wdiff rfc9448v1.txt rfc9448.txt

Internet Engineering Task Force (IETF) C. Wendt
Request for Comments: 9448 Somos Inc. D. Hancock
Category: Standards Track D. Hancock Somos Inc.
ISSN: 2070-1721 Comcast M. Barnes
J. Peterson
Neustar Inc.
July
September 2023

TNAuthList Profile of Automated Certificate Management Environment
(ACME) Authority Token

Abstract

This document defines a profile of the Automated Certificate
Management Environment (ACME) Authority Token for the automated and
authorized creation of certificates for Voice over IP (VoIP)
telephone providers to support Secure Telephone Identity (STI) using
the TNAuthList defined by STI certificates.

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/rfc9448.

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 Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.

Table of Contents

1. Introduction
2. Requirements Language
3. ACME New-Order Identifiers for TNAuthList
4. TNAuthList Identifier Authorization
5. TNAuthList Authority Token
5.1. "iss" Claim
5.2. "exp" Claim
5.3. "jti" Claim
5.4. "atc" Claim
5.5. Acquiring the Token from the Token Authority
5.6. Token Authority Responsibilities
5.7. Scope of the TNAuthList
6. Validating the TNAuthList Authority Token
7. Using ACME-Issued Certificates with JSON Web Signature
8. Usage Considerations
8.1. Large Number of Noncontiguous TNAuthList Values
9. IANA Considerations
10. Security Considerations
11. References
11.1. Normative References
11.2. Informative References
Acknowledgements
Authors' Addresses

1. Introduction

[RFC8555] describes a mechanism for automating certificate management
on the Internet. It enables administrative entities to prove
effective control over resources like domain names, and it automates
the process of generating and issuing certificates. [RFC9447]
extends ACME to provide a general method of extending the authority
and authorization of entities to control a resource via a third party
Token Authority beyond the certification authority (CA).

This document is a profile document using the Authority Token
mechanism defined in [RFC9447]. It is a profile that specifically
addresses the Secure Telephone Identity Revisited (STIR) problem
statement described in [RFC7340], which identifies the need for
Internet credentials that can attest authority for the originator of
VoIP calls in order to detect impersonation, which is currently an
enabler for common attacks associated with illegal robocalling,
voicemail hacking, and swatting. These credentials are used to sign
Personal Assertion Tokens (PASSporTs) [RFC8225], which can be carried
in using protocols such as SIP [RFC8224]. Currently, the only
defined credentials for this purpose are the certificates specified
in [RFC8226] using the TNAuthList. This document defines the use of
the TNAuthList Authority Token in the ACME challenge to prove the
authoritative use of the contents of the TNAuthList, including a
Service Provider Code (SPC), a telephone number, or a set of
telephone numbers or telephone number blocks.

This document also describes the ability for a telephone authority to
authorize the creation of CA types of certificates for delegation, as
defined in [RFC9060].

2. 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
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

3. ACME New-Order Identifiers for TNAuthList

Section 7 of [RFC8555] defines the procedure that an ACME client uses
to order a new certificate from a CA. The new-order request contains
an identifier field that specifies the identifier objects the order
corresponds to. This document defines a new type of identifier
object called TNAuthList. A TNAuthList identifier contains the
identity information to be populated in the TN Authorization List TNAuthList of the new
certificate. For the TNAuthList identifier, the new-order request
includes a type set to the string "TNAuthList". The value of the
TNAuthList identifier MUST be set to the details of the TNAuthList
requested.

The format of the string that represents the TNAuthList MUST be constructed using
base64url encoding, as per [RFC8555] base64url
encoding described in Section 5 of [RFC4648] according to the profile
specified in JSON Web Signature and as
defined in Section 2 of JSON Web Signature [RFC7515]. The base64url
encoding MUST NOT include any padding characters, and the TNAuthList
ASN.1 object MUST be encoded using DER encoding rules.

An example of an ACME order object "identifiers" field containing a
TNAuthList certificate is as follows:

"identifiers": [{"type":"TNAuthList","value":"F83n2a...avn27DN3"}]

where the "value" object string represents the arbitrary length of
the base64url-encoded string.

A full new-order request would look as follows:

POST /acme/new-order HTTP/1.1
Host: example.com
Content-Type: application/jose+json

{
"protected": base64url({
"alg": "ES256",
"kid": "https://example.com/acme/acct/evOfKhNU60wg",
"nonce": "5XJ1L3lEkMG7tR6pA00clA",
"url": "https://example.com/acme/new-order"
}),
"payload": base64url({
"identifiers": [{"type":"TNAuthList","value":"F83n...n27DN3"}],
"notBefore": "2021-01-01T00:00:00Z",
"notAfter": "2021-01-08T00:00:00Z"
}),
"signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g"
}

On receiving a valid new-order request, the ACME server creates an
authorization object ([RFC8555], Section 7.1.4), containing the
challenge that the ACME client must satisfy to demonstrate authority
for the identifiers specified by the new order (in this case, the
TNAuthList identifier). The CA adds the authorization object URL to
the "authorizations" field of the order object and returns the order
object to the ACME client in the body of a 201 (Created) response.

HTTP/1.1 201 Created
Content-Type: application/json
Replay-Nonce: MYAuvOpaoIiywTezizk5vw
Location: https://example.com/acme/order/1234

{
"status": "pending",
"expires": "2022-01-08T00:00:00Z",

"notBefore": "2022-01-01T00:00:00Z",
"notAfter": "2022-01-08T00:00:00Z",
"identifiers":[{"type":"TNAuthList",
"value":"F83n2a...avn27DN3"}],

"authorizations": [
"https://example.com/acme/authz/1234"
],
"finalize": "https://example.com/acme/order/1234/finalize"
}

4. TNAuthList Identifier Authorization

On receiving the new-order response, the ACME client queries the
referenced authorization object to obtain the challenges for the
identifier contained in the new-order request, as shown in the
following example request and response.

POST /acme/authz/1234 HTTP/1.1
Host: example.com
Content-Type: application/jose+json

{
"protected": base64url({
"alg": "ES256",
"kid": " https://example.com/acme/acct/evOfKhNU60wg",
"nonce": "uQpSjlRb4vQVCjVYAyyUWg",
"url": "https://example.com/acme/authz/1234"
}),
"payload": "",
"signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps"
}

HTTP/1.1 200 OK
Content-Type: application/json
Link: <https://example.com/acme/some-directory>;rel="index"

{
"status": "pending",
"expires": "2022-01-08T00:00:00Z",

"identifier": {
"type":"TNAuthList",
"value":"F83n2a...avn27DN3"
},

"challenges": [
{
"type": "tkauth-01",
"tkauth-type": "atc",
"token-authority": "https://authority.example.org",
"url": "https://example.com/acme/chall/prV_B7yEyA4",
"token": "IlirfxKKXAsHtmzK29Pj8A"
}
]
}

When processing a certificate order containing an identifier of type
"TNAuthList", a CA uses the Authority Token challenge type of
"tkauth-01" with a "tkauth-type" of "atc" in [RFC9447] to verify that
the requesting ACME client has authenticated and authorized control
over the requested resources represented by the "TNAuthList" value.

The challenge "token-authority" parameter is only used in cases where
the VoIP telephone network requires the CA to identify the Token
Authority. This is currently not the case for the Signature-based
Handling of Asserted information using toKENs (SHAKEN) [ATIS-1000080]
certificate framework governance but may be used by other frameworks.
If a "token-authority" parameter is present, then the ACME client MAY
use the "token-authority" value to identify the URL representing the
Token Authority that will provide the TNAuthList Authority Token
response to the challenge. If the "token-authority" parameter is not
present, then the ACME client MUST identify the Token Authority based
on locally configured information or local policies.

The ACME client responds to the challenge by posting the TNAuthList
Authority Token to the challenge URL identified in the returned ACME
authorization object, an example of which follows:

POST /acme/chall/prV_B7yEyA4 HTTP/1.1
Host: boulder.example.com
Content-Type: application/jose+json

{
"protected": base64url({
"alg": "ES256",
"kid": "https://example.com/acme/acct/evOfKhNU60wg",
"nonce": "Q_s3MWoqT05TrdkM2MTDcw",
"url": "https://boulder.example.com/acme/authz/asdf/0"
}),
"payload": base64url({
"tkauth": "DGyRejmCefe7v4N...vb29HhjjLPSggwiE"
}),
"signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ"
}

The "tkauth" field is defined as a new field in the challenge object
specific to the tkauth-01 challenge type that should contain the
TNAuthList Authority Token defined in the next section.

5. TNAuthList Authority Token

The Telephone Number Authority List TNAuthList Authority Token (TNAuthList
Authority Token) is a profile instance of the ACME
Authority Token defined in [RFC9447].

The TNAuthList Authority Token Protected protected header MUST comply with the
Authority Token Protected header, as defined in [RFC9447].
"Request Authentication" (Section 6.2 of [RFC8555]).

The TNAuthList Authority Token Payload MUST include the mandatory
claims "exp", "jti", and "atc" and MAY include the optional claims
defined for the Authority Token detailed in the next subsections.

5.1. "iss" Claim

The "iss" claim is an optional claim defined in [RFC7519],
Section 4.1.1. It can be used as a URL identifying the Token
Authority that issued the TNAuthList Authority Token beyond the "x5u"
or other header claims that identify the location of the certificate
or certificate chain of the Token Authority used to validate the
TNAuthList Authority Token.

5.2. "exp" Claim

The "exp" claim, defined in [RFC7519], Section 4.1.4, MUST be
included and contains the DateTime value of the ending date and time
that the TNAuthList Authority Token expires.

5.3. "jti" Claim

The "jti" claim, defined in [RFC7519], Section 4.1.7, MUST be
included and contains a unique identifier for this TNAuthList
Authority Token transaction.

5.4. "atc" Claim

The "atc" claim MUST be included and is defined in [RFC9447]. It
contains a JSON object with the following elements:

* a "tktype" key with a string value equal to "TNAuthList" to
represent a TNAuthList profile of the Authority Token [RFC9447]
defined by this document. "tktype" is a required key and MUST be
included.

* a "tkvalue" key with a string value equal to the base64url
encoding of the TN Authorization List TNAuthList certificate extension ASN.1 object
using DER encoding rules. "tkvalue" is a required key and MUST be
included.

* a "ca" key with a boolean value set to either true when the
requested certificate is allowed to be a CA cert for delegation
uses or false when the requested certificate is not intended to be
a CA cert, only an end-entity certificate. "ca" is an optional
key; if not included, the "ca" value is considered false by
default.

* a "fingerprint" key constructed as defined in [RFC8555],
Section 8.1, corresponding to the computation of the "Thumbprint"
step using the ACME account key credentials. "fingerprint" is a
required key and MUST be included.

An example of the TNAuthList Authority Token is as follows:

{
"protected": base64url({
"typ":"JWT",
"alg":"ES256",
"x5u":"https://authority.example.org/cert"
}),
"payload": base64url({
"iss":"https://authority.example.org",
"exp":1640995200,
"jti":"id6098364921",
"atc":{"tktype":"TNAuthList",
"tkvalue":"F83n2a...avn27DN3",
"ca":false,
"fingerprint":"SHA256 56:3E:CF:AE:83:CA:4D:15:B0:29:FF:1B:71:
D3:BA:B9:19:81:F8:50:9B:DF:4A:D4:39:72:E2:B1:F0:B9:38:E3"}
}),
"signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ"
}

5.5. Acquiring the Token from the Token Authority

Following [RFC9447], Section 5, the Authority Token should be
acquired using a RESTful HTTP POST transaction as follows:

POST /at/account/:id/token HTTP/1.1
Host: authority.example.org
Content-Type: application/json

The request will pass the account identifier as a string in the
request parameter "id". This string will be managed as an identifier
specific to the Token Authority's relationship with a Communications
Service Provider (CSP). There is assumed to also be a corresponding
authentication procedure that can be verified for the success of this
transaction, for example, an HTTP authorization header containing
valid authorization credentials, as defined in [RFC7231], [RFC9110],
Section 14.8. 11.6.2.

The body of the POST request MUST contain a JSON object with key
value pairs corresponding to values that are requested as the content
of the claims in the issued token. As an example, the body SHOULD
contain a JSON object as follows:

{
"tktype":"TNAuthList",
"tkvalue":"F83n2a...avn27DN3",
"ca":false,
"fingerprint":"SHA256 56:3E:CF:AE:83:CA:4D:15:B0:29:FF:1B:71:D3
:BA:B9:19:81:F8:50:9B:DF:4A:D4:39:72:E2:B1:F0:B9:38:E3"
}

If successful, the response to the POST request returns a 200 (OK)
with a JSON body that contains, at a minimum, the TNAuthList
Authority Token as a JSON object with a key of "token" and the
base64url-encoded string representing the atc token. JSON is easily
extensible, so users of this specification may want to pass other
pieces of information relevant to a specific application.

An example of a successful response would be as follows:

HTTP/1.1 200 OK
Content-Type: application/json

{"token": "DGyRejmCefe7v4N...vb29HhjjLPSggwiE"}

If the request is not successful, the response should indicate the
error condition. Specifically, for the case that the authorization
credentials are invalid or if the account identifier provided does
not exist, the response code MUST be 403 (Forbidden). Other 4xx and
5xx responses MUST follow standard HTTP error condition conventions
[RFC7231].
[RFC9110].

5.6. Token Authority Responsibilities

When creating the TNAuthList Authority Token, the Token Authority
MUST validate that the information contained in the ASN.1 TNAuthList
accurately represents the service provider code (SPC) or telephone
number (TN) resources the requesting party is authorized to represent
based on their pre-established, verified, and secure relationship
between the Token Authority and the requesting party. Note that the
fingerprint in the token request is not meant to be verified by the
Token Authority but rather is meant to be signed as part of the token
so that the party that requests the token can, as part of the
challenge response, allow the ACME server to validate that the token
requested and used came from the same party that controls the ACME
client.

5.7. Scope of the TNAuthList

Because this specification specifically involves the TNAuthList
defined in [RFC8226], which involves SPC, TNBlock, telephone number ranges,
and individual
TNs, telephone numbers, the client may also request an
Authority Token with some subset of its own authority as the
TNAuthList provided in the "tkvalue" element in the "atc" JSON
object. Generally, the scope of authority representing a CSP is
represented by a particular SPC (e.g., in North America, an operating
company number (OCN) or service provider identifier (SPID)). Based
on number allocations, that provider is also generally associated
with a particular set of different TN
Blocks telephone number ranges and/or TNs.
telephone numbers. The TNAuthList can be constructed to define a
limited scope of the TNBlocks TelephoneNumberRanges or TNs TelephoneNumbers
([RFC8226], Section 9) either associated with an SPC or with the
scope of TN Blocks telephone number ranges or TNs telephone numbers the client has
authority over.

As recommended in the Security Considerations section in [RFC9447],
an Authority Token can either have a scope that attests all of the
resources that a client is eligible to receive certificates for or
potentially a more limited scope that is intended to capture only
those resources for which a client will receive a certificate from a
particular certification authority. Any certification authority that
sees an Authority Token can learn information about the resources a
client can claim. In cases where this incurs a privacy risk,
Authority Token scopes should be limited to only the resources that
will be attested by the requested ACME certificate.

6. Validating the TNAuthList Authority Token

Upon receiving a response to the challenge, the ACME server MUST
perform the following steps to determine the validity of the
response.

1. Verify that the value of the "atc" claim is a well-formed JSON
object containing the mandatory key values.

2. If there is an "x5u" parameter, verify the "x5u" parameter is an
HTTPS URL with a reference to a certificate representing the
trusted issuer of Authority Tokens for the ecosystem.

3. If there is an "x5c" parameter, verify the certificate array
contains a certificate representing the trusted issuer of
Authority Tokens for the ecosystem.

4. Verify the TNAuthList Authority Token signature using the public
key of the certificate referenced by the token's "x5u" or "x5c"
parameter.

5. Verify that "atc" claim contains a "tktype" identifier with the
value "TNAuthList".

6. Verify that the "atc" claim "tkvalue" identifier contains the
equivalent base64url-encoded TNAuthList certificate extension
string value as the identifier specified in the original
challenge.

7. Verify that the remaining claims are valid (e.g., verify that
token has not expired).

8. Verify that the "atc" claim "fingerprint" is valid and matches
the account key of the client making the request.

9. Verify that the "atc" claim "ca" identifier boolean corresponds
to the CA boolean in the Basic Constraints extension in the
Certificate Signing Request (CSR) for either CA certificate or
end-entity certificate.

If all steps in the token validation process pass, then the ACME
server MUST set the challenge object "status" to "valid". If any
step of the validation process fails, the "status" in the challenge
object MUST be set to "invalid".

7. Using ACME-Issued Certificates with JSON Web Signature

JSON Web Signature (JWS) [RFC7515] objects can include an "x5u"
header parameter to refer to a certificate that is used to validate
the JWS signature. For example, the STIR PASSporT framework
[RFC8225] uses "x5u" to indicate the STIR certificate used to
validate the PASSporT JWS object. The URLs used in "x5u" are
expected to provide the required certificate in response to a GET
request, not a POST-as-GET, as required for the "certificate" URL in
the ACME order object. Thus, the current mechanism generally
requires the ACME client to download the certificate and host it on a
public URL to make it accessible to relying parties. This section
defines an optional mechanism for the certification authority (CA) to
host the certificate directly and provide a URL that the ACME client
owner can directly reference in the "x5u" of their signed PASSporTs.

As described in Section 7.4 of [RFC8555], when the certificate is
ready for making a "finalize" request, the server will return a 200
(OK) with the updated order object. In this response, an ACME server
can add a newly defined field called "x5u" that can pass this URL to
the ACME client for usage in generated PASSporTs as a publicly
available URL for PASSporT validation.

x5u (optional, string): a URL that can be used to reference the
certificate in the "x5u" parameter of a JWS object [RFC7515]

The publishing of the certificates at the new "x5u" URL should follow
the GET request requirement as mentioned above and should be
consistent with the timely publication according to the durations of
the certificate life cycle.

The following is an example of the use of "x5u" in the response when
the certificate status is "valid".

HTTP/1.1 200 OK
Content-Type: application/json
Replay-Nonce: CGf81JWBsq8QyIgPCi9Q9X
Link: <https://example.com/acme/directory>;rel="index"
Location: https://example.com/acme/order/TOlocE8rfgo

{
"status": "valid",
"expires": "2016-01-20T14:09:07.99Z",

"notBefore": "2016-01-01T00:00:00Z",
"notAfter": "2016-01-08T00:00:00Z",

"identifiers": [
"type":"TNAuthList",
"value":"F83n2a...avn27DN3"
],

"authorizations": ["https://sti-ca.com/acme/authz/1234"],

"finalize": "https://example.com/acme/order/TOlocE8rfgo/finalize",

"certificate": "https://example.com/acme/cert/mAt3xBGaobw",

"x5u": "https://example.com/cert-repo/giJI53km23.pem"
}

8. Usage Considerations

8.1. Large Number of Noncontiguous TNAuthList Values

There are many scenarios and reasons to have various combinations of
SPCs, TNs, and TN ranges. [RFC8226] has provided a somewhat
unbounded set of combinations. It's possible that a complex
noncontiguous set of telephone numbers are being managed by a CSP.
Best practice may be simply to split a set of noncontiguous numbers
under management into multiple STI certificates to represent the
various contiguous parts of the greater noncontiguous set of TNs,
particularly if the length of the set of values in an identifier
object grows to be too large.

9. IANA Considerations

Per this document, IANA has added a new identifier object type to the
"ACME Identifier Types" registry defined in Section 9.7.7 of
[RFC8555].

+============+===========+
| Label | Reference |
+============+===========+
| TNAuthList | RFC 9448 |
+------------+-----------+

Table 1

10. Security Considerations

The token represented by this document has the credentials to
represent the scope of a telephone number, a block of telephone
numbers, or an entire set of telephone numbers represented by an SPC.
The creation, transport, and any storage of this token MUST follow
the strictest of security best practices beyond the recommendations
of the use of encrypted transport protocols in this document to
protect it from getting in the hands of bad actors with illegitimate
intent to impersonate telephone numbers.

This document inherits the security properties of [RFC9447].
Implementations should follow the best practices identified in
[RFC8725].

This document only specifies SHA256 for the fingerprint hash.
However, the syntax of the fingerprint object would permit other
algorithms if, due to concerns about algorithmic agility, a more
robust algorithm were required at a future time. Future
specifications can define new algorithms for the fingerprint object
as needed.

11. References

11.1. Normative References

[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>.

[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.

[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.

[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>.

[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>.

[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>.

[RFC8226] Peterson, J. and S. Turner, "Secure Telephone Identity
Credentials: Certificates", RFC 8226,
DOI 10.17487/RFC8226, February 2018,
<https://www.rfc-editor.org/info/rfc8226>.

[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
<https://www.rfc-editor.org/info/rfc8555>.

[RFC8725] Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
Current Practices", BCP 225, RFC 8725,
DOI 10.17487/RFC8725, February 2020,
<https://www.rfc-editor.org/info/rfc8725>.

[RFC9060] Peterson, J., "Secure Telephone Identity Revisited (STIR)
Certificate Delegation", RFC 9060, DOI 10.17487/RFC9060,
September 2021, <https://www.rfc-editor.org/info/rfc9060>.

[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>.

[RFC9447] Peterson, J., Barnes, M., Hancock, D., and C. Wendt,
"Automated Certificate Management Environment (ACME)
Challenges Using an Authority Token", RFC 9447,
DOI 10.17487/RFC9447, July August 2023,
<https://www.rfc-editor.org/info/rfc9447>.

11.2. Informative References

[ATIS-1000080]
ATIS, "Signature-based Handling of Asserted information
using toKENs (SHAKEN): Governance Model and Certificate
Management", ATIS-1000080.v005, December 2022,
<https://access.atis.org/apps/group_public/
download.php/69428/ATIS-1000080.v005.pdf>.

[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>.

[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>.

[RFC8225] Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
<https://www.rfc-editor.org/info/rfc8225>.

Acknowledgements

We would like to thank Richard Barnes and Russ Housley for valuable
contributions to this document.

Authors' Addresses

Chris Wendt
Somos Inc.
United States of America
Email: chris-ietf@chriswendt.net

David Hancock
Comcast
Somos Inc.
United States of America
Email: davidhancock.ietf@gmail.com

Mary Barnes
Neustar Inc.
United States of America
Email: mary.ietf.barnes@gmail.com

Jon Peterson
Neustar Inc.
Suite 570
1800 Sutter St
Concord, CA 94520
United States of America
Email: jon.peterson@neustar.biz