Internet DRAFT - draft-barnes-acme-token-challenge
draft-barnes-acme-token-challenge
Network Working Group M. Barnes
Internet-Draft iconectiv
Intended status: Standards Track March 5, 2018
Expires: September 6, 2018
ACME Token Identifier and Challenges
draft-barnes-acme-token-challenge-02
Abstract
This document specifies an identifier and challenge type required to
enable the Automated Certificate Management Environment (ACME) to
issue certificates using a token for the challenge response. This
token is issued by a administrative authority with whom the
Certification Authority (CA) has a trust relationship. The entity
requesting a certificate also has a relationship with the
administrative authority, such that the administrative authority
assigns a unique code to the entity. This entity code is included as
part of the token that the administrative authority issues.
Status of This Memo
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This Internet-Draft will expire on September 6, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Identifier for Entity Codes . . . . . . . . . . . . . . . . . 4
5. Challenges for Entity Codes . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6.1. ACME Entity Code Identifier . . . . . . . . . . . . . . . 7
6.2. ACME Entity Code Challenge . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
[I-D.ietf-acme-acme] 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.
This document specifies an identifier and challenge type to enable
the Automated Certificate Management Environment (ACME) to issue
certificates using a token for the challenge response. This token is
issued by a administrative authority with whom the Certification
Authority (CA) has a trust relationship. The entity requesting a
certificate also has a relationship with the administrative
authority, such that the administrative authority assigns a unique
code to the entity. This entity code is included as part of the
token that the administrative authority issues.
The following diagram summarizes these trust relationships and
protocols:
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+-------------+
| |
+--------| CA |
| | |
| +-------------+
+----------------+ | ^
| | HTTPS | |
| Administrative +<---------------------+ |
| Authority | | ACME
| +----------------------+ |
+----------------+ Entity | |
Code | v
Token | +-------------+
| | |
+------->| Entity |
| (code) |
| |
+-------------+
Figure 1: Relationships and Interfaces
There are several use cases that can leverage a mechanism using a
generic token for the challenge response, in particular for Secure
Telephony Identity Revisited (STIR). The STIR problem statement
[RFC7340] 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
[I-D.ietf-stir-passport], which can be carried in using protocols
such as SIP [I-D.ietf-stir-rfc4474bis]. Currently, the only defined
credentials for this purpose are the certificates specified in
[I-D.ietf-stir-certificates].
[I-D.ietf-stir-certificates] describes certificate extensions
suitable for associating telephone numbers and service provider codes
with certificates. [I-D.ietf-acme-telephone] specifies the use of
ACME extensions to enable certification authorities to issue
certificates based on telephone numbers.
[I-D.ietf-acme-service-provider] specifies the use of ACME extensions
to enable certification authorities to issue certificates based on
service provider codes.
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2. Conventions and 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. Overview
The intent of the challenges in this document is to provide evidence
that an established administrative authority has authorized the
entity requesting the issuance of certificates. The model is based
on the entity that is requesting certificates being assigned a unique
entity code by the administrative authority. The expectation is that
the Entity code would be stable and not change frequently, if at all.
The entity also requests the token that is to be used in the
challenge response from the administrative authority, prior to
requesting issuance of a certificate. Entities that are using this
mechanism SHOULD define the lifecycle management for the entity code
token - e.g., the frequency at which it should be renewed. This is
expected to vary depending upon the use case.
4. Identifier for Entity Codes
In order to issue certificates based on entity code values, a new
ACME identifier type is required for use in ACME authorization
objects. The baseline ACME specification defines one type of
identifier, for a fully-qualified domain name ("dns"). This document
defines a new ACME identifier type for entity codes ("EntityCode").
5. Challenges for Entity Codes
The new "EntityCode" identifier introduces a slightly different
authorization process. A mechanism is required to allow the entity
requesting certificates to prove it has the authority to request
certificates. This document defines a new ACME challenge type of
"ec-token-01" to support entity code tokens.
The following is the response that the ACME client receives when it
sends a GET for the challenges in the case of a "EntityCode"
identifer:
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HTTP/1.1 200 OK
Content-Type: application/json
Link: <https://example.com/acme/some-directory>;rel="directory"
{
"status": "pending",
"identifier": {
"type": "EntityCode",
"value": ["1234-0111"]
},
"challenges": [
{
"type": "ec-token-01",
"url": "https://example-ca.com/authz/asdf/0"
"token": "DGyRejmCefe7v4NfDGDKfA" }
],
}
A client responds to this challenge by providing an entity code
token. The entity code token is a standard JWT token [RFC7519] using
a JWS defined signature string [RFC7515].
The entity code token JWT Protected Header MUST include the
following:
alg: Defines the algorithm used in the signature of the token.
typ: Set to standard "JWT" value.
x5u: Defines the URL of the certificate of the administrative
authority validating the Service Code.
The authorization code token JWT Payload MUST include the following:
sub: Entity Code value being validated in the form of an ASCII
string.
iat: DateTime value of the time and date the token was issued.
nbf: DateTime value of the starting time and date that the token
is valid.
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exp: DateTime value of the ending time and date that the token
expires.
fingerprint: : Fingerprint of the ACME credentials the requestor
used to create an account with the CA. The fingerprint is of
the form: base64url(JWK_Thumbprint(accountKey)).
The "JWK_Thumbprint" step indicates the computation specified
in [RFC7638], using the SHA-256 digest [FIPS180-4]. As noted
in JWA [RFC7518] any prepended zero octets in the JWK object
MUST be stripped before doing the computation.
To respond to an entity code token challenge, the ACME client
constructs an entity code authorization ("ec-authz") using the
"token" value provided in the challenge and the entity code token
("ecAuthzToken") that has been previously obtained from the
administrative authority. These two values are concatenated and
separated by a "." character as follows:
ecAuthorization = token || '.' || ecAuthzToken
The token for a challenge is a string comprised entirely of
characters in the URL- safe base64 alphabet. The "||" operator
indicates concatenation of strings.
An example of the use of the "ec-token-01" in a challenge response
sent by the ACME client is provided below:
POST /acme/authz/asdf/0 HTTP/1.1
Host: example-ca.com
Content-Type: application/jose+json
{
"protected": base64url({
"alg": "ES256",
"kid": "https://example-ca.com/acme/reg/asdf",
"nonce": "Q_s3MWoqT05TrdkM2MTDcw",
"url": "https://example-ca.com/acme/authz/asdf/0"
}),
"payload": base64url({
"ecAuthorization": "DGyRejmCefe7v4N...vb29HhjjLPSggwiE"
}),
"signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ"
}
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Upon receiving a response to the challenge, the ACME server
determines the validity of the response. The ACME server MUST verify
that the "token" in the response matches the "token" in the original
challenge. To determine if the "ecAuthzToken" is valid, the server
MUST use the URL in the JWT header in the "ecAuthzToken" to obtain
the certificate associated with the JWT payload. The server MUST
validate the signature and verify the claims. The "sub" field MUST
be the value that was included in the "EntityCode" in the original
challenge. The server MUST verify that the "fingerprint" field
matches the ACME credentials for the ACME client that created the
account with the CA. If the validation is successful, the "status"
in the challenge object is set to "valid". If any step of the
validation process fails, the "status" in the challenge object MUST
be set to "invalid". [Editor's Note: Likely we should describe
specific error responses for the above.]
6. IANA Considerations
This document defines a new ACME Identifier type and ACME Challenge
type to be registered.
[[ RFC EDITOR: Please replace XXXX above with the RFC number assigned
to this document ]]
6.1. ACME Entity Code Identifier
This document defines the "EntityCode" ACME Challenge type in the
ACME Identifier Type registry as follows:
+-----------------------+-----------+
| Identifier Type | Reference |
+-----------------------+-----------+
| EntityCode | RFC XXXX |
+-----------------------+-----------+
6.2. ACME Entity Code Challenge
This document defines the "ec-token-01" ACME Challenge type in the
ACME Challenge Types registry as follows:
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+--------------+--------------------+-----------+
| Label | Identifier Type | Reference |
+--------------+--------------------+-----------+
| ec-token-01 | EntityCode | RFC XXXX |
+--------------+--------------------+-----------+
7. Security Considerations
This document relies on the security considerations established for
the ACME protocol per [I-D.ietf-acme-acme]. The new "EntityCode"
identifier and "ec-token-01" validation challenges introduce a
slightly different authorization process. However, the challenges
still have a binding between the account private key and the
validation query made by the server, since the fingerprint of the
account key is contained in the service code token used for
authorization.
The entity code token is initially obtained through a secure exchange
between the entity requesting certificates and the administrative
authority that is responsible for determining what entities can
request certificates.
8. References
8.1. Normative References
[FIPS180-4]
Department of Commerce, National, "NIST FIPS 180-4, Secure
Hash Standard", March 2012.
[I-D.ietf-acme-acme]
Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", draft-ietf-acme-acme-09 (work in progress),
December 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>.
[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>.
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[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>.
8.2. Informative References
[I-D.ietf-acme-service-provider]
Barnes, M. and C. Wendt, "ACME Identifiers and Challenges
for VoIP Service Providers", draft-ietf-acme-service-
provider-02 (work in progress), October 2017.
[I-D.ietf-acme-telephone]
Peterson, J. and R. Barnes, "ACME Identifiers and
Challenges for Telephone Numbers", draft-ietf-acme-
telephone-01 (work in progress), October 2017.
[I-D.ietf-stir-certificates]
Peterson, J. and S. Turner, "Secure Telephone Identity
Credentials: Certificates", draft-ietf-stir-
certificates-18 (work in progress), December 2017.
[I-D.ietf-stir-passport]
Wendt, C. and J. Peterson, "Personal Assertion Token
(PASSporT)", draft-ietf-stir-passport-11 (work in
progress), February 2017.
[I-D.ietf-stir-rfc4474bis]
Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
"Authenticated Identity Management in the Session
Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-16
(work in progress), February 2017.
[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>.
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Author's Address
Mary Barnes
iconectiv
Email: mary.ietf.barnes@gmail.com
Barnes Expires September 6, 2018 [Page 10]
