted.





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   The 'server_certificate_type' in the client hello indicates the types
   of certificates the client is able to process when provided by the
   server in a subsequent certificate payload.  If the client hello
   indicates support of raw public keys in the 'server_certificate_type'
   extension and the server chooses to use raw public keys then the TLS
   server MUST place the SubjectPublicKeyInfo structure into the
   Certificate payload.  With the 'server_certificate_type' in the
   server hello the TLS server indicates the certificate type carried in
   the Certificate payload.  This additional indication allows to avoid
   parsing ambiguities since the Certificate payload may contain either
   the X.509 certificate or a SubjectPublicKeyInfo structure.  Note that
   only a single value is permitted in the 'server_certificate_type'
   extension when carried in the server hello.

4.3.  Client Authentication

   Authentication of the TLS client to the TLS server is supported only
   through authentication of the received client SubjectPublicKeyInfo
   via an out-of-band method.

5.  Examples

   Figure 6, Figure 7, and Figure 8 illustrate example exchanges.  Note
   that TLS ciphersuites using a Diffie-Hellman exchange offering
   forward secrecy can be used with raw public keys although we do not
   show the information exchange at that level with the subsequent
   message flows.

5.1.  TLS Server uses Raw Public Key

   This section shows an example where the TLS client indicates its
   ability to receive and validate raw public keys from the server.  In
   our example the client is quite restricted since it is unable to
   process other certificate types sent by the server.  It also does not
   have credentials at the TLS layer it could send to the server and
   therefore omits the 'client_certificate_type' extension.  Hence, the
   client only populates the 'server_certificate_type' extension with
   the raw public key type, as shown in [1].

   When the TLS server receives the client hello it processes the
   extension.  Since it has a raw public key it indicates in [2] that it
   had chosen to place the SubjectPublicKeyInfo structure into the
   Certificate payload [3].

   The client uses this raw public key in the TLS handshake together
   with an out-of-band validation technique, such as DANE, to verify it.





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client_hello,
server_certificate_type=(RawPublicKey) // [1]
                       ->
                       <- server_hello,
                          server_certificate_type=(RawPublicKey), // [2]
                          certificate, // [3]
                          server_key_exchange,
                          server_hello_done

client_key_exchange,
change_cipher_spec,
finished               ->

                       <- change_cipher_spec,
                          finished

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


     Figure 6: Example with Raw Public Key provided by the TLS Server.

5.2.  TLS Client and Server use Raw Public Keys

   This section shows an example where the TLS client as well as the TLS
   server use raw public keys.  This is one of the use case envisioned
   for smart object networking.  The TLS client in this case is an
   embedded device that is configured with a raw public key for use with
   TLS and is also able to process raw public keys sent by the server.
   Therefore, it indicates these capabilities in [1].  As in the
   previously shown example the server fulfills the client's request,
   indicates this via the "RawPublicKey" value in the
   server_certificate_type payload [2], and provides a raw public key
   into the Certificate payload back to the client (see [3]).  The TLS
   server, however, demands client authentication and therefore a
   certificate_request is added [4].  The certificate_type payload in
   [5] indicates that the TLS server accepts raw public keys.  The TLS
   client, who has a raw public key pre-provisioned, returns it in the
   Certificate payload [6] to the server.













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client_hello,
client_certificate_type=(RawPublicKey) // [1]
server_certificate_type=(RawPublicKey) // [1]
                         ->
                         <-  server_hello,
                             server_certificate_type=(RawPublicKey)//[2]
                             certificate, // [3]
                             client_certificate_type=(RawPublicKey)//[5]
                             certificate_request, // [4]
                             server_key_exchange,
                             server_hello_done

certificate, // [6]
client_key_exchange,
change_cipher_spec,
finished                  ->

                         <- change_cipher_spec,
                            finished

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


   Figure 7: Example with Raw Public Key provided by the TLS Server and
                                the Client.

5.3.  Combined Usage of Raw Public Keys and X.509 Certificate

   This section shows an example combining raw public keys and X.509
   certificates.  The client uses a raw public key for client
   authentication and the server provides an X.509 certificate.  This
   exchange starts with the client indicating its ability to process
   X.509 certificates and raw public keys, if provided by the server.
   Additionally, the client indicates that is has a raw public key for
   client-side authentication (see [1]).  The server provides the X.509
   certificate in [3] with the indication present in [2].  For client
   authentication the server indicates in [4] that it selected the raw
   public key format and requests a certificate from the client in [5].
   The TLS client provides a raw public key in [6] after receiving and
   processing the TLS server hello message.











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client_hello,
server_certificate_type=(X.509, RawPublicKey)
client_certificate_type=(RawPublicKey) // [1]
                         ->
                         <-  server_hello,
                             server_certificate_type=(X.509)//[2]
                             certificate, // [3]
                             client_certificate_type=(RawPublicKey)//[4]
                             certificate_request, // [5]
                             server_key_exchange,
                             server_hello_done
certificate, // [6]
client_key_exchange,
change_cipher_spec,
finished                  ->

                          <- change_cipher_spec,
                             finished

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


                   Figure 8: Hybrid Certificate Example.

6.  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 naturally smaller than an entire
   certificate.  There are also advantages from a code size point of
   view for parsing and processing these keys.  The cryptographic
   procedures for associating 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.  Without a secure binding between
   identifier and key, the protocol will be vulnerable to man-in-the-
   middle attacks.  This document assumes that such binding can be made
   out-of-band and we list a few examples in Section 1.  DANE [RFC6698]
   offers one such approach.  In order to address these vulnerabilities,
   specifications that make use of the extension need to specify how the
   identifier and public key are bound.  In addition to ensuring the
   binding is done out-of-band an implementation also needs to check the
   status of that binding.

   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



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   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.

   An attacker might try to influence the handshake exchange to make the
   parties select different certificate types than they would normally
   choose.

   For this attack, an attacker must actively change one or more
   handshake messages.  If this occurs, the client and server will
   compute different values for the handshake message hashes.  As a
   result, the parties will not accept each others' Finished messages.
   Without the master_secret, the attacker cannot repair the Finished
   messages, so the attack will be discovered.

7.  IANA Considerations

   IANA is asked to register a new value in the "TLS Certificate Types"
   registry of Transport Layer Security (TLS) Extensions
   [TLS-Certificate-Types-Registry], as follows:


   Value: 2
   Description: Raw Public Key
   Reference: [[THIS RFC]]


   This document asks IANA to allocate two new TLS extensions,
   "client_certificate_type" and "server_certificate_type", from the TLS
   ExtensionType registry defined in [RFC5246].  These extensions are
   used in both the client hello message and the server hello message.
   The new extension type is used for certificate type negotiation.  The
   values carried in these extensions are taken from the TLS Certificate
   Types registry [TLS-Certificate-Types-Registry].

8.  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.





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   We would like to thank the following persons for their review
   comments: Martin Rex, Bill Frantz, Zach Shelby, Carsten Bormann,
   Cullen Jennings, Rene Struik, Alper Yegin, Jim Schaad, Barry Leiba,
   Paul Hoffman, Robert Cragie, Nikos Mavrogiannopoulos, Phil Hunt, John
   Bradley, Klaus Hartke, Stefan Jucker, Kovatsch Matthias, Daniel Kahn
   Gillmor, Peter Sylvester, Hauke Mehrtens, Alexey Melnikov, Stephen
   Farrell, Richard Barnes, and James Manger.  Nikos Mavrogiannopoulos
   contributed the design for re-using the certificate type registry.
   Barry Leiba contributed guidance for the IANA consideration text.
   Stefan Jucker, Kovatsch Matthias, and Klaus Hartke provided
   implementation feedback regarding the SubjectPublicKeyInfo structure.

   Christer Holmberg provided the General Area (Gen-Art) review, Yaron
   Sheffer provided the Security Directorate (SecDir) review, Bert
   Greevenbosch provided the Applications Area Directorate review, and
   Linda Dunbar provided the Operations Directorate review.

   We would like to thank our TLS working group chairs, Eric Rescorla
   and Joe Salowey, for their guidance and support.  Finally, we would
   like to thank Sean Turner, who is the responsible security area
   director for this work for his review comments and suggestions.

9.  References

9.1.  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.

   [RFC3279]  Bassham, L., Polk, W., and R. Housley, "Algorithms and
              Identifiers for the Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 3279, April 2002.

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

   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
              "Elliptic Curve Cryptography Subject Public Key
              Information", RFC 5480, March 2009.

   [TLS-Certificate-Types-Registry]




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              "TLS Certificate Types Registry", February 2013,
              <http://www.iana.org/assignments/
              tls-extensiontype-values#tls-extensiontype-values-2>.

   [X.690]    "Information technology - ASN.1 encoding rules: >
              Specification of Basic Encoding Rules (BER), Canonical >
              Encoding Rules (CER) and Distinguished Encoding Rules >
              (DER).", RFC 5280, 2002.

9.2.  Informative References

   [ASN.1-Dump]
              Gutmann, P., "ASN.1 Object Dump Program", February 2013,
              <http://www.cs.auckland.ac.nz/~pgut001/>.

   [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]
              Shelby, Z., Hartke, K., and C. Bormann, "Constrained
              Application Protocol (CoAP)", draft-ietf-core-coap-18
              (work in progress), June 2013.

   [I-D.ietf-tls-cached-info]
              Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension", draft-ietf-tls-
              cached-info-15 (work in progress), October 2013.

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

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, August 2012.

Appendix A.  Example Encoding

   For example, the hex sequence shown in Figure 9 describes a
   SubjectPublicKeyInfo structure inside the certificate payload.









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          0     1     2     3     4     5     6     7     8     9
      +------+-----+-----+-----+-----+-----+-----+-----+-----+-----
   1  | 0x30, 0x81, 0x9f, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48,
   2  | 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x01, 0x05, 0x00, 0x03, 0x81,
   3  | 0x8d, 0x00, 0x30, 0x81, 0x89, 0x02, 0x81, 0x81, 0x00, 0xcd,
   4  | 0xfd, 0x89, 0x48, 0xbe, 0x36, 0xb9, 0x95, 0x76, 0xd4, 0x13,
   5  | 0x30, 0x0e, 0xbf, 0xb2, 0xed, 0x67, 0x0a, 0xc0, 0x16, 0x3f,
   6  | 0x51, 0x09, 0x9d, 0x29, 0x2f, 0xb2, 0x6d, 0x3f, 0x3e, 0x6c,
   7  | 0x2f, 0x90, 0x80, 0xa1, 0x71, 0xdf, 0xbe, 0x38, 0xc5, 0xcb,
   8  | 0xa9, 0x9a, 0x40, 0x14, 0x90, 0x0a, 0xf9, 0xb7, 0x07, 0x0b,
   9  | 0xe1, 0xda, 0xe7, 0x09, 0xbf, 0x0d, 0x57, 0x41, 0x86, 0x60,
   10 | 0xa1, 0xc1, 0x27, 0x91, 0x5b, 0x0a, 0x98, 0x46, 0x1b, 0xf6,
   11 | 0xa2, 0x84, 0xf8, 0x65, 0xc7, 0xce, 0x2d, 0x96, 0x17, 0xaa,
   12 | 0x91, 0xf8, 0x61, 0x04, 0x50, 0x70, 0xeb, 0xb4, 0x43, 0xb7,
   13 | 0xdc, 0x9a, 0xcc, 0x31, 0x01, 0x14, 0xd4, 0xcd, 0xcc, 0xc2,
   14 | 0x37, 0x6d, 0x69, 0x82, 0xd6, 0xc6, 0xc4, 0xbe, 0xf2, 0x34,
   15 | 0xa5, 0xc9, 0xa6, 0x19, 0x53, 0x32, 0x7a, 0x86, 0x0e, 0x91,
   16 | 0x82, 0x0f, 0xa1, 0x42, 0x54, 0xaa, 0x01, 0x02, 0x03, 0x01,
   17 | 0x00, 0x01


      Figure 9: Example SubjectPublicKeyInfo Structure Byte Sequence.

   The decoded byte-sequence shown in Figure 9 (for example using
   Peter's ASN.1 decoder [ASN.1-Dump]) illustrates the structure, as
   shown in Figure 10.


   Offset  Length   Description
   -------------------------------------------------------------------
      0     3+159:   SEQUENCE {
      3      2+13:     SEQUENCE {
      5       2+9:      OBJECT IDENTIFIER Value (1 2 840 113549 1 1 1)
                 :             PKCS #1, rsaEncryption
     16       2+0:      NULL
                 :      }
     18     3+141:    BIT STRING, encapsulates {
     22     3+137:      SEQUENCE {
     25     3+129:        INTEGER Value (1024 bit)
    157       2+3:        INTEGER Value (65537)
                 :        }
                 :      }
                 :    }


      Figure 10: Decoding of Example SubjectPublicKeyInfo Structure.





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Authors' Addresses

   Paul Wouters (editor)
   Red Hat

   Email: paul@nohats.ca


   Hannes Tschofenig (editor)
   Cambridge  CBI 9NJ
   UK

   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at


   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









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