Network Working Group C. Wendt
Internet-Draft D. Hancock
Intended status: Standards Track Comcast
Expires: September 27, 2021 M. Barnes
Independent
J. Peterson
Neustar Inc.
March 26, 2021
TNAuthList profile of ACME Authority Token
draft-ietf-acme-authority-token-tnauthlist-08
Abstract
This document defines a profile of the Automated Certificate
Management Environment (ACME) Authority Token for the automated and
authorized creation of certificates for VoIP Telephone Providers to
support Secure Telephony Identity (STI) using the TNAuthList defined
by STI certificates.
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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This Internet-Draft will expire on September 27, 2021.
Copyright Notice
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document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. ACME new-order identifiers for TNAuthList . . . . . . . . . . 3
4. TNAuthList Identifier Authorization . . . . . . . . . . . . . 5
5. TNAuthList Authority Token . . . . . . . . . . . . . . . . . 6
5.1. "iss" claim . . . . . . . . . . . . . . . . . . . . . . . 7
5.2. "exp" claim . . . . . . . . . . . . . . . . . . . . . . . 7
5.3. "jti" claim . . . . . . . . . . . . . . . . . . . . . . . 7
5.4. "atc" claim . . . . . . . . . . . . . . . . . . . . . . . 7
5.5. Acquiring the token from the Token Authority . . . . . . 8
5.6. Token Authority Responsibilities . . . . . . . . . . . . 9
5.7. Scope of the TNAuthList token authority . . . . . . . . . 10
6. Validating the TNAuthList Authority Token . . . . . . . . . . 10
7. Usage Considerations . . . . . . . . . . . . . . . . . . . . 11
7.1. Large number of Non-contiguous TNAuthList values . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
[RFC8555] is a mechanism for automating certificate management on the
Internet. It enables administrative entities to prove effective
control over resources like domain names, and automates the process
of generating and issuing certificates.
[I-D.ietf-acme-authority-token] 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.
This document addresses the STIR problem statement [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 PASSporTs [RFC8225], which can be
carried in using protocols such as SIP [RFC8224]. Currently, the
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only defined credentials for this purpose are the certificates
specified in [RFC8226].
This document also describes the ability for a telephone authority to
authorize the creation of CA types of certificates for delegation as
defined in [I-D.ietf-stir-cert-delegation].
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. ACME new-order identifiers for TNAuthList
In [RFC8555], Section 7 defines the procedure that an ACME client
uses to order a new certificate from a Certification Authority. The
new-order request contains an identifier field that specifies the
identifier objects the order corresponds to. This draft defines a
new type of identifier object called TNAuthList. A TNAuthList
identifier contains the identity information to be populated in the
TN Authorization List 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 as a base64 [RFC4648] encoding of the TN Authorization
List certificate extension ASN.1 object. The TN Authorization List
certificate extension ASN.1 syntax is defined in [RFC8226] section 9.
An example of an ACME order object "identifiers" field containing a
TNAuthList certificate would look as follows,
"identifiers": [{"type":"TNAuthList","value":"F83n2a...avn27DN3=="}]
where the "value" object string represents the arbitrary length
base64 encoded string.
A full new-order request would look as follows,
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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/1",
"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 CA 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
Replay-Nonce: MYAuvOpaoIiywTezizk5vw
Location: https://example.com/acme/order/1234
{
"status": "pending",
"expires": "2015-03-01T14:09:00Z",
"notBefore": "2021-01-01T00:00:00Z",
"notAfter": "2021-01-08T00:00:00Z",
"identifiers":[{"type:"TNAuthList",
"value":"F83n2a...avn27DN3=="}],
"authorizations": [
"https://example.com/acme/authz/1234"
],
"finalize": "https://example.com/acme/order/1234/finalize"
}
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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/1",
"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": "2018-03-03T14:09:00Z",
"identifier": {
"type:"TNAuthList",
"value":"F83n2a...avn27DN3=="
},
"challenges": [
{
"type": "tkauth-01",
"tkauth-type": "atc",
"token-authority": "https://authority.example.org/authz",
"url": "https://boulder.example.com/authz/asdf/0"
"token": "IlirfxKKXAsHtmzK29Pj8A"
}
]
}
When processing a certificate order containing an identifier of type
"TNAuthList", a CA uses the Authority Token challenge type of
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"tkauth-01" with a "tkauth-type" of "atc" in
[I-D.ietf-acme-authority-token] 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 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/authz/asdf/0 HTTP/1.1
Host: boulder.example.com
Content-Type: application/jose+json
{
"protected": base64url({
"alg": "ES256",
"kid": "https://example.com/acme/acct/1",
"nonce": "Q_s3MWoqT05TrdkM2MTDcw",
"url": "https://boulder.example.com/acme/authz/asdf/0"
}),
"payload": base64url({
"atc": "DGyRejmCefe7v4N...vb29HhjjLPSggwiE"
}),
"signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ"
}
The specifics of the construction of the TNAuthList specific "atc"
token is defined in the next section.
5. TNAuthList Authority Token
The Telephone Number Authority List Authority Token (TNAuthList
Authority Token) is an extension of the ACME Authority Token defined
in [I-D.ietf-acme-authority-token].
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The TNAuthList Authority Token Protected header MUST comply with the
Authority Token Protected header as defined in
[I-D.ietf-acme-authority-token].
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. It can be used as a URL
identifying the Token Authority that issued the TNAuthList Authority
Token beyond the "x5u" Header claim that identifies the location of
the certificate of the Token Authority used to validate the
TNAuthList Authority Token.
5.2. "exp" claim
The "exp" claim 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 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 the only claim specifically
defined in this document. It contains a JSON object of three
elements.
o a "tktype" key that is required with a string value equal to
"TNAuthList" to represent a TNAuthList profile of the authority
token [I-D.ietf-acme-authority-token] defined by this document.
o a "tkvalue" key with a string value equal to the TNAuthList
identifier "value" string which contains the base64 encoding of
the TN Authorization List certificate extension ASN.1 object.
"tkvalue" is a required key and MUST be included.
o 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 it not included the "ca" value is considered false by
default.
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o a "fingerprint" key with a fingerprint value equal to the
fingerprint, as defined in [RFC4949], of the ACME account
credentials. Specifically, the fingerprint value is a secure one-
way hash of the Distinguished Encoding Rules (DER) form of the
public key corresponding to the key pair the SP used to create the
account with the ACME server. The fingerprint value consists of
the name of the hash function, which shall be 'SHA256' for this
specification, followed by the hash value itself. The hash value
is represented as a sequence of uppercase hexadecimal bytes,
separated by colons. The number of bytes is defined by the hash
function. "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/authz",
"exp":1300819380,
"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 [I-D.ietf-acme-authority-token] 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.com
Content-Type: application/json
The request will pass the account id 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 CSP. There is
assumed to also be a corresponding authentication procedure that can
be verified for the success of this transaction. For example, an
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HTTP authorization header containing a valid authorization
credentials as defined in [RFC7231] Section 14.8.
The body of the POST request MUST contain the "atc" JSON object that
should be embedded in the token that is requested, for example the
body should contain a JSON object as shown:
{
"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"}
}
The response to the POST request if successful 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 base64 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 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, the response code MUST be 403 - Forbidden.
If the Account ID provided does not exist or does not match
credentials in Authorization header, the response MUST be 404 -
Invalid account ID. Other 4xx and 5xx responses MUST follow standard
[RFC7231] HTTP error condition conventions.
5.6. Token Authority Responsibilities
When the Token Authority creates the TNAuthList Authority Token, it
is the responsibility of the Token Authority to validate that the
information contained in the ASN.1 TNAuthList accurately represents
the SPC or telephone number resources the ACME client is authorized
to represent.
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5.7. Scope of the TNAuthList token authority
Because this specification specifically involves the TNAuthList
defined in [RFC8226] which involves SPC, TNBlock, and individual TNs,
the client may also request an Authority Token with some subset of
its own authority the TNAuthList provided in the "tkvalue" element in
the "atc" JSON object. Generally, the scope of authority
representing a communications service provider is represented by a
particular SPC (e.g. in North America, an OCN or SPID) which is
associated with a particular set of different TN Blocks and/or TNs,
although more often the former typically through a set of regulated
authoritative registries or databases. TNAuthList can be constructed
to define a limited scope of the TNBlocks or TNs either associated
with an SPC or with the scope of TN Blocks or TNs the client has
authority over.
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.
o Verify that the token contained in the Payload "atc" field is a
valid TNAuthList Authority Token.
o Verify the TNAuthList Authority Token signature using the public
key of the certificate referenced by the token's "x5u" parameter.
o Verify that "atc" claim contains an identifier type of
"TNAuthList".
o Verify that the "atc" claim contains the equivalent base64 encoded
TNAuthList certificate extension string value as the Identifier
specified in the original challenge.
o Verify that the remaining claims are valid (e.g., verify that
token has not expired)
o Verify that the "atc" claim "fingerprint" is valid
o Verify that the "ca" claim boolean corresponds to the CSR request
for either CA certificate or end-entity certificate
If all steps in the token validation process pass, then the CA 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".
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7. Usage Considerations
7.1. Large number of Non-contiguous 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 non-
contiguous set of telephone numbers are being managed by a CSP. Best
practice may be simply to split a set of non-contiguous numbers under
management into multiple STI certificates to represent the various
contiguous parts of the greater non-contiguous set of TNs,
particularly if length of the set of values in identifier object
grows to be too large.
8. 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 a 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
[I-D.ietf-acme-authority-token].
9. IANA Considerations
This document requests the addition of a new identifier object type
to the "ACME Identifier Types" registry defined in Section 9.7.7 of
[RFC8555].
+------------+-----------+
| Label | Reference |
+------------+-----------+
| TNAuthList | RFCThis |
+------------+-----------+
10. Acknowledgements
We would like to thank Richard Barnes and Russ Housley for valuable
contributions to this document.
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11. References
11.1. Normative References
[I-D.ietf-acme-authority-token]
Peterson, J., Barnes, M., Hancock, D., and C. Wendt, "ACME
Challenges Using an Authority Token", draft-ietf-acme-
authority-token-05 (work in progress), March 2020.
[I-D.ietf-stir-cert-delegation]
Peterson, J., "STIR Certificate Delegation", draft-ietf-
stir-cert-delegation-03 (work in progress), July 2020.
[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>.
[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>.
[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>.
11.2. Informative References
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[ATIS-1000080]
ATIS/SIP Forum NNI Task Group, "Signature-based Handling
of Asserted information using toKENs (SHAKEN) Governance
Model and Certificate Management
<https://access.atis.org/apps/group_public/
download.php/32237/ATIS-1000080.pdf>", July 2017.
[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>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[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>.
Authors' Addresses
Chris Wendt
Comcast
One Comcast Center
Philadelphia, PA 19103
USA
Email: chris-ietf@chriswendt.net
David Hancock
Comcast
Email: davidhancock.ietf@gmail.com
Mary Barnes
Independent
Email: mary.ietf.barnes@gmail.com
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Jon Peterson
Neustar Inc.
1800 Sutter St Suite 570
Concord, CA 94520
US
Email: jon.peterson@neustar.biz
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