STIR

The Session Initiation Protocol (SIP) Identity header field conveys cryptographic identity information about the originators of SIP requests. However, the Secure Telephone Identity Revisited (STIR) framework provides no means for determining the identity of the called party in a conventional telephone-calling scenario. This document updates prior guidance on the "connected identity" problem to reflect the changes to SIP identity that accompanied STIR. It also considers a revised problem space for connected identity as a means of detecting calls that have been retargeted to a party impersonating the intended destination and preventing the spoofing of mid-dialog or dialog-terminating events by intermediaries or third parties.

The Secure Telephone Identity Revisited (STIR) framework defines means of carrying its Personal Assertion Tokens (PASSporTs) either in-band, within the headers of a Session Initiation Protocol (SIP) request, or out-of-band, through a service that stores PASSporTs for retrieval by relying parties. This specification defines a way that the out-of-band conveyance of PASSporTs can be used to support large service providers for cases in which in-band STIR conveyance is not universally available.

This document extends Personal Assertion Token (PASSporT), a token for conveying cryptographically signed call information about personal communications, to include rich metadata about a call and caller that can be signed and integrity protected, transmitted, and subsequently rendered to the called party. This framework is intended to include and extend caller- and call-specific information beyond human-readable display name, comparable to the "Caller ID" function common on the telephone network. It is also enhanced with an integrity mechanism that is designed to protect the authoring and transport of this information for different authoritative use cases.

Secure Telephone Identity Revisited (STIR) provides a means of attesting the identity of a telephone caller via a signed token in order to prevent impersonation of a calling party number, which is a key enabler for illegal robocalling. Similar impersonation is sometimes leveraged by bad actors in the text and multimedia messaging space. This document explores the applicability of STIR's Personal Assertion Token (PASSporT) and certificate issuance framework to text and multimedia messaging use cases, including support for both messages carried as a payload in SIP requests and messages sent in sessions negotiated by SIP.

This document defines a profile of the Automated Certificate Management Environment (ACME) Authority Token for the automated and authorized creation of certificates for Voice over IP (VoIP) telephone providers to support Secure Telephone Identity (STI) using the TNAuthList defined by STI certificates.

This document extends the current error-handling procedures for mapping of verification failure reasons to 4xx codes for Secure Telephone Identity Revisited (STIR) and the Authenticated Identity Management in the Session Initiation Protocol (SIP). It extends the ability to use the Reason header field as an option for conveying an error associated with an Identity header field to the upstream authentication service when local policy dictates that the call should continue in the presence of a verification failure. This document also defines procedures that enable a failure reason to be mapped to a specific Identity header field for scenarios that use multiple Identity header fields, where some may have errors and others may not. The handling of those situations is also defined.

In network protocol exchanges, it is often useful for one end of a communication to know whether the other end is in an intended operating state. This document provides an architectural overview of the entities involved that make such tests possible through the process of generating, conveying, and evaluating evidentiary Claims. It provides a model that is neutral toward processor architectures, the content of Claims, and protocols.

The Secure Telephone Identity Revisited (STIR) certificate profile provides a way to attest authority over telephone numbers and related identifiers for the purpose of preventing telephone number spoofing. This specification details how that authority can be delegated from a parent certificate to a subordinate certificate. This supports a number of use cases, including those where service providers grant credentials to enterprises or other customers capable of signing calls with STIR.

RFC 8226 specifies the use of certificates for Secure Telephone Identity Credentials; these certificates are often called "Secure Telephone Identity Revisited (STIR) Certificates". RFC 8226 provides a certificate extension to constrain the JSON Web Token (JWT) claims that can be included in the Personal Assertion Token (PASSporT), as defined in RFC 8225. If the PASSporT signer includes a JWT claim outside the constraint boundaries, then the PASSporT recipient will reject the entire PASSporT. This document updates RFC 8226; it provides all of the capabilities available in the original certificate extension as well as an additional way to constrain the allowable JWT claims. The enhanced extension can also provide a list of claims that are not allowed to be included in the PASSporT.

This document adds new assertion values for a Resource Priority Header ("rph") claim and a new SIP Priority Header ("sph") claim for protection of the "psap-callback" value as part of the "rph" Personal Assertion Token (PASSporT) extension in support of the security of emergency services networks for emergency call origination and callback.

The Personal Assertion Token (PASSporT) is specified in RFC 8225 to convey cryptographically signed information about the people involved in personal communications. This document extends PASSporT to include an indication that a call has been diverted from its original destination to a new one. This information can greatly improve the decisions made by verification services in call forwarding scenarios. Also specified here is an encapsulation mechanism for nesting a PASSporT within another PASSporT that assists relying parties in some diversion scenarios.

This document updates RFC 8224.

The Personal Assertion Token (PASSporT) format defines a token that can be carried by signaling protocols, including SIP, to cryptographically attest the identity of callers. However, not all telephone calls use Internet signaling protocols, and some calls use them for only part of their signaling path, while some cannot reliably deliver SIP header fields end-to-end. This document describes use cases that require the delivery of PASSporT objects outside of the signaling path, and defines architectures and semantics to provide this functionality.

This document defines the 608 (Rejected) Session Initiation Protocol (SIP) response code. This response code enables calling parties to learn that an intermediary rejected their call attempt. No one will deliver, and thus answer, the call. As a 6xx code, the caller will be aware that future attempts to contact the same User Agent Server will likely fail. The initial use case driving the need for the 608 response code is when the intermediary is an analytics engine. In this case, the rejection is by a machine or other process. This contrasts with the 607 (Unwanted) SIP response code in which a human at the target User Agent Server indicates the user did not want the call. In some jurisdictions, this distinction is important. This document also defines the use of the Call-Info header field in 608 responses to enable rejected callers to contact entities that blocked their calls in error. This provides a remediation mechanism for legal callers that find their calls blocked.

This document extends the Personal Assertion Token (PASSporT), which is a token object that conveys cryptographically signed information about the participants involved in communications. The extension is defined based on the "Signature-based Handling of Asserted information using toKENs (SHAKEN)" specification by the ATIS/SIP Forum IP-NNI Task Group. It provides both (1) a specific set of levels of confidence in the correctness of the originating identity of a call originated in a SIP-based telephone network as well as (2) an identifier that allows the Service Provider (SP) to uniquely identify the origin of the call within its network.

This document extends the Personal Assertion Token (PASSporT) specification defined in RFC 8225 to allow the inclusion of cryptographically signed assertions of authorization for the values populated in the Session Initiation Protocol (SIP) 'Resource-Priority' header field, which is used for communications resource prioritization.

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.

As the Internet and the telephone network have become increasingly interconnected and interdependent, attackers can 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. This document analyzes threats in the resulting system, enumerating actors, reviewing the capabilities available to and used by attackers, and describing scenarios in which attacks are launched.

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.