Network Working Group J. Richer, Ed.
Internet-Draft Bespoke Engineering
Intended status: Standards Track L. Johansson
Expires: March 16, 2018 Swedish University Network
September 12, 2017
Vectors of Trust
draft-richer-vectors-of-trust-06
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", "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 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 March 16, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. An Identity Model . . . . . . . . . . . . . . . . . . . . 5
1.3. Component Architecture . . . . . . . . . . . . . . . . . 5
2. Component Definitions . . . . . . . . . . . . . . . . . . . . 5
2.1. Identity Proofing . . . . . . . . . . . . . . . . . . . . 6
2.2. Primary Credential Usage . . . . . . . . . . . . . . . . 7
2.3. Primary Credential Management . . . . . . . . . . . . . . 7
2.4. Assertion Presentation . . . . . . . . . . . . . . . . . 7
3. Vectors of Trust Default Component Value Definitions . . . . 8
3.1. Identity Proofing . . . . . . . . . . . . . . . . . . . . 8
3.2. Primary Credential Usage . . . . . . . . . . . . . . . . 8
3.3. Primary Credential Management . . . . . . . . . . . . . . 9
3.4. Assertion Presentation . . . . . . . . . . . . . . . . . 9
4. Communicating Vector Values to RPs . . . . . . . . . . . . . 10
4.1. On the Wire Representation . . . . . . . . . . . . . . . 10
4.2. In OpenID Connect . . . . . . . . . . . . . . . . . . . . 11
4.3. In SAML . . . . . . . . . . . . . . . . . . . . . . . . . 12
5. Requesting Vector Values . . . . . . . . . . . . . . . . . . 13
5.1. In OpenID Connect . . . . . . . . . . . . . . . . . . . . 13
5.2. In SAML . . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Trustmark . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Defining New Vector Values . . . . . . . . . . . . . . . . . 16
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
10.1. Vector Of Trust Components Registry . . . . . . . . . . 17
10.1.1. Registration Template . . . . . . . . . . . . . . . 17
10.1.2. Initial Registry Contents . . . . . . . . . . . . . 18
10.2. Additions to the OAuth Parameters Registry . . . . . . . 18
10.3. Additions to JWT Claims Registry . . . . . . . . . . . . 19
11. Security Considerations . . . . . . . . . . . . . . . . . . . 19
12. Privacy Considerations . . . . . . . . . . . . . . . . . . . 19
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
13.1. Normative References . . . . . . . . . . . . . . . . . . 20
13.2. Informative References . . . . . . . . . . . . . . . . . 20
Appendix A. Document History . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
This document defines a mechanism for measuring and signaling several
aspects of digital identity and authentication 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.
At one extreme, all attributes can be communicated with full
provenance and associated trust markings. This approach seeks to
create a fully-distributed attribute system to support functions such
as 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 incredibly detailed and robust, the
complexity of such a system is often prohibitive to realize,
especially across security domains. In particular, a large burden is
placed on relying parties needing to process the sea of disparate
attributes when making a security decision.
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-800-63-2] up to and including version 2
defines a linear scale Level of Assurance (LoA) measure that combines
multiple aspects about an identity transaction into such a single
measure. While this definition was originally narrowly targeted for
a specific set of government use cases, the LoA scale appeared to be
applicable with a wide variety of authentication scenarios in
different domains. This has led to a proliferation of incompatible
interpretations of the same scale in different contexts, preventing
interoperability between each LoA definition in spite of their common
measurement. LoA is artificially limited due to the original goal of
creating a single linear scale. 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 that do not fit the government's original
model. 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 is in contrast with a government employee accessing a
government system, where the identity of the individual would need to
be highly proofed and strongly credentialed at the same time. In
fact, the latest update of NIST special publication 800-63
[SP-800-63-3] (version 3) has done away with this single linear scale
for exactly these reasons.
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The Vectors of Trust (VoT) effort seeks to find a balance between
these two extremes by creating a data model that combines attributes
of the user and aspects of the authentication context into several
values that can be communicated separately but in parallel with each
other. This approach is both coarser grained than the distributed
attributes model and finer grained than the single scalar model, with
the hope that it is a viable balance of expressibility 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 in the larger identity ecosystem while providing a single
value for RPs to process.
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.
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 means 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.
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Vector Component One of several constituent parts that make up a
vector.
1.2. An Identity Model
This document assumes the following model for identity based on
identity federation technologies:
The identity subject (also known as the user) is associated with an
identity provider which acts as a trusted third 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
the 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
identity provider (or an agent thereof) to verify the identity of the
real-world person. This is all carried by an identity assertion
across the network to the relying party during the authentication
transaction.
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
values.
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 such that
no aspect of a component overlaps an aspect of another component, as
much as is possible.
2. Component Definitions
This specification defines four orthogonal components: identity
proofing, primary credential usage, primary credential management,
and assertion presentation. These dimensions MUST be evaluated by
the RP in the context of a trust framework and SHOULD be combined
with other information when making a trust and authorization
decision.
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This specification also defines values for each component to be used
in the absence of a more specific trust framework in Section 3. 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.
Each component is identified by a demarcator consisting of a single
uppercase ASCII letter in the range "[A-Z]". The demarcator SHOULD
reflect the category with which it is associated in a natural manner.
Demarcators for components MUST be registered as described in
Section 10. It is anticipated that trust framework definitions will
use this registry to define specialized components, though it is
RECOMMENDED that trust frameworks re-use existing components wherever
possible.
The value for a given component within a vector of trust is defined
by its demarcator character followed by a single digit or lowercase
ASCII letter in the range "[0-9a-z]". Categories which have a
natural ordering SHOULD use digits, with "0" as the lowest value.
Categories which do not have a natural ordering, or which can have an
ambiguous ordering, SHOULD use letters. Categories MAY use both
letter style and number style value indicators. For example, a
category could define "0" as a special "empty" value while using
letters such as "a", "b", "c" for normal values can to differentiate
between these types of options.
Regardless of the type of value indicator used, the values assigned
to each component of a vector MUST NOT be assumed always to have
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 better
than "1" in a given transaction.
Each component MAY be repeated with multiple different values within
a single vector. The same component and value MUST NOT be repeated
within a single vector.
2.1. Identity Proofing
The Identity Proofing dimension defines, overall, how strongly the
set of identity attributes have been verified and vetted. In other
words, this dimension describes how likely it is that a given digital
identity transaction corresponds to a particular (real-world)
identity subject.
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This dimension SHALL be represented by the "P" demarcator and a
single-character level value, such as "P0", "P1", etc. Most
definitions of identity proofing will have a natural ordering, as
more or less stringent proofing can be applied to an individual. In
such cases it is RECOMMENDED that a digit style value be used for
this component and that only a single value be allowed to be
communicated in a transaction.
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, 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 "Ca", "Cb", etc. Most
definitions of credential usage will not have an overall natural
ordering, as there may be several equivalent classes described within
a trust framework. In such cases it is RECOMMENDED that a letter
style value be used for this component and that multiple distinct
credential usage factors be allowed to 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. In other words, the use and
strength of policies, practices, and security controls used in
managing the credential at the IdP and its binding to the intended
individual.
This dimension SHALL be represented by the "M" demarcator and a
single-character level value, such as "Ma", "Mb", etc. Most
definitions of credential management will not have an overall natural
ordering, though there can be preference and comparison between
values in some circumstances. In such cases it is RECOMMENDED that a
letter style value be used for this component and that multiple
distinct values be allowed to be communicated simultaneously.
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 was actually asserted by a given identity provider
for a given transaction. While this information is largely already
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known by the RP as a side effect of processing an identity assertion,
this dimension is still very useful when the RP requests a login
(Section 5) and when describing the capabilities of an IdP
(Section 7).
This dimension SHALL be represented by the "A" demarcator and a level
value, such as "Aa", "Ab", etc. Most definitions of assertion
presentation will not have an overall natural ordering. In such
cases, it is RECOMMENDED that a letter style value be used for this
component and that multiple values be allowed to be communicated
simultaneously.
3. Vectors of Trust Default Component Value 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 ]].
Extensions of this specification SHOULD define their own component
values as described in Section 8.
3.1. Identity Proofing
The identity proofing component of this vector definition represents
increasing scrutiny during the proofing process. Higher levels are
largely subsumptive of lower levels, such that "P2" fulfills
requirements for "P1", etc. Mutltiple distinct values from this
category MUST NOT be used in a single transaction.
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)
3.2. Primary Credential Usage
The primary credential usage component of this vector definition
represents distinct categories of primary credential that MAY be used
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together in a single transaction. Multiple distinct values from this
category MAY be used in a single transaction.
C0 No credential is used / anonymous public service
Ca Simple session cookies (with nothing else)
Cb Known device
Cc Shared secret such as a username and password combination
Cd Cryptographic proof of key possession using shared key
Ce Cryptographic proof of key possession using asymmetric key
Cf Sealed hardware token / trusted biometric / TPM-backed keys
3.3. Primary Credential Management
The primary credential management component of this vector definition
represents distinct categories of management that MAY be considered
separately or together in a single transaction. Many trust framework
deployments MAY use a single value for this component as a baseline
for all transactions and thereby omit it. Multiple distinct values
from this category MAY be used in a single transaction.
Ma Self-asserted primary credentials (user chooses their own
credentials and must rotate or revoke them manually) / no
additional verification for primary credential issuance or
rotation
Mb Remote issuance and rotation / use of backup recover credentials
(such as email verification) / deletion on user request
Mc Full proofing required for each issuance and rotation / revocation
on suspicious activity
3.4. Assertion Presentation
The assertion presentation component of this vector definition
represents distinct categories of assertion which are RECOMMENDED to
be used in a subsumptive manner but MAY be used together. Multiple
distinct values from this category MAY be used in a single
transaction.
Aa No protection / unsigned bearer identifier (such as a session
cookie in a web browser)
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Ab Signed and verifiable assertion, passed through the user agent
(web browser)
Ac Signed and verifiable assertion, passed through a back channel
Ad Assertion encrypted to the relying parties key and audience
protected
4. Communicating Vector Values to RPs
A vector of trust is designed to be used in the context of an
identity and authentication transaction, providing information about
the context of a federated credential. The vector therefore needs to
be able to be communicated in the context of the federated credential
in a way that is strongly bound to the assertion representing the
federated credential.
This vector has several requirements for use.
o All applicable vector components and values need to be combined
into a single vector.
o The vector can be communicated across the wire unbroken and
untransformed.
o All vector components need to remain individually available, not
"collapsed" into a single value.
o The vector needs to be protected in transit.
o The vector needs to be cryptographically bound to the assertion
which it is describing.
These requirements lead us to defining a simple string-based
representation of the vector that can be incorporated within a number
of different locations and protocols without further encoding.
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
a logical AND of the values. A specific value of a vector component
MUST NOT occur more than once in a single vector. That is, while
"Cc.Cd" is a valid vector, "Cc.Cc" is not.
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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 vector is making no claim for that component. This MAY
be distinct from a specific component value stating that a component
was not used.
Vector values MUST be communicated along side of a trustmark
definition to give the components context. The trustmark MUST be
cryptographically bound to the vector value, such as in a signed
assertion. A vector value without context is unprocessable, and
vectors defined in different contexts are not directly comparable as
whole values. Different trustmarks MAY re-use component definitions
(including their values), allowing comparison of individual
components across contexts without requiring complete understanding
of all aspects of a context. The proper processing of such cross-
context values is outside the scope of this specification.
For example, the vector value "P1.Cc.Ab" translates to "pseudonymous,
proof of shared key, signed browser-passed verified assertion, and no
claim made toward credential management" in the context of this
specification's definitions (Section 3). The vector value of
"Cb.Mc.Cd.Ac" translates to "known device, full proofing require for
issuance and rotation, cryptographic proof of possession of a shared
key, signed back-channel verified assertion, and no claim made toward
identity proofing" in the same context.
4.2. In OpenID Connect
In OpenID Connect [OpenID], the IdP MUST send the vector as a string
within the "vot" (vector of trust) claim in the ID token. The
trustmark (Section 6) 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, the body of an ID token claiming "pseudonymous, proof of
shared key, signed back-channel verified token, and no claim made
toward credential management" could look like this JSON object
payload of the ID token.
{
"iss": "https://idp.example.com/",
"sub": "jondoe1234",
"vot": "P1.Cc.Ac",
"vtm": "https://trustmark.example.org/trustmark/idp.example.com"
}
The body of the ID token is signed and optionally encrypted using
JOSE, as per the OpenID Connect specification. By putting the "vot"
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and "vtm" values inside the ID token, the vector and its context are
strongly bound to the federated credential represented by the ID
token.
4.3. In SAML
In SAML, a vector is communicated as an
"AuthenticationContextDeclRef". A vector is represented by prefixing
it with the "urn urn:ietf:param:[TBD]" to form a full URN. The
"AuthenticationContextDeclaration" corresponding to a given vector is
a "AuthenticationContextDeclaration" element containing an
"Extension" element with components of the vector represented by the
following XML schema:
This represents a set of
vector components.
For instance the vector P1.Cc.Ac is represented by the
AuthenticationContextDeclRef URN "urn:ietf:param:[TBD]:P1.Cc.Ac" (or
"urn:ietf:param:[TBD]:Cc.P1.Ac" or ...) which corresponds to the
following "AuthenticationContextDeclaration":
P1.Cc.Ac
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5. Requesting Vector Values
In some identity protocols, the RP can request that particular vector
components be applied to a given identity transaction. Using the
same syntax as defined in Section 4.1, an RP can indicate that it
desires particular aspects be present in the authentication.
Processing and fulfillment of these requests are in the purview of
the IdP and details are outside the scope of this specification.
5.1. In OpenID Connect
In OpenID Connect [OpenID], the client MAY 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 component values within each vector are ANDed
together while the separate vectors are ORed together. For example,
a list of vectors in the form "["P1.Cb.Cc.Ab", "Ce.Ab"]" is stating
that either the full set of "P1 AND Cb AND Cc AND Ab" simultaneously
OR the set of "Ce AND Ab" simultaneously are acceptable to this RP
for this transaction.
Vector request values MAY omit components, indicating that any value
is acceptable for that component category, including omission of that
component in the response vector.
The mechanism by which the IdP processes the "vtr" and maps that to
the authentication transaction are out of scope of this
specification.
5.2. In SAML
In SAML (Section 4.3) the client can request a set of acceptable VoT
values by including the corresponding "AuthenticationContextDeclRef"
URIs together with an "AuthenticationContextClassRef" corresponding
to the trust mark (cf below). The processing rules in Section 4.3
apply.
6. 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,
including the vector itself.
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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.
Vector component values offered by this IdP are be listed in a using
their demarcator. For the four component categories defined in this
specification:
P Array of strings containing identity proofing values for which the
identity provider has been assessed and approved.
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 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.
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": ["C0", "Ca", "Cb"],
"M": ["Mb"],
"A": ["Ab", "Ac"]
}
An RP 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
RP MAY cache the information returned from the trustmark URL.
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The operational aspects of the IdP MAY be included in the trustmark
definition. For example, if a trustmark can indicate that an IdP
uses multiple redundant hosts, encrypts all data at rest, or other
operational security mechanisms that affect the trustworthiness of
assertions made by the IdP. The definition of these additional
aspects is outside the scope of this specfication.
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": ["P0", "P1"],
"C": ["C0", "Ca", "Cb"],
"M": ["Mb"],
"A": ["Ab", "Ac"]
}
7. 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. In this context, 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 trustmark
URLs for this IdP.
{
"iss": "https://idp.example.org/",
"trustmarks": {
"https://trustmark.example.org/":
"https://trustmark.example.org/trustmark/idp.example.org",
"https://trust.example.net/":
"https://trust.example.net/trustmark/idp.example.org"
}
}
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8. Defining New Vector Values
Vectors of Trust is meant to be a flexible and reusable framework for
communicating authentication data between networked parties in an
identity federation protocol. However, the exact nature of the
information needed is reliant on the parties requiring the
information and the relationship between them. While this document
does define a usable default set of values, it is anticipated that
many situations will require an extension of this specification for
their own use.
Components categories such as those defined in Section 2 are intended
to be general purpose and reusable in a variety of circumstances.
Extension specifications SHOULD re-use existing category definitions
where possible. Extensions MAY create additional categories where
needed by using the registry defined in Section 10. The registry
encourages re-use and discovery of existing categories across
different implementations. In other words, the "P" category in
another framework SHOULD be used for identity proofing and related
information.
The values of components such as those defined in Section 3 are
intended to be contextual to the defining trust document. While this
specification's component values are intended to be general-purpose
and extensions MAY re-use the values and their definitions,
extensions MUST define all allowable values. As these values are
always interpreted in the context of a trustmark, these values are
not recorded in a central registry. Consequently, a "P1" value from
one framework and a "P1" value from another framework could have very
different interpretations depending on their contextual trustmark
documents.
Extensions to this specification SHOULD choose either a numerical
ordering or a group category approach to component values as
described in . Extensions to this specification MUST specify whether
multiple values are allowed for each category, and while any
component category is generally allowed to have multiple distinct
values, a specific definition of a set of values in an extension MAY
limit a given component category to a single value per transaction.
9. 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, and the members of the ISOC Trust and Identity team for
their support.
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10. IANA Considerations
This specification creates one registry and registers several values
into existing registries.
10.1. Vector Of Trust Components Registry
This specification establishes the Vectors of Trust Components
Registry.
Component demarcators are registered by Specification Required
[RFC5226] after a two-week review period on the vot@ietf.org mailing
list, on the advice of one or more Designated Experts.
Criteria that should be applied by the Designated Experts includes
determining whether the proposed registration duplicates existing
functionality, whether it is likely to be of general applicability or
whether it is useful only for a single application, and whether the
registration description is clear.
Registration requests sent to the mailing list for review should use
an appropriate subject (e.g., "Request to register Vector of Trust
Component name: example"). Within the review period, the Designated
Expert(s) will either approve or deny the registration request,
communicating this decision to the review list and IANA. Denials
should include an explanation and, if applicable, suggestions as to
how to make the request successful. IANA must only accept registry
updates from the Designated Expert(s) and should direct all requests
for registration to the review mailing list.
10.1.1. Registration Template
Demarcator Symbol
An uppercase ASCII letter in the range [A-Z] representing this
component (e.g., "X").
Description:
Brief description of the component (e.g., "Example description").
Change controller:
For Standards Track RFCs, state "IESG". For other documents, give
the name of the responsible party. Other details (e.g., postal
address, email address, home page URI) may also be included.
Specification document(s):
Reference to the document(s) that specify the token endpoint
authorization method, preferably including a URI that can be used
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to retrieve a copy of the document(s). An indication of the
relevant sections may also be included but is not required.
10.1.2. Initial Registry Contents
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 Change Controller: IESG
o Specification document(s):: [[ this document ]]
o Demarcator Symbol: C
o Description: Primary credential usage
o Change Controller: IESG
o Specification document(s):: [[ this document ]]
o Demarcator Symbol: M
o Description: Primary credential management
o Change Controller: IESG
o Specification document(s):: [[ this document ]]
o Demarcator Symbol: A
o Description: Assertion presentation
o Change Controller: IESG
o Specification document(s):: [[ this document ]]
10.2. Additions to the OAuth Parameters Registry
This specification adds the following values to the OAuth Parameters
Registry established by [RFC6749].
o Demarcator Symbol: vtr
o Description: Vector of Trust request
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o Change Controller: IESG
o Document: [[ this document ]]
10.3. Additions to JWT Claims Registry
This specification adds the following values to the JSON Web Token
Claims Registry established by [RFC7519].
o Claim name: vot
o Description: Vector of Trust value
o Change Controller: IESG
o Document: [[ this document ]]
o Demarcator Symbol: vtm
o Description: Vector of Trust trustmark
o Change Controller: IESG
o Document: [[ this document ]]
11. Security Considerations
The vector of trust value MUST be cryptographically protected in
transit, using TLS as described in [BCP195]. 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. A signed OpenID Connect ID Token and a
signed SAML assertion both fulfil this requirement.
The VoT framework provides a mechanism for describing and conveying
trust information. It does not define any policies for asserting the
values of the vector, nor does it define any policies for applying
the values of a vector to an RP's security decision process. These
policies must be agreed upon by the IdP and RP, and they should be
expressed in detail in an associated human-readable trust framework
document.
12. Privacy Considerations
By design, vector of trust values contain information about the
user's authentication and associations that can be made thereto.
Therefore, all aspects of a vector of trust contain potentially
privacy-sensitive information and must be guarded as such. Even in
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the absence of specific attributes about a user, knowledge that the
user has been highly proofed or issued a strong token could provide
more information about the user than was intended. It is recommended
that systems in general use the minimum vectors applicable to their
use case in order to prevent inadvertent information disclosure.
13. References
13.1. 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,
.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, .
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
.
13.2. Informative References
[BCP195] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, .
[SP-800-63-2]
and , "Electronic Authentication Guideline", August 2013,
.
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[SP-800-63-3]
and , "Electronic Authentication Guideline", June 2017,
.
Appendix A. Document History
-06
o Added section on extensions to VoT.
o Made it so that every component category could be multi-valued.
o Added reference to updated 800-63-3.
o Fixed example text width.
o Switched document back to standards-track from experimental now
that there are extensions in the wild.
-05
o Updated IANA considerations section to include instructions.
o Made security and privacy considerations non-normative.
-04
o Updated SAML example to be consistent.
-03
o Clarified language of LoA's in introduction.
o Added note on operational security in trustmarks.
o Removed empty sections and references.
-02
o Converted C, M, and A values to use letters instead of numbers in
examples.
o Updated SAML to a structured example pending future updates.
o Defined guidance for when to use letters vs. numbers in category
values.
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o Restricted category demarcators to uppercase and values to
lowercase and digits.
o Applied clarifying editorial changes from list comments.
- 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.
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
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