Network Working Group H. Birkholz
Internet-Draft Fraunhofer SIT
Intended status: Standards Track M. Wiseman
Expires: September 13, 2019 GE Global Research
H. Tschofenig
ARM Ltd.
N. Smith
Intel
March 12, 2019
Architecture and Reference Terminology for Remote Attestation Procedures
draft-birkholz-rats-architecture-01
Abstract
Remote ATtestation ProcedureS (RATS) architecture facilitates the
attestation of device characteristics that, in general, are based on
specific trustworthiness qualities intrinsic to a device or service.
It includes trusted computing functionality provided by device
hardware and software that allows trustworthiness qualities to be
asserted and verified as part of, or pre-requisite to, the device's
normal operation. The RATS architecture maps corresponding
attestation functions and capabilities to specific RATS Roles. The
goal is to enable an appropriate conveyance of evidence about device
trustworthiness via network protocols. RATS Roles provide the
endpoint context for understanding the various interaction semantics
of the attestation lifecycle. The RATS architecture provides the
building block concepts, semantics, syntax and framework for
interoperable attestation while remaining hardware-agnostic. This
flexibility is intended to address a significant variety of use-cases
and scenarios involving interoperable attestation. Example usages
include, but are not limited to: financial transactions, voting
machines, critical safety systems, network equipment health, or
trustworthy end-user device management. Existing industry
attestation efforts may be helpful toward informing RATS
architecture. Such as: Remote Integrity VERification (RIVER), the
creation of Entity Attestation Tokens (EAT), software integrity
Measurement And ATtestation (MAAT)
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
Birkholz, et al. Expires September 13, 2019 [Page 1]
Internet-Draft RATS Arch & Terms March 2019
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 September 13, 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
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. What is Remote Attestation . . . . . . . . . . . . . . . 4
1.2. The purpose of RATS Architecture and Terminology . . . . 4
1.3. Requirements notation . . . . . . . . . . . . . . . . . . 4
2. RATS Architecture . . . . . . . . . . . . . . . . . . . . . . 4
3. Architectural Components . . . . . . . . . . . . . . . . . . 5
3.1. RATS Roles . . . . . . . . . . . . . . . . . . . . . . . 5
4. RATS Actors . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. RATS Duties . . . . . . . . . . . . . . . . . . . . . . . 7
4.1.1. Attester Duties . . . . . . . . . . . . . . . . . . . 8
4.1.2. Verifier Duties . . . . . . . . . . . . . . . . . . . 8
4.1.3. Claimant Duties . . . . . . . . . . . . . . . . . . . 8
4.1.4. Relying Party Duties . . . . . . . . . . . . . . . . 8
4.1.5. RATS Interactions . . . . . . . . . . . . . . . . . . 9
5. Application of RATS . . . . . . . . . . . . . . . . . . . . . 10
5.1. Trust and Trustworthiness . . . . . . . . . . . . . . . . 11
5.2. Claims and Evidence . . . . . . . . . . . . . . . . . . . 12
5.3. RATS Information Flows . . . . . . . . . . . . . . . . . 12
6. Exemplary Composition of Roles . . . . . . . . . . . . . . . 13
6.1. Conveyance of Trusted Claim Sets Validated by Signature . 13
6.2. Conveyance of Attestation Evidence Appraised by a
Birkholz, et al. Expires September 13, 2019 [Page 2]
Internet-Draft RATS Arch & Terms March 2019
Verifier . . . . . . . . . . . . . . . . . . . . . . . . 14
7. The Scope of RATS . . . . . . . . . . . . . . . . . . . . . . 14
7.1. The Lying Endpoint Problem . . . . . . . . . . . . . . . 15
7.1.1. How the RATS Architecture Addresses the Lying
Endpoint Problem . . . . . . . . . . . . . . . . . . 16
8. RATS Terminology . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Computing Context . . . . . . . . . . . . . . . . . . . . 18
8.1.1. Characteristics of a Computing Context . . . . . . . 19
8.1.2. Computing Context Semantic Relationships . . . . . . 19
8.1.3. Computing Context Identity . . . . . . . . . . . . . 21
8.2. Remote Attestation Concepts . . . . . . . . . . . . . . . 21
8.3. Core RATS Terminology . . . . . . . . . . . . . . . . . . 22
8.4. RATS Information Model Terminology . . . . . . . . . . . 22
8.5. RATS Work-Flow Terminology . . . . . . . . . . . . . . . 23
8.6. RATS Reference Use Cases . . . . . . . . . . . . . . . . 24
8.6.1. Use Case A . . . . . . . . . . . . . . . . . . . . . 24
8.6.2. Use Case B . . . . . . . . . . . . . . . . . . . . . 24
8.7. RATS Reference Terminology . . . . . . . . . . . . . . . 24
8.8. Interpretations of RFC4949 Terminology for Attestation . 26
8.9. Building Block Vocabulary (Not in RFC4949) . . . . . . . 28
9. IANA considerations . . . . . . . . . . . . . . . . . . . . . 28
10. Security Considerations . . . . . . . . . . . . . . . . . . . 29
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29
12. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 29
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
13.1. Normative References . . . . . . . . . . . . . . . . . . 29
13.2. Informative References . . . . . . . . . . . . . . . . . 29
13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
In general, this document provides normative guidance how to use,
create or adopt network protocols that facilitate remote attestation
procedures. The RATS Architecture anticipates broad deployment
contexts that range from IoT to Cloud and Edge ecosystems. The
foundation of the RATS architecture is the specification of RATS
Roles that can be chained via RATS Interactions and - as a result -
may be composed into use-case specific Remote Attestation Procedures.
RATS Actors establish an ecosystem neutral context where RATS Roles
are hosted and where a variety of Remote Attestation Procedure
interactions are defined independent of specific conveyance protocols
or message formats. In summary, the goal of the RATS Architecture is
to enable interoperable interaction between the RATS Roles. Hence,
the RATS Architecture is designed to enable interoperability via
well-defined semantics of the information model (attestation
assertions/claims), associated with RATS Roles following a conveyance
Birkholz, et al. Expires September 13, 2019 [Page 3]
Internet-Draft RATS Arch & Terms March 2019
model (RATS Interactions) that may be used to compose domain-specific
remote attestation solutions.
1.1. What is Remote Attestation
Unfortunately, the term Attestation itself is an overloaded term. In
consequence, the term Remote Attestation covers a spectrum of
meanings. The common denominator encompasses the creation,
conveyance, and appraisal of evidence pertaining to the
trustworthiness characteristics of the creator of the evidence. In
essence, RATS are used to enable the assessment of the
trustworthiness of a communication partner.
1.2. The purpose of RATS Architecture and Terminology
To consolidate the utilization of existing and emerging network
protocols in the context of RATS, this document provides a detailed
definition of Attestation Terminology that enables interoperability
between different types pf RATS. Specifically, this document
illustrates and remediates the impedance mismatch of terms related to
Remote Attestation Procedures used in different domains today. As an
additional contribution, new terms defined by this document provide a
common basis that simplifies future work on RATS in the IETF and
beyond.
1.3. Requirements notation
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.
2. RATS Architecture
One of the goals of the RATS Architecture is to provide the building
blocks - the roles defined by the RATS Architecture - to enable the
composition of service-chains/hierarchies and work-flows that can
create and appraise evidence about the trustworthiness of devices and
services.
The RATS Architecture is based on the use-cases defined in
[I-D.richardson-rats-usecases].
The RATS architecture specifies:
o The building blocks to create remote attestation procedures
applicable Actors, Roles, Duties, and Interactions,
Birkholz, et al. Expires September 13, 2019 [Page 4]
Internet-Draft RATS Arch & Terms March 2019
o Mandatory and optional trust relationships between its Roles, that
may assume a Root-of-Trust context,
o The interaction between Roles that reside on separate Actors and
interact via network protocols,
o Protocol/message framing that allows for well-defined and opaque
payloads,
o The means to prove, preserve and convey trust properties, such as
identity, varacity, freshness, or provenance, and
o Primitives necessary for the construction of interoperable
attestation payloads.
3. Architectural Components
The basic architectural components defined in this document are:
o RATS Roles
o RATS Actors
o RATS Duties
o RATS Interactions
The following sub-section define and elaborate on these terms:
3.1. RATS Roles
A Role in the context of usage scenarios for remote attestation
procedures is providing a service to other Roles. Roles are building
blocks that can be providers and consumers of information. In the
RATS architecture, devices or services can take on RATS roles. They
are composites of internal functions (RATS Duties) and external
functions (RATS Interactions) that facilitate a required (sometimes
optional) task in a remote attestation procedure.
The base set of RATS roles is:
Claimant: The producer of trustworthiness assertions pertaining to
an Attester; that may or not have a root-of-trust for measurement.
It is not guaranteed that a Verifier Role can appraise the output
of a Claimant via reference values (in contrast to the output of
an Attester).
Birkholz, et al. Expires September 13, 2019 [Page 5]
Internet-Draft RATS Arch & Terms March 2019
Examples of Claimant assertions include: * The hardware, firmware
and software components of the Attester. * The manufactuer of
Attester components. * The Attester's current configuration. *
The Attester's current location - e.g. GPS coordinates. * The
method by which binding of an attester to an RTR. * The
identifier(s) available for identifying and authenticating the
Attester - e.g. Universal Entity ID (UEID).
Typically, claimant role are taken on by RATS Actors that supply
chain entities (SCE). Various assertions (often represented as
Claims or Trusted Claims Sets, e.g. [I-D.mandyam-eat] or
[I-D.tschofenig-rats-psa-token]).
Attester: The producer of attestation evidence that has a root of
trust for reporting (RTR) and implements a conveyance protocol,
authenticates using an attestation credential, consumes assertions
about itself and presents it to a consumer of evidence (e.g. a
relying party or a verifier). Every output of an attester can be
appraised via reference values.
Authentication Checker: The consumer of signed assertions such as
trusted claim sets or attestation evidence that assesses the
trustworthiness or other trust relationships of the information
consumed via trusted third parties or external trust authorities,
such as a privacy certificate authority. In certain environments,
an Authentication Checker can assess a system's trustworthiness
via external trust anchors, implicitly.
Verifier: The consumer of attestation evidence that has a root of
trust for verification (RTV), implements conveyance protocols,
appraises attestation evidence against reference values or
policies, and makes verification results available to relying
parties.
Relying Party: The consumer and assessor of verifier or
Authentication Checker results for the purpose of improved risk
management, operational efficiency, security, privacy (natural or
legal person) or safety. The verifier and/or authentication
checker roles and the relying party role may be tightly
integrated.
4. RATS Actors
RATS Actors may be any entity, such as an user, organization,
execution environment, device or service provider, that takes on
(implements) one or more RATS Roles and performs RATS Duties and/or
RATS Interactions. RATS Interactions occur between RATS Actors. The
methods whereby RATS Actors are identified, discovered, and
Birkholz, et al. Expires September 13, 2019 [Page 6]
Internet-Draft RATS Arch & Terms March 2019
connectivity established are out-of-scope for this architecture. In
contrast, if multiple RATS Roles reside on a single RATS Actor, the
definition of RATS Interactions is out-of-scope of the RATS
architecture, if no network protocols are required.
+------------------+ +------------------+
| Actor 1 | | Actor 2 |
| +------------+ | | +------------+ |
| | | | | | | |
| | Role 1 |<-|---|->| Role 2 | |
| | | | | | | |
| +------------+ | | +------------+ |
| | | |
| +-----+------+ | | +-----+------+ |
| | | | | | | |
| | Role 2 |<-|---|->| Role 3 | |
| | | | | | | |
| +------------+ | | +------------+ |
| | | |
+------------------+ +------------------+
Figure 1: RATS Actor-Role Interactions
RATS Actors have the following properties: * Multiplicity - Multiple
instances of RATS Actors that possess the same RATS Roles can exist.
* Decomposability - A singleton RATS Actor possessing multiple RATS
Roles can be separated into multiple RATS Actors. RATS Interactions
may occur between them. * Composablility - RATS Actors possessing
different RATS Roles can be combined into a singleton RATS Actor
possessing the union of RATS Roles. RATS Interactions between
combined RATS Actors ceases.
Interactions between RATS Roles belonging to the same RATS Actor are
generally believed to be uninteresting. Actor operations that apply
resiliency, scaling, load balancing or replication are generally
believed to be uninteresting.
4.1. RATS Duties
A RATS Role can take on one ore more duties. RATS Duties are role-
internal functions that do not require interaction with other RATS
Roles. In general, and RATS Duties are typically associated with a
RATS Role. The list presented in this document is exhaustive. Also,
there can be usage scenario where RATS Duties are associated with
other RATS Roles than illustrated below:
Birkholz, et al. Expires September 13, 2019 [Page 7]
Internet-Draft RATS Arch & Terms March 2019
4.1.1. Attester Duties
o Acquisition or collection of assertions about itself
o Provide or create proof that an assertion is bound to the Attester
o Create Evidence from assertion bundles via roots-of-trust
4.1.2. Verifier Duties
o Acquisition and storage of assertion semantics
o Acquisition and storage of appraisal policies
o Verification of Attester Identity (attestation provenance)
o Comparing assertions or evidence with reference values according
to appraisal policies
o Validate authentication information based on public keys,
signatures, secrets that are shielded, or secrets that are access
restricted via protection profiles
4.1.3. Claimant Duties
o Hardens the device or service that implements the Attester role
o Provisions device identities and/or key material accessible to the
Attester role
o Evaluates trustworthiness during manufacturing, supply chain and
onboarding
o Produces trustworthiness assertions applicable to the Attestor
role
o Embeds trustworthiness assertions about the Attester role in the
device or service during manufacturing, supply chain or onboarding
4.1.4. Relying Party Duties
o Evaluate assertions/evidence locally as far as possible
o Compare trust policies to attestation-results based on assertions
or evidence
o Enforce policies or create input for risk engines
Birkholz, et al. Expires September 13, 2019 [Page 8]
Internet-Draft RATS Arch & Terms March 2019
4.1.5. RATS Interactions
The flow of information between RATS Roles located on RATS Actors
compose individual remote attestation procedures. The RATS
Architecture provides a set of standard interactions between the RATS
Roles defined in this document in order to enable this composability.
In this section, common interactions between roles are specified.
This list of interactions is not exhaustive, but provides the basis
to create various standard RATS.
Every RATS Interaction specified below is based on the information
flow between two RATS Roles defined above. Every RATS Interaction is
conducted via an Interconnect between corresponding RATS Roles that
RATS Actors take on. If more than one RATS Role resides on the same
RATS Actor, a network protocol might not be required. If RATS Roles
are collapsed into a singular RATS Actor in this way, the method of
conveying information is out-of-scope of this document. If network
protocols are used to convey corresponding information between RATS
Roles (collapsed on a singular RATS Actor or not), the definitions
and requirements defined in this document apply.
In essence, an Interconnect is an abstract "distance-less" channel
between RATS Actors that can range from General Purpose Input Output
(GPIO) interfaces to the Internet.
Attester/Verifier: The most basic RATS interaction is between the
creator of evidence (Attester) and its complementary remote
attestation service (Verifier). In order to convey evidence (or
assertions that are not accompanied by a proof of their validity)
this RATS Interaction is required.
Attester/Relying-Party: A Relying Party typically requires external
help to either validate authentication information or to appraise
evidence presented by an Attester. In most cases, a Relying Party
requires a corresponding Verifier to process the assertions/
evidence received. In consequence, (a subset of) the information
received by an Attester must be relayed securely to a Verifier.
Relying-Party/Verifier: Typically, trusted assertions or evidence
are conveyed from an Attester to a Relying Party. In an open
ecosystem, such as the Internet, the appraisal of the evidence
presented by an Attester provided in order to assess its
trustworthiness requires a remote attestation service. Hence,
either the RATS roles of Verifier and Relying Party are collapsed
and compose a single RATS Actor, or - if they reside on separate
RATS Actors - a Relying Party requires appropriate configuration
or a discovery/join/rendezvous service to initiate a RATS
Interaction with an appropriate and trusted Verifier.
Birkholz, et al. Expires September 13, 2019 [Page 9]
Internet-Draft RATS Arch & Terms March 2019
Attestation information originating from an Attester that is
relayed via a Relying Party must be protected from replay or relay
attacks, accordingly. In a closed ecosystem, trustworthiness with
respect to the Attester can be achieved via a simply query to the
Verifier. In an open ecosystem, the information conveyed in this
interaction can include integrity measurements of every
distinguishable software component that has been executed since
its last boot cycle.
In the scope of RATS, this interaction encompasses the largest
variety of information conveyed.
Claimant/Verifier: The intended operational state an Attester is
intended to be in, is defined by the supply chain entities that
manufacture and maintain the Attestor. In order to appraise
trusted assertions or evidence conveyed by the Attester, every
distinguishable system component the Attester is composed of can
provide trusted assertions or evidence about its trustworthiness.
A corresponding verifier that is tasked with assessing the
trustworthiness of the Attester potentially requires a multitude
of sources of reference values according to policies and the
information provided. As Relying Parties often have to discover
an appropriate Verifier, a Verifier has to obtain and potentially
store appropriate reference values in order to asses assertions or
evidence about trustworthiness.
Claimant/Attester: To enable RATS, trustworthy assertions have to be
embedded in an Attester by its manufactorer. In some cases this
involves various types of roots of trust. In other cases shielded
pre-master secrets in combination with key derivation functions
(KDF) provide this binding of trusted information to an Attester.
A supply chain entity can embed additional trusted assertions to
an Attester. These assertion can also be used to assert the
trustworthiness on behalf of a separate RATS Actor or they can
originate from an external entity (e.g. a security certification
authority).
5. Application of RATS
Attester are typically composite devices (in the case of atomically
integrated devices that would result in a composite device with one
component) or services. Services are software components - e.g. a
daemon, a virtual network function (vnf) or a network security
function (nsf) - that can reside on one or more Attester and are not
necessarily bound to a specific set of hardware devices.
Birkholz, et al. Expires September 13, 2019 [Page 10]
Internet-Draft RATS Arch & Terms March 2019
Relevant decision-factors that influence the composition of RATS
Roles on RATS Actors, which result in specific work-flows are
(amongst others):
o which RATS Role (or correspondingly, which RATS Actore that is
taking on specific RATS roles) is triggering a Remote Attestation
Procedure
o which entities are involved in a Remote Attestation Procedure
(e.g. the Attester itself, trusted third parties, specific trust
anchors, or other sources of assertions)
o the capabilities of the protocols used (e.g. challenge-response
based, RESTful, or uni-directional)
o the security requirements and security capabilities of systems in
a domain of application
o the risks and corresponding threats that are intended to be
mitigated
5.1. Trust and Trustworthiness
[RFC4949] provides definitions that highlight the difference between
a "trusted system" and a "trustworthy system". The following
definitions exclude the explicit specialization of concepts that are
"environmental disruption" as well as "human user and operator
errors".
A trusted system in the context of RATS "operates as expected,
according to design and policy, doing what is required and not doing
other things" [RFC4949]. A trustworthy system is a system "that not
only is trusted, but also warrants that trust because the system's
behavior can be validated in some convincing way, such as through
formal analysis or code review" [RFC4949].
The goal of RATS is to convey information about system component
characteristics, such as integrity or authenticity, that can be
appraised in a convincing way.
RATS require trust relationships with third parties that qualify
assertions about, for example, origin of data, the manufacturer or
the capabilities of a system, or the origination of attestation
evidence (attestation provenance). Without trusted authorities (e.g.
a certificate authority) it is virtually impossible to assess the
level of assurance (or resulting level of confidence,
correspondingly) of information produced by RATS. Trusting a system
does not make it trustworthy. Assessing trustworthiness requires the
Birkholz, et al. Expires September 13, 2019 [Page 11]
Internet-Draft RATS Arch & Terms March 2019
conveyance of evidence that a system is a trustworthy system, which
has to originate from the system itself and has to be convincing. If
the convincing information is not originating from the system itself,
it comprises trusted claim sets and not evidence. In essence, the
attestation provenance of attestation evidence is the system that
intends to present its trustworthiness in a believable manner.
The essential basis for trust in the information created via RATS are
roots of trust.
Roots of trust are defined by the NIST special publication 800-164
draft as "security primitives composed of hardware, firmware and/or
software that provide a set of trusted, security-critical functions.
They must always behave in an expected manner because their
misbehavior cannot be detected. As such, RoTs need to be secured by
their design. Hardware RoTs are preferred over software RoTs due to
their immutability, smaller attack surface, and more reliable
behavior."
If the root of trust involved is a root of trust for measurement
(RTM), the producer of information takes on the role of a asserter.
An asserter can also make use of a root of trust for integrity (RTI)
in order to increase the level of assurance in the assertions
produced. If the root of trust involved is a root of trust for
reporting (RTR), the producer of information takes on the role of an
attester.
5.2. Claims and Evidence
The RATS asserter role produces measurements about the system's
characteristics in the form of signed (sometimes un-signed) claim
sets in order to convey information. A secret signing key is
required for this procedure, which is typically stored in a shielded
location that can be trusted, for example, via a root of trust for
storage (RTS).
The RATS attester role produces signed attestation evidence in order
to convey information. The secret key required for this procedure is
stored in a shielded location that only allows access to that key, if
a specific operational state of the system is met. The trust with
respect to this origination is based on a root of trust for
reporting.
5.3. RATS Information Flows
There are six roles defined in the RATS architecture. iFigure 2
provides a simplified overview of the RATS Roles defined above,
Birkholz, et al. Expires September 13, 2019 [Page 12]
Internet-Draft RATS Arch & Terms March 2019
illustrating a general Interconnect in the center that facilitates
all RATS Interactions.
+------------+ +------------------+
| | | |
| Attester | +->| Verifier |
| | | | |
+------------+ | +------------------+
^ |
| |
| +----------------+ |
+---->| |<-+
| Interconnect |
+---->| |<-+
| +----------------+ |
v |
+------------+ | +------------------+
| | | | |
| Claimant | +->| Relying Party |
| | | |
+------------+ +------------------+
Figure 2: Overall Relationships of Roles in the RATS Architecture
6. Exemplary Composition of Roles
In order to provide an intuitive understanding how the roles used in
RATS can be composed into work-flows, this document provides a few
example work-flows. Boxes in the following examples that include
more than one role are systems that take on more than one role.
6.1. Conveyance of Trusted Claim Sets Validated by Signature
If there is a trust relationship between a trusted third party that
can assert that signed claims created by a claimant guarantee a
trustworthy origination of claim, the work-flow depicted in Figure 3
can facilitate a trust-based implicit remote attestation procedure.
The information conveyed are signed claim sets that are trusted via
an authoritative third party. In this work-flow claim emission is
triggered by the claimant. Variations based on requests emitted by
the relying party can be easily facilitated by the same set of roles.
Birkholz, et al. Expires September 13, 2019 [Page 13]
Internet-Draft RATS Arch & Terms March 2019
+-----------+
+------------+ +----------------+ | |
| | | | | Relying |
| Claimant |->| Interconnect |--->| Party |
| | | | | |
+------------+ +----------------+ +-----------+
Figure 3: Conveyance of Trusted Claim Sets Validated by Signature
6.2. Conveyance of Attestation Evidence Appraised by a Verifier
If there is trust in the root of trust for reporting based on the
assertions of a trusted third party, the work-flow depicted in
Figure 4 can facilitate an evidence-based explicit remote attestation
procedure. The information conveyed is signed attestation evidence
that is created by the trusted verifier. In this work-flow claims do
not necessarily have to be signed and the work-flow is triggered by
the attestor that aggregates claims from a root of trust of
measurement. Variations based on requests emitted by the verifier
can be easily facilitated by the same set of roles.
+------------------+ +----------------------+
| | | +----------------+ |
| +------------+ | +----------------+ | | | |
| | | | | | | | | |
| | Attester |--+->| Interconnect |--+->| Verifier | |
| | | | | | | | | |
| +------------+ | +----------------+ | +----------------+ |
| ^ | | | |
| | | | v |
| | | | +-----------+ |
| +-----+------+ | | | | |
| | | | | | Relying | |
| | Claimant | | | | Party | |
| | | | | | | |
| +------------+ | | +-----------+ |
| | | |
+------------------+ +----------------------+
Figure 4: Conveyance of Attestation Evidence Appraised by a Verifier
7. The Scope of RATS
During its evolution, the term Remote Attestation has been used in
multiple contexts and multiple scopes and in consequence accumulated
various connotations with slightly different semantic meaning.
Birkholz, et al. Expires September 13, 2019 [Page 14]
Internet-Draft RATS Arch & Terms March 2019
Correspondingly, Remote Attestation Procedures (RATS) are employed in
various usage scenarios and different environments.
In order to better understand and grasp the intent and meaning of
specific RATS in the scope of the security area - including the
requirements that are addressed by them - this document provides an
overview of existing work, its background, and common terminology.
As the contribution, from that state-of-the-art a set of terms that
provides a stable basis for future work on RATS in the IETF is
derived.
In essence, a prerequisite for providing an adequate set of terms and
definitions for the RATS architecute is a general understanding and a
common definitions of "what" RATS can accomplish "how" RATS can to be
used.
Please note that this section is still missing various references and
is considered "under construction". The majority of definitions is
still only originating from IETF work. Future iterations will pull
in more complementary definitions from other SDO (e.g. Global
Platform, TCG, etc.) and a general structure template to highlight
semantic relationships and capable of resolving potential
discrepancies will be introduced. A section of context awareness
will provide further insight on how Attestation procedures are vital
to ongoing work in the IETF (e.g. I2NSF & tokbind). The definitions
in the section about RATS are still self-describing in this version.
Additional explanatory text will be added to provide more context and
coherence.
7.1. The Lying Endpoint Problem
A very prominent goal of RATS is to address the "lying endpoint
problem". The lying endpoint problem is characterized as a condition
of a Computing Context where the information or behavior embedded,
created, relayed, stored, or emitted by the Computing Context is not
"correct" according to expectations of the authorized system
designers, operators and users. There can be multiple reasons why
these expectations are incorrect, either from malicious Activity,
unanticipated conditions or accidental means. The observed behavior,
nevertheless, appears to be a compromised Computing Context.
Attempts to "scrub" the data or "proxy" control elements implies the
existence of a more fundamental trusted endpoint that is operating
correctly. Therefore, Remote Attestation - the technology designed
to detect and mitigate the "lying endpoint problem" - must be trusted
to behave correctly independent of other controls.
Consequently, a "lying endpoint" cannot also be a "trusted system".
Birkholz, et al. Expires September 13, 2019 [Page 15]
Internet-Draft RATS Arch & Terms March 2019
Remote Attestation procedures are intended to enable the consumer of
information emitted by a Computing Context to assess the validity and
integrity of the information transferred. The approach is based, for
example, on the assumption that if attestation evidence can be
provided in order to prove the integrity of every software instance
installed involved in the activity of creating the emitted
information in question, the emitted information can be considered
valid and integer.
In contrast, such Evidence has to be impossible to create if the
software instances used in a Computing Context are compromised.
Attestation activities that are intended to create this Evidence
therefore also provide guarantees about the validity of the Evidence
they can create.
7.1.1. How the RATS Architecture Addresses the Lying Endpoint Problem
RATS imply the involvement of at least two players (roles) who seek
to overcome the lying endpoint problem. The Verifier wishes to
consume application data supplied by a Computing Context. But before
application data is consumed, the Verifier obtains Attestation
Evidence about the Computing Context to assess likelihood of poisoned
data due to endpoint compromise or failure. Remote Attestation
argues that a systems's integrity characteristics should not be
believed until rationale for believability is presented to the
relying party seeking to interact with the system.
An Interconnect defines an untrusted channel between subject and
object wherein the rationale for believability is securely exchanged.
The type of interconnect technology could vary widely, ranging from
GPIO pins, to a PC peripheral IO bus, to the Internet, to a direct
physical connection, to a wireless radio-receiver association, or to
a world wide mesh of peers. In other words, virtually every kind
communication path could be used as the "Interconnect" in RATS. In
fact, a single party could take on all roles at the same time (e.g.
Self Encrypting Devices).
Attestation evidence can be thought of as the topics of the exchange
that is created the operational primitives of a root of trust for
reporting. Evidence may be structured in an interoperable format
called claims that may include references to the claimants which are
asserting the claims. RATS aims to define "interoperable Remote
Attestation" such that evidence can be created and consumed by
different ecosystem systems and can be securely exchanged by a broad
set of network protocols.
Birkholz, et al. Expires September 13, 2019 [Page 16]
Internet-Draft RATS Arch & Terms March 2019
8. RATS Terminology
This document relies on terminology found in [RFC4949]. This
document presumes the reader is familiar with the following terms.
o Cryptography
o Entity (System entity)
o Identity
o Object
o Principal
o Proof-of-possession protocol
o Security environment (Environment)
o Security perimeter
o Subject
o Subsystem
o System
o Target-of-Evaluation (TOE)
o Trusted Computing Base (TCB)
o Trusted Platform Module (TPM)
o Trusted (Trustworthy) system
o Verification
Terminology defined by this document is preceded by a dollar sign ($)
to distinguish it from terms defined elsewhere and as a way to
disambiguate term definition from explanatory text.
Terms defined by this document that are subsequently used by this
document are distinguished by capitalizing the first letter of the
term (e.g. Term or First_word Second_word).
Birkholz, et al. Expires September 13, 2019 [Page 17]
Internet-Draft RATS Arch & Terms March 2019
8.1. Computing Context
This section introduces the term Computing Context in order to
specialize the notions of environment and endpoint to terminology
that has relevance to trusted computing. Attestation is a discipline
of trusted computing.
A Computing Context could refer to a large variety of endpoints.
Examples include but are not limited to: the compartmentalization of
physical resources, the separation of software instances with
different dependencies in dedicated containers, and the nesting of
virtual components via hardware-based and software-based solutions.
The number of approaches and techniques to construct an endpoint
continuously changes with new innovation. Hence, it isn't a goal of
this document to define remote attestation for a fixed set of
endpoints. Rather, it attempts to define endpoints conceptually and
rely on Claims management as a way to clarify the details and
specific attributes of conceptual endpoints.
Computing Contexts may be recursive in nature in that it could be
composed of a system that is itself a composite of subsystems. In
consequence, a system may be composed of other systems that may be
further composed of one or more Computing Contexts capable of taking
on the RATS roles. The scope and application of these roles can
range from:
o Continuous mutual Attestation procedures of every subsystem inside
a composite device, to
o Sporadic Remote Attestation of unknown parties via heterogeneous
Interconnects.
Analogously, the increasing number of features and functions that
constitute components of a device start to blur the lines that are
required to categorize each solution and approach precisely. To
address this increasingly challenging categorization, the term
Computing Context defines the characteristics of the (sub)systems
that can take on the role of an Attester and/or the role of a
Verifier. This approach is intended to provide a stable basis of
definitions for future solutions that continuous to remain viable
long-term.
$ Computing Context : An umbrella term that combines the scope of
the definitions of endpoint [ref NEA], device [ref 1ar], and thing
[ref t2trg], including hardware-based and software-based sub-
contexts that constitute independent, isolated and distinguishable
slices of a Computing Context created by compartmentalization
Birkholz, et al. Expires September 13, 2019 [Page 18]
Internet-Draft RATS Arch & Terms March 2019
mechanisms, such as Trusted Execution Environments (TEE), Hardware
Security Modules (HSM) or Virtual Network Function (VNF) contexts.
8.1.1. Characteristics of a Computing Context
While the semantic relationships highlighted above constitute the
fundamental basis to provide a define Computing Context, the
following list of object characteristics is intended to improve the
application of the term and provide a better understanding of its
meaning:
$ Computing Context Characteristics: A representation of the
identity, composition, configuration and state of a Computing
Context.
Computing context characteristics provide the following: * An
independent environment in regard to executing and running
software, * An isolated control plane state (by potentially
interacting with other Computing Contexts), * A dedicated
management interface by which control plane behavior can be
effected, * Unique identification towards reliable disambiguation
within a given scope.
Computing context characteristics do not necessarily include a
network interface with associated network addresses (as required by
the definition of an endpoint) - although it is very likely to have
(access to) one.
[Issue: This conclusion could be incorrect] In contrast, a container
[ref docker, find a more general term here] context is not a
distinguishable isolated slice of an information system and therefore
is not an independent Computing Context. [more feedback on this
statement is required as the capabilities of docker-like functions
evolve continuously]
Examples include: a smart phone, a nested virtual machine, a
virtualized firewall function running distributed on a cluster of
physical and virtual nodes, or a trust-zone.
8.1.2. Computing Context Semantic Relationships
Computing Contexts may relate to other Computing Contexts that are
decomposable in a variety of ways.
o Singleton,
o Tuples (e.g. 2-tuple, n-tuple),
Birkholz, et al. Expires September 13, 2019 [Page 19]
Internet-Draft RATS Arch & Terms March 2019
o Nested,
o Clustered (homogeneous),
o Grouped (heterogenous).
The scope of Computing Context encompasses a broad spectrum of
systems including, but not limited to:
o An information system,
o An object,
o A composition of objects,
o A system component,
o A system sub-component,
o A composition of system sub-components,
o A system entity,
o A composition of system entities.
A Computing Context may be realized in a variety of ways including,
but not limited to:
o A process, thread or task as defined by an operating system,
o A privileged operating system task, interrupt handler or event
handler,
o A virtual machine,
o A virtual machine monitor,
o A processor mode (e.g. system management mode),
o A co-processor,
o A peripheral device,
o A secure element,
o A trusted execution environment,
o A controller, sensor, actutor, switch, router or gateway,
Birkholz, et al. Expires September 13, 2019 [Page 20]
Internet-Draft RATS Arch & Terms March 2019
o An FPGA,
o An ASIC,
o A memory resource,
o A storage resource.
Analogously, a computing sub-context is a decomposition of a
Computing Context; a subsystem is a decomposition of a system; a sub-
component is a decomposition of a component; and a peer node is a
decomposition of a node cluster.
A formal semantic relationship is therefore expressed using an
information model that captures interactions, relationships, bindings
and interfaces among systems, subsystems, system components, system
entities or objects.
[Issue: A tangible relationship to an information model is required
here] An information model that richly captures Computing Context
semantics is therefore believed to be relevant if not fundamental to
Remote Attestation.
8.1.3. Computing Context Identity
The identity of a Computing Context implies there is a binding
operation between an identifier and the Computing Context.
$ Computing Context Identity: Computing Context Identity provides
the basis for associating attestation Evidence about a particular
Computing Context to create believable knowledge about attestation
provenance.
Confidence in the identity assurance level [NIST SP-800-63-3] or the
assurance levels for identity authentication [RFC4949] is a property
of the identifier uniqueness properties and binding operation
veracity. Such properties impact the trustworthiness of associated
attestation Evidence.
8.2. Remote Attestation Concepts
Attestation Evidence created by RATS is a form of telemetry about a
computing environment that enables better security risk management
through disclosure of security properties of the environment.
Attestation may be performed locally (within the same computing
environment) or remotely (between different computing environments).
The exchange of attestation evidence can be formalized to include
well-defined protocol, message syntax and semantics.
Birkholz, et al. Expires September 13, 2019 [Page 21]
Internet-Draft RATS Arch & Terms March 2019
8.3. Core RATS Terminology
$ Attestation: The creation of evidence by the Attester based on
measurements or other claimant output.
A form of telemetry involving the delivery of Claims describing
various security properties of a Computing Context by an Attester,
such that the Claims can be used as Evidence toward convincing a
Verifier regarding trustworthiness of the Computing Context.
$ Conveyance: The transfer of Evidence from the Attester to the
Verifier.
$ Verification: The appraisal of Evidence by the Verifier who
evaluates it against a reference policy. See also RFC4949 [1].
$ Remote Attestation: A procedure involving Attestation, Conveyance
and Verification.
8.4. RATS Information Model Terminology
Evidence conveyed to a Verifier by an Attester is structured to
facilitate syntactic and semantic interoperability. An information
model defines the tag namespaces used to create tag-value pairs
containing discrete bits of Evidence.
$ Evidence: A set of Measurements, quality metrics, quality
procedures or assurance criteria about an Computing Context's
behavioral, operational and intrinsic characteristics.
$ Claim: Structured Evidence asserted about a Computing Context. It
contains metadata that informs regarding the type, class,
representation and semantics of Evidence information. A Claim is
represented as a name-value pair consisting of a Claim Name and a
Claim Value [RFC7519]. In the context of SACM, a Claim is also
specialized as an attribute-value pair that is intended to be
related to a statement [I-D.ietf-sacm-terminology].
$ Attestable Claim: Structured Evidence including one or more Claims
that are asserted by a Claimant (Note: an Attester role doubles as
a Claimant role). An Attestable Claim has the following
structure:
1. A Claim or Claims.
2. A Claimant identity.
3. Proof of Claimant identity.
Birkholz, et al. Expires September 13, 2019 [Page 22]
Internet-Draft RATS Arch & Terms March 2019
4. Proof the Claimant intended to make these Claims.
Note: Proofs of Claims assertions may be separated from the Claim
itself. For example, a secure transport over which Claims are
conveyed where Claimant's signing key integrity protects the
transport payload could be used as proof of Claim assertion.
Alternatively, each Claim could be separately signed by a Claimant.
$ Attested (Asserted) Claim: An Attestable Claim where the proof
elements are populated.
$ Evidence (Claims) Creation: Instantiation of Attested Claims by a
Claimant.
$ Evidence (Claims) Collection: Assembling of Attested Claims by an
Attester for the purpose of Conveyance.
$ Verified (Valid) Claim: An Attested Claim where the proof elements
have been verified by a Verifier according to a policy that
identifies trusted Claimants and/or trusted Evidence values.
8.5. RATS Work-Flow Terminology
This section introduces terms and definitions that are required to
illustrate the scope and the granularity of RATS workflows in the
domain of security automation. Terms defined in the following
sections will be based on this workflow-related definitions.
In general, RATS are composed of iterative activities that can be
conducted in intervals. It is neither a generic set of actions nor
simply a task, because the actual actions to be conducted by RATS can
vary significantly depending on the protocols employed and types of
Computing Contexts involved.
$ Activity: A sequence of actions conducted by Computing Contexts
that compose a Remote Attestation procedure. The actual
composition of actions can vary, depending on the characteristics
of the Computing Context they are conducted by/in and the
protocols used to utilize an Interconnect. A single Activity
provides only a minimal amount of semantic context, e.g.defined by
the Activity's requirements imposed upon the Computing Context, or
via the set of actions it is composed of. Example: The Conveyance
of cryptographic Evidence or the appraisal of Evidence via
imperative guidance.
$ Task: A unit of work to be done or undertaken.
Birkholz, et al. Expires September 13, 2019 [Page 23]
Internet-Draft RATS Arch & Terms March 2019
In the scope of RATS, a task is a procedure to be conducted.
Example: A Verifier can be tasked with the appraisal of Evidence
originating from a specific type of Computing Contexts providing
appropriate identities.
$ Action: The accomplishment of a thing usually over a period of
time, in stages, or with the possibility of repetition.
In the scope of RATS, an action is the execution of an operation
or function in the scope of an Activity conducted by a Computing
Context. A single action provides no semantic context by itself,
although it can limit potential semantic contexts of RATS to a
specific scope. Example: Signing an existing public key via a
specific openssl library, transmitting data, or receiving data are
actions.
$ Procedure: A series of actions that are done in a certain way or
order.
In the scope of RATS, a procedure is a composition of activities
(sequences of actions) that is intended to create a well specified
result with a well established semantic context. Example: The
activities of Attestation, Conveyance and Verification compose a
Remote Attestation procedure.
8.6. RATS Reference Use Cases
A "lying endpoint" is not trustworthy.
This document provides NNN prominent examples of use cases
Attestation procedures are intended to address:
o Verification of the source integrity of a Computing Context via
data integrity proofing of installed software instances that are
executed, and
o Verification of the identity proofing of a Computing Context.
8.6.1. Use Case A
8.6.2. Use Case B
8.7. RATS Reference Terminology
$ Attestable Computing Context: A Computing Context where a Claimant
is able to create Claims, an Attester is able to Attest those
Claims and a Verifier is able to verify the Claims.
Birkholz, et al. Expires September 13, 2019 [Page 24]
Internet-Draft RATS Arch & Terms March 2019
$ Attestation Identity: An identity that refers to an Attester.
$ Attestation Identity Credential: A credential used to authenticate
an Attestation Identity.
$ Attestation Identity Key (AIK): An Attestation Identity Credential
in the form of an asymmetric cryptographic key where the AIK
private key is protected by a Computing Context with protection
properties that are stronger than the Computing Context about
which the AIK attests. A root-of-trust Computing Context normally
protects AIK private keys.
$ Claimant Identity: An identity that refers to an Claimant.
$ Claimant Identity Credential: A credential used to authenticate a
Claimant Identity.
$ Measurements / Integrity Measurements: Metrics of Computing
Context characteristics (i.e. composition, configuration and
state) that affect the confidence in the trustworthiness of a
Computing Context. Digests of integrity Measurements can be
stored in shielded locations (e.g. a PCR of a TPM).
$ Reference Integrity Measurements: Signed Measurements about a
Computing Context's characteristics that are provided by a vendor
or manufacturer and are intended to be used as declarative
guidannce [I-D.ietf-sacm-terminology] (e.g. a signed CoSWID).
$ Root-of-trust: The Computing Context that protects the following
where no other Computing Context is expected to provide its
Attestation Evidence: + Attestation Evidence. + AIKs. + Code
used during the collection and reporting of Attestation Evidence.
$ Root-of-trust-for-measurement (RTM): A trusted Computing Context
where a Claimant creates integrity Measurements and other Evidence
about a Computing Context where no other Computing Context is
expected to provide its Attestation Evidence.
$ Root-of-trust-for-reporting (RTR): A trusted Computing Context
where an Attester stages reporting of Claims where no other
Computing Context is expected to provide its Attestation Evidence.
$ Root-of-trust-for-storage (RTS): A trusted Computing Context where
a Claimaint or Attester stores Claims, Evidence, credentials or
policies associated with Attestation where no other Computing
Context is expected to provide its Attestation Evidence.
Birkholz, et al. Expires September 13, 2019 [Page 25]
Internet-Draft RATS Arch & Terms March 2019
$ Trustworthy Computing Context: A Computing Context that guarantees
trustworthy behavior and/or composition (with respect to certain
declarative guidance and a scope of confidence). A trustworthy
Computing Context is a trustworthy system.
<NMS: is this necessary?> Trustworthy Statement: Evidence conveyed
by a Computing Context that is not necessarily trustworthy.
[update with tamper related terms]
8.8. Interpretations of RFC4949 Terminology for Attestation
Assurance: An attribute of an information system that provides
grounds for having confidence that the system operates such that
the system's security policy is enforced [RFC4949] (see Trusted
System below).
In common criteria, assurance is the basis for the metric level of
assurance, which represents the "confidence that a system's
principal security features are reliably implemented".
The NIST Handbook [get ref from 4949] notes that the levels of
assurance defined in Common Criteria represent "a degree of
confidence, not a true measure of how secure the system actually
is. This distinction is necessary because it is extremely
difficult-and in many cases, virtually impossible-to know exactly
how secure a system is."
Historically, assurance was well-defined in the Orange Book
[http://csrc.nist.gov/publications/history/dod85.pdf] as
"guaranteeing or providing confidence that the security policy has
been implemented correctly and that the protection-relevant
elements of the system do, indeed, accurately mediate and enforce
the intent of that policy. By extension, assurance must include a
guarantee that the trusted portion of the system works only as
intended."
Confidence: The definition of correctness integrity in [RFC4949]
notes that "source integrity refers to confidence in data values".
Hence, confidence in an Attestation procedure is referring to the
degree of trustworthiness of an Attestation Activity that produces
Evidence (Attester), of an Conveyance Activity that transfers
Evidence (interconnect), and of a Verification Activity that
appraises Evidence (Verifier), in respect to correctness
integrity.
Correctness: The property of a system that is guaranteed as the
result of formal Verification activities.
Birkholz, et al. Expires September 13, 2019 [Page 26]
Internet-Draft RATS Arch & Terms March 2019
Correctness integrity: The property that the information represented
by data is accurate and consistent.
Data Integrity: (a) The property that data has not been changed,
destroyed, or lost in an unauthorized or accidental manner. (See:
data integrity service. Compare: correctness integrity, source
integrity.)
(b) The property that information has not been modified or
destroyed in an unauthorized manner.
Entity: A principal, Subject, relying party or stake holder in an
Attestation ecosystem.
Identity: The set of attributes that distinguishes a principal.
Identifier: The set of attributes that distinguishes an object.
Identity Proofing: A vetting process that verifies the information
used to establish the identity of a system entity.
(Information) System: An organized assembly of computing and
communication resources and procedures - i.e., equipment and
services, together with their supporting infrastructure,
facilities, and personnel - that create, collect, record, process,
store, transport, retrieve, display, disseminate, control, or
dispose of information to accomplish a specified set of functions.
Object: A system component that contains or receives information.
Source Integrity: The property that data is trustworthy (i.e.,
worthy of reliance or trust), based on the trustworthiness of its
sources and the trustworthiness of any procedures used for
handling data in the system.
Subject: A Computing Context acting in accordance with the interests
of a principal.
Subsystem: A collection of related system components that together
perform a system function or deliver a system service.
System Component: An instance of a system resource that (a) forms a
physical or logical part of the system, (b) has specified
functions and interfaces, and (c) is extant (e.g., by policies or
specifications) outside of other parts of the system. (See:
subsystem.)
Birkholz, et al. Expires September 13, 2019 [Page 27]
Internet-Draft RATS Arch & Terms March 2019
An identifiable and self-contained part of a $Target-of-
Evaluation.
Token: A data structure suitable for containing Claims.
Trusted (Trustworthy) System: A system that operates as expected,
according to design and policy, doing what is required - despite
environmental disruption, human user and operator errors, and
attacks by hostile parties - and not doing other things.
Verification: (a) The process of examining information to establish
the truth of a claimed fact or value.
(b) The process of comparing two levels of system specification
for proper correspondence, such as comparing a security model with
a top-level specification, a top-level specification with source
code, or source code with object code.
8.9. Building Block Vocabulary (Not in RFC4949)
[working title, pulled from various sources, vital]
Attribute: TBD
Characteristic: TBD
Context: TBD
Endpoint: TBD
Environment: TBD
Manifest: TBD
Telemetry: An automated communications process by which data,
readings, Measurements and Evidence are collected at remote points
and transmitted to receiving equipment for monitoring and
analysis. Derived from the Greek roots tele = remote, and metron
= measure.
9. IANA considerations
This document will include requests to IANA:
o first item
o second item
Birkholz, et al. Expires September 13, 2019 [Page 28]
Internet-Draft RATS Arch & Terms March 2019
10. Security Considerations
There are always some.
11. Acknowledgements
Maybe.
12. Change Log
No changes yet.
13. References
13.1. 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>.
[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>.
13.2. Informative References
[I-D.ietf-sacm-terminology]
Birkholz, H., Lu, J., Strassner, J., Cam-Winget, N., and
A. Montville, "Security Automation and Continuous
Monitoring (SACM) Terminology", draft-ietf-sacm-
terminology-16 (work in progress), December 2018.
[I-D.mandyam-eat]
Mandyam, G., Lundblade, L., Lundblade, L., Ballesteros,
M., and J. O'Donoghue, "The Entity Attestation Token
(EAT)", draft-mandyam-eat-01 (work in progress), November
2018.
[I-D.richardson-rats-usecases]
Richardson, M., "Use cases for Remote Attestation common
encodings", draft-richardson-rats-usecases-00 (work in
progress), March 2019.
Birkholz, et al. Expires September 13, 2019 [Page 29]
Internet-Draft RATS Arch & Terms March 2019
[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-00 (work in
progress), March 2019.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
13.3. URIs
[1] https://tools.ietf.org/html/rfc4949
Authors' Addresses
Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
Darmstadt 64295
Germany
Email: henk.birkholz@sit.fraunhofer.de
Monty Wiseman
GE Global Research
USA
Email: monty.wiseman@ge.com
Hannes Tschofenig
ARM Ltd.
110 Fulbourn Rd
Cambridge CB1 9NJ
UK
Email: hannes.tschofenig@gmx.net
Birkholz, et al. Expires September 13, 2019 [Page 30]
Internet-Draft RATS Arch & Terms March 2019
Ned Smith
Intel Corporation
USA
Email: ned.smith@intel.com
Birkholz, et al. Expires September 13, 2019 [Page 31]