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Versions: 00 01

Network Working Group                                            S. Raza
Internet-Draft                                               J. Hoeglund
Intended status: Standards Track                                 RISE AB
Expires: January 14, 2021                                    G. Selander
                                                             J. Mattsson
                                                             Ericsson AB
                                                              M. Furuhed
                                                             Nexus Group
                                                           July 13, 2020


                   CBOR Profile of X.509 Certificates
               draft-mattsson-cose-cbor-cert-compress-01

Abstract

   This document specifies a CBOR encoding/compression of RFC 7925
   profiled certificates.  By using the fact that the certificates are
   profiled, the CBOR certificate compression algorithms can in many
   cases compress RFC 7925 profiled certificates with over 50%. This
   document also specifies COSE headers for CBOR encoded certificates as
   well as the use of the CBOR certificate compression algorithm with
   TLS Certificate Compression in TLS 1.3 and DTLS 1.3.

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 https://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 January 14, 2021.

Copyright Notice

   Copyright (c) 2020 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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   (https://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.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   4
   3.  CBOR Encoding . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Deployment settings . . . . . . . . . . . . . . . . . . . . .   7
   5.  Expected Certificate Sizes  . . . . . . . . . . . . . . . . .   8
   6.  Native CBOR Certificates  . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  CBOR Certificate Types Registry . . . . . . . . . . . . .   9
     8.2.  CBOR Certificate Signature Algorithms Registry  . . . . .   9
     8.3.  CBOR Certificate Public Key Algorithms Registry . . . . .  10
     8.4.  COSE Header Parameters Registry . . . . . . . . . . . . .  10
     8.5.  TLS Certificate Compression Algorithm IDs Registry  . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  Example CBOR Certificates  . . . . . . . . . . . . .  13
     A.1.  Example X.509 Certificate . . . . . . . . . . . . . . . .  13
     A.2.  Example CBOR Certificate Compression  . . . . . . . . . .  15
     A.3.  Example Native CBOR Certificate . . . . . . . . . . . . .  15
   Appendix B.  X.509 Certificate Profile, ASN.1 . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   One of the challenges with deploying a Public Key Infrastructure
   (PKI) for the Internet of Things (IoT) is the size and encoding of
   X.509 public key certificates [RFC5280], since those are not
   optimized for constrained environments [RFC7228].  More compact
   certificate representations are desirable.  Due to the current PKI
   usage of X.509 certificates, keeping X.509 compatibility is necessary
   at least for a transition period.  However, the use of a more compact
   encoding with the Concise Binary Object Representation (CBOR)
   [RFC7049] reduces the certificate size significantly which has known
   performance benefits in terms of decreased communication overhead,
   power consumption, latency, storage, etc.





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   CBOR is a data format designed for small code size and small message
   size.  CBOR builds on the JSON data model but extends it by e.g.
   encoding binary data directly without base64 conversion.  In addition
   to the binary CBOR encoding, CBOR also has a diagnostic notation that
   is readable and editable by humans.  The Concise Data Definition
   Language (CDDL) [RFC8610] provides a way to express structures for
   protocol messages and APIs that use CBOR.  [RFC8610] also extends the
   diagnostic notation.

   CBOR data items are encoded to or decoded from byte strings using a
   type-length-value encoding scheme, where the three highest order bits
   of the initial byte contain information about the major type.  CBOR
   supports several different types of data items, in addition to
   integers (int, uint), simple values (e.g. null), byte strings (bstr),
   and text strings (tstr), CBOR also supports arrays [] of data items,
   maps {} of pairs of data items, and sequences of data items.  For a
   complete specification and examples, see [RFC7049], [RFC8610], and
   [RFC8742].

   RFC 7925 [RFC7925] specifies a certificate profile for Internet of
   Things deployments which can be applied for lightweight certificate
   based authentication with e.g.  TLS [RFC8446], DTLS
   [I-D.ietf-tls-dtls13], COSE [RFC8152], or EDHOC
   [I-D.ietf-lake-edhoc].  This document specifies the CBOR encoding/
   compression of RFC 7925 profiled X.509 certificates based on
   [X.509-IoT].  Two variants are defined using exactly the same CBOR
   encoding and differing only in what is being signed:

   o  The CBOR compressed X.509 certificate, which can be decompressed
      into a certificate that can be verified by code compatible with
      RFC 7925.

   o  The "native" CBOR encoded certificate, which further optimizes the
      performance in constrained environments but is not backwards
      compatible with RFC 7925, see Section 6.

   Other work has looked at reducing the size of X.509 certificates.
   The purpose of this document is to stimulate a discussion on CBOR
   based certificates: what field values (in particular for
   'issuer'/'subject') are relevant for constrained IoT applications,
   what is the maximum compression that can be expected with CBOR, and
   what is the right trade-off between compactness and generality.

   This document specifies COSE headers for use of the CBOR certificate
   encoding with COSE.  The document also specifies the CBOR certificate
   compression algorithm for use as TLS Certificate Compression with TLS
   1.3 and DTLS 1.3.




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2.  Notational Conventions

   The key words "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.

   This specification makes use of the terminology in [RFC7228].

3.  CBOR Encoding

   This section specifies the content and encoding for CBOR
   certificates, with the overall objective to produce a very compact
   representation of the certificate profile defined in [RFC7925].  The
   CBOR certificate can be either a CBOR compressed X.509 certificate,
   in which case the signature is calculated on the DER encoded ASN.1
   data in the X.509 certificate, or a native CBOR certificate, in which
   case the signature is calculated directly on the CBOR encoded data
   (see Section 6).  In both cases the certificate content is adhering
   to the restrictions given by [RFC7925].  The corresponding ASN.1
   schema is given in Appendix A.

   The encoding and compression has several components including: ASN.1
   DER and base64 encoding are replaced with CBOR encoding, static
   fields are elided, and elliptic curve points are compressed.  The
   X.509 fields and their CBOR encodings are listed below.  Combining
   these different components reduces the certificate size
   significantly, which is not possible with general purpose
   compressions algorithms, see Figure 1.

   CBOR certificates are defined in terms of RFC 7925 profiled X.509
   certificates:

   o  version.  The 'version' field is known (fixed to v3), and is
      omitted in the CBOR encoding.

   o  serialNumber.  The 'serialNumber' field is encoded as a CBOR byte
      string.  This allows encoding of all lengths with minimal
      overhead.

   o  signature.  The 'signature' field is always the same as the
      'signatureAlgorithm' field and always omitted from the CBOR
      encoding.

   o  issuer.  In the general case, the Distinguished Name is encoded as
      CBOR map, but if only CN is present the value can be encoded as a
      single text value.



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   o  validity.  The 'notBefore' and 'notAfter' UTCTime fields are ASCII
      string of the form "yymmddHHMMSSZ".  They are encoded as the
      unsigned integers using the following invertible encoding
      (Horner's method with different bases).  The resulting integer n
      always fit in a 32 bit usigned integer.

      n = SS + 60 * (MM + 60 * (HH + 24 * (dd + 32 * (mm + 13 * yy))))

      Decoding can be done by a succession of modulo and substraction
      operations.  I.e.  SS = n mod 60, MM = ((n - SS) / 60) mod 60,
      etc.

   o  subject.  The 'subject' field is restricted to specifying the
      value of the common name.  By RFC 7925 an IoT subject is
      identified by either an EUI-64 for clients, or by a FQDN for
      servers.  An EUI-64 mapped from a 48-bit MAC address is encoded as
      a CBOR byte string of length 6.  Other EUI-64 is encoded as a CBOR
      byte string of length 8.  A FQDN is encoded as a CBOR text string.

   o  subjectPublicKeyInfo.  If the 'algorithm' field is the default
      (id-ecPublicKey and prime256v1), it is omitted in the CBOR
      encoding, otherwise it is included in the
      subjectPublicKeyInfo_algorithm field encoded as an int, (see
      Section 8).  The 'subjectPublicKey' is encoded as a CBOR byte
      string.  Public keys of type id-ecPublicKey are point compressed
      as defined in Section 2.3.3 of [SECG].

   o  extensions.  The 'extensions' field is encoded as a CBOR array
      where each extension is represented with an int.  This is the most
      compact representation of the allowed extensions.  The extensions
      mandated to be supported by RFC 7925 is encodeded as specified
      below, where critical extensions are encoded with a negative sign.
      TODO: need to make things mod 3 instead.

      I.e. non-critical keyUsage keyAgreement is encoded as 5, critical
      basicConstraints cA is encodes as -3, and non-criticical
      extKeyUsage id-kp-codeSigning + id-kp-OCSPSigning is encoded as
      22.

      If subjectAltName is present, the value is placed at the end of
      the array encoded as a byte or text string following the encoding
      rules for the subject field.  If the array contains a single int,
      extensions is encoded as the int instead of an array.

      subjectAltName = 1

      basicConstraints = 2 + cA




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      keyUsage = 3 + digitalSignature
               + 2 * keyAgreement + 4 * keyCertSign

      extKeyUsage = 10 + id-kp-serverAuth + 2 * id-kp-clientAuth
                  + 4 * id-kp-codeSigning + 8 * id-kp-OCSPSigning

   o  signatureAlgorithm.  If the 'signatureAlgorithm' field is the
      default (ecdsa-with-SHA256) it is omitted in the CBOR encoding,
      otherwise it is included in the signatureAlgorithm field encoded
      as an CBOR int (see Section 8).

   o  signatureValue.  Since the signature algorithm and resulting
      signature length are known, padding and extra length fields which
      are present in the ASN.1 encoding are omitted and the
      'signatureValue' field is encoded as a CBOR byte string.  For
      native CBOR certificates the signatureValue is calculated over the
      certificate CBOR sequence excluding the signatureValue.

   In addition to the above fields present in X.509, the CBOR ecoding
   introduces an additional field

   o  type.  A CBOR int used to indicate the type of CBOR certificate.
      Currently type can be a native CBOR certificate (type = 0) or a
      CBOR compressed X.509 certificates (type = 1), see Section 8.

   The following Concise Data Definition Language (CDDL) defines a
   group, the elements of which are to be used in an unadorned CBOR
   Sequence [RFC8742].  The member names therefore only have documentary
   value.

   certificate = (
      type : int,
      serialNumber : bytes,
      issuer : { + int => bytes } / text,
      validity_notBefore: uint,
      validity_notAfter: uint,
      subject : text / bytes
      subjectPublicKey : bytes
      extensions : [ *4 int, ? text / bytes ] / int,
      signatureValue : bytes,
      ? ( signatureAlgorithm : int,
          subjectPublicKeyInfo_algorithm : int )
   )

   The signatureValue for native CBOR certificates is calculated over
   the CBOR sequence:





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   (
      type : int,
      serialNumber : bytes,
      issuer : { + int => bytes } / text,
      validity_notBefore: uint,
      validity_notAfter: uint,
      subject : text / bytes
      subjectPublicKey : bytes
      extensions : [ *4 int, ? text / bytes ] / int,
      ? ( signatureAlgorithm : int,
          subjectPublicKeyInfo_algorithm : int )
   )

   TODO - Specify exactly how issuer is encoded into a map / text and
   back again.  This is a compromise between compactness and complete
   generality.

4.  Deployment settings

   CBOR certificates can be deployed with legacy X.509 certificates and
   CA infrastructure.  In order to verify the signature, the CBOR
   certificate is used to recreate the original X.509 data structure to
   be able to verify the signature.

   For protocols like TLS/DTLS 1.2, where the handshake is sent
   unencrypted, the actual encoding and compression can be done at
   different locations depending on the deployment setting.  For
   example, the mapping between CBOR certificate and standard X.509
   certificate can take place in a 6LoWPAN border gateway which allows
   the server side to stay unmodified.  This case gives the advantage of
   the low overhead of a CBOR certificate over a constrained wireless
   links.  The conversion to X.509 within an IoT device will incur a
   computational overhead, however, measured in energy this is
   negligible compared to the reduced communication overhead.

   For the setting with constrained server and server-only
   authentication, the server only needs to be provisioned with the CBOR
   certificate and does not perform the conversion to X.509.  This
   option is viable when client authentication can be asserted by other
   means.

   For protocols like IKEv2, TLS/DTLS 1.3, and EDHOC, where certificates
   are encrypted, the proposed encoding needs to be done fully end-to-
   end, through adding the encoding/decoding functionality to the
   server.






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5.  Expected Certificate Sizes

   The CBOR encoding of the sample certificate given in Appendix A
   results in the numbers shown in Figure 1.  After RFC 7925 profiling,
   most duplicated information has been removed, and the remaining text
   strings are minimal in size.  Therefore the further size reduction
   reached with general compression mechanisms will be small, mainly
   corresponding to making the ASN.1 endcoding more compact.  The zlib
   number was calculated with zlib-flate.

   zlib-flate -compress < cert.der > cert.compressed

   +------------------+--------------+------------+--------------------+
   |                  |   RFC 7925   |    zlib    |  CBOR Certificate  |
   +------------------+---------------------------+--------------------+
   | Certificate Size |     314      |     295    |         136        |
   +------------------+--------------+------------+--------------------+

             Figure 1: Comparing Sizes of Certificates (bytes)

6.  Native CBOR Certificates

   The difference between CBOR compressed X.509 certificate and native
   CBOR certificate is that the signature is calculated over the CBOR
   encoding rather than the DER encoded ASN.1 data.  This removes
   entirely the need for ASN.1 DER and base64 encoding which reduces the
   processing in the authenticating devices, and avoids known
   complexities with these encodings.

   Native CBOR certificates can be applied in devices that are only
   required to authenticate to native CBOR certificate compatible
   servers.  This is not a major restriction for many IoT deployments,
   where the parties issuing and verifying certificates can be a
   restricted ecosystem which not necessarily involves public CAs.

   CBOR compressed X.509 certificates provides an intermediate step
   between RFC 7925 profiled X.509 certificates and native CBOR
   certificates: An implementation of CBOR compressed X.509 certificates
   contains both the CBOR encoding of the X.509 certificate and the
   signature operations sufficient for native CBOR certificates.

7.  Security Considerations

   The CBOR profiling of X.509 certificates does not change the security
   assumptions needed when deploying standard X.509 certificates but
   decreases the number of fields transmitted, which reduces the risk
   for implementation errors.




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   Conversion between the certificate formats can be made in constant
   time to reduce risk of information leakage through side channels.

   The mechanism in this draft does not reveal any additional
   information compared to X.509.  Because of difference in size, it
   will be possible to detect that this profile is used.  The gateway
   solution described in Section 4 requires unencrypted certificates and
   is not recommended.

8.  IANA Considerations

   For all items, the 'Reference' field points to this document.

8.1.  CBOR Certificate Types Registry

   IANA has created a new registry titled "CBOR Certificate Types" under
   the new heading "CBOR Certificate".  The registration procedure is
   "Expert Review".  The columns of the registry are Value, Description,
   and Reference, where Value is an integer and the other columns are
   text strings.  The initial contents of the registry are:

             +-------+---------------------------------------+
             | Value | Description                           |
             +=======+=======================================+
             |     0 | Native CBOR Certificate.              |
             |     1 | CBOR Compressed X.509 Certificate     |
             +-------+---------------------------------------+

                     Figure 2: CBOR Certificate Types

8.2.  CBOR Certificate Signature Algorithms Registry

   IANA has created a new registry titled "CBOR Certificate Signature
   Algorithms" under the new heading "CBOR Certificate".  The
   registration procedure is "Expert Review".  The columns of the
   registry are Value, X.509 Algorithm, and Reference, where Value is an
   integer and the other columns are text strings.  The initial contents
   of the registry are:













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             +-------+---------------------------------------+
             | Value | X.509 Signature Algorithm             |
             +=======+=======================================+
             |     0 | ecdsa-with-SHA384                     |
             |     1 | ecdsa-with-SHA512                     |
             |     2 | id-ecdsa-with-shake128                |
             |     3 | id-ecdsa-with-shake256                |
             |     4 | id-Ed25519                            |
             |     5 | id-Ed448                              |
             +-------+---------------------------------------+

              Figure 3: CBOR Certificate Signature Algorithms

8.3.  CBOR Certificate Public Key Algorithms Registry

   IANA has created a new registry titled "CBOR Certificate Public Key
   Algorithms" under the new heading "CBOR Certificate".  The
   registration procedure is "Expert Review".  The columns of the
   registry are Value, X.509 Algorithm, and Reference, where Value is an
   integer and the other columns are text strings.  The initial contents
   of the registry are:

             +-------+---------------------------------------+
             | Value | X.509 Public Key Algorithm            |
             +=======+=======================================+
             |     0 | id-ecPublicKey + prime384v1           |
             |     1 | id-ecPublicKey + prime512v1           |
             |     2 | id-X25519                             |
             |     3 | id-X448                               |
             |     4 | id-Ed25519                            |
             |     5 | id-Ed448                              |
             +-------+---------------------------------------+

             Figure 4: CBOR Certificate Public Key Algorithms

8.4.  COSE Header Parameters Registry

   This document registers the following entries in the "COSE Header
   Parameters" registry under the "CBOR Object Signing and Encryption
   (COSE)" heading.  The formatting and processing are the same as the
   corresponding x5chain and x5u defined in [I-D.ietf-cose-x509] except
   that the certificates are CBOR encoded instead of DER encoded.









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   +-----------+-------+----------------+---------------------+
   | Name      | Label | Value Type     | Description         |
   +===========+=======+================+=====================+
   | CBORchain | TBD1  | COSE_CBOR_Cert | An ordered chain of |
   |           |       |                | CBOR certificates   |
   +-----------+-------+----------------+---------------------+
   | CBORu     | TBD2  | uri            | URI pointing to a   |
   |           |       |                | CBOR certificate    |
   +-----------+-------+----------------+---------------------+

8.5.  TLS Certificate Compression Algorithm IDs Registry

   This document registers the following entry in the "Certificate
   Compression Algorithm IDs" registry under the "Transport Layer
   Security (TLS) Extensions" heading.

   +------------------+------------------------------+
   | Algorithm Number | Description                  |
   +==================+==============================+
   | TBD3             | CBOR Certificate             |
   +------------------+------------------------------+

9.  References

9.1.  Normative References

   [I-D.ietf-tls-certificate-compression]
              Ghedini, A. and V. Vasiliev, "TLS Certificate
              Compression", draft-ietf-tls-certificate-compression-10
              (work in progress), January 2020.

   [I-D.ietf-tls-dtls13]
              Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", draft-ietf-tls-dtls13-38 (work in progress), May
              2020.

   [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>.

   [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
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.




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   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [RFC7925]  Tschofenig, H., Ed. and T. Fossati, "Transport Layer
              Security (TLS) / Datagram Transport Layer Security (DTLS)
              Profiles for the Internet of Things", RFC 7925,
              DOI 10.17487/RFC7925, July 2016,
              <https://www.rfc-editor.org/info/rfc7925>.

   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.

   [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>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/info/rfc8610>.

   [RFC8742]  Bormann, C., "Concise Binary Object Representation (CBOR)
              Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
              <https://www.rfc-editor.org/info/rfc8742>.

9.2.  Informative References

   [I-D.ietf-cose-x509]
              Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Header parameters for carrying and referencing X.509
              certificates", draft-ietf-cose-x509-06 (work in progress),
              March 2020.

   [I-D.ietf-lake-edhoc]
              Selander, G., Mattsson, J., and F. Palombini, "Ephemeral
              Diffie-Hellman Over COSE (EDHOC)", draft-ietf-lake-
              edhoc-00 (work in progress), July 2020.







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   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <https://www.rfc-editor.org/info/rfc7228>.

   [SECG]     "Elliptic Curve Cryptography, Standards for Efficient
              Cryptography Group, ver. 2", 2009,
              <https://secg.org/sec1-v2.pdf>.

   [X.509-IoT]
              Forsby, F., Furuhed, M., Papadimitratos, P., and S. Raza,
              "Lightweight X.509 Digital Certificates for the Internet
              of Things.", Springer, Cham. Lecture Notes of the
              Institute for Computer Sciences, Social Informatics and
              Telecommunications Engineering, vol 242., July 2018,
              <https://doi.org/10.1007/978-3-319-93797-7_14>.

Appendix A.  Example CBOR Certificates

A.1.  Example X.509 Certificate

   Example of RFC 7925 profiled X.509 certificate parsed with OpenSSL.





























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   Certificate:
       Data:
           Version: 3 (0x2)
           Serial Number: 128269 (0x1f50d)
           Signature Algorithm: ecdsa-with-SHA256
           Issuer: CN=RFC test CA
           Validity
               Not Before: Jan  1 00:00:00 2020 GMT
               Not After : Feb  2 00:00:00 2021 GMT
           Subject: CN=01-23-45-FF-FE-67-89-AB
           Subject Public Key Info:
               Public Key Algorithm: id-ecPublicKey
                   Public-Key: (256 bit)
                   pub:
                       04:ae:4c:db:01:f6:14:de:fc:71:21:28:5f:dc:7f:
                       5c:6d:1d:42:c9:56:47:f0:61:ba:00:80:df:67:88:
                       67:84:5e:e9:a6:9f:d4:89:31:49:da:e3:d3:b1:54:
                       16:d7:53:2c:38:71:52:b8:0b:0d:f3:e1:af:40:8a:
                       95:d3:07:1e:58
                   ASN1 OID: prime256v1
                   NIST CURVE: P-256
           X509v3 extensions:
               X509v3 Key Usage:
                   Digital Signature
       Signature Algorithm: ecdsa-with-SHA256
            30:44:02:20:37:38:73:ef:87:81:b8:82:97:ef:23:5c:1f:ac:
            cf:62:da:4e:44:74:0d:c2:a2:e6:a3:c6:c8:82:a3:23:8d:9c:
            02:20:3a:d9:35:3b:a7:88:68:3b:06:bb:48:fe:ca:16:ea:71:
            17:17:34:c6:75:c5:33:2b:2a:f1:cb:73:38:10:a1:fc


   The DER encoding of the above certificate is 314 bytes.

   308201363081DEA003020102020301F50D300A06082A8648CE3D040302301631
   14301206035504030C0B5246432074657374204341301E170D32303031303130
   30303030305A170D3231303230323030303030305A30223120301E0603550403
   0C1730312D32332D34352D46462D46452D36372D38392D41423059301306072A
   8648CE3D020106082A8648CE3D03010703420004AE4CDB01F614DEFC7121285F
   DC7F5C6D1D42C95647F061BA0080DF678867845EE9A69FD4893149DAE3D3B154
   16D7532C387152B80B0DF3E1AF408A95D3071E58A30F300D300B0603551D0F04
   0403020780300A06082A8648CE3D04030203470030440220373873EF8781B882
   97EF235C1FACCF62DA4E44740DC2A2E6A3C6C882A3238D9C02203AD9353BA788
   683B06BB48FECA16EA71171734C675C5332B2AF1CB733810A1FC








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A.2.  Example CBOR Certificate Compression

   The CBOR certificate compression of the X.509 in CBOR diagnostic
   format is:

   (
     1,
     h'01f50d',
     "RFC test CA",
     721699200,
     760492800,
     h'0123456789AB',
     h'02ae4cdb01f614defc7121285fdc7f5c6d1d42c95647f061ba
       0080df678867845e',
     5,
     h'373873EF8781B88297EF235C1FACCF62DA4E44740DC2A2E6A3
       C6C882A3238D9C3AD9353BA788683B06BB48FECA16EA711717
       34C675C5332B2AF1CB733810A1FC'
   )

   The CBOR encoding (CBOR sequence) of the CBOR certificate is 136
   bytes.

   014301F50D6B52464320746573742043411A2B0441801A2D5433004601234567
   89AB582102AE4CDB01F614DEFC7121285FDC7F5C6D1D42C95647F061BA0080DF
   678867845E055840373873EF8781B88297EF235C1FACCF62DA4E44740DC2A2E6
   A3C6C882A3238D9C3AD9353BA788683B06BB48FECA16EA71171734C675C5332B
   2AF1CB733810A1FC

A.3.  Example Native CBOR Certificate

   The corresponding native CBOR certificate in CBOR diagnostic format
   is identical except for type and signatureValue.

   (
     0,
     h'01f50d',
     "RFC test CA",
     721699200,
     760492800,
     h'0123456789AB',
     h'02ae4cdb01f614defc7121285fdc7f5c6d1d42c95647f061
       ba0080df678867845e',
     5,
     h'7F10A063DA8DB2FD49414440CDF85070AC22A266C7F1DFB1
       577D9A35A295A8742E794258B76968C097F85542322A0796
       0199C13CC0220A9BC729EF2ECA638CFE'
   )



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   The CBOR encoding (CBOR sequence) of the CBOR certificate is 136
   bytes.

   004301F50D6B52464320746573742043411A2B0441801A2D5433004601234567
   89AB582102AE4CDB01F614DEFC7121285FDC7F5C6D1D42C95647F061BA0080DF
   678867845E0558407F10A063DA8DB2FD49414440CDF85070AC22A266C7F1DFB1
   577D9A35A295A8742E794258B76968C097F85542322A07960199C13CC0220A9B
   C729EF2ECA638CFE

Appendix B.  X.509 Certificate Profile, ASN.1

   TODO - This ASN.1 profile should probably be in a document that
   updates RFC 7925.

   IOTCertificate DEFINITIONS EXPLICIT TAGS ::= BEGIN

   Certificate  ::= SEQUENCE {
     tbsCertificate        TBSCertificate,
     signatureAlgorithm    AlgorithmIdentifier,
     signatureValue        BIT STRING
   }

   TBSCertificate  ::= SEQUENCE {
     version           [0] INTEGER {v3(2)},
     serialNumber          INTEGER (1..MAX),
     signature             AlgorithmIdentifier,
     issuer                Name,
     validity              Validity,
     subject               Name,
     subjectPublicKeyInfo  SubjectPublicKeyInfo,
     extensions        [3] Extensions OPTIONAL
   }

   Name  ::= SEQUENCE SIZE (1) OF DistinguishedName

   DistinguishedName  ::= SET SIZE (1) OF CommonName

   CommonName  ::= SEQUENCE {
     type              OBJECT IDENTIFIER (id-at-commonName),
     value             UTF8String
   }

   Validity  ::= SEQUENCE {
     notBefore         UTCTime,
     notAfter          UTCTime
   }

   SubjectPublicKeyInfo  ::= SEQUENCE {



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     algorithm         AlgorithmIdentifier,
     subjectPublicKey  BIT STRING
   }

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

   Extensions  ::= SEQUENCE SIZE (1..MAX) OF Extension

   Extension  ::= SEQUENCE {
     extnId            OBJECT IDENTIFIER,
     critical          BOOLEAN DEFAULT FALSE,
     extnValue         OCTET STRING
    }

   id-at-commonName    OBJECT IDENTIFIER   ::=
            {joint-iso-itu-t(2) ds(5) attributeType(4) 3}

   END

Authors' Addresses

   Shahid Raza
   RISE AB

   Email: shahid.raza@ri.se


   Joel Hoeglund
   RISE AB

   Email: joel.hoglund@ri.se


   Goeran Selander
   Ericsson AB

   Email: goran.selander@ericsson.com


   John Preuss Mattsson
   Ericsson AB

   Email: john.mattsson@ericsson.com





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   Martin Furuhed
   Nexus Group

   Email: martin.furuhed@nexusgroup.com















































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