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Network Working Group                                       P. Porambage
Internet-Draft                                       University of Oulou
Intended status: Standards Track                              C. Schmitt
Expires: August 18, 2014                            University of Zurich
                                                               A. Gurtov
                                                        Aalto University
                                                               S. Gerdes
                                                 Universitaet Bremen TZI
                                                       February 14, 2014


    X.509 Public Key Infrastructure Certificates for the Constrained
                      Application Protocol (CoAP)
                   <draft-porambage-core-ace-x509-00>

Abstract

   The Constrained Application Protocol (CoAP) is a web transfer
   protocol designed for resource limited nodes in constrained networks.
   For securing the protocol, CoAP defines a binding to Datagram
   Transport Layer Security (DTLS) with four security modes.  One of
   them is the Certificate mode where the device has an asymmetric key
   pair with an X.509 certificate.  However, the intrinsic properties of
   x.509 certificates impede the application on the resource constrained
   nodes.  This draft describes the necessary adjustments and derives a
   modified profile for X.509 certificates to cope with the resource
   limitations of low-power low-performing devices

Status of this Memo

   This Internet-Draft is submitted to IETF 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-
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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 August 18, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the



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   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.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Document Structure  . . . . . . . . . . . . . . . . . . . . 3

   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3

   3.  Design Requirements . . . . . . . . . . . . . . . . . . . . . . 4

   4.  Overview of the approach  . . . . . . . . . . . . . . . . . . . 4

   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4

   6.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 5

   7.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 5

   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     8.1.  Norminative References  . . . . . . . . . . . . . . . . . . 5
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 6

   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6
















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1.  Introduction

   The Constrained Application Protocol (CoAP) [I-D.ietf-core-coap] is
   proposed as a lightweight alternative for HTTP protocol, in order to
   support web services while realizing the REST architecture on top of
   the most constrained nodes and networks.  CoAP is designed for the
   special requirements of this constrained environments, especially
   considering energy, building automation and other machine-to-machine
   (M2M) applications.

   CoAP defines a binding to Datagram Transport Layer Security (DTLS)
   [RFC6347] and specifies four security modes: NoSec, PreSharedKey,
   RawPublicKey and Certificate.  In the Certificate Mode, the device
   has an X.509 certificate [RFC5280], which binds the public key of the
   device to its Authority name and is signed by a common trust root.

   Complex asymmetric algorithms like RSA use a lot of resources such as
   processing power and memory.  Devices may have to dedicate the major
   portion of these resources on security algorithms instead of spending
   them on the application they are intended for.  Therefore, it is
   necessary to adapt a low cost solution for the DTLS Certificate mode
   in CoAP.

   Mismatches of X.509 certificates in their original formats; According
   to [RFC5280] the content of X.509 certificates is mainly composed of
   three parts: TBSCertificate, Signature Algorithm and Signature Value.
   We would like to focus on the internal configurations and attributes
   of TBSCertificate component.  The standard X.509 certificates use RSA
   public key algorithm and keys as the public key infrastructure.
   According to the definitions of Classes of devices as given in
   [I-D.ietf-lwig-terms] class 0 and 1 are the most constrained devices.
   These low performing devices are not capable of handling RSA PKI
   algorithms due to their limited memory capacities and processing
   capabilities.

1.1.  Document Structure

   Section 2 mentions conventions used in this draft.  Afterwards the
   assumed design requirements are briefly mentioned in Section 3.
   Section 4 describes the proposed approach using X.509 public key
   infrastructure (PKI) certificates for CoAP,followed by security
   considerations.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this



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   document are to be interpreted as described in [RFC2119].


3.  Design Requirements

   The key design goal is to profile the content and operations of X.509
   certificates in such a way to balance the resource constraints of the
   devices along with the security requirements.  Therefore, we
   emphasize the following design requirements: Low memory consumption;
   Less complexity of mathematical operations for authentication and
   authorization processes; Support interoperability among different
   vendor devices.  Alternatively, we focus on profiling X.509
   certificates according to the specifications of CoAP enabled devices.


4.  Overview of the approach

   It is obvious that the utilization of X.509 certificates with RSA
   public key algorithm would not be a lightweight solution.  We can
   adjust the size and the complexity of the certificate by changing the
   attributes in TBSCertificate part in the original certificates.
   Elliptic Curve Cryptography (ECC) algorithms would be suitable
   candidate for PKI replacement in X.509 certificates.  Alternatively
   this could be reusable for digital signature in the certificates too.
   For instance the algorithm in Elliptic Curve Qu-Vanstone Implicit
   Certificate Scheme (ECQV) would be a feasible solution for this[1].


5.  Security Considerations

   The following security goals are addressed by the key idea presented
   in this draft similar to proposed considerations in
   [I-D.draft-schmitt-two-way-authentication-for-iot]:

   Authenticity

      Recipients of a message can identify their communication partners
      and can detect if the sender information has been forged.

   Integrity

      Communication partners can detect changes to a message during
      transmission.








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   Confidentiality

      Attackers cannot gain knowledge about the content of a secured
      message.



6.  Acknowledgement

   This work has been supported by Tekes under Massive Scale Machine-to-
   Machine Service (MAMMotH) project and Academy of Finland project
   SEMOHealth.

   The ongoing work is supported partially by the SmartenIT [2] and the
   FLAMINGO [3] projects, funded by the EU FP7 Program under Contract
   No.  FP7-2012-ICT-317846 and No.  FP7-2012-ICT-318488, respectively.


7.  Formal Syntax

   CoAP - Constrained Application Protocol

   DTLS - Datagram Transport Layer Security

   ECC - Elliptic Curve Cryptography

   ECQV - Elliptic Curve Qu-Vanstone Implicit Certificate Scheme

   IETF - Internet Engineering Task Force

   M2M - Machine-to-Machine

   PKI - Public Key Infrastructure


8.  References

8.1.  Norminative References

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

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List



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              (CRL) Profile", RFC 5280, May 2008.

   [I-D.ietf-core-coap]
              Shelby, Z., Hartke, K., and C. Bormann, "Constrained
              Application Protocol (CoAP), http://www.ietf.org/
              internet-drafts/draft-ietf-core-coap-18.txt",
              draft-ietf-core-coap-18 (work in progress), March 2013.

   [I-D.ietf-lwig-terms]
              Bormann, C. and M. Ersue, "Terminology for Constrained
              Node Networks, http://www.ietf.org/internet-drafts/
              draft-ietf-lwig-terms-00.txt", draft-bormann-lwig-terms-00
              (work in progress), November 2012.

   [I-D.draft-schmitt-two-way-authentication-for-iot]
              Schmitt, C. and B. Stiller, "DTLS-based Security with two-
              way Authentication for IoT, http://www.ietf.org/id/
              draft-schmitt-two-way-authentication-for-iot-02.txt",
              draft-schmitt-two-way-authentication-for-iot-02 (work in
              progress), February 2014.

8.2.  Informative References

   [1]        "Elliptic Curve Qu-Vanstone Implicit Certificate Scheme
              (ECQV), v0.97,
              http://www.secg.org/download/aid-785/sec4-0.97.pdf",
              SEC 4, March 2011.

   [2]        SmartenIT Consortium, "Socially-aware Management of New
              Overlay Application Traffic combined with Energy
              Efficiency in the Internet (SmartenIT),
              http://www.smartenit.eu/", 20103.

   [3]        Flamingo Consortium, "FLAMINGO - Management of the Future
              Internet, http://www.fp7-flamingo.eu/", 2013.


Authors' Addresses

   Pawani Porambage
   University of Oulou
   P.O. Box 4500
   Oulu  90014
   Finland

   Email: pporamba@ee.oulu.fi





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   Corinna Schmitt
   Univerity of Zurich
   Department for Informatics
   Communication Systems Group
   Binzmuehlestrasse 14
   Zurich  8050
   Switzerland

   Email: schmitt@ifi.uzh.ch


   Andrei Gurtov
   Aalto University
   Otakaari 1
   Espoo  02150
   Finland

   Email: gurtov@hiit.fi


   Stefanie Gerdes
   Universitaet Bremen TZI
   Postfach 330440
   Bremen  28359
   Germany

   Email: gerdes@tzi.org
























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