Network Working Group J. Peterson
Internet-Draft Neustar
Intended status: Standards Track S. Turner
Expires: September 22, 2016 Sn3rd
March 21, 2016
Secure Telephone Identity Credentials: Certificates
draft-ietf-stir-certificates-03.txt
Abstract
In order to prevent the impersonation of telephone numbers on the
Internet, some kind of credential system needs to exist that
cryptographically proves authority over telephone numbers. This
document describes the use of certificates in establishing authority
over telephone numbers, as a component of a broader architecture for
managing telephone numbers as identities in protocols like SIP.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 22, 2016.
Copyright Notice
Copyright (c) 2016 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
(http://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
Peterson & Turner Expires September 22, 2016 [Page 1]
Internet-Draft STIR Certs March 2016
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Authority for Telephone Numbers in Certificates . . . . . . . 3
4. Enrollment and Authorization using the TN Authorization List 5
4.1. Certificate Extension Scope and Structure . . . . . . . . 6
5. Provisioning Private Keying Material . . . . . . . . . . . . 7
6. Acquiring Credentials to Verify Signatures . . . . . . . . . 7
7. Verifying Certificate Scope with TN Authorization List . . . 8
8. Certificate Freshness and Revocation . . . . . . . . . . . . 10
8.1. Choosing a Verification Method . . . . . . . . . . . . . 10
8.2. Using OCSP with TN Auth List . . . . . . . . . . . . . . 11
8.2.1. OCSP Extension Specification . . . . . . . . . . . . 12
8.3. Acquiring TN Lists By Reference . . . . . . . . . . . . . 13
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
11. Security Considerations . . . . . . . . . . . . . . . . . . . 15
12. Informative References . . . . . . . . . . . . . . . . . . . 15
Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
The STIR problem statement [I-D.ietf-stir-problem-statement]
identifies the primary enabler of robocalling, vishing, swatting and
related attacks as the capability to impersonate a calling party
number. The starkest examples of these attacks are cases where
automated callees on the PSTN rely on the calling number as a
security measure, for example to access a voicemail system.
Robocallers use impersonation as a means of obscuring identity; while
robocallers can, in the ordinary PSTN, block (that is, withhold)
their caller identity, callees are less likely to pick up calls from
blocked identities, and therefore appearing to calling from some
number, any number, is preferable. Robocallers however prefer not to
call from a number that can trace back to the robocaller, and
therefore they impersonate numbers that are not assigned to them.
One of the most important components of a system to prevent
impersonation is the implementation of credentials which identify the
parties who control telephone numbers. With these credentials,
parties can prove that they are in fact authorized to use telephony
numbers, and thus distinguish themselves from impersonators unable to
present such credentials. This document describes credential systems
for telephone numbers based on X.509 version 3 certificates in
Peterson & Turner Expires September 22, 2016 [Page 2]
Internet-Draft STIR Certs March 2016
accordance with [RFC5280]. While telephone numbers have long been a
part of the X.509 standard, this document extends X.509 with a
Telephone Number Authorization List which binds certificates to
authority for particular telephone numbers, or potentially telephone
number blocks or ranges.
In the STIR in-band architecture specified in
[I-D.ietf-stir-rfc4474bis], two basic types of entities need access
to these credentials: authentication services, and verification
services (or verifiers). An authentication service must be operated
by an entity enrolled with the certification authority (see
Section 4), whereas a verifier need only trust the root certificate
of the authority, and have a means to access and validate the public
keys associated with these certificates. Although the guidance in
this document is written with the STIR in-band architecture in mind,
the credential system described in this document could be useful for
other protocols that want to make use of certificates to prove
authority over telephone numbers on the Internet.
This document specifies only the credential syntax and semantics
necessary to support this architecture. It does not assume any
particular certification authority or deployment environment. We
anticipate that some deployment experience will be necessary to
determine optimal operational models.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in RFC 2119 [RFC2119] and RFC 6919 [RFC6919].
3. Authority for Telephone Numbers in Certificates
At a high level, this specification details two non-exclusive
approaches that can be employed to determine authority over telephone
numbers with certificates.
The first approach is to leverage the subject of the certificate to
ascertain that the holder of the certificate is authorized to claim
authority over a telephone number. The subject might be represented
as a domain name in the SubjectAltName, such as an "example.net"
where that domain is known to relying parties as a carrier, or
represented with other identifiers related to the operation of the
telephone network including Service Provider Identifiers (SPIDs)
could serve as a subject as well. A relying party could then employ
an external data set or service that determines whether or not a
specific telephone number is under the authority of the carrier
Peterson & Turner Expires September 22, 2016 [Page 3]
Internet-Draft STIR Certs March 2016
identified as the subject of the certificate, and use that to
ascertain whether or not the carrier should have authority over a
telephone number. Potentially, a certificate extension to convey the
URI of such an information service trusted by the issuer of the
certificate could be developed (though this specification does not
propose one). Alternatively, some relying parties could form
bilateral or multilateral trust relationships with peer carriers,
trusting one another's assertions just as telephone carriers in the
SS7 network today rely on transitive trust when displaying the
calling party telephone number received through SS7 signaling.
The second approach is to extend the syntax of certificates to
include a new attribute, defined here as TN Authorization List, which
contains a list of telephone numbers defining the scope of authority
of the certificate. Relying parties, if they trust the issuer of the
certificate as a source of authoritative information on telephone
numbers, could therefore use the TN Authorization List instead of the
subject of the certificate to make a decision about whether or not
the signer has authority over a particular telephone number. The TN
Authorization List could be provided in one of two ways: as a literal
value in the certificate, or as a network service that allows relying
parties to query in real time to determine that a telephone number is
in the scope of a certificate. Using the TN Authorization list
rather than the certificate subject makes sense when, for example,
for privacy reasons, the certificate owner would prefer not to be
identified, or in cases where the holder of the certificate does not
participate in the sort of traditional carrier infrastructure taht
the first approach assumes.
The first approach requires little change to existing PKI
certificates; for the second approach, we must define an appropriate
enrollment and authorization process. For the purposes of STIR, the
over-the-wire format specified in [I-D.ietf-stir-rfc4474bis]
accommodates either of these approaches: the methods for
canonicalizing, signing, for identifying and accessing the
certificate and so on remain the same; it is only the verifier
behavior and authorization decision that will change depending on the
approach to telephone number authority taken by the certificate. For
that reason, the two approaches are not mutually exclusive, and in
fact a certificate issued to a traditional telephone network service
provider could contain a TN Authorization List or not, depending on
the certification authority issuing the credential. Regardless of
which approaches is used, certificates that assert authority over
telephone numbers are subject to the ordinary operational procedures
that govern certificate use per [RFC5280]. This means that
verification services must be mindful of the need to ensure that they
trust the root certificate authority that issued the certificate, and
Peterson & Turner Expires September 22, 2016 [Page 4]
Internet-Draft STIR Certs March 2016
that they have some means to determine the freshness of the
certificate (see Section 8).
4. Enrollment and Authorization using the TN Authorization List
This document assumes a threefold model for certificate enrollment
when using the TN Authorization List extension.
The first enrollment model is one where the certification authority
acts in concert with national numbering authorities to issue
credentials to those parties to whom numbers are assigned. In the
United States, for example, telephone number blocks are assigned to
Local Exchange Carriers (LECs) by the North American Numbering Plan
Administrator (NANPA), who is in turn directed by the national
regulator. LECs may also receive numbers in smaller allocations,
through number pooling, or via an individual assignment through
number portability. LECs assign numbers to customers, who may be
private individuals or organizations - and organizations take
responsibility for assigning numbers within their own enterprise.
This model requires top-down adoption of the model from regulators
through to carriers.
The second enrollment model is a bottom-up approach where a
certification authority requires that an entity prove control by
means of some sort of test, which, as with certification authorities
for web PKI, might either be automated or a manual administrative
process. As an example of an automated process, an authority might
send a text message to a telephone number containing a URL (which
might be dereferenced by the recipient) as a means of verifying that
a user has control of terminal corresponding to that number. Checks
of this form are frequently used in commercial systems today to
validate telephone numbers provided by users. This is comparable to
existing enrollment systems used by some certificate authorities for
issuing S/MIME credentials for email by verifying that the party
applying for a credential receives mail at the email address in
question.
The third enrollment model is delegation: that is, the holder of a
certificate (assigned by either of the two methods above) might
delegate some or all of their authority to another party. In some
cases, multiple levels of delegation could occur: a LEC, for example,
might delegate authority to a customer organization for a block of
100 numbers used by an IP PBX, and the organization might in turn
delegate authority for a particular number to an individual employee.
This is analogous to delegation of organizational identities in
traditional hierarchical Public Key Infrastructures (PKIs) who use
the name constraints extension [RFC5280]; the root CA delegates names
in sales to the sales department CA, names in development to the
Peterson & Turner Expires September 22, 2016 [Page 5]
Internet-Draft STIR Certs March 2016
development CA, etc. As lengthy certificate delegation chains are
brittle, however, and can cause delays in the verification process,
this document considers optimizations to reduce the complexity of
verification.
[TBD] Future versions of this specification may address adding a
level of assurance indication to certificates to differentiate those
enrolled from proof-of-possession versus delegation.
[TBD] Future versions of this specification may also discuss methods
of partial delegation, where certificate holders delegate only part
of their authority. For example, individual assignees may want to
delegate to a service authority for text messages associated with
their telephone number, but not for other functions.
4.1. Certificate Extension Scope and Structure
This specification places no limits on the number of telephone
numbers that can be associated with any given certificate. Some
service providers may be assigned millions of numbers, and may wish
to have a single certificate that is capable of signing for any one
of those numbers. Others may wish to compartmentalize authority over
subsets of the numbers they control.
Moreover, service providers may wish to have multiple certificates
with the same scope of authority. For example, a service provider
with several regional gateway systems may want each system to be
capable of signing for each of their numbers, but not want to have
each system share the same private key.
The set of telephone numbers for which a particular certificate is
valid is expressed in the certificate through a certificate
extension; the certificate's extensibility mechanism is defined in
[RFC5280] but the TN Authorization List extension is specified in
this document.
The subjects of certificates containing the TN Authorization List
extension are typically the administrative entities to whom numbers
are assigned or delegated. For example, a LEC might hold a
certificate for a range of telephone numbers. In some cases, the
organization or individual issued such a certificate may not want to
associate themselves with a certificate; for example, a private
individual with a certificate for a single telephone number might not
want to distribute that certificate publicly if every verifier
immediately knew their name. The certification authorities issuing
certificates with the TN Authorization List extensions may, in
accordance with their policies, obscure the identity of the subject,
Peterson & Turner Expires September 22, 2016 [Page 6]
Internet-Draft STIR Certs March 2016
though mechanisms for doing so are outside the scope of this
document.
5. Provisioning Private Keying Material
In order for authentication services to sign calls via the procedures
described in [I-D.ietf-stir-rfc4474bis], they must hold a private key
corresponding to a certificate with authority over the calling
number. This specification does not require that any particular
entity in a SIP deployment architecture sign requests, only that it
be an entity with an appropriate private key; the authentication
service role may be instantiated by any entity in a SIP network. For
a certificate granting authority only over a particular number which
has been issued to an end user, for example, an end user device might
hold the private key and generate the signature. In the case of a
service provider with authority over large blocks of numbers, an
intermediary might hold the private key and sign calls.
The specification recommends distribution of private keys through
PKCS#8 objects signed by a trusted entity, for example through the
CMS package specified in [RFC5958].
6. Acquiring Credentials to Verify Signatures
This specification documents multiple ways that a verifier can gain
access to the credentials needed to verify a request. As the
validity of certificates does not depend on the method of their
acquisition, there is no need to standardize any single mechanism for
this purpose. All entities that comply with
[I-D.ietf-stir-rfc4474bis] necessarily support SIP, and consequently
SIP itself can serve as a way to acquire certificates.
[I-D.ietf-stir-rfc4474bis] provides an "info" parameter of the
Identity header which contains a URI where the credential used to
generate the Identity header, and requires documents which define
credential systems to list the URI schemes that may be present in the
"info" parameter. For implementations compliant with this
specification, three URI schemes are REQUIRED: the CID URI, the SIP
URI, and the HTTP URI.
The simplest way for a verifier to acquire the certificate needed to
verify a signature is for the certificate be conveyed in a SIP
request along with the signature itself. In SIP, for example, a
certificate could be carried in a multipart MIME body [RFC2046], and
the URI in the Identity header "info" parameter could specify that
body with a CID URI [RFC2392]. However, in many environments this is
not feasible due to message size restrictions or lack of necessary
support for multipart MIME.
Peterson & Turner Expires September 22, 2016 [Page 7]
Internet-Draft STIR Certs March 2016
More commonly, the Identity header "info" parameter in a SIP request
may contain a URI that the verifier dereferences with a network call.
Implementations of this specification are required to support the use
of SIP for this function (via the SUBSCRIBE/NOTIFY mechanism), as
well as HTTP, via the Enrollment over Secure Transport mechanisms
described in RFC 7030 [RFC7030].
Note well that as an optimization, a verifier may have access to a
service, a cache or other local store that grants access to
certificates for a particular telephone number. However, there may
be multiple valid certificates that can sign a call setup request for
a telephone number, and as a consequence, there needs to be some
discriminator that the signer uses to identify their credentials.
The Identity header "info" parameter itself can serve as such a
discriminator, provided implementations use that parameter as a key
when accessing certificates from caches or other sources. Verifiers
still
7. Verifying Certificate Scope with TN Authorization List
The subjects of certificates containing the TN Authorization List
extension are the administrative entities to whom numbers are
assigned or delegated. When a verifier is validating a caller's
identity, local policy always determines the circumstances under
which any particular subject may be trusted, but the purpose of the
TN Authorization List extension particular is to allow a verifier to
ascertain when the certification authority has designed that the
subject has authority over a particular telephone number or number
range.
The Telephony Number (TN) Authorization List certificate extension is
identified by the following object identifier:
id-ce-TNAuthList OBJECT IDENTIFIER ::= { TBD }
The TN Authorization List certificate extension has the following
syntax:
Peterson & Turner Expires September 22, 2016 [Page 8]
Internet-Draft STIR Certs March 2016
TNAuthorizationList ::= SEQUENCE SIZE (1..MAX) OF TNAuthorization
TNAuthorization ::= SEQUENCE SIZE (1..MAX) OF TNEntry
TNEntry ::= CHOICE {
spid ServiceProviderIdentifierList,
range TelephoneNumberRange,
one E164Number }
ServiceProviderIdentifierList ::= SEQUENCE SIZE (1..3) OF
OCTET STRING
-- When all three are present: SPID, Alt SPID, and Last Alt SPID
TelephoneNumberRange ::= SEQUENCE {
start E164Number,
count INTEGER }
E164Number ::= IA5String (SIZE (1..15)) (FROM ("0123456789"))
[TBD- do we really need to do IA5String? The alternative would be
UTF8String, e.g.: UTF8String (SIZE (1..15)) (FROM ("0123456789")) ]
The TN Authorization List certificate extension indicates the
authorized phone numbers for the call setup signer. It indicates one
or more blocks of telephone number entries that have been authorized
for use by the call setup signer. There are three ways to identify
the block: 1) a Service Provider Identifier (SPID) can be used to
indirectly name all of the telephone numbers associated with that
service provider, 2) telephone numbers can be listed in a range, and
3) a single telephone number can be listed.
Note that because large-scale service providers may want to associate
many numbers, possibly millions of numbers, with a particular
certificate, optimizations are required for those cases to prevent
certificate size from becoming unmanageable. In these cases, the TN
Peterson & Turner Expires September 22, 2016 [Page 9]
Internet-Draft STIR Certs March 2016
Authorization List may be given by reference rather than by value,
through the presence of a separate certificate extension that permits
verifiers to either securely download the list of numbers associated
with a certificate, or to verify that a single number is under the
authority of this certificate. This optimization will be detailed in
future version of this specification.
8. Certificate Freshness and Revocation
Regardless of which of the approaches in Section 3 is followed for
using certificates, some sort of certificate verification mechanism
is required. However, the traditional problem of certificate
freshness gains a new wrinkle when using the TN Authorization List
extension, because verifiers must establish not only that a
certificate remains valid, but also that the certificate's scope
contains the telephone number that the verifier is validating.
Dynamic changes to number assignments can occur due to number
portability, for example. So even if a verifier has a valid cached
certificate for a telephone number (or a range containing the
number), the verifier must determine that the entity that signed is
still a proper authority for that number.
To verify the status of the certificate, the verifier needs to
acquire the certificate if necessary (via the methods described in
Section 6), and then would need to either:
Rely on short-lived certificates and not check the certificate's
status, or
Rely on status information from the authority
The tradeoff between short lived certificates and using status
information is the former's burden is on the front end (i.e.,
enrollment) and the latter's burden is on the back end (i.e.,
verification). Both impact call setup time, but it is assumed that
performing enrollment for each call is more of an impact that using
status information. This document therefore recommends relying on
status information.
8.1. Choosing a Verification Method
There are three common certificate verification mechanisms employed
by CAs:
Certificate Revocation Lists (CRLs) [RFC5280]
Online Certificate Status Protocol (OCSP) [RFC6960], and
Peterson & Turner Expires September 22, 2016 [Page 10]
Internet-Draft STIR Certs March 2016
Server-based Certificate Validation Protocol (SCVP) [RFC5055].
When relying on status information, the verifier needs to obtain the
status information - but before that can happen, the verifier needs
to know where to locate it. Placing the location of the status
information in the certificate makes the certificate larger, but it
eases the client workload. The CRL Distribution Point certificate
extension includes the location of the CRL and the Authority
Information Access certificate extension includes the location of
OCSP and/or SCVP servers; both of these extensions are defined in
[RFC5280]. In all cases, the status information location is provided
in the form of an URI.
CRLs are an obviously attractive solution because they are supported
by every CA. CRLs have a reputation of being quite large (10s of
MBytes), because CAs maintain and issue one monolithic CRL with all
of their revoked certificates, but CRLs do support a variety of
mechanisms to scope the size of the CRLs based on revocation reasons
(e.g., key compromise vs CA compromise), user certificates only, and
CA certificates only as well as just operationally deciding to keep
the CRLs small. However, scoping the CRL introduces other issues
(i.e., does the RP have all of the CRL partitions).
CAs in the STIR architecture will likely all create CRLs for audit
purposes, but it NOT RECOMMENDED that they be relying upon for status
information. Instead, one of the two "online" options is preferred.
Between the two, OCSP is much more widely deployed and this document
therefore recommends the use of OCSP in high-volume environments for
validating the freshness of certificates, based on [RFC6960],
incorporating some (but not all) of the optimizations of [RFC5019].
8.2. Using OCSP with TN Auth List
Certificates compliant with this specification therefore SHOULD
include a URL pointing to an OCSP service in the Authority
Information Access (AIA) certificate extension, via the "id-ad-ocsp"
accessMethod specified in [RFC5280]. Baseline OCSP however supports
only three possible response values: good, revoked, or unknown. With
some extension, OCSP would not indicate whether the certificate is
authorized for a particular telephone number that the verifier is
validating.
[TBD] What would happen in the unknown case? Can we profile OCSP
usage so that unknown is never returned for our extension?
At a high level, there are two ways that a client might pose this
authorization question:
Peterson & Turner Expires September 22, 2016 [Page 11]
Internet-Draft STIR Certs March 2016
For this certificate, is the following number currently in its
scope of validity?
What are all the telephone numbers associated with this
certificate, or this certificate subject?
Only the former lends itself to piggybacking on the OCSP status
mechanism; since the verifier is already asking an authority about
the certificate's status, why not reuse that mechanism, instead of
creating a new service that requires additional round trips? Like
most PKIX-developed protocols, OCSP is extensible; OCSP supports
request extensions (including sending multiple requests at once) and
per-request extensions. It seems unlikely that the verifier will be
requesting authorization checks on multiple telephone numbers in one
request, so a per-request extension is what is needed.
[TBD] HVE OCSP requires SHA-1 be used as the hash algorithm,
we're6960 obviously going to change this to be SHA-256.
The requirement to consult OCSP in real time results in a network
round-trip time of day, which is something to consider because it
will add to the call setup time. OCSP server implementations
commonly pre-generate responses, and to speed up HTTPS connections,
servers often provide OCSP responses for each certificate in their
hierarchy. If possible, both of these OCSP concepts should be
adopted for use with STIR.
8.2.1. OCSP Extension Specification
The extension mechanism for OCSP follows X.509 v3 certificate
extensions, and thus requires an OID, a criticality flag, and ASN.1
syntax as defined by the OID. The criticality specified here is
optional: per [RFC6960] Section 4.4, support for all OCSP extensions
is optional. If the OCSP server does not understand the requested
extension, it will still provide the baseline validation of the
certificate itself. Moreover, in practical STIR deployments, the
issuer of the certificate will set the accessLocation for the OCSP
AIA extension to point to an OCSP service that supports this
extension, so the risk of interoperability failure due to lack of
support for this extension is minimal.
The OCSP TNQuery extension is included as one of the
requestExtensions in requests. It may also appear in the
responseExtensions. When an OCSP server includes a number in the
responseExtensions, this informs the client that the certificate is
still valid for the number that appears in the TNQuery extension
field. If the TNQuery is absent from a response to a query
containing a TNQuery in its requestExtensions, then the server is not
Peterson & Turner Expires September 22, 2016 [Page 12]
Internet-Draft STIR Certs March 2016
able to validate that the number is still in the scope of authority
of the certificate.
id-pkix-ocsp-stir-tn OBJECT IDENTIFIER ::= { id-pkix-ocsp TBD }
TNQuery ::= E164Number
Note that HVE OCSP profile [RFC5019] prohibits the use of per-request
extensions. As it is anticipated that STIR will use OCSP in a high-
volume environment, many of the optimizations recommended by HVE are
desirable for the STIR environment. This document therefore uses
these extensions in a baseline OCSP environment with some HVE
optimizations. [More TBD]
Ideally, once a certificate has been acquired by a verifier, some
sort of asynchronous mechanism could notify and update the verifier
if the scope of the certificate changes so that verifiers could
implement a cache. While not all possible categories of verifiers
could implement such behavior, some sort of event-driven notification
of certificate status is another potential subject of future work.
One potential direction is that a future SIP SUBSCRIBE/NOTIFY-based
accessMethod for AIA might be defined (which would also be applicable
to the method described in the following section) by some future
specification.
Strategies for stapling OCSP [RFC6961] have become common in some web
PKI environments as an optimization which allows web servers to send
up-to-date certificate status information acquired from OCSP to
clients as TLS is negotiated. A similar mechanism could be
implemented for SIP requests, in which the authentication service
adds status information for its certificate to the SIP request, which
would save the verifier the trouble of performing the OCSP dip
itself. Especially for high-volume authentication and verification
services, this could result in significant performance improvements.
This is left as an optimization for future work.
8.3. Acquiring TN Lists By Reference
Acquiring a list of the telephone numbers associated with a
certificate or its subject lends itself to an application-layer
query/response interaction outside of OCSP, one which could be
initiated through a separate URI included in the certificate. The
AIA extension (see [RFC5280]) supports such a mechanism: it
designates an OID to identify the accessMethod and an accessLocation,
which would most likely be a URI. A verifier would then follow the
Peterson & Turner Expires September 22, 2016 [Page 13]
Internet-Draft STIR Certs March 2016
URI to ascertain whether the list of TNs authorized for use by the
caller.
HTTPS is the most obvious candidate for a protocol to be used for
fetching the list of telephone number associated with a particular
certificate. This document defines a new AIA accessMethod, called
"id-ad-stir-tn", which uses the following AIA OID:
id-ad-stir-tn OBJECT IDENTIFIER ::= { id-ad TBD }
When the "id-ad-stir-tn" accessMethod is used, the accessLocation
MUST be an HTTPS URI. The document returned by dereferencing that
URI will contain the complete TN Authorization List (see Section 7)
for the certificate.
Delivering the entire list of telephone numbers associated with a
particular certificate will divulge to STIR verifiers information
about telephone numbers other than the one associated with the
particular call that the verifier is checking. In some environments,
where STIR verifiers handle a high volume of calls, maintaining an
up-to-date and complete cache for the numbers associated with crucial
certificate holders could give an important boost to performance.
9. Acknowledgments
Russ Housley, Brian Rosen, Cullen Jennings and Eric Rescorla provided
key input to the discussions leading to this document.
10. IANA Considerations
This document makes use of object identifiers for the TN Certificate
Extension defined in Section 7, TN-HVE OCSP extension in
Section 8.2.1, and the TN by reference AIA access descriptor defined
in Section 8.3. It therefore requests that the IANA make the
following assignments:
- TN Certificate Extension in the SMI Security for PKIX
Certificate Extension registry: http://www.iana.org/assignments/
smi-numbers/smi-numbers.xhtml#smi-numbers-1.3.6.1.5.5.7.1
- TN-HVE OCSP extension in the SMI Security for PKIX Online
Certificate Status Protocol (OCSP) registry:
http://www.iana.org/assignments/smi-numbers/smi-numbers.xhtml#smi-
numbers-1.3.6.1.5.5.7.48.1
Peterson & Turner Expires September 22, 2016 [Page 14]
Internet-Draft STIR Certs March 2016
- TNS by reference access descriptor in the SMI Security for PKIX
Access Descriptor registry: http://www.iana.org/assignments/smi-
numbers/smi-numbers.xhtml#smi-numbers-1.3.6.1.5.5.7.48
11. Security Considerations
This document is entirely about security. For further information on
certificate security and practices, see RFC 3280 [RFC3280], in
particular its Security Considerations.
12. Informative References
[I-D.ietf-stir-problem-statement]
Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
Telephone Identity Problem Statement and Requirements",
draft-ietf-stir-problem-statement-05 (work in progress),
May 2014.
[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-07
(work in progress), February 2016.
[I-D.peterson-sipping-retarget]
Peterson, J., "Retargeting and Security in SIP: A
Framework and Requirements", draft-peterson-sipping-
retarget-00 (work in progress), February 2005.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<http://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,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, DOI 10.17487/RFC2392, August 1998,
<http://www.rfc-editor.org/info/rfc2392>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<http://www.rfc-editor.org/info/rfc2818>.
Peterson & Turner Expires September 22, 2016 [Page 15]
Internet-Draft STIR Certs March 2016
[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,
<http://www.rfc-editor.org/info/rfc3261>.
[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263,
DOI 10.17487/RFC3263, June 2002,
<http://www.rfc-editor.org/info/rfc3263>.
[RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
DOI 10.17487/RFC3280, April 2002,
<http://www.rfc-editor.org/info/rfc3280>.
[RFC5019] Deacon, A. and R. Hurst, "The Lightweight Online
Certificate Status Protocol (OCSP) Profile for High-Volume
Environments", RFC 5019, DOI 10.17487/RFC5019, September
2007, <http://www.rfc-editor.org/info/rfc5019>.
[RFC5055] Freeman, T., Housley, R., Malpani, A., Cooper, D., and W.
Polk, "Server-Based Certificate Validation Protocol
(SCVP)", RFC 5055, DOI 10.17487/RFC5055, December 2007,
<http://www.rfc-editor.org/info/rfc5055>.
[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,
<http://www.rfc-editor.org/info/rfc5280>.
[RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958,
DOI 10.17487/RFC5958, August 2010,
<http://www.rfc-editor.org/info/rfc5958>.
[RFC6919] Barnes, R., Kent, S., and E. Rescorla, "Further Key Words
for Use in RFCs to Indicate Requirement Levels", RFC 6919,
DOI 10.17487/RFC6919, April 2013,
<http://www.rfc-editor.org/info/rfc6919>.
[RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A.,
Galperin, S., and C. Adams, "X.509 Internet Public Key
Infrastructure Online Certificate Status Protocol - OCSP",
RFC 6960, DOI 10.17487/RFC6960, June 2013,
<http://www.rfc-editor.org/info/rfc6960>.
Peterson & Turner Expires September 22, 2016 [Page 16]
Internet-Draft STIR Certs March 2016
[RFC6961] Pettersen, Y., "The Transport Layer Security (TLS)
Multiple Certificate Status Request Extension", RFC 6961,
DOI 10.17487/RFC6961, June 2013,
<http://www.rfc-editor.org/info/rfc6961>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<http://www.rfc-editor.org/info/rfc7030>.
[RFC7299] Housley, R., "Object Identifier Registry for the PKIX
Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014,
<http://www.rfc-editor.org/info/rfc7299>.
[X.680] USC/Information Sciences Institute, "Information
Technology - Abstract Syntax Notation One.", ITU-T X.680,
ISO/IEC 8824-1:2002, 2002.
[X.681] USC/Information Sciences Institute, "Information
Technology - Abstract Syntax Notation One: Information
Object Specification", ITU-T X.681, ISO/IEC 8824-2:2002,
2002.
[X.682] USC/Information Sciences Institute, "Information
Technology - Abstract Syntax Notation One: Constraint
Specification", ITU-T X.682, ISO/IEC 8824-3:2002, 2002.
[X.683] USC/Information Sciences Institute, "Information
Technology - Abstract Syntax Notation One:
Parameterization of ASN.1 Specifications", ITU-T X.683,
ISO/IEC 8824-4:2002, 2002.
Appendix A. ASN.1 Module
This appendix provides the normative ASN.1 [X.680] definitions for
the structures described in this specification using ASN.1, as
defined in [X.680] through [X.683].
TBD
Authors' Addresses
Jon Peterson
Neustar, Inc.
Email: jon.peterson@neustar.biz
Peterson & Turner Expires September 22, 2016 [Page 17]
Internet-Draft STIR Certs March 2016
Sean Turner
Sn3rd
Email: sean@sn3rd.com
Peterson & Turner Expires September 22, 2016 [Page 18]
