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RATS Working Group                                         M. Richardson
Internet-Draft                                  Sandelman Software Works
Intended status: Informational                             June 19, 2019
Expires: December 21, 2019


           Use cases for Remote Attestation common encodings
                   draft-richardson-rats-usecases-02

Abstract

   This document details mechanisms created for performing Remote
   Attestation that have been used in a number of industries.  The
   document intially focuses on existing industry verticals, mapping
   terminology used in those specifications to the more abstract
   terminology used by RATS.

   The document aspires to describe possible future use cases that would
   be enabled by common formats.

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
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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 December 21, 2019.

Copyright Notice

   Copyright (c) 2019 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



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   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 . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Static attestions . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Session attestions  . . . . . . . . . . . . . . . . . . .   3
     2.3.  Statements  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   4.  Overview of Sources of Use Cases  . . . . . . . . . . . . . .   3
   5.  Use case summaries  . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Trusted Computing Group (TCG) . . . . . . . . . . . . . .   4
     5.2.  Android Keystore system . . . . . . . . . . . . . . . . .   5
     5.3.  Fast IDentity Online (FIDO) Alliance  . . . . . . . . . .   6
   6.  Privacy Considerations. . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Appendix A.  Changes  . . . . . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The recently chartered IETF RATS WG intends to create a system of
   attestations that can be shared across a multitude of different
   users.

   This document exists as place to collect use cases for the common
   RATS technologies in support of the IETF RATS charter point 1.  This
   document is not expected to be published as an RFC, but remain open
   as a working document.  It could become an appendix to provide
   motivation for a protocol standards document.

   This document will probably not deal with use cases from an end-user
   point of view, but rather on the technology verticals that wish to
   use RATS concepts (such as EAT) in their deployments.

   End-user use cases that would either directly leverage RATS
   technology, or would serve to inform technology choices are welcome,
   however.





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2.  Terminology

   Critical to dealing with and constrasting different technologies is
   to collect terms with are compatible, to distinguish those terms
   which are similar but used in different ways.

   This section will grow to include forward and external references to
   terms which have been seen.  When terms need to be disambiguated they
   will be prefixed with their source, such as "TCG(claim)" or
   "FIDO(relying party)"

   Platform attestions generally come in two categories.  This document
   will attempt to indicate for a particular attestion technology falls
   into this.

2.1.  Static attestions

   A static attestion says something about the platform on which the
   code is running.

2.2.  Session attestions

   A session attestion says something about how the shared session key
   was created.

2.3.  Statements

   The term "statement" is used as the generic term for the semantic
   content which is being attested to.

3.  Requirements Language

   This document is not a standards track document and does not make any
   normative protocol requirements using terminology described in
   [RFC2119].

4.  Overview of Sources of Use Cases

   The following specifications have been convered in this document:

   o  The Trusted Computing Group "Network Attestation System" (private
      document)

   o  Android Keystore

   o  Fast Identity Online (FIDO) Alliance attestation,

   This document will be expanded to include summaries from:



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   o  Trusted Computing Group (TCG) Trusted Platform Module
      (TPM)/Trusted Software Stack (TSS)

   o  ARM "Platform Security Architecture"
      [I-D.tschofenig-rats-psa-token]

   And any additional sources suggested.

5.  Use case summaries

5.1.  Trusted Computing Group (TCG)

   The TCG is trying to solve the problem of knowing if a networking
   device should be part of a network, if it belongs to the operator,
   and if it is running approriate software.

   This proposal is a work-in-progress, and is available to TCG members
   only.  The goal is to be multi-vendor, scalable and extensible.  The
   proposal intentionally limits itself to:

   o  "non-privacy-preserving applications (i.e., networking, Industrial
      IoT )",

   o  that the firmware is provided by the device manufacturer

   o  that there is a manufacturer installed hardware root of trust
      (such as a TPM and boot room)

   Service providers and enterprises deploy hundreds of routers, many of
   them in remote locations where they're difficult to access or secure.
   The point of remote attestation is to:

   o  identify a remote box in a way that's hard to spoof

   o  report the inventory of software was launched on the box in a way
      that can not be spoofed

   The use case described is to be able to monitor the authenticity of
   software versions and configurations running on each device.  This
   allows owners and auditors to detect deviation from approved software
   and firmware versions and configurations, potentially identifying
   infected devices.

   Attestation may be performed by network management systems.
   Networking Equipment is often highly interconnected, so it's also
   possible that attestation could be performed by neighboring devices.





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   Specifically listed to be out of scope includes: Linux processes,
   assemblies of hardware/software created by end-customers, and
   equipment that is sleepy (check term).

   The TCG Attestion leverages the TPM to make a series of measurements
   during the boot process, and to have the TPM sign those measurements.
   The resulting "PCG" hashes are then available to an external
   verifier.

   The TCG uses the following terminology:

   o  Device Manufacuter

   o  Attester ("device under attestation")

   o  Verifier (Network Management Station)

   o  "Explicit Attestation" is the TCG term for a static (platform)
      statement.

   o  "Implicit Attestation" is the TCG term for a session statement.

   o  Reference Integrity Measurements (RIM), which are signed my device
      manufacturer and integrated into firmware.

   o  Quotes: measured values (having been signed), and RIMs

   o  Reference Integrity Values (RIV)

   o  devices have a Initial Attestion Key (IAK), which is provisioned
      at the same time as the IDevID.

   o  PCR - Platform Configuration Registry (deals with hash chains)

   The TCG document builds upon a number of IETF technologies: SNMP
   (Attestion MIB), YANG, XML, JSON, CBOR, NETCONF, RESTCONF, CoAP, TLS
   and SSH.  The TCG document leverages the 802.1AR IDevID and LDevID
   processes.

5.2.  Android Keystore system

   [keystore] describes a system used in smart phones that run the
   Android operation system.  The system is primarily a software
   container to contain and control access to cryptographic keys, and
   therefore provides many of the same functions that a hardware Trusted
   Platform Module might provide.





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   On hardware which is supported, the Android Keystore will make use of
   whatever trusted hardware is available, including use of Trusted
   Execution Environment (TEE) or Secure Element (SE)).  The Keystore
   therefore abstracts the hardware, and guarantees to applications that
   the same APIs can be used on both more and less capable devices.

   A great deal of focus from the Android Keystore seems to be on
   providing fine-grained authorization of what keys can be used by
   which applications.

   XXX - clearly there must be additional (intended?) use cases that
   provide some kind of attestion.

   Android 9 on Pixel 2 and 3 can provided protected confirmation
   messages.  This uses hardware access from the TPM/TEE to display a
   message directly to the user, and receives confirmation directly from
   the user.  A hash of the contents of the message can provided in an
   attestation that the device provides.

   In addition, the Android Keystore provides attestion information
   about itself for use by FIDO.

   QUOTE: Finally, the Verified Boot state is included in key
   attestation certificates (provided by Keymaster/Strongbox) in the
   deviceLocked and verifiedBootState fields, which can be verified by
   apps as well as passed onto backend services to remotely verify boot
   integrity [**21]

5.3.  Fast IDentity Online (FIDO) Alliance

   The FIDO Alliance [fido] has a number of specifications aimed
   primarily at eliminating the need for passwords for authentication to
   online services.  The goal is to leverage asymmetric cryptographic
   operations in common browser and smart-phone platforms so that users
   can easily authentication.

   FIDO specifications extend to various hardware second factor
   authentication devices.

   Terminology includes:

   o  "relying party" validates a claim

   o  "relying party application" makes FIDO Authn calls

   o  "browser" provides Web Authentication JS API

   o  "platform" is the base system



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   o  "internal authenticator" is some credential built-in to the device

   o  "external authenticator" may be connected by USB, bluetooth, wifi,
      and may be an stand-alone device, USB connected key, phone or
      watch.

   FIDO2 had a Key Attestion Format [fidoattestation], and a Signature
   Format [fidosignature], but these have been combined into the W3C
   document [fido_w3c] specification.

   A FIDO use case involves a relying party that having a attestion on
   the biometric system that identifies a human.  It is the state of the
   biometric system that is being attested to, not the identity of the
   human.

   FIDO does provides a transport in the form of the WebAuthn and FIDO
   CTAP protocols.

   According to [fidotechnote] FIDO uses attestion to make claims about
   the kind of device which is be used to enroll.  Keypairs are
   generated on a per-device _model_ basis, with a certificate having a
   trust chain that leads back to a well-known root certificate.  It is
   expected that as many as 100,000 devices in a production run would
   have the same public and private key pair.  One assumes that this is
   stored in a tamper-proof TPM so it is relatively difficult to get
   this key out.  The use of this key attests to the the device type,
   and the kind of protections for keys that the relying party may
   assume, not to the identity of the end user.

6.  Privacy Considerations.

   TBD

7.  Security Considerations

   TBD.

8.  IANA Considerations

   TBD.

9.  Acknowledgements

10.  References







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10.1.  Normative References

   [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>.

10.2.  Informative References

   [android_security]
              Kralevich, R., "The Android Platform Security Model",
              n.d., <https://arxiv.org/pdf/1904.05572.pdf>.

   [fido]     FIDO Alliance, ., "FIDO Specification Overview", n.d.,
              <https://fidoalliance.org/specifications/>.

   [fido_w3c]
              W3C, ., "Web Authentication: An API for accessing Public
              Key Credentials Level 1", n.d.,
              <https://www.w3.org/TR/webauthn-1/>.

   [fidoattestation]
              FIDO Alliance, ., "FIDO 2.0: Key Attestation", n.d.,
              <https://fidoalliance.org/specs/fido-v2.0-ps-20150904/
              fido-key-attestation-v2.0-ps-20150904.html>.

   [fidosignature]
              FIDO Alliance, ., "FIDO 2.0: Signature Format", n.d.,
              <https://fidoalliance.org/specs/fido-v2.0-ps-20150904/
              fido-signature-format-v2.0-ps-20150904.html>.

   [fidotechnote]
              FIDO Alliance, ., "FIDO TechNotes: The Truth about
              Attestation", n.d., <https://fidoalliance.org/
              fido-technotes-the-truth-about-attestation/>.

   [I-D.tschofenig-rats-psa-token]
              Tschofenig, H., Frost, S., Brossard, M., and A. Shaw,
              "Arm's Platform Security Architecture (PSA) Attestation
              Token", draft-tschofenig-rats-psa-token-01 (work in
              progress), April 2019.

   [keystore]
              Google, ., "Android Keystore System", n.d.,
              <https://developer.android.com/training/articles/
              keystore>.





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Appendix A.  Changes

   o  added comments from Guy, Jessica, Henk and Ned on TCG description.

Author's Address

   Michael Richardson
   Sandelman Software Works

   Email: mcr+ietf@sandelman.ca









































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