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sec STIR 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.

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. extends ACME to provide a general method of extending the Authority and authorization of entities to control a resource via a third party Authority beyond the Certification Authority. This document addresses the STIR problem statement 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 , which can be carried in using protocols such as SIP . Currently, the only defined credentials for this purpose are the certificates specified in . describes certificate extensions suitable for associating telephone numbers and service provider codes with certificates. Specifically, the TN Authorization List defined in Section 9, defines the ability to associate a STI certificate with a specific set of Service Provider Codes (SPC), Telephone Numbers (TNs), or Telephone Number ranges (TN ranges). Typically, these identifiers have been associated to a Communications Service Provider (CSP) that is authorized to use a set of telephone numbers or telephone number ranges in association with a Service Provider Code as defined in . The SPC is a unique code or string managed by a national regulatory body that has the authority over those code associations.

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 .

In , Section 7.4 defines the procedure that an ACME client uses to order a new certificate from a Certificate Authority. The new-order request contains an identifier object that specifies the identifiers the order corresponds to. For the TNAuthList identifier, the new-order request MUST include a type set to the string “TNAuthList”. The value of the identifier MUST be set to the details of the TNAuthList requested. The format of the string that represents the TNAuthList MUST be constructed as follows. The TNAuthList as defined in can include three types of identifiers. Service Provider Code (SPC) identified as “spc” Telephone Number (TN) identified as “tn” Telephone Number Range (TNRange) identified as “tnrange” The above types of identifiers and the corresponding strings should be used as a JSON key part of an array of JSON key and value pairs. The JSON value would be the string representing the corresponding SPC, TN, or TNRange values. For example, a request for a TNAuthList certificate with a SPC value of “1234” and a TN value of “2155551212” would look as follows,

A full new-order request would look as follows,

On receiving a valid new-order request, the CA creates an authorization challenge and can be queried by the following example request and response.

;rel="index" { "status": "pending", "expires": "2018-03-03T14:09:00Z", "identifier": { "type:"TNAuthList", "value":"["spc":"1234","tn":"2155551212"]" }, "challenges": [ { "type": "tkauth-01", "tkauth-type": "ATC", "token-authority": "https://authority.example.org/authz", "url": "https://boulder.example.com/authz/asdf/0" "token": "IlirfxKKXAsHtmzK29Pj8A" } ] } ]]>

This follows with a specific identifier corresponding to the specific challenge as defined previously in this document. When processing a certificate order containing an identifier of type “TNAuthList”, a CA MUST use the Authority Token challenge mechanism defined in to verify that the requesting ACME client has control over the requested “TNAuthList” value. The challenge “token-authority” parameter is optional and only used in cases where the VoIP telephone network requires a CA to determine the authority. This is currently not the case for the SHAKEN 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 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 Authority based on locally configured information or local policies. A client responds to this challenge by providing an TNAuthList Authority Token to the CA. The ACME client MUST respond to the challenge by posting the TNAuthList Authority Token to the URL identified in the ACME challenge with a request, an example of which follows.

The specifics of the construction of the “ATC” token is defined in the next section.

The Telephone Number Authority List Authority Token (TNAuthList Authority Token) is an extension of the ACME Authority Token defined in . The TNAuthList Authority Token Protected header MUST comply with the Authority Token Protected header as defined in . The TNAuthList Authority Token Payload MUST include the claims defined for the Authority Token. These are detailed in the next subsections.

The “iss” claim is an optional claim. It can be used as a URL identifying the Authority that issued the TNAuthList Authority Token beyond the “x5u” Header claim that identifies the location of the certificate of the Authority used to validate the Authority Token.

The “exp” claim contains the DateTime value of the ending time and date that the TNAuthList Authority Token expires.

The “jti” claim contains a unique identifier for the TNAuthList Authority Token transaction.

The “atc” claim is the only claim specifically defined in this document. It contains an array of three elements; a string set to “TNAuthList”, an identifier value which is an array of the identifiers to be included in the TNAuthList of the requesting SP, and a nonce. An example of the TNAuthList Authority Token is as follows,

Similar to how the TNAuthList identifier value is defined, the identifier value in the “atc” should also include the same JSON array of TNAuthList values with key/value pairs representing each part of the TNAuthList.

The specifics of how the token is acquired from the authority is out of the scope of this document.

Upon receiving a response to the challenge, the ACME server MUST perform the following steps to determine the validity of the response. Verify that the token contained in the Payload “ATC” field is an TNAuthList Authority Token. Verify the TNAuthList Authority Token signature using the public key of the certificate referenced by the token’s “x5u” parameter. Verify that “atc” claim contains an identifier type of “TNAuthList”, Verify that the “atc” claim contains keys and values that matches the keys and values of the Identifier specified in the original challenge. Verify that the remaining claims are valid (e.g., verify that token has not expired) 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”.

This section provides some TNAuthList Authority Token examples.

TNAuthList Authority Token authorizing a TNAuthList containing a single SPC value

TNAuthList Authority Token authorizing a TNAuthList identifier containing an SPC value plus a range of TNs

TNAuthList Authority Token authorizing a TNAuthList identifier containing a single TN

There are many scenarios and reasons to have various combinations of SPCs, TNs, and TN Ranges. 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.

TBD

We would like to thank you for your review of this document.

Certificates in PKI using X.509 (PKIX) are used for a number of purposes, the most significant of which is the authentication of domain names. Thus, certificate authorities in the Web PKI are trusted to verify that an applicant for a certificate legitimately represents the domain name(s) in the certificate. Today, this verification is done through a collection of ad hoc mechanisms. This document describes a protocol that a certification authority (CA) and an applicant can use to automate the process of verification and certificate issuance. The protocol also provides facilities for other certificate management functions, such as certificate revocation. RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH: The source for this draft is maintained in GitHub. Suggested changes should be submitted as pull requests at https://github.com/ietf-wg-acme/acme [1]. Instructions are on that page as well. Editorial changes can be managed in GitHub, but any substantive change should be discussed on the ACME mailing list (acme@ietf.org). A number of proposed challenges for the Automated Certificate Management Environment (ACME) effectively rely on an external authority issuing a token according to a particular policy. This document specifies a generic Authority Token challenge for ACME which admits of subtypes for different identifiers or namespaces. Over the past decade, Voice over IP (VoIP) systems based on SIP have replaced many traditional telephony deployments. Interworking VoIP systems with the traditional telephone network has reduced the overall level of calling party number and Caller ID assurances by granting attackers new and inexpensive tools to impersonate or obscure calling party numbers when orchestrating bulk commercial calling schemes, hacking voicemail boxes, or even circumventing multi-factor authentication systems trusted by banks. Despite previous attempts to provide a secure assurance of the origin of SIP communications, we still lack effective standards for identifying the calling party in a VoIP session. This document examines the reasons why providing identity for telephone numbers on the Internet has proven so difficult and shows how changes in the last decade may provide us with new strategies for attaching a secure identity to SIP sessions. It also gives high-level requirements for a solution in this space. The baseline security mechanisms in the Session Initiation Protocol (SIP) are inadequate for cryptographically assuring the identity of the end users that originate SIP requests, especially in an interdomain context. This document defines a mechanism for securely identifying originators of SIP requests. It does so by defining a SIP header field for conveying a signature used for validating the identity and for conveying a reference to the credentials of the signer.This document obsoletes RFC 4474. This document defines a method for creating and validating a token that cryptographically verifies an originating identity or, more generally, a URI or telephone number representing the originator of personal communications. The Personal Assertion Token, PASSporT, is cryptographically signed to protect the integrity of the identity of the originator and to verify the assertion of the identity information at the destination. The cryptographic signature is defined with the intention that it can confidently verify the originating persona even when the signature is sent to the destination party over an insecure channel. PASSporT is particularly useful for many personal-communications applications over IP networks and other multi-hop interconnection scenarios where the originating and destination parties may not have a direct trusted relationship. In order to prevent the impersonation of telephone numbers on the Internet, some kind of credential system needs to exist that cryptographically asserts 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. ATIS/SIP Forum NNI Task Group ATIS/SIP Forum NNI Task Group In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.