Constrained Voucher Profile for Bootstrapping Protocols
draft-richardson-anima-ace-constrained-voucher-02

Abstract

This document defines a strategy to securely assign a pledge to an owner, using an artifact signed, directly or indirectly, by the pledge's manufacturer. This artifact is known as a "voucher".

This document builds upon the work in [I-D.ietf-anima-voucher], encoding the resulting artifact in CBOR. Use with two signature technologies are described.

Additionally, this document explains how constrained vouchers may be transported in the [I-D.vanderstok-ace-coap-est] protocol.

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/.

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This Internet-Draft will expire on June 14, 2018.

Copyright Notice

Copyright (c) 2017 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 (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. Terminology
• 3. Requirements Language
• 4. Survey of Voucher Types
• 5. Artifacts
• 5.1. Voucher Request artifact
• 5.1.1. Tree Diagram
• 5.1.2. SID values
• 5.1.3. YANG Module
• 5.1.4. Example voucher request artifacts
• 5.2. Voucher artifact
• 5.3. Tree Diagram
• 5.4. SID values
• 5.5. YANG Module
• 5.5.1. Example voucher artifacts
• 5.6. CMS format voucher and voucher-request artifacts
• 5.7. COSE format voucher and voucher-request artifacts
• 6. Design Considerations
• 7. Security Considerations
• 7.1. Clock Sensitivity
• 7.2. Protect Voucher PKI in HSM
• 7.3. Test Domain Certificate Validity when Signing
• 8. IANA Considerations
• 8.1. The IETF XML Registry
• 8.2. The YANG Module Names Registry
• 8.3. The SMI Security for S/MIME CMS Content Type Registry
• 8.4. The SID registry
• 8.5. CoAP Content-Type
• 9. Acknowledgements
• 10. References
• 10.1. Normative References
• 10.2. Informative References
• Author's Address

1. Introduction

Enrollment of new nodes into constrained networks with constrained nodes present unique challenges.

There are bandwidth and code space issues to contend. A solution such as [I-D.ietf-anima-bootstrapping-keyinfra] may be too large in terms of code space or bandwidth required.

This document defines a constrained version of [I-D.ietf-anima-voucher]. Rather than serializing the YANG definition in JSON, it is serialized into CBOR ([RFC7049]).

This document follows a similar, but not identical structure as [I-D.ietf-anima-voucher]. Some sections are left out entirely.

The CBOR definitions for this constrained voucher format are defined using the mechanism describe in [I-D.ietf-core-yang-cbor] using the SID mechanism explained in [I-D.ietf-core-sid]. As the tooling to convert YANG documents into an list of SID keys is still in its infancy, the table of SID values presented here should be considered normative rather than the output of the pyang tool.

Two methods of signing the resulting CBOR object are described in this document. One is CMS [RFC5652]. The other is COSE [RFC8152] signatures.

2. Terminology

The following terms are defined in [I-D.ietf-anima-voucher], and are used identically as in that document: artifact, imprint, domain, Join Registrar/Coordinator (JRC), Manufacturer Authorized Signing Authority (MASA), pledge, Trust of First Use (TOFU), and Voucher.

3. Requirements Language

In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 [RFC2119] and indicate requirement levels for compliant STuPiD implementations.

4. Survey of Voucher Types

[I-D.ietf-anima-voucher] provides for vouchers that assert proximity, that authenticate the registrar and that include different amounts of anti-replay protection.

This document does not make any extensions to the types of vouchers.

Time based vouchers are included in this definition, but given that constrained devices are extremely unlikely to know the correct time, their use is very unlikely. Most users of these constrained vouchers will be online and will use live nonces to provide anti-replay protection.

[I-D.ietf-anima-voucher] defined only the voucher artifact, and not the Voucher Request artifact, which was defined in [I-D.ietf-anima-bootstrapping-keyinfra].

This document defines both a constrained voucher and a constrained voucher-request. They are presented in the order voucher-request, followed by voucher response as this is the time order that they occur.

5. Artifacts

This section describes the abstract (tree) definition as explained in [I-D.ietf-netmod-yang-tree-diagrams] first. This provides a high-level view of the contents of each artifact.

Then the assigned SID values are presented. These have been assigned using the rules in [I-D.ietf-core-yang-cbor], with an allocation that was made via the http://comi.space service. ((EDNOTE: it is unclear if there is further IANA work))

5.1. Voucher Request artifact

5.1.1. Tree Diagram

module: ietf-cwt-voucher-request

  grouping voucher-request-cwt-grouping
    +---- voucher
       +---- created-on
       |       yang:date-and-time
       +---- expires-on?
       |       yang:date-and-time
       +---- assertion
       |       enumeration
       +---- serial-number                                  string
       +---- idevid-issuer?                                 binary
       +---- pinned-domain-cert                             binary
       +---- domain-cert-revocation-checks?                 boolean
       +---- nonce?                                         binary
       +---- last-renewal-date?
       |       yang:date-and-time
       +---- proximity-registrar-subject-public-key-info?   binary

5.1.2. SID values

5.1.3. YANG Module

<CODE BEGINS> file "ietf-cwt-voucher-request@2017-12-11.yang"
/* -*- c -*- */
module ietf-cwt-voucher-request {
  yang-version 1.1;

  namespace
    "urn:ietf:params:xml:ns:yang:ietf-cwt-voucher-request";
  prefix "vcwt";

  import ietf-voucher {
    prefix "v";
  }

  organization
   "IETF 6tisch Working Group";

  contact
   "WG Web:   <http://tools.ietf.org/wg/6tisch/>
    WG List:  <mailto:6tisch@ietf.org>
    Author:   Michael Richardson
              <mailto:mcr+ietf@sandelman.ca>";

  description
   "This module defines the format for a voucher, which is produced by
    a pledge's manufacturer or delegate (MASA) to securely assign one
    or more pledges to an 'owner', so that the pledges may establish a
    secure connection to the owner's network infrastructure.

    This version provides a very restricted subset appropriate
    for very constrained devices.
    In particular, it assumes that nonce-ful operation is
    always required, that expiration dates are rather weak, as no
    clocks can be assumed, and that the Registrar is identified
    by a pinned Raw Public Key.

    The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',
    'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in
    the module text are to be interpreted as described in RFC 2119.";

  revision "2017-12-11" {
    description
     "Initial version";
    reference
     "RFC XXXX: Voucher Profile for Constrained Devices";
  }

  // Grouping defined for future usage
  grouping voucher-request-cwt-grouping {
    description
      "Grouping to allow reuse/extensions in future work.";

    uses v:voucher-artifact-grouping {
      augment "voucher" {
        description "Base the CWT voucher-request upon the regular one";
        leaf proximity-registrar-subject-public-key-info {
          type binary;
          description
            "The proximity-registrar-subject-public-key-info replaces
         the proximit-registrar-cert in constrained uses of
         the voucher-request.
         The proximity-registrar-subject-public-key-info is the
         Raw Public Key of the Registrar. This field is encoded
         as specified in RFC7250, section 3.
         The ECDSA algorithm MUST be supported.
         The EdDSA algorithm as specified in
         draft-ietf-tls-rfc4492bis-17 SHOULD be supported.
         Support for the DSA algorithm is not recommended.
         Support for the RSA algorithm is a MAY.";
        }
      }
    }
  }
}
<CODE ENDS>

5.1.4. Example voucher request artifacts

TBD

5.2. Voucher artifact

The voucher's primary purpose is to securely assign a pledge to an owner. The voucher informs the pledge which entity it should consider to be its owner.

This document defines a voucher that is a CBOR encoded instance of the YANG module defined in Section 5.3 that has been signed with CMS or with COSE.

5.3. Tree Diagram

module: ietf-cwt-voucher

  grouping voucher-cwt-grouping
    +---- voucher
       +---- created-on
       |       yang:date-and-time
       +---- expires-on?
       |       yang:date-and-time
       +---- assertion                                enumeration
       +---- serial-number                            string
       +---- idevid-issuer?                           binary
       +---- pinned-domain-cert                       binary
       +---- domain-cert-revocation-checks?           boolean
       +---- nonce?                                   binary
       +---- last-renewal-date?
       |       yang:date-and-time
       +---- pinned-domain-subject-public-key-info?   binary

5.4. SID values

           
      SID Assigned to
--------- -------------------------------------------------- 
  1001100 module ietf-cwt-voucher
  1001101 module ietf-restconf
  1001102 module ietf-voucher
  1001103 module ietf-yang-types
  1001104 data .../ietf-cwt-voucher:voucher
  1001105 data .../assertion
  1001106 data .../created-on
  1001107 data .../domain-cert-revocation-checks
  1001108 data .../expires-on
  1001109 data .../idevid-issuer
  1001110 data .../last-renewal-date
  1001111 data .../nonce
  1001112 data .../pinned-domain-cert
  1001113 data .../pinned-domain-subject-public-key-info
  1001114 data .../serial-number
       No .sid file

5.5. YANG Module

<CODE BEGINS> file "ietf-cwt-voucher@2017-12-11.yang"
/* -*- c -*- */
module ietf-cwt-voucher {
  yang-version 1.1;

  namespace
    "urn:ietf:params:xml:ns:yang:ietf-cwt-voucher";
  prefix "vcwt";

  import ietf-voucher {
    prefix "v";
  }

  organization
   "IETF 6tisch Working Group";

  contact
   "WG Web:   <http://tools.ietf.org/wg/6tisch/>
    WG List:  <mailto:6tisch@ietf.org>
    Author:   Michael Richardson
              <mailto:mcr+ietf@sandelman.ca>";

  description
   "This module defines the format for a voucher, which is produced by
    a pledge's manufacturer or delegate (MASA) to securely assign one
    or more pledges to an 'owner', so that the pledges may establish a
    secure connection to the owner's network infrastructure.

    This version provides a very restricted subset appropriate
    for very constrained devices.
    In particular, it assumes that nonce-ful operation is
    always required, that expiration dates are rather weak, as no
    clocks can be assumed, and that the Registrar is identified
    by a pinned Raw Public Key.

    The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',
    'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in
    the module text are to be interpreted as described in RFC 2119.";

  revision "2017-12-11" {
    description
     "Initial version";
    reference
     "RFC XXXX: Voucher Profile for Constrained Devices";
  }

  // Grouping defined for future usage
  grouping voucher-cwt-grouping {
    description
      "Grouping to allow reuse/extensions in future work.";

    uses v:voucher-artifact-grouping {
      augment "voucher" {
        description "Base the CWT voucher upon the regular one";
        leaf pinned-domain-subject-public-key-info {
          type binary;
          description
            "The pinned-domain-subject replaces the
         pinned-domain-certificate in constrained uses of
         the voucher.  The pinned-domain-public-key-info is the
         Raw Public Key of the Registrar. This field is encoded
         as specified in RFC7250, section 3.
         The ECDSA algorithm MUST be supported.
         The EdDSA algorithm as specified in
         draft-ietf-tls-rfc4492bis-17 SHOULD be supported.
         Support for the DSA algorithm is not recommended.
         Support for the RSA algorithm is a MAY.";
        }
      }
    }
  }
}
<CODE ENDS>

5.5.1. Example voucher artifacts

TBD

5.6. CMS format voucher and voucher-request artifacts

The IETF evolution of PKCS#7 is CMS [RFC5652]. The CMS signed voucher is much like the equivalent voucher defined in [I-D.ietf-anima-voucher].

A different eContentType of TBD1 is used to indicate that the contents are in a different format than in [I-D.ietf-anima-voucher].

The ContentInfo structure contains a payload consisting of the CBOR encoded voucher. The [I-D.ietf-core-yang-cbor] use of delta encoding creates a canonical ordering for the keys on the wire. This canonical ordering is not important as there is no expectation that the content will be reproduced during the validation process.

Normally the recipient is the pledge and the signer is the MASA.

[I-D.ietf-anima-bootstrapping-keyinfra] supports both signed and unsigned voucher requests from the pledge to the JRC. In this specification, voucher-request artifact is not signed from the pledge to the registrar. From the JRC to the MASA, the voucher-request artifact MUST be signed by the domain owner key which is requesting ownership.

The considerations of [RFC5652] section 5.1, concerning validating CMS objects which are really PKCS7 objects (cmsVersion=1) applies.

The CMS structure SHOULD also contain all the certificates leading up to and including the signer's trust anchor certificate known to the recipient. The inclusion of the trust anchor is unusual in many applications, but without it third parties can not accurately audit the transaction.

The CMS structure MAY also contain revocation objects for any intermediate certificate authorities (CAs) between the voucher-issuer and the trust anchor known to the recipient. However, the use of CRLs and other validity mechanisms is discouraged, as the pledge is unlikely to be able to perform online checks, and is unlikely to have a trusted clock source. As described below, the use of short-lived vouchers and/or pledge provided nonce provides a freshness guarantee.

5.7. COSE format voucher and voucher-request artifacts

This section to be added.

6. Design Considerations

The design considerations for the CBOR encoding of vouchers is much the same as for [I-D.ietf-anima-voucher].

One key difference is that the names of the leafs in the YANG does not have a material affect on the size of the resulting CBOR, as the SID translation process assigns integers to the names.

7. Security Considerations

7.1. Clock Sensitivity

TBD.

7.2. Protect Voucher PKI in HSM

TBD.

7.3. Test Domain Certificate Validity when Signing

TBD.

8. IANA Considerations

8.1. The IETF XML Registry

This document registers two URIs in the IETF XML registry [RFC3688]. Following the format in [RFC3688], the following registration is requested:

  URI: urn:ietf:params:xml:ns:yang:ietf-cwt-voucher
  Registrant Contact: The ANIMA WG of the IETF.
  XML: N/A, the requested URI is an XML namespace.

  URI: urn:ietf:params:xml:ns:yang:ietf-cwt-voucher-request
  Registrant Contact: The ANIMA WG of the IETF.
  XML: N/A, the requested URI is an XML namespace.

8.2. The YANG Module Names Registry

This document registers two YANG modules in the YANG Module Names registry [RFC6020]. Following the format defined in [RFC6020], the the following registration is requested:

  name:         ietf-cwt-voucher
  namespace:    urn:ietf:params:xml:ns:yang:ietf-cwt-voucher
  prefix:       vch
  reference:    RFC XXXX

  name:         ietf-cwt-voucher-request
  namespace:    urn:ietf:params:xml:ns:yang:ietf-cwt-voucher-request
  prefix:       vch
  reference:    RFC XXXX

8.3. The SMI Security for S/MIME CMS Content Type Registry

This document registers an OID in the "SMI Security for S​/​MIME CMS Content Type" registry (1.2.840.113549.1.9.16.1), with the value:

  Decimal  Description                             References
  -------  --------------------------------------  ----------
  TBD1      id-ct-animaCBORVoucher                 [ThisRFC]

EDNOTE: should a seperate value be used for Voucher Requests?

8.4. The SID registry

The SID range 1001100 was allocated by comi.space to the IETF-CWT-VOUCHER yang module.

The SID range 1001150 was allocated by comi.space to the IETF-CWT-VOUCHER-REQUEST yang module.

EDNOTE: it is unclear if there is further IANA work required.

8.5. CoAP Content-Type

A CoAP Content-Type may be have to be defined to match application/cms.

9. Acknowledgements

TBD

10. References

10.1. Normative References

10.2. Informative References

Author's Address