Network Working Group J. Richer, Ed.
Internet-Draft Bespoke Engineering
Intended status: Standards Track L. Johansson
Expires: March 7, 2016 Swedish University Network
September 4, 2015
Vectors of Trust
draft-richer-vectors-of-trust-01
Abstract
This document defines a mechanism for describing and signaling
several aspects that are used to calculate trust placed in a digital
identity transaction.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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 http://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 March 7, 2016.
Copyright Notice
Copyright (c) 2015 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
Richer & Johansson Expires March 7, 2016 [Page 1]
Internet-Draft vectors-of-trust September 2015
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
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. An Identity Model . . . . . . . . . . . . . . . . . . . . 4
1.3. Component Architecture . . . . . . . . . . . . . . . . . 5
2. Core Components . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Identity Proofing . . . . . . . . . . . . . . . . . . . . 6
2.2. Primary Credential Usage . . . . . . . . . . . . . . . . 6
2.3. Primary Credential Management . . . . . . . . . . . . . . 6
2.4. Assertion Presentation . . . . . . . . . . . . . . . . . 6
3. Vectors of Trust Inititial Component Definitions . . . . . . 7
4. Communicating Vector Values to RPs . . . . . . . . . . . . . 8
4.1. On the Wire Representation . . . . . . . . . . . . . . . 8
4.2. In OpenID Connect . . . . . . . . . . . . . . . . . . . . 9
4.3. In SAML . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Requesting Vector Values . . . . . . . . . . . . . . . . . . 10
5.1. In OpenID Connect . . . . . . . . . . . . . . . . . . . . 10
6. Discovery and Verification . . . . . . . . . . . . . . . . . 10
6.1. Trustmark . . . . . . . . . . . . . . . . . . . . . . . . 10
6.2. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8.1. Vector Of Trust Components Registry . . . . . . . . . . . 12
8.2. Additions to JWT Claims Registry . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
10. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Document History . . . . . . . . . . . . . . . . . . 14
Appendix B. Example Extension . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
This document defines a mechanism for describing and signaling
several aspects of digital identity transactions that are used to
determine a level of trust in that transaction. In the past, there
have been two extremes of communicating authentication transaction
information. On one end, all attributes are communicated with full
provenance and associated trust markings. This approach seeks to
Richer & Johansson Expires March 7, 2016 [Page 2]
Internet-Draft vectors-of-trust September 2015
create a fully distributed attribute system that can be used for
things like attribute based access control (ABAC). These attributes
can be used to describe the end user, the identity provider, the
relying party, or even the transaction itself. While the information
that can be expressed in this model is incredible, the complexity of
such a system is often prohibitive to align across security domains,
especially to relying parties needing to process the sea of disparate
attributes.
At the other extreme there are systems that collapse all of the
attributes and aspects into a single scalar value that communicates,
in sum, how much a transaction can be trusted. The NIST special
publication 800-63 [SP-800-63] defines a linear scale Level of
Assurance (LoA) measure that combines multiple attributes about an
identity transaction into a single measure of the level of trust a
relying party should place on an identity transaction. Even though
this definition was originally made for a specific government use
cases, the LoA scale appeared to be applicable with a wide variety of
authentication use cases. This has led to a proliferation of
incompatible interpretations of the same scale in different trust
frameworks, preventing interoperability between these frameworks in
spite of their common measurement. Since identity proofing strength
increases linearly along with credential strength in the LoA scale,
this scale is too limited for describing many valid and useful forms
of an identity transaction. For example, an anonymously assigned
hardware token can be used in cases where the real world identity of
the subject cannot be known, for privacy reasons, but the credential
itself can be highly trusted.
This work seeks to find a balance between these two extremes by
creating a data model that combines attributes of the user and
aspects of the authenticaiton context into several values that can be
communicated together. This approach is both coarser grained than
the distributed attributes model and finer grained than the single
value model, with the hope that it is a viable balance of
expressivity and processability. Importantly, these three levels of
granularity can be mapped to each other. The information of several
attributes can be folded into a vector component, while the vector
itself can be folded into an assurance category. As such, the
vectors of trust seeks to complement, not replace, these other
identity and trust mechanisms.
1.1. Terminology
Identity Provider (IdP) A system that manages identity information
and is able to assert this information across the network through
an identity API.
Richer & Johansson Expires March 7, 2016 [Page 3]
Internet-Draft vectors-of-trust September 2015
Identity Subject The person (user) engaging in the identity
transaction, being identified by the identity provider and
identified to the relying party.
Primary Credential The credential used by the identity subject to
authenticate to the identity provider.
Federated Credential The assertion presented by the IdP to the RP
across the network to authenticate the user.
Relying Party (RP) A system that consumes identity information from
an IdP for the purposes of authenticating the user.
Trust Framework A document containing business rules and legal
clauses that defines how different parties in an identity
transaction may act.
Trustmark A verifiable attestation that a party has proved to follow
the constraints of a trust framework.
Trustmark Provider A system that issues and provides verification
for trustmarks.
Vector A multi-part data structure, used here for conveying
information about an authentication transaction.
Vector Component One of several constituent parts that make up a
vector.
1.2. An Identity Model
This document assumes the following (incomplete) model for identity.
The identity subject (aka user) is associated with an identity
provider which acts as a trusted 3rd party on behalf of the user with
regard to a relying party by making identity assertions about the
user to the relying party.
The real-world person represented by the identity subject is in
possession of a primary credential bound to the identity subject by
identity provider (or an agent thereof) in such a way that the
binding between the credential and the real-world user is a
representation of the identity proofing process performed by the the
identity provider (or an agent thereof) to verify the identity of the
real-world person.
Richer & Johansson Expires March 7, 2016 [Page 4]
Internet-Draft vectors-of-trust September 2015
1.3. Component Architecture
The term Vectors of Trust is based on the mathematical construct of a
Vector, which is defined as an item composed of multiple independent
scalar values. A vector is a set of coordinates that specifies a
point in a (multi-dimensional) Cartesian coordinate space. The
reader is encouraged to think of a vector of trust as a point in a
coordinate system, in the simples form (described below) a 3
dimensional space that is intended to be a recognizable, if somewhat
elided, model of identity subject trust.
An important goal for this work is to balance the need for simplicity
(particularly on the part of the relying party) with the need for
expressiveness. As such, this vector construct is designed to be
composable and extensible.
All components of the vector construct MUST be orthogonal in the
sense that no aspect of a component overlap an aspect of another
component.
The values assigned to each component of a vector is sometimes
written as an ordinal number (e.g. an integer) but MUST NOT be
assumed as having inherent ordinal properties when compared to the
same or other components in the vector space. In other words, 1 is
different from 2, but it is dangerous to assume that 2 is always
"more" (better) than 1.
2. Core Components
This specification defines four orthogonal components: identity
proofing, primary credential usge, primary credential management, and
assertion presentation. These dimensions MUST be evaluated in the
context of a trust framework and SHOULD be combined with other
information when making a trust and authorization decision.
This specification also defines values for each component to be used
in the absence of a more specific trust framework. It is expected
that trust frameworks will provide context, semantics, and mapping to
legal statutes and business rules for each value in each component.
Consequently, a particular vector value can only be compared with
vectors defined in the same context. The RP MUST understand and take
into account the trust framework context in which a vector is being
expressed in order for it to be processed securely.
It is anticipated that trust frameworks will also define additional
components using the component registry established in Section 8.
Richer & Johansson Expires March 7, 2016 [Page 5]
Internet-Draft vectors-of-trust September 2015
Each component is identified by a demarcator consisting of a single
case-sensitive ASCII character in the range [A-Za-z]. A value for a
given component is defined by its demarcator character followed by a
single case-sensitive ASCII character in the range [0-9A-Za-z].
2.1. Identity Proofing
The Identity Proofing dimension defines, overall, how strongly the
set of identity attributes have been verified and vetted, and how
strongly they are tied to a particular credential set. In other
words, this dimension describes how likely it is that a given digital
identity corresponds to a particular (real-world) identity subject.
This dimension SHALL be represented by the "P" demarcator and a
single-character level value, such as "P1", "P2", etc.
2.2. Primary Credential Usage
The primary credential usage dimension defines how strongly the
primary credential can be verified by the IdP. In other words, and
how easily that credential could be spoofed or stolen.
This dimension SHALL be represented by the "C" demarcator and a
single-character level value, such as "C1", "C2", etc. Multiple
credential usage factors MAY be communicated simultaneously, such as
when Multi-Factor Authentication is used.
2.3. Primary Credential Management
The primary credential management dimension conveys information about
the expected lifecycle of the primary credential in use, including
its binding, rotation, and revocation. This component defines how
strongly the primary credential can be trusted to be presented by the
party represented by the credential based on knowledge of the
management of the credentials at the IdP. In other words, this
dimension describes how likely it is that the right person is
presenting the credential to the identity provider.
This dimension SHALL be represented by the "M" demarcator and a
single-character level value, such as "M1", "M2", etc.
2.4. Assertion Presentation
The Assertion Presentation dimension defines how well the given
digital identity can be communicated across the network without
information leaking to unintended parties, and without spoofing. In
other words, this dimension describes how likely it is that a given
digital identity asserted was actually asserted by a given identity
Richer & Johansson Expires March 7, 2016 [Page 6]
Internet-Draft vectors-of-trust September 2015
provider for a given transaction. While this information is largely
already known by the RP by the nature of processing an identity
assertion, this dimension is still useful when the RP requests a
login (Section 5) and when describing the capabilities of an IdP
(Section 6.2).
This dimension SHALL be represented by the "A" demarcator and a level
value, such as "A1", "A2", etc.
3. Vectors of Trust Inititial Component Definitions
This specification defines the following general-purpose component
definitions, which MAY be used when a more specific set is
unavailable. These component values are referenced in a trustmark
definition defined by [[ this document URL ]].
P0 No proofing is done, data is not guaranteed to be persistent
across sessions
P1 Attributes are self-asserted but consistent over time, potentially
pseudonymous
P2 Identity has been proofed either in person or remotely using
trusted mechanisms (such as social proofing)
P3 There is a binding relationship between the identity provider and
the identified party (such as signed/notarized documents,
employment records)
C0 No credential is used / anonymous public service / simple session
cookies (with nothing else)
C1 Known device
C2 Shared secret such as a username and password combination
C3 Cryptographic proof of key possession using shared key
C4 Cryptographic proof of key possession using asymmetric key
C5 Sealed hardware token / trusted biometric / TPM-backed keys
M0 Self-asserted credentials
M1 Remote issuance and rotation / use of backup recover credentials
(such as email verification) / deletion on user request
Richer & Johansson Expires March 7, 2016 [Page 7]
Internet-Draft vectors-of-trust September 2015
M2 Full proofing required for each issuance and rotation / revocation
on suspicious activity
A0 No protection / unsigned bearer identifier (such as a session
cookie)
A1 Signed and verifiable token, passed through the browser
A2 Signed and verifiable token, passed through a back channel
A3 Token encrypted to the relying parties key and audience protected
4. Communicating Vector Values to RPs
All four of these dimensions (and others, as they are defined in
extension work) MUST be combined into a single vector that can be
communicated across the wire unbroken. All vector components MUST be
individually available, MUST NOT be "collapsed" into a single value
without also presenting the constituent dimensions as well.
When communicating the vectors across the wire, they MUST be
protected in transit and MUST signed by the asserting authority (such
as the IdP).
4.1. On the Wire Representation
The vector MUST be represented as a period-separated ('.') list of
vector components, with no specific order. A vector component type
MAY occur multiple times within a single vector, with each component
separated by periods. Multiple values for a component are considered
an AND of the values. A single value of a vector component MUST NOT
occur more than once in a single vector. In order to simplify
processing by RPs, it is RECOMMENDED that trust framework definitions
carefully define component values such that they are mutually
exclusive or subsumptive in order to avoid repeated vector components
where possible.
Vector components MAY be omitted from a vector. No holding space is
left for an omitted vector component. If a vector component is
omitted, the IdP is making no claim for that category.
For example, the vector value "P1.C3.A2" translates to pseudonymous,
proof of shared key, signed back-channel verified token in the
context of this specification's definitions (Section 3).
Vector values MUST be communicated along side of a trustmark
definition to give the components context. A vector value without
context is unprocessable.
Richer & Johansson Expires March 7, 2016 [Page 8]
Internet-Draft vectors-of-trust September 2015
4.2. In OpenID Connect
In OpenID Connect [OpenID], the IdP MUST send the vector value as a
string with the "vot" (vector of trust) claim in the ID token. The
trustmark (Section 6.1) that applies to this vector MUST be sent as
an HTTPS URL in the "vtm" (vector trust mark) claim to provide
context to the vector.
For example:
{
"iss": "https://idp.example.com/",
"sub": "jondoe1234",
"vot": "P1.C3.A2",
"vtm": "https://trustmark.example.org/trustmark/idp.example.com"
}
4.3. In SAML
In SAML a VoT vector is communicated as an
AuthenticationContextClassRef, a sample definition of which might
look something like this:
VoT vector P1.C3.A2
Richer & Johansson Expires March 7, 2016 [Page 9]
Internet-Draft vectors-of-trust September 2015
5. Requesting Vector Values
In some identity protocols, the RP can request that particular
attributes be applied to a given identity transaction.
5.1. In OpenID Connect
In OpenID Connect [OpenID], the client can request a set of
acceptable VoT values with the "vtr" (vector of trust request) claim
request as part of the Request Object. The value of this field is an
array of JSON strings, each string identifying an acceptable set of
vector components. The components within each vector are ANDed
together while the individual vector strings are ORed together.
Vector request values MAY omit components, indicating that any value
is acceptable.
{
"vtr": ["P1.C2.C3.A2", "C5.A2"]
}
6. Discovery and Verification
6.1. Trustmark
When an RP receives a specific vector from an IdP, it needs to make a
decision to trust the vector within a specific context. A trust
framework can provide such a context, allowing legal and business
rules to give weight to an IdP's claims. A trustmark is a verifiable
claim to conform to a specific component of a trust framework, such
as a verified identity provider. The trustmark conveys the root of
trustworthiness about the claims and assertions made by the IdP.
The trustmark MUST be available from an HTTPS URL served by the trust
framework provider. The contents of this URL are a JSON [RFC7159]
document with the following fields:
idp The issuer URL of the identity provider that this trustmark
pertains to. This MUST match the corresponding issuer claim in
the identity token, such as the OpenID Connect "iss" field. This
MUST be an HTTPS URL.
trustmark_provider The issuer URL of the trustmark provider that
issues this trustmark. The URL that a trustmark is fetched from
MUST start with the "iss" URL in this field. This MUST be an
HTTPS URL.
P Array of strings containing identity proofing values for which the
identity provider has been assessed and approved
Richer & Johansson Expires March 7, 2016 [Page 10]
Internet-Draft vectors-of-trust September 2015
C Array of strings containing primary credential usage values for
which the identity provider has been assessed and approved
M Array of strings containing primary credential management values
for which the identitity provider has been assessed and approved
A Array of strings containing assertion strength values for which
the identity provider has been assessed and approved
Additional vector component values MUST be listed in a similar
fashion using their demarcator.
For example, the following trustmark provided by the
trustmark.example.org organization applies to the idp.example.org
identity provider:
{
"idp": "https://idp.example.org/",
"trustmark_provider": "https://trustmark.example.org/",
"P": ["P0", "P1"],
"C": ["C1", "C2", "C3"],
"M": ["M2"],
"A": ["C2", "C3"]
}
A client wishing to check the claims made by an IdP can fetch the
information from the trustmark provider about what claims the IdP is
allowed to make in the first place and process them accordingly.
The means by which the RP decides which trustmark providers it trusts
is out of scope for this specification and is generally configured
out of band.
Though most trust frameworks will provide a third-party independent
verification service for components, an IdP MAY host its own
trustmark. For example, a self-hosted trustmark would look like:
{
"idp": "https://idp.example.org/",
"trustmark_provider": "https://idp.example.org/",
"P": ["C0", "C1"],
"C": ["C1", "C2", "C3"],
"M": ["M2"],
"A": ["C2", "C3"]
}
Richer & Johansson Expires March 7, 2016 [Page 11]
Internet-Draft vectors-of-trust September 2015
6.2. Discovery
The IdP MAY list all of its available trustmarks as part of its
discovery document, such as the OpenID Connect Discovery server
configuration document. Trustmarks are listed in the trustmarks
element which contains a single JSON [RFC7159] object. The keys of
this JSON object are trustmark provider issuer URLs and the values of
this object are the corresponding trustmarks for this IdP.
{
"trustmark": {
"https://trustmark.example.org/": "https://trustmark.example.org/trustmark/idp.example.org/
}
}
7. Acknowledgements
The authors would like to thank the members of the Vectors of Trust
mailing list in the IETF for discussion and feedback on the concept
and document.
8. IANA Considerations
This specification creates one registry and registers several values
into an existing registry.
8.1. Vector Of Trust Components Registry
The Vector of Trust Components Registry contains the definitions of
vector components and their associated demarcators.
o Demarcator Symbol: P
o Description: Identity proofing
o Document: [[ this document ]]
o Demarcator Symbol: C
o Description: Primary credential usage
o Document: [[ this document ]]
o Demarcator Symbol: M
o Description: Primary credential management
o Document: [[ this document ]]
Richer & Johansson Expires March 7, 2016 [Page 12]
Internet-Draft vectors-of-trust September 2015
o Demarcator Symbol: A
o Description: Assertion presentation
o Document: [[ this document ]]
8.2. Additions to JWT Claims Registry
This specification adds the following values to the JWT Claims
Registry.
o Claim name: vot
o Description: Vector of Trust value
o Document: [[ this document ]]
o Demarcator Symbol: vtm
o Description: Vector of Trust Trustmark
o Document: [[ this document ]]
o Demarcator Symbol: vtr
o Description: Vector of Trust Request
o Document: [[ this document ]]
9. Security Considerations
The vector of trust value MUST be cryptographically protected in
transit, using TLS. The vector of trust value MUST be associated
with a trustmark marker, and the two MUST be carried together in a
cryptographically bound mechanism such as a signed identity
assertion.
10. Privacy Considerations
By design, vector of trust values contain information about a user's
identity and assications that can be made thereto. Therefore, all
aspects of a vector of trust contain potentially privacy-sensitive
information and MUST be guarded as such.
Richer & Johansson Expires March 7, 2016 [Page 13]
Internet-Draft vectors-of-trust September 2015
11. References
11.1. Normative References
[OpenID] Sakimura, N., Bradley, J., and M. Jones, "OpenID Connect
Core 1.0", November 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, .
11.2. Informative References
[SP-800-63]
, , , , , , and , "Electronic Authentication Guideline",
August 2013.
Appendix A. Document History
- 01
o Added IANA registry for components.
o Added preliminary security considerations and privacy
considerations.
o Split "credential binding" into "primary credential usage" and
"primary credential management".
- 00
o Created initial IETF drafted based on strawman proposal discussed
on VoT list.
o Split vector component definitions into their own section to allow
extension and override.
o Solidified trustmark document definition.
Richer & Johansson Expires March 7, 2016 [Page 14]
Internet-Draft vectors-of-trust September 2015
Appendix B. Example Extension
To extend the vector component definitions, a specification MUST
register its contents in the
Authors' Addresses
Justin Richer (editor)
Bespoke Engineering
Email: ietf@justin.richer.org
Leif Johansson
Swedish University Network
Thulegatan 11
Stockholm
Sweden
Email: leifj@sunet.se
URI: http://www.sunet.se
Richer & Johansson Expires March 7, 2016 [Page 15]