Internet DRAFT - draft-ietf-acme-service-provider
draft-ietf-acme-service-provider
Network Working Group M. Barnes
Internet-Draft iconectiv
Intended status: Informational C. Wendt
Expires: May 3, 2018 Comcast
October 30, 2017
ACME Identifiers and Challenges for VoIP Service Providers
draft-ietf-acme-service-provider-02
Abstract
This document specifies identifiers and challenges required to enable
the Automated Certificate Management Environment (ACME) to issue
certificates for VoIP service providers to support Secure Telephony
Identity (STI).
Status of This Memo
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This Internet-Draft will expire on May 3, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Identifier for Service Provider Codes . . . . . . . . . . . . 3
4. Challenges for Service Providers . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. ACME TNAuthList Identifier . . . . . . . . . . . . . . . 6
5.2. ACME Service Provider Challenge . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Informative References . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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.
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 ACME
extensions to enable certification authorities to issue certificates
based on telephone numbers. This specification defines extensions to
ACME to enable certification authorities to issue certificates based
on service provider codes.
2. Overview
The document [ATIS-1000080] provides a framework and model for using
certificates based on service provider codes. In this model, each
service provider requires only a few certificates, which are used in
conjunction with a PASSporT that contains additional information
attesting to a service provider's knowledge of the originator of the
call. Further details on the PASSporT extensions for this model are
provided in the SHAKEN Framework [ATIS-1000074].
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In the SHAKEN Certificate Management framework [ATIS-1000080], there
is an administrative entity that is responsible for allocating
service provider codes. This is referred to as the STI Policy
Administrator (STI-PA). This allows a certification authority to
validate that the entity requesting issuance of a certificate is
authorized to request certificates on behalf of the entity that has
been assigned a specific service provider code. A single VoIP
service provider can be allocated multiple service provider codes. A
service provider can choose to use the same certificate for multiple
service providers as reflected by the structure of the TN
Authorization List certificate extension defined in
[I-D.ietf-stir-certificates].
The intent of the challenges in this document is not to establish
that an entity is a valid service provider but rather to provide
evidence that an established administrative authority entity has
authorized the entity to provide VoIP services in the network and
thus to request credentials on behalf of the VoIP users in the
network.
3. Identifier for Service Provider Codes
In order to issue certificates for service providers based on service
provider 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"). The document [I-D.ietf-acme-telephone] defines an ACME
identifier type for telephone numbers ("tn"). This document defines
a new ACME identifier type for service provider codes ("TNAuthList").
The "TNAuthList" identifier is the same type that is specified in the
TN Authorization List certificate extension
[I-D.ietf-stir-certificates] for service provider codes.
4. Challenges for Service Providers
The new "TNAuthList" identifier introduces a slightly different
authorization process. A mechanism is required to allow the service
provider to prove it has the authority to request certificates on
behalf of the entities for whom it is providing VoIP services. This
document defines a new ACME challenge type of "spc-token-01" to
support the authorization of service provider 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 "TNAuthList"
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": "TNAuthList",
"value": ["1234-0111"]
},
"challenges": [
{
"type": "spc-token-01",
"url": "https://sti-ca.com/authz/asdf/0"
"token": "DGyRejmCefe7v4NfDGDKfA" }
],
}
A client responds to this challenge by providing a service provider
code token. In the SHAKEN Certificate Management framework, the
Service Provider has a secure exchange with the STI-PA to obtain a
service provider code token that can be used for authorization by the
CA when requesting a certificate. The service provider code token is
a standard JWT token [RFC7519] using a JWS defined signature string
[RFC7515]. It is RECOMMENDED that the lifetime of the service
provider code token be greater than the certificate lifetime, in
particular in cases where multiple certificates are being issued
using the same service provider code token.
The service provider code token JWT Protected Header MUST include the
following:
alg: Defines the algorithm used in the signature of the token.
For Service Provider Code tokens, the algorithm MUST be
"ES256".
typ: Set to standard "JWT" value.
x5u: Defines the URL of the certificate of the STI-PA validating
the Service Provider Code.
The service provide code token JWT Payload MUST include the
following:
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sub: Service Provider 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.
exp: DateTime value of the ending time and date that the token
expires.
fingerprint: : Fingerprint of the ACME credentials the Service
Provider 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 a service provider code token challenge, the ACME
client constructs a service provider code authorization ("spc-authz")
using the "token" value provided in the challenge and the service
provider code token ("spcAuthzToken") that has been previously
obtained from the STI-PA. These two values are concatenated and
separated by a "." character as follows:
spcAuthorization = token || '.' || spcAuthzToken
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 "spc-token-01" in a challenge response
sent by the ACME client is provided below:
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POST /acme/authz/asdf/0 HTTP/1.1
Host: sti-ca.com
Content-Type: application/jose+json
{
"protected": base64url({
"alg": "ES256",
"kid": "https://sti-ca.com/acme/reg/asdf",
"nonce": "Q_s3MWoqT05TrdkM2MTDcw",
"url": "https://sti-ca.com/acme/authz/asdf/0"
}),
"payload": base64url({
"spcAuthorization": "DGyRejmCefe7v4N...vb29HhjjLPSggwiE"
}),
"signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ"
}
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 "spcAuthzToken" is valid, the server
MUST use the URL in the JWT header in the "spcAuthzToken" to obtain
the certificate associated with the JWT payload. The server MUST
validate the signature and verify the claims. The "sub" field MUST
be a value that is included in the values for the "TN-Auth-List" 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.]
5. 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 ]]
5.1. ACME TNAuthList Identifier
This document defines the "TNAuthList" ACME Challenge type in the
ACME Identifier Type registry as follows:
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+-----------------------+-----------+
| Identifier Type | Reference |
+-----------------------+-----------+
| TNAuthList | RFC XXXX |
+-----------------------+-----------+
5.2. ACME Service Provider Challenge
This document defines the "spc-token-01" ACME Challenge type in the
ACME Challenge Types registry as follows:
+--------------+--------------------+-----------+
| Label | Identifier Type | Reference |
+--------------+--------------------+-----------+
| spc-token-01 | TNAuthList | RFC XXXX |
+--------------+--------------------+-----------+
6. Security Considerations
This document relies on the security considerations established for
the ACME protocol per [I-D.ietf-acme-acme]. The new "TNAuthList"
identifier and "spc-token-01" validation challenges introduce a
slightly different authorization process. Although, 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 provider code token used for
authorization.
The service provider code token is initially obtained through a
secure exchange between the service provider and the entity in the
network that is responsible for determining what entities can operate
as VoIP service providers (the STI Policy Administrator). Further
details on this are provided in [ATIS-1000080].
7. Informative References
[ATIS-1000074]
ATIS/SIP Forum NNI Task Group, "Signature-based Handling
of Asserted information using toKENs (SHAKEN)", January
2017.
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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", May 2017.
[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., and J. Kasten, "Automatic
Certificate Management Environment (ACME)", draft-ietf-
acme-acme-07 (work in progress), June 2017.
[I-D.ietf-acme-telephone]
Peterson, J. and R. Barnes, "ACME Identifiers and
Challenges for Telephone Numbers", draft-ietf-acme-
telephone-00 (work in progress), July 2017.
[I-D.ietf-stir-certificates]
Peterson, J. and S. Turner, "Secure Telephone Identity
Credentials: Certificates", draft-ietf-stir-
certificates-14 (work in progress), May 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>.
[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>.
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[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>.
Authors' Addresses
Mary Barnes
iconectiv
Email: mary.ietf.barnes@gmail.com
Chris Wendt
Comcast
One Comcast Center
Philadelphia, PA 19103
US
Email: chris-ietf@chriswendt.net
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