STIR C. Wendt, Ed.
Internet-Draft Comcast
Intended status: Standards Track J. Peterson
Expires: August 24, 2016 Neustar Inc.
February 21, 2016
Persona Assertion Token
draft-ietf-stir-passport-00
Abstract
This document defines a token format for verifying with non-
repudiation the sender of and authorization to send information
related to the originator of personal communications. A
cryptographic signature is defined to protect the integrity of the
information used to identify the originator of a personal
communications session toward a terminating entity. The
cryptographic signature is defined with the intention that it can
confidently verify the originating persona even when the signature is
sent to the terminating party over a potentially unsecure channel.
The Persona Assertion Token (PASSporT) is particularly useful for
many personal communications applications over IP networks and other
multi-hop interconnection scenarios where the originating and
terminating parties may not have a direct trusted relationship.
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
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on August 24, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Token Overview . . . . . . . . . . . . . . . . . . . . . . . 3
3. PASSporT Definition . . . . . . . . . . . . . . . . . . . . . 3
3.1. PASSporT Header . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. "typ" (Type) Header Parameter . . . . . . . . . . . . 4
3.1.2. "alg" (Algorithm) Header Parameter . . . . . . . . . 4
3.1.3. "x5u" (X.509 URL) Header Parameter . . . . . . . . . 4
3.2. PASSporT Token Claim . . . . . . . . . . . . . . . . . . 5
3.3. PASSporT Signature . . . . . . . . . . . . . . . . . . . 5
4. Extending PASSporT . . . . . . . . . . . . . . . . . . . . . 6
4.1. "ppt" (PASSporT) header parameter . . . . . . . . . . . . 6
4.2. Extended PASSporT Claims . . . . . . . . . . . . . . . . 6
4.3. Alternate PASSporT Extension . . . . . . . . . . . . . . 7
4.4. Registering PASSporT Extensions . . . . . . . . . . . . . 7
5. Deterministic JSON Serialization . . . . . . . . . . . . . . 7
6. Human Readability . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7.1. Avoidance of replay and cut and paste attacks . . . . . . 8
7.2. Solution Considerations . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8.1. Media Type Registration . . . . . . . . . . . . . . . . . 9
8.1.1. Media Type Registry Contents Additions Requested . . 9
8.2. JSON Web Token Claims Registration . . . . . . . . . . . 10
8.2.1. Registry Contents Additions Requested . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
In today's IP-enabled telecommunications world, there is a growing
concern about the ability to trust incoming invitations for
communications sessions, including video, voice and messaging. As an
example, modern telephone networks provide the ability to spoof the
telephone number for many legitimate purposes including providing
network features and services on the behalf of a legitimate telephone
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number. However, as we have seen, bad actors have taken advantage of
this ability for illegitimate and fraudulent purposes meant to trick
telephone users to believe they are someone they are not. This
problem can be extended to many emerging forms of personal
communications.
This document defines a common method for creating and validating a
token that cryptographically verifies an originating identity, or
more generally a URI or application specific identity string
representing the originator of personal communications. Through
extended profiles other information associated with the originating
party or the transport of the personal communications can be attached
to the token. The primary goal of PASSporT is to provide a common
framework for signing persona related information in an extensible
way. A secondary goal is to provide this functionality independent
of any specific personal communications signaling call logic, so that
creation and verification of persona information can be implemented
in a flexible way and can be used in many personal communications
applications including end-to-end applications that require different
signaling protocol interworking. It is anticipated that signaling
protocol specific guidance will be provided in other related
documents and specifications to specify how to use and transport
PASSporT tokens, however this is intentionally out of scope for this
document.
Note: As of the authoring of this document,
[I-D.ietf-stir-rfc4474bis] provides details of how to use PASSporT
within SIP signaling for the signing and verification of telephone
numbers and there is a parallel.
2. Token Overview
Tokens are a convenient way of encapsulating information with
associated digital signatures. They are used in many applications
that require authentication, authorization, encryption and other use
cases. JSON Web Token (JWT) [RFC7519] and JSON Web Signature (JWS)
[RFC7515] are designed to provide a compact form for many of these
purposes and define a specific method and syntax for signing a
specific set of information or "claims" within the token and
therefore providing an extensible set of claims. Additionally, JWS
provides extensible mechanisms for specifying the method and
cryptographic algorithms used for the associated digital signatures.
3. PASSporT Definition
The PASSporT is constructed based on JWT [RFC7519] and JWS [RFC7515]
specifications. JWS defines the use of JSON data structures in a
specified canonical format for signing data corresponding to JOSE
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header, JWS Payload, and JWS Signature. JWT defines specific set of
claims that are represented by specified key value pairs which can be
extended with custom keys for specific applications.
3.1. PASSporT Header
The JWS token header is a JOSE header [RFC7515] that defines the type
and encryption algorithm used in the token.
An example of the header for the case of a RSASSA-PKCS1-v1_5 SHA-256
digital signature would be the following,
{ "typ":"passport",
"alg":"RS256",
"x5u":"https://cert.example.org/passport.crt" }
3.1.1. "typ" (Type) Header Parameter
JWS defines the "typ" (Type) Header Parameter to declare the media
type [IANA.MediaTypes] of the JWS.
This represents that the encoded token is a JWT, and the JWT is a JWS
using the RSASSA-PKCS1-v1_5 SHA-256 algorithm.
For PASSporT Token the "typ" header MUST minimally include and begin
with "passport".
3.1.2. "alg" (Algorithm) Header Parameter
For PASSporT, the "alg" should be defined as RS256 as the recommended
algorithm. Note that JWA [RFC7518] defines other algorithms that may
be utilized or updated in the future depending on cryptographic
strength requirements guided by current security best practice.
3.1.3. "x5u" (X.509 URL) Header Parameter
As defined in JWS, the "x5u" header parameter is used to provide a
URI [RFC3986] referring to the resource for the X.509 public key
certificate or certificate chain [RFC5280] corresponding to the key
used to digitally sign the JWS. Note: The definition of what the URI
represents in terms of the actor serving the X.509 public key is out
of scope of this document. However, generally this would correspond
to an HTTPS or DNSSEC resource with the guidance that it MUST be a
TLS protected, per JWS spec.
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3.2. PASSporT Token Claim
The token claim should consist of the information which needs to be
verified at the terminating party. This claim should correspond to a
JWT claim and be encoded as defined by the JWS Payload.
The PASSporT defines the use of a number of standard JWT defined
headers as well as two new custom headers corresponding to the two
parties associated with personal communications, the originator and
terminator. These headers or key value pairs are detailed below.
The JSON claim MUST include the following registered JWT defined
claims:
o "iat" - issued at, time the JWT was issued, used for expiration.
This is included for securing the token against replay and cut and
paste attacks, as explained further in the security considerations
in section 7.
Verified Token specific claims that MUST be included:
o "orig" - the originating identity claimed. (e.g. for SIP, the FROM
or P-AssertedID [RFC3325] associated e.164 telephone number, TEL
or SIP URI) This SHOULD be in URI format as defined in [RFC3986]
if appropriate but could also be an application specific identity
string.
o "term" - the terminating identity claimed as the intended
destination by the originating party. (e.g. for SIP, the TO
associated e.164 telephone number, TEL or SIP URI) This SHOULD be
in URI format as defined in [RFC3986] if appropriate but could
also be an application specific identity string.
An example claim is as follows,
{ "iat": 1443208345,
"orig":"+12155551212",
"term":"sip:+12155551213@example.com" }
3.3. PASSporT Signature
The signature of the PASSporT is created as specified by JWS using
the private key corresponding to the X.509 public key certificate
referenced by the "x5u" header parameter.
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4. Extending PASSporT
PASSporT represents the bare minimum set of claims needed to assert
the originating identity, however there will certainly be new and
extended applications and usage of PASSPorT that will need to
extending claims to represent other information specific to the
origination identities beyond the identity itself.
There are two mechanisms defined to extend PASSporT. The first
includes an extension of the base passport claims to include
additional claims. An alternative method of extending PASSporT is
for applications of PASSporT unrelated to the base set of claims,
that will define it's own set of claims. Both are described below.
4.1. "ppt" (PASSporT) header parameter
For extended profiles of PASSporT, a new JWS header parameter "ppt"
MUST be used with a string that uniquely identifies the profile
specification that defines any new claims that would extend the base
set of claims of PASSporT.
An example header with an extended PASSporT profile of "foo" is as
follows:
{ "typ":"passport",
"ppt":"foo",
"alg":"RS256",
"x5u":"https://tel.example.org/passport.crt" }
4.2. Extended PASSporT Claims
Future specifications that define such extensions to the PASSporT
mechanism MUST explicitly designate what claims they include, the
order in which they will appear, and any further information
necessary to implement the extension. All extensions MUST
incorporate the baseline JWT elements specified in Section 3; claims
may only be appended to the claims object specified in there, they
can never be subtracted re-ordered. Specifying new claims follows
the baseline JWT procedures ([RFC7519] Section 10.1). Note that
understanding an extension as a verifier is always optional for
compliance with this specification (though future specifications or
profiles for deployment environments may make other "ppt" values
mandatory). The creator of a PASSporT object cannot assume that
verifiers will understand any given extension. Verifiers that do
support an extension may then trigger appropriate application-level
behavior in the presence of an extension; authors of extensions
should provide appropriate extension-specific guidance to application
developers on this point.
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4.3. Alternate PASSporT Extension
Some applications may want to use the mechanism of the PASSporT
digital signature that is not a superset of the base set of claims of
the PASSporT token as defined in Section 3. Rather, a specification
may use PASSporT with its own defined set of claims.
In this case, the specification should define its own MIME media type
[RFC2046] in the "Media Types" registry [IANA.MediaTypes]. It is
recommended that the MIME subtype start with the string "passport-"
to signify that it is related to the PASSporT token. For example,
for the "foo" application the MIME type/sub-type could be defined as
"application/passport-foo".
4.4. Registering PASSporT Extensions
In order for interoperability and maintaining uniqueness of the
extended PASSporT profile header parameter string, there SHOULD be an
industry registry that tracks the definition of the profile strings.
5. Deterministic JSON Serialization
In order to provide a deterministic representation of the PASSporT
Header and Claims, particularly if PASSporT is used across multiple
signaling environments, the JSON header object and JSON Claim object
MUST be computed as follows.
The JSON object MUST follow the rules for the construction of the
thumbprint of a JSON Web Key (JWK) as defined in [RFC7638] Section 3.
Each JSON object MUST contain no whitespace or line breaks before or
after any syntactic elements and with the required members ordered
lexicographically by the Unicode [UNICODE] code points of the member
names.
In addition, the JSON header and claim members MUST follow the
lexicographical ordering and character and string rules defined in
[RFC7638] Section 3.3.
6. Human Readability
For many applications, JWT [RFC7519] and JWS [RFC7515] can use Base64
encoding to the Header and Claims sections as specified. However,
many personal communications protocols, such as SIP and XMPP, use a
"human readable" format to allow for ease of use and ease of
operational debugging and monitoring. As such, specifications using
PASSporT may provide guidance on whether Base64 encoding or plain
text will be used for the construction of the PASSporT Header and
Claim sections.
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7. Security Considerations
7.1. Avoidance of replay and cut and paste attacks
There are a number of security considerations for use of the token
for avoidance of replay and cut and paste attacks. Verified tokens
must be sent along with other application level protocol information
(e.g. for SIP an INVITE as defined in [RFC3261]). There should be a
link between various information provided in the token and
information provided by the application level protocol information.
These would include:
o "iat" claim should closely correspond to a date/time the message
was originated. It should also be within a relative delta time
that is reasonable for clock drift and transmission time
characteristics associated with the application using the verified
token.
o "term" claim is included to prevent the ability to use a
previously originated message to send to another terminating party
7.2. Solution Considerations
It should be recognized that the use of this token should not, in
it's own right, be considered a full solution for absolute non-
repudiation of the persona being asserted. This only provides non-
repudiation of the signer of PASSporT. If the signer and the persona
are not one in the same, which can and often can be the case in
telecommunications networks today, protecting the terminating party
for being spoofed may take some interpretation or additional
verification of the link between the PASSporT signature and the
persona being asserted.
In addition, the telecommunications systems and specifications that
use PASSporT should in practice provide mechanisms for:
o Managing X.509 certificates and X.509 certificate chains to an
authorized trust anchor that can be a trusted entity to all
participants in the telecommunications network
o Accounting for entities that may route calls from other peer or
interconnected telecommunications networks that are not part of
the "trusted" communications network or may not be following the
usage of PASSporT or the profile of PASSporT appropriate to that
network
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o Following best practices around management and security of X.509
certificates
8. IANA Considerations
8.1. Media Type Registration
8.1.1. Media Type Registry Contents Additions Requested
This section registers the "application/passport" media type
[RFC2046] in the "Media Types" registry [IANA.MediaTypes] in the
manner described in [RFC6838], which can be used to indicate that the
content is a PASSporT defined JWT and JWS.
o Type name: application
o Subtype name: passport
o Required parameters: n/a
o Optional parameters: n/a
o Encoding considerations: 8bit; application/passport values are
encoded as a series of base64url-encoded values (some of which may
be the empty string), each separated from the next by a single
period ('.') character.
o Security considerations: See the Security Considerations section
of RFC 7515.
o Interoperability considerations: n/a
o Published specification: draft-ietf-stir-passport-00
o Applications that use this media type: STIR and other applications
that require identity related assertion
o Fragment identifier considerations: n/a
o Additional information:
* Magic number(s): n/a
* File extension(s): n/a
* Macintosh file type code(s): n/a
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o Person and email address to contact for further information: Chris
Wendt, chris-ietf@chriswendt.net
o Intended usage: COMMON
o Restrictions on usage: none
o Author: Chris Wendt, chris-ietf@chriswendt.net
o Change Controller: IESG
o Provisional registration? No
8.2. JSON Web Token Claims Registration
8.2.1. Registry Contents Additions Requested
o Claim Name: "orig"
o Claim Description: Originating Identity String
o Change Controller: IESG
o Specification Document(s): Section 3.2 of draft-ietf-stir-
passport-00
o Claim Name: "term"
o Claim Description: Terminating Identity String
o Change Controller: IESG
o Specification Document(s): Section 3.2 of draft-ietf-stir-
passport-00
9. Acknowledgements
Particular thanks to members of the ATIS and SIP Forum NNI Task Group
including Jim McEchern, Martin Dolly, Richard Shockey, John Barnhill,
Christer Holmberg, Victor Pascual Avila, Mary Barnes, and Eric Burger
for their review, ideas, and contributions. Also thanks to Henning
Schulzrinne, Russ Housley, Alan Johnston, and Richard Barnes for
valuable feedback on the technical and security aspects of the
document.
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10. References
[I-D.ietf-stir-rfc4474bis]
Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
"Authenticated Identity Management in the Session
Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-07
(work in progress), February 2016.
[IANA.MediaTypes]
"IANA, "Media Types"", <Media Types>.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<http://www.rfc-editor.org/info/rfc2046>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.
[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
Extensions to the Session Initiation Protocol (SIP) for
Asserted Identity within Trusted Networks", RFC 3325,
DOI 10.17487/RFC3325, November 2002,
<http://www.rfc-editor.org/info/rfc3325>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<http://www.rfc-editor.org/info/rfc6838>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <http://www.rfc-editor.org/info/rfc7515>.
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[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015,
<http://www.rfc-editor.org/info/rfc7518>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<http://www.rfc-editor.org/info/rfc7519>.
[RFC7638] Jones, M. and N. Sakimura, "JSON Web Key (JWK)
Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
2015, <http://www.rfc-editor.org/info/rfc7638>.
[UNICODE] "The Unicode Consortium, "The Unicode Standard"",
<http://www.unicode.org/versions/latest/>.
Authors' Addresses
Chris Wendt (editor)
Comcast
One Comcast Center
Philadelphia, PA 19103
USA
Email: chris-ietf@chriswendt.net
Jon Peterson
Neustar Inc.
1800 Sutter St Suite 570
Concord, CA 94520
US
Email: jon.peterson@neustar.biz
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