One document matched: draft-richer-vectors-of-trust-00.txt
Network Working Group J. Richer, Ed.
Internet-Draft Bespoke Engineering
Intended status: Standards Track L. Johansson
Expires: December 28, 2015 Swedish University Network
June 26, 2015
Vectors of Trust
draft-richer-vectors-of-trust-00
Abstract
This document defines a mechanism for describing and signaling
several aspects that go into a determination of 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
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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
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This Internet-Draft will expire on December 28, 2015.
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
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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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 . . . . . . . . . . . . . . . . . . . . . . . 2
2. Background and Motivation . . . . . . . . . . . . . . . . . . 3
2.1. An Identity Model . . . . . . . . . . . . . . . . . . . . 3
2.2. Component Architecture . . . . . . . . . . . . . . . . . 4
3. Core components . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Identity Proofing . . . . . . . . . . . . . . . . . . . . 5
3.2. Credential Management . . . . . . . . . . . . . . . . . . 5
3.3. Assertion Presentation . . . . . . . . . . . . . . . . . 5
4. Vectors of Trust Inititial component definitions . . . . . . 6
5. Communicating Vector Values to RPs . . . . . . . . . . . . . 7
5.1. On the Wire Representation . . . . . . . . . . . . . . . 7
5.2. In OpenID Connect . . . . . . . . . . . . . . . . . . . . 7
5.3. In SAML . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Requesting Vector Values . . . . . . . . . . . . . . . . . . 8
6.1. In OpenID Connect . . . . . . . . . . . . . . . . . . . . 9
7. Discovery and Verification . . . . . . . . . . . . . . . . . 9
7.1. Trustmark . . . . . . . . . . . . . . . . . . . . . . . . 9
7.2. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Document History . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
This document defines a mechanism for describing and signaling
several aspects that go into a determination of trust placed in a
digital identity transaction. Instead of communicating
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.
Relying Party (RP) A system that consumes identity information from
an IdP for the purposes of logging users in.
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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.
2. Background and Motivation
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, the LoA scale is also 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 or is verified
through some out of band mechanism.
This work seeks to decompose the elements of the LoA values in a way
that they can be independently communicated from an Identity Provider
to a Relying Party, making comparison between trust frameworks
possible.
2.1. 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
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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 (cryptographic) primary credential bound to the user
by (an agent of) identity provider 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 (agent of) the
identity provider to verify the identity of the real-world person.
2.2. 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.
3. Core components
This specification defines three orthogonal components: identity
proofing, credential binding, and assertion presentation. These
dimensions (as described below) are intentionally elided and SHOULD
be combined with other information to form trust frameworks can be
used as a basis for audits of identity providers and relying parties.
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
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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.
3.1. 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 level
value, such as "P1", "P2", etc.
3.2. Credential Management
Below we use the term "credential" to denote the credential used by
the identity subject to authenticate to the identity provider.
The Credential Binding dimension defines how strongly the credential
can be verified by the IdP and trusted to be presented by the party
represented by a given credential. In other words, this dimension
describes how likely it is that the right person is presenting the
credential to the identity provider, and how easily that credential
could be spoofed or stolen. This component is intended to be a
general category
This dimension SHALL be represented by the "C" demarcator and a level
value, such as "C1", "C2", etc. Multiple credential factors MAY be
communicated simultaneously, such as when Multi-Factor Authentication
is used.
3.3. 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
provider for a given transaction.
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This dimension SHALL be represented by the "A" demarcator and a level
value, such as "A1", "A2", etc.
4. 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
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 legal or contractual 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 Shared secret such as a username and password combination
C2 Known device with trusted enrollment process
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
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
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5. Communicating Vector Values to RPs
All three 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 signed by the asserting authority (such as
the IdP).
5.1. 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, separated by
periods, in which case it is considered an AND of the two values. 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 this
situation 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 4).
Vector values MUST be communicated along side of a trustmark
definition to give the components context.
5.2. 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 7.1) 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:
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{
"iss": "https://idp.example.com/",
"sub": "jondoe1234",
"vot": "P1.C3.A2",
"vtm": "https://trustmark.example.org/trustmark/idp.example.com"
}
5.3. In SAML
In SAML a VoT vector is communicated as an
AuthenticationContextClassRef, a sample definition of which might
look something like this:
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
targetNamespace="urn:x-vot:P1:C3:A2"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns="urn:x-vot:P1:C3:A2"
finalDefault="extension"
blockDefault="substitution"
version="2.0">
<xs:redefine
schemaLocation="saml-schema-authn-context-loa-profile.xsd"/>
<xs:annotation>
<xs:documentation>VoT vector P1.C3.A2</xs:documentation>
</xs:annotation>
<xs:complexType name="GoverningAgreementRefType">
<xs:complexContent>
<xs:restriction base="GoverningAgreementRefType">
<xs:attribute name="governingAgreementRef"
type="xs:anyURI"
fixed="draft-ietf-vot-this-document-00.txt"
use="required"/>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
</xs:redefine>
</xs:schema>
6. Requesting Vector Values
In some identity protocols, the RP can request that particular
attributes be applied to a given identity transaction.
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6.1. 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 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"]
}
7. Discovery and Verification
7.1. 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 by the trust
framework provider. The contents of this URL are a JSON [RFC7159]
document with the following fields:
sub 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.
iss 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
C Array of strings containing credential strength values for which
the identity provider has been assessed and approved
A Array of strings containing assertion strength values for which
the identity provider has been assessed and approved
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For example, the following trustmark provided by the
trustmark.example.org organization applies to the idp.example.org
identity provider:
{
"sub": "https://idp.example.org/",
"iss": "https://trustmark.example.org/",
"P": ["0", "1"],
"C": ["1", "2", "3"],
"A": ["2", "3"]
}
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:
{
"sub": "https://idp.example.org/",
"iss": "https://idp.example.org/",
"P": ["0", "1"],
"C": ["1", "2", "3"],
"A": ["2", "3"]
}
7.2. Discovery
The IdP MAY list all of its available trustmarks as part of its
discovery 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/
}
}
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8. 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.
9. References
9.1. 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, March 1997.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, March 2014.
9.2. Informative References
[SP-800-63]
, , , , , , and , "Electronic Authentication Guideline",
August 2013.
Appendix A. Document History
- 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.
Authors' Addresses
Justin Richer (editor)
Bespoke Engineering
Email: ietf@justin.richer.org
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Leif Johansson
Swedish University Network
Thulegatan 11
Stockholm
Sweden
Email: leifj@sunet.se
URI: http://www.sunet.se
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