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Internet Engineering Task Force (IETF) C. Wendt
Request for Comments: 8225 Comcast
Category: Standards Track J. Peterson
ISSN: 2070-1721 Neustar Inc.
February 2018
PASSporT: Personal Assertion Token
Abstract
This document defines a method for creating and validating a token
that cryptographically verifies an originating identity or, more
generally, a URI or telephone number representing the originator of
personal communications. The Personal Assertion Token, PASSporT, is
cryptographically signed to protect the integrity of the identity of
the originator and to verify the assertion of the identity
information at the destination. The cryptographic signature is
defined with the intention that it can confidently verify the
originating persona even when the signature is sent to the
destination party over an insecure channel. PASSporT is particularly
useful for many personal-communications applications over IP networks
and other multi-hop interconnection scenarios where the originating
and destination parties may not have a direct trusted relationship.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8225.
Wendt & Peterson Standards Track [Page 1]
RFC 8225 PASSporT February 2018
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Wendt & Peterson Standards Track [Page 2]
RFC 8225 PASSporT February 2018
Table of Contents
1. Introduction ....................................................4
2. Terminology .....................................................4
3. PASSporT Overview ...............................................5
4. PASSporT Header .................................................6
4.1. "typ" (Type) Header Parameter ..............................6
4.2. "alg" (Algorithm) Header Parameter .........................6
4.3. "x5u" (X.509 URL) Header Parameter .........................6
4.4. Example PASSporT Header ....................................7
5. PASSporT Payload ................................................7
5.1. JWT-Defined Claims .........................................7
5.1.1. "iat" (Issued At) Claim .............................7
5.2. PASSporT-Specific Claims ...................................8
5.2.1. Originating and Destination Identity Claims .........8
5.2.2. "mky" (Media Key) Claim ............................10
6. PASSporT Signature .............................................11
7. Compact Form of PASSporT .......................................12
7.1. Example Compact Form of PASSporT ..........................13
8. Extending PASSporT .............................................13
8.1. "ppt" (PASSporT) Header Parameter .........................13
8.2. Example Extended PASSporT Header ..........................14
8.3. Extended PASSporT Claims ..................................14
9. Deterministic JSON Serialization ...............................15
9.1. Example PASSporT Deterministic JSON Form ..................16
10. Security Considerations .......................................17
10.1. Avoidance of Replay and Cut-and-Paste Attacks ............17
10.2. Solution Considerations ..................................18
11. IANA Considerations ...........................................18
11.1. Media Type Registration ..................................18
11.2. Registrations in "JSON Web Token Claims" .................19
11.3. Registration in "JSON Web Signature and
Encryption Header Parameters" ............................20
11.4. PASSporT Extensions Registry .............................20
12. References ....................................................20
12.1. Normative References .....................................20
12.2. Informative References ...................................22
Appendix A. Example ES256-Based PASSporT JWS Serialization and
Signature .............................................23
A.1. X.509 Private Key in PKCS #8 Format for ES256 Example ......24
A.2. X.509 Public Key for ES256 Example .........................25
Acknowledgments ...................................................25
Authors' Addresses ................................................25
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RFC 8225 PASSporT February 2018
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
[RFC7340]. As an example, modern telephone networks provide the
ability to spoof the calling party's telephone number for many
legitimate purposes, including providing network features and
services on behalf of a legitimate telephone number. However, as we
have seen, bad actors have taken advantage of this ability for
illegitimate and fraudulent purposes meant to trick telephone users
into believing that they are someone they are not. This problem can
be extended to many emerging forms of personal communications.
This document defines a method for creating and validating a token
that cryptographically verifies an originating identity or, more
generally, a URI or telephone number representing the originator of
personal communications. Through the extensions defined in Section 8
of this document, other information relevant to the personal
communications can also be added to the token. The goal of PASSporT
is to provide a common framework for signing information related to
the originating identity in an extensible way. Additionally, this
functionality is independent of any specific call logic for
personal-communications signaling, so that the assertion of
information related to the originating identity can be implemented in
a flexible way and can be used in such applications as end-to-end
applications that require different signaling protocols or gateways
between different communications systems. It is anticipated that
guidance specific to the signaling protocol will be provided in other
related documents and specifications to specify how to use and
transport PASSporTs; however, this is intentionally out of scope for
this document.
[RFC8224] provides details of the use of PASSporT within the SIP
[RFC3261] signaling protocol for the signing and verification of
telephone numbers and SIP URIs.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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RFC 8225 PASSporT February 2018
3. PASSporT Overview
"JSON Web Token (JWT)" [RFC7519], "JSON Web Signature (JWS)"
[RFC7515], and other related specifications define a standard token
format that can be used as a way of encapsulating claimed or asserted
information with an associated digital signature using X.509-based
certificates. JWT provides a set of claims in JSON format that can
conveniently accommodate asserted originating-identity information
and that are easily extensible for use in the extension mechanisms
defined below. Additionally, JWS provides a path for updating
methods and cryptographic algorithms used for the associated digital
signatures.
JWS defines the use of JSON data structures in a specified canonical
format for signing data corresponding to the JSON Object Signing and
Encryption (JOSE) Header, JWS Payload, and JWS Signature. JWT
defines a set of claims that are represented by specified JSON
objects that can be extended with custom keys for specific
applications. The next sections define the header and claims that
MUST be minimally used with JWT and JWS for PASSporT.
PASSporT specifically uses this token format and defines claims that
convey the identity of the origination and destination of personal
communications. The primary value asserted in a PASSporT object is
the originating identity representing the identity of the calling
party or the initiator of a personal-communications session. The
signer of a PASSporT object may or may not correspond to the
originating identity. For a given application's use or using
protocol of PASSporT, the creation of the PASSporT object is
performed by an entity that is authoritative to assert the caller's
identity. This authority is represented by the certificate
credentials and the signature, and the PASSporT object is created and
initiated to the destination(s) per the application's choice of
authoritative point(s) in the network. For example, the PASSporT
object could be created at a device that has authenticated with a
user or at a network entity with an authenticated trust relationship
with that device and its user. Destination identities represent the
intended destination of the personal communications, i.e., the
identity(s) being called by the caller. The destination point or
points determined by the application need to have the capability to
verify the PASSporT and the digital signature. The PASSporT-
associated certificate is used to validate the authority of the
originating signer, generally via a certificate chain to the trust
anchor for that application.
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RFC 8225 PASSporT February 2018
4. PASSporT Header
The JWS token header is a JOSE Header ([RFC7515], Section 4) that
defines the type and encryption algorithm used in the token.
The PASSporT header should include, at a minimum, the Header
Parameters defined in the next three subsections.
4.1. "typ" (Type) Header Parameter
The "typ" (Type) Header Parameter is defined in JWS ([RFC7515],
Section 4.1.9) to declare the media type of the complete JWS.
For the PASSporT, the "typ" header MUST be the string "passport".
This signifies that the encoded token is a JWT of type "passport".
4.2. "alg" (Algorithm) Header Parameter
The "alg" (Algorithm) Header Parameter is defined in JWS ([RFC7515],
Section 4.1.1). This definition includes the ability to specify the
use of a cryptographic algorithm for the signature part of the JWS.
It also refers to a list of defined "alg" values as part of a
registry established by JSON Web Algorithms (JWA) ([RFC7518],
Section 3.1).
For the creation and verification of PASSporTs and their digital
signatures, implementations MUST support ES256 as defined in JWA
([RFC7518], Section 3.4). Implementations MAY support other
algorithms registered in the "JSON Web Signature and Encryption
Algorithms" registry created by [RFC7518]. The contents of that
registry may be updated in the future, depending on cryptographic
strength requirements guided by current security best practices. The
mandatory-to-support algorithm for PASSporTs may likewise be updated
in future updates to this document.
Implementations of PASSporT digital signatures using ES256 as defined
above SHOULD use the deterministic Elliptic Curve Digital Signature
Algorithm (ECDSA) if or when supported for the reasons stated in
[RFC6979].
4.3. "x5u" (X.509 URL) Header Parameter
As defined in JWS ([RFC7515], Section 4.1.5), the "x5u" Header
Parameter defines 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. Generally,
as defined in JWS ([RFC7515], Section 4.1.5), this would correspond
to an HTTPS or DNSSEC resource using integrity protection.
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RFC 8225 PASSporT February 2018
4.4. Example PASSporT Header
An example of the header would be the following, including the
specified passport type, ES256 algorithm, and a URI referencing the
network location of the certificate needed to validate the PASSporT
signature.
{
"typ":"passport",
"alg":"ES256",
"x5u":"https://cert.example.org/passport.cer"
}
5. PASSporT Payload
The token claims consist of the information that needs to be verified
at the destination party. These claims follow the definition of a
JWT claim ([RFC7519], Section 4) and are encoded as defined by the
JWS Payload ([RFC7515], Section 3).
PASSporT defines the use of a standard JWT-defined claim as well as
custom claims corresponding to the two parties associated with
personal communications -- the originator and destination, as
detailed below.
For PASSporT, any claim names MUST use the ASCII character set. Any
claim values can contain characters that are outside the ASCII range,
consistent with the rules of creating a JWT Claims Set as defined in
[RFC7519], Section 7.1.
5.1. JWT-Defined Claims
5.1.1. "iat" (Issued At) Claim
The JSON claim MUST include the "iat" (Issued At) claim ([RFC7519],
Section 4.1.6). As defined, the "iat" claim should be set to the
date and time of issuance of the JWT and MUST indicate the date and
time of the origination of the personal communications. The time
value should be of the NumericDate format as defined in [RFC7519],
Section 2. This is included for securing the token against replay
and cut-and-paste attacks, as explained further in Section 10
("Security Considerations").
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RFC 8225 PASSporT February 2018
5.2. PASSporT-Specific Claims
5.2.1. Originating and Destination Identity Claims
The originating identity and the destination identity are represented
by two claims that are required for PASSporT -- the "orig" and "dest"
claims. Both "orig" and "dest" MUST contain claim values that are
identity claim JSON objects where the child claim name represents an
identity type and the claim value is the identity string, both
defined in subsequent subsections. Currently, these identities can
be represented as either telephone numbers or Uniform Resource
Indicators (URIs).
The "orig" claim is a JSON object with the claim name of "orig" and a
claim value that is a JSON object representing the asserted identity
of any type (currently either "tn" or "uri") of the originator of the
personal-communications signaling. There MUST be exactly one "orig"
claim with exactly one identity claim object in a PASSporT object.
Note: As explained in Section 3, the originating identity represents
the calling party and may or may not correspond to the authoritative
signer of the token.
The "dest" claim is a JSON object with the claim name of "dest" and
MUST have at least one identity claim object. The "dest" claim value
is an array containing one or more identity claim JSON objects
representing the destination identities of any type (currently "tn"
or "uri"). If the "dest" claim value array contains both "tn" and
"uri" claim names, the JSON object should list the "tn" array first
and the "uri" array second. Within the "tn" and "uri" arrays, the
identity strings should be put in lexicographical order, including
the scheme-specific portion of the URI characters.
Note: As explained in Section 3, the destination identity represents
the called party and may or may not correspond to the authoritative
party verifying the token signature.
5.2.1.1. "tn" (Telephone Number) Identity
If the originating or destination identity is a telephone number, the
claim name representing the identity MUST be "tn".
The claim value for the "tn" claim is the telephone number and MUST
be canonicalized according to the procedures specified in [RFC8224],
Section 8.3.
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RFC 8225 PASSporT February 2018
5.2.1.2. "uri" (URI) Identity
If any of the originating or destination identities is in the form of
a URI as defined in [RFC3986], the claim name representing the
identity MUST be "uri", and the claim value is the URI form of the
identity.
5.2.1.3. Future Identity Forms
We recognize that in the future there may be other standard
mechanisms for representing identities. The "orig" and "dest" claims
currently support "tn" and "uri" but could be extended in the future
to allow for other identity types with new IANA-registered unique
types to represent these forms.
5.2.1.4. Examples
The following is an example of a single originator with telephone
number identity +12155551212, to a single destination with URI
identity "sip:alice@example.com":
{
"dest":{"uri":["sip:alice@example.com"]},
"iat":1443208345,
"orig":{"tn":"12155551212"}
}
The following is an example of a single originator with telephone
number identity +12155551212, to multiple destination identities with
telephone number identity +12125551212 and two URI identities --
"sip:alice@example.com" and "sip:bob@example.com":
{
"dest":{
"tn":["12125551212"],
"uri":["sip:alice@example.com",
"sip:bob@example.net"]
},
"iat":1443208345,
"orig":{"tn":"12155551212"}
}
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RFC 8225 PASSporT February 2018
5.2.2. "mky" (Media Key) Claim
Some protocols that use PASSporT may also want to protect media
security keys delivered within their signaling in order to bind those
keys to the identities established in the signaling layers. The
"mky" claim is an optional PASSporT claim defining the assertion of
media key fingerprints carried in the Session Description Protocol
(SDP) [RFC4566] via the "a=fingerprint" attribute ([RFC4572],
Section 5). This claim can support either a single fingerprint or
multiple fingerprints appearing in a single SDP body corresponding to
one or more media streams offered as defined in [RFC8122].
The "mky" claim MUST be formatted as a JSON object with an array that
includes the "alg" and "dig" claims with the corresponding algorithm
and hexadecimal values. If there is more than one fingerprint value
associated with different media streams in SDP, the fingerprint
values MUST be constructed as a JSON array denoted by square brackets
("[" and "]"). For the "dig" claim, the claim value MUST be the hash
of the hexadecimal value without any colons.
The "mky" claim is a JSON object with a claim name of "mky" and a
claim value of a JSON array denoted by brackets. The "mky" claim
value JSON array MUST be constructed as follows:
1. Take each "a=fingerprint" line carried in the SDP.
2. Sort the lines based on the UTF-8 [RFC3629] encoding of the
concatenation of the "alg" and "dig" claim value strings.
3. Encode the array in the order of the sorted lines, where each
"mky" array element is a JSON object with two elements
corresponding to the "alg" and "dig" objects, with "alg" first
and "dig" second.
Wendt & Peterson Standards Track [Page 10]
RFC 8225 PASSporT February 2018
An example claim with the "mky" claim is as follows:
For an SDP offer that includes the following fingerprint values,
a=fingerprint:sha-256 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:
5D:49:6B:19:E5:7C:AB:3E:4B:65:2E:7D:46:3F:54:42:CD:54:F1
a=fingerprint:sha-256 02:1A:CC:54:27:AB:EB:9C:53:3F:3E:4B:65
:2E:7D:46:3F:54:42:CD:54:F1:7A:03:A2:7D:F9:B0:7F:46:19:B2
the PASSporT Payload object would be:
{
"dest":{"uri":["sip:alice@example.com"]},
"iat":1443208345,
"mky":[
{
"alg":"sha-256",
"dig":"021ACC5427ABEB9C533F3E4B652E7D463F5442CD54
F17A03A27DF9B07F4619B2"
},
{
"alg":"sha-256",
"dig":"4AADB9B13F82183B540212DF3E5D496B19E57C
AB3E4B652E7D463F5442CD54F1"
}
],
"orig":{"tn":"12155551212"}
}
6. PASSporT Signature
The signature of the PASSporT is created as specified by JWS
([RFC7515], Section 5.1, Steps 1 through 6). PASSporT MUST use the
JWS Protected Header. For the JWS Payload and the JWS Protected
Header, however, the lexicographic ordering and whitespace rules
described in Sections 4 and 5 of this document, and the JSON
serialization rules in Section 9 of this document, MUST be followed.
Appendix A of this document has a detailed example of how to follow
the steps to create the JWS Signature.
Step 7 of the JSON serialization procedure in [RFC7515], Section 5.1
is not supported for PASSporT.
[RFC7515], Section 5.1, Step 8 describes the method to create the
final JWS Compact Serialization form of the PASSporT.
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RFC 8225 PASSporT February 2018
7. Compact Form of PASSporT
For a using protocol of PASSporT, the PASSporT claims as well as the
PASSporT header may include redundant or default information that
could be reconstructed at the destination based on information
provided in the signaling protocol transporting the PASSporT object.
In this case, it may be advantageous to have a more compact form of
PASSporT to save the transmission of the bytes needed to represent
the header and claims.
This specification defines the compact form of the PASSporT, in the
spirit of the form defined in [RFC7515], Appendix F, with the use of
two periods ("..") to represent the header and claim objects being
removed, followed by the PASSporT signature as defined in Section 6,
and the need for the destination to reconstruct the header and claim
objects in order to verify the signature.
In order to construct the compact form of the PASSporT string, the
procedure described in Section 6 MUST be used, with the exception of
[RFC7515], Section 5.1, Step 8. This step would be replaced by the
following construction of the compact form of PASSporT, ".." ||
BASE64URL(JWS Signature).
The using protocol of the compact form of PASSporT MUST be
accompanied by a specification for how the header and claims objects
can be reconstructed from information in the signaling protocol being
used.
Note that the full form of the PASSporT, containing the entire
header, payload, and signature, should also use the lexicographic
ordering and whitespace serialization rules, particularly in the case
where some using protocols or interworking between protocols may
require switching between full and compact forms and maintaining the
integrity of the signature.
Wendt & Peterson Standards Track [Page 12]
RFC 8225 PASSporT February 2018
7.1. Example Compact Form of PASSporT
The compact form of the following example token (with line breaks
between periods used for readability purposes only)
eyJhbGciOiJFUzI1NiIsInR5cCI6InBhc3Nwb3J0IiwieDV1IjoiaHR0cHM6Ly9j
ZXJ0LmV4YW1wbGUub3JnL3Bhc3Nwb3J0LmNlciJ9
.
eyJkZXN0Ijp7InVyaSI6WyJzaXA6YWxpY2VAZXhhbXBsZS5jb20iXX0sImlhdCI
6IjE0NDMyMDgzNDUiLCJvcmlnIjp7InRuIjoiMTIxNTU1NTEyMTIifX0
.
rq3pjT1hoRwakEGjHCnWSwUnshd0-zJ6F1VOgFWSjHBr8Qjpjlk-cpFYpFYsojN
CpTzO3QfPOlckGaS6hEck7w
would be as follows:
..rq3pjT1hoRwakEGjHCnWSwUnshd0-zJ6F1VOgFWSjHBr8Qjpjlk-cpFYpFYsojN
CpTzO3QfPOlckGaS6hEck7w
8. Extending PASSporT
PASSporT includes the bare-minimum set of claims needed to securely
assert the originating identity and support the secure properties
discussed in various parts of this document. JWT supports a
straightforward way to add additional asserted or signed information
by simply adding new claims. PASSporT can be extended beyond the
defined base set of claims to represent other information requiring
assertion or validation beyond the originating identity itself as
needed.
8.1. "ppt" (PASSporT) Header Parameter
Any using protocol can extend the payload of PASSporT with additional
JWT claims. JWT claims are managed by the "JSON Web Token Claims"
IANA registry as defined in [RFC7519], Section 10.1. Implementations
of PASSporT MUST support the baseline claims defined in Section 5.2
and MAY support extended claims. If it is necessary for an extension
to PASSporT to require that a relying party support a particular
extended claim or set of claims in the PASSporT object, it can do so
by specifying a "ppt" element for the PASSporT JOSE Header. All
values of "ppt" need to be defined in a specification that associates
the new value of the "ppt" element with the required claims and
behaviors. Relying parties MUST fail to validate PASSporT objects
containing an unsupported "ppt".
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RFC 8225 PASSporT February 2018
Using protocols MUST explicitly define how they carry each claim and
the rules for how the header and payload objects are constructed
beyond the lexicographical and serialization rules defined in this
document.
Using protocols that carry the compact form of PASSporT (Section 7)
instead of the full form MUST use only mandatory extensions signaled
with "ppt" -- if a using protocol were to add additional optional
claims to a PASSporT object it carried in compact form, relying
parties would have no way to reconstruct the token. Moreover, using
protocols that support the compact form of PASSporT MUST have some
field to signal "ppt" to relying parties, as the compact form of
PASSporT omits the JOSE Header.
8.2. Example Extended PASSporT Header
An example header with a PASSporT extension type of "foo" is as
follows:
{
"alg":"ES256",
"ppt":"foo",
"typ":"passport",
"x5u":"https://tel.example.org/passport.cer"
}
8.3. Extended PASSporT Claims
Specifications that define extensions to the PASSporT mechanism MUST
explicitly specify what claims they include beyond the base set of
claims from this document, the order in which they will appear, and
any further information necessary to implement the extension. All
extensions MUST include the baseline PASSporT claim elements
specified in Section 5; claims may only be appended to the claims
object specified; they can never be removed or reordered. Specifying
new claims follows the baseline JWT procedures ([RFC7519],
Section 10.1). Understanding an extension or new claims defined by
the extension on the destination verification of the PASSporT is
optional. The creator of a PASSporT object cannot assume that
destination systems will understand any given extension.
Verification of PASSporTs by destination systems 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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RFC 8225 PASSporT February 2018
An example set of extended claims, extending the first example in
Section 5.2.1.4 using "bar" as the newly defined claim, would be as
follows:
{
"bar":"beyond all recognition"
"dest":{"uri":["sip:alice@example.com"]},
"iat":1443208345,
"orig":{"tn":"12155551212"}
}
9. Deterministic JSON Serialization
JSON objects can include spaces and line breaks, and key value pairs
can occur in any order. It is therefore a non-deterministic string
format. In order to make the digital signature verification work
deterministically, the JSON representation of the JWS Protected
Header object and JWS Payload object MUST be computed as follows.
The JSON object MUST follow the following rules. These rules are
based on the thumbprint of a JSON Web Key (JWK) as defined in
Section 3 Step 1 of [RFC7638].
1. The JSON object MUST contain no whitespace or line breaks before
or after any syntactic elements.
2. JSON objects MUST have the keys ordered lexicographically by the
Unicode [UNICODE] code points of the member names.
3. JSON value literals MUST be lowercase.
4. JSON numbers are to be encoded as integers unless the field is
defined to be encoded otherwise.
5. Encoding rules MUST be applied recursively to member values and
array values.
Note: For any PASSporT extension claims, member names within the
scope of a JSON object MUST NOT be equal to other member names;
otherwise, serialization will not be deterministic.
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RFC 8225 PASSporT February 2018
9.1. Example PASSporT Deterministic JSON Form
This section demonstrates the deterministic JSON serialization for
the example PASSporT Payload shown in Section 5.2.1.4.
The initial JSON object is shown here:
{
"dest":{"uri":["sip:alice@example.com"]},
"orig":{"tn":"12155551212"}
"iat":1443208345,
"mky":[
{
"alg":"sha-256",
"dig":"021ACC5427ABEB9C533F3E4B652E7D463F5442CD54
F17A03A27DF9B07F4619B2"
},
{
"alg":"sha-256",
"dig":"4AADB9B13F82183B540212DF3E5D496B19E57C
AB3E4B652E7D463F5442CD54F1"
}
],
}
The parent members of the JSON object are as follows:
o "dest"
o "orig"
o "iat"
o "mky"
Their lexicographic order is:
o "dest"
o "iat"
o "mky"
o "orig"
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RFC 8225 PASSporT February 2018
The final constructed deterministic JSON serialization
representation, with whitespace and line breaks removed (with line
breaks used for display purposes only), is:
{"dest":{"uri":["sip:alice@example.com"],"iat":1443208345,"mky":
[{"alg":"sha-256","dig":"021ACC5427ABEB9C533F3E4B652E7D463F5442CD5
4F17A03A27DF9B07F4619B2"},{"alg":"sha-256","dig":"4AADB9B13F82183B5
40212DF3E5D496B19E57CAB3E4B652E7D463F5442CD54F1"}],
"orig":{"tn":"12155551212"}}
10. Security Considerations
10.1. Avoidance of Replay and Cut-and-Paste Attacks
There are a number of security considerations regarding the use of
the token for the avoidance of replay and cut-and-paste attacks.
PASSporTs SHOULD only be sent with application-level protocol
information (e.g., for SIP, an INVITE as defined in [RFC3261])
corresponding to the required fields in the token. A unique set of
token claims and token signature is constructed using the originating
identity being asserted with the "orig" claim along with the
following two claims:
o The "iat" claim should correspond to a date/time that the message
was originated. It should also be within a relative time that is
reasonable for clock drift and transmission time characteristics
associated with the application using the PASSporT. Therefore,
validation of the token should consider date and time correlation,
which could be influenced by usage specific to the signaling
protocol and by network time differences.
o The "dest" claim is included to further restrict the use of a
valid PASSporT being sent as a replay attack to other destination
parties. The verification of the PASSporT at the destination
should verify that the "dest" claim matches the destination party
as the intended recipient of the message.
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RFC 8225 PASSporT February 2018
10.2. Solution Considerations
The use of PASSporTs based on the validation of the digital signature
and the associated certificate requires consideration of the
authentication and authority or reputation of the signer to attest to
the identity being asserted. The following considerations should be
recognized when using PASSporT:
o The use of this token should not, in its own right, be considered
a full solution for absolute non-repudiation of the identity being
asserted.
o In many applications, the signer and the end user represented by
the asserted identity may not be one and the same. For example,
when a service provider signs and validates the token on behalf of
the user consuming the service, the provider MUST have an
authenticated and secure relationship with the end user or the
device initiating and terminating the communications signaling.
o Applications that use PASSporT should ensure that the verification
of the signature includes a means for verifying that the signer is
authoritative through the use of an application-specific or
service-specific set of common trust anchors for the application.
11. IANA Considerations
11.1. Media Type Registration
This section registers the "application/passport" media type (see
[RFC2046] for the definition of "media type") in the "Media Types"
registry in the manner described in [RFC6838], to indicate that the
content is a PASSporT-defined JWT.
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) separated by period (".") characters.
o Security considerations: See the Security Considerations section
of [RFC7515].
Wendt & Peterson Standards Track [Page 18]
RFC 8225 PASSporT February 2018
o Interoperability considerations: N/A
o Published specification: RFC 8225
o Applications that use this media type: Secure Telephone Identity
Revisited (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
o Person & 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
11.2. Registrations in "JSON Web Token Claims"
Claim Name: "orig"
Claim Description: Originating Identity String
Change Controller: IESG
Reference: Section 5.2.1 of RFC 8225
Claim Name: "dest"
Claim Description: Destination Identity String
Change Controller: IESG
Reference: Section 5.2.1 of RFC 8225
Claim Name: "mky"
Claim Description: Media Key Fingerprint String
Change Controller: IESG
Reference: Section 5.2.2 of RFC 8225
Wendt & Peterson Standards Track [Page 19]
RFC 8225 PASSporT February 2018
11.3. Registration in "JSON Web Signature and Encryption Header
Parameters"
Header Parameter Name: "ppt"
Header Parameter Description: PASSporT extension identifier
Header Parameter Usage Location(s): JWS
Change Controller: IESG
Reference: Section 8.1 of RFC 8225
11.4. PASSporT Extensions Registry
The IANA has created a new PASSporT Type registry for "ppt" parameter
values. That parameter and its values are defined in Section 8.1.
New registry entries must contain the name of the "ppt" parameter
value and the specification in which the value is described. The
policy for this registry is Specification Required [RFC8126].
12. References
12.1. Normative References
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/info/rfc2046>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of
ISO 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629,
November 2003, <https://www.rfc-editor.org/info/rfc3629>.
[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,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <https://www.rfc-editor.org/info/rfc4566>.
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RFC 8225 PASSporT February 2018
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session
Description Protocol (SDP)", RFC 4572,
DOI 10.17487/RFC4572, July 2006,
<https://www.rfc-editor.org/info/rfc4572>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.
[RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature
Algorithm (DSA) and Elliptic Curve Digital Signature
Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979,
August 2013, <https://www.rfc-editor.org/info/rfc6979>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515,
May 2015, <https://www.rfc-editor.org/info/rfc7515>.
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015,
<https://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,
<https://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, <https://www.rfc-editor.org/info/rfc7638>.
[RFC8122] Lennox, J. and C. Holmberg, "Connection-Oriented Media
Transport over the Transport Layer Security (TLS) Protocol
in the Session Description Protocol (SDP)", RFC 8122,
DOI 10.17487/RFC8122, March 2017,
<https://www.rfc-editor.org/info/rfc8122>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in
RFC 2119 Key Words", BCP 14, RFC 8174,
DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/rfc8174>.
Wendt & Peterson Standards Track [Page 21]
RFC 8225 PASSporT February 2018
[RFC8224] Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
"Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 8224,
DOI 10.17487/RFC8224, February 2018,
<https://www.rfc-editor.org/info/rfc8224>.
[UNICODE] The Unicode Consortium, "The Unicode Standard",
<http://www.unicode.org/versions/latest/>.
12.2. Informative References
[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,
<https://www.rfc-editor.org/info/rfc3261>.
[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,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC7340] Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
Telephone Identity Problem Statement and Requirements",
RFC 7340, DOI 10.17487/RFC7340, September 2014,
<https://www.rfc-editor.org/info/rfc7340>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
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RFC 8225 PASSporT February 2018
Appendix A. Example ES256-Based PASSporT JWS Serialization and
Signature
For PASSporT, there will always be a JWS with the following members:
o "protected", with the value BASE64URL(UTF8(JWS Protected Header))
o "payload", with the value BASE64URL(JWS Payload)
o "signature", with the value BASE64URL(JWS Signature)
This example will follow the steps in JWS ([RFC7515], Section 5.1,
Steps 1-6 and 8); it incorporates the additional serialization steps
required for PASSporT.
Step 1 for JWS references the JWS Payload. An example PASSporT
Payload is as follows:
{
"dest":{"uri":["sip:alice@example.com"]}
"iat":1471375418,
"orig":{"tn":"12155551212"}
}
This would be serialized to the following form (with line break used
for display purposes only):
{"dest":{"uri":["sip:alice@example.com"]},"iat":1471375418,
"orig":{"tn":"12155551212"}}
Step 2 computes the BASE64URL(JWS Payload), producing this value
(with line break used for display purposes only):
eyJkZXN0Ijp7InVyaSI6WyJzaXA6YWxpY2VAZXhhbXBsZS5jb20iXX0sImlhdCI
6MTQ3MTM3NTQxOCwib3JpZyI6eyJ0biI6IjEyMTU1NTUxMjEyIn19
For Step 3, an example PASSporT Protected Header constructed as a
JOSE Header is as follows:
{
"alg":"ES256",
"typ":"passport",
"x5u":"https://cert.example.org/passport.cer"
}
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RFC 8225 PASSporT February 2018
This would be serialized to the following form (with line break used
for display purposes only):
{"alg":"ES256","typ":"passport","x5u":"https://cert.example.org
/passport.cer"}
Step 4 performs the BASE64URL(UTF8(JWS Protected Header)) operation
and encoding, producing this value (with line break used for display
purposes only):
eyJhbGciOiJFUzI1NiIsInR5cCI6InBhc3Nwb3J0IiwieDV1IjoiaHR0cHM6Ly9j
ZXJ0LmV4YW1wbGUub3JnL3Bhc3Nwb3J0LmNlciJ9
Steps 5 and 6 perform the computation of the digital signature of the
PASSporT Signing Input ASCII(BASE64URL(UTF8(JWS Protected Header)) ||
"." || BASE64URL(JWS Payload)), using ES256 as the algorithm and the
BASE64URL(JWS Signature).
VLBCIVDCaeK6M4hLJb6SHQvacAQVvoiiEOWQ_iUkqk79UD81fHQ0E1b3_GluIkb
a7UWYRM47ZbNFdOJquE35cw
Step 8 describes how to create the final PASSporT, concatenating the
values in the order Header.Payload.Signature with period (".")
characters. For the above example values, this would produce the
following (with line breaks between periods used for readability
purposes only):
eyJhbGciOiJFUzI1NiIsInR5cCI6InBhc3Nwb3J0IiwieDV1IjoiaHR0cHM6Ly9j
ZXJ0LmV4YW1wbGUub3JnL3Bhc3Nwb3J0LmNlciJ9
.
eyJkZXN0Ijp7InVyaSI6WyJzaXA6YWxpY2VAZXhhbXBsZS5jb20iXX0sImlhdCI
6MTQ3MTM3NTQxOCwib3JpZyI6eyJ0biI6IjEyMTU1NTUxMjEyIn19
.
VLBCIVDCaeK6M4hLJb6SHQvacAQVvoiiEOWQ_iUkqk79UD81fHQ0E1b3_GluIkb
a7UWYRM47ZbNFdOJquE35cw
A.1. X.509 Private Key in PKCS #8 Format for ES256 Example
-----BEGIN PRIVATE KEY-----
MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgi7q2TZvN9VDFg8Vy
qCP06bETrR2v8MRvr89rn4i+UAahRANCAAQWfaj1HUETpoNCrOtp9KA8o0V79IuW
ARKt9C1cFPkyd3FBP4SeiNZxQhDrD0tdBHls3/wFe8++K2FrPyQF9vuh
-----END PRIVATE KEY-----
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RFC 8225 PASSporT February 2018
A.2. X.509 Public Key for ES256 Example
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8HNbQd/TmvCKwPKHkMF9fScavGeH
78YTU8qLS8I5HLHSSmlATLcslQMhNC/OhlWBYC626nIlo7XeebYS7Sb37g==
-----END PUBLIC KEY-----
Acknowledgments
Particular thanks to members of the ATIS and SIP Forum NNI Task
Group, including Jim McEachern, Martin Dolly, Richard Shockey, John
Barnhill, Christer Holmberg, Victor Pascual Avila, Mary Barnes, and
Eric Burger, for their review, ideas, and contributions. Thanks also
to Henning Schulzrinne, Russ Housley, Alan Johnston, Richard Barnes,
Mark Miller, Ted Hardie, Dave Crocker, Robert Sparks, and Jim Schaad
for valuable feedback on the technical and security aspects of the
document. Additional thanks to Harsha Bellur for assistance in
coding the example tokens.
Authors' Addresses
Chris Wendt
Comcast
One Comcast Center
Philadelphia, PA 19103
United States of America
Email: chris-ietf@chriswendt.net
Jon Peterson
Neustar Inc.
1800 Sutter St. Suite 570
Concord, CA 94520
United States of America
Email: jon.peterson@neustar.biz
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