Target Identity

Description

In 3GPP lawful interception architecture, a Target Identity is a fundamental concept used to specify which subscriber or service is subject to interception. It serves as the unique reference that distinguishes a target from all other non-targets within one or more Communication Service Provider (CSP) services. The target identity is not a single fixed identifier but rather a flexible set of possible identifiers that can be used to designate an interception subject. This flexibility is essential because a single target may be reachable through multiple identities, such as an IMSI, MSISDN, IMEI, or even a SIP URI, depending on the service and access technology.

The target identity can be categorized into several types. A long-term subscription-based identity is typically an IMSI or MSISDN that is permanently associated with a subscriber. A short-term network identity could be a temporary identifier like a TMSI or GUTI, which is dynamically assigned. A publicly available identity might be a phone number or a public user identity in IMS. An internal (private) identity could be an internal network identifier used by the CSP for routing or management purposes. The interception system must be able to map any of these identities to the actual target and ensure that all communications involving that target are intercepted, regardless of the identity used.

From an architectural perspective, the Target Identity is used by Law Enforcement Agencies (LEAs) when requesting interception. The LEA provides one or more target identities to the CSP, which then configures its network elements (e.g., MME, SGSN, IMS core) to intercept traffic associated with those identities. The network elements use the target identity to filter and replicate the target's traffic towards the Lawful Interception Gateway (LIG) or Delivery Function (DF). The target identity must be unique within the scope of the interception, meaning that it should not accidentally match non-target subscribers. This uniqueness is achieved through careful provisioning and validation by the CSP.

The 3GPP specifications 33.106, 33.108, and 33.126 define the requirements and procedures for lawful interception, including the handling of target identities. These specifications ensure that interception is performed in a consistent and secure manner across different network technologies and generations. The target identity concept has evolved over releases, with the definition becoming more precise and encompassing a wider range of identity types. In later releases, the definition explicitly includes the possibility of multiple CSP services and clarifies that the identity can be public or internal.

The Target Identity is crucial for the correct operation of lawful interception. Without a clear and unambiguous target identity, interception could either miss the target's communications or inadvertently intercept non-targets, leading to privacy violations and legal issues. Therefore, the 3GPP standards emphasize the need for accurate and unique identification of targets, and the target identity serves as the cornerstone of this process.

Purpose & Motivation

The Target Identity concept exists to provide a precise and unambiguous way to identify the subject of lawful interception within a telecommunications network. Before its formalization, interception systems might have used various ad-hoc identifiers, leading to potential errors, missed interceptions, or over-interception of non-targets. The Target Identity solves this by defining a standardized set of identity types that can be used to uniquely designate a target across different services and network technologies. This ensures that law enforcement requests are accurately fulfilled while minimizing the impact on other subscribers.

Historically, as networks evolved from circuit-switched to packet-switched and later to all-IP, the number of identities associated with a user increased. A single user could have multiple devices, multiple subscriptions, and multiple service-specific identities. The Target Identity concept was introduced to handle this complexity by allowing one target to have several target identities, each representing a different aspect of the target's presence in the network. This flexibility is essential for effective interception in modern multi-service, multi-access networks.

Furthermore, the Target Identity supports the legal requirement that interception must be targeted and proportionate. By clearly defining what constitutes a target identity, the standards help CSPs implement interception in a way that is both effective and respectful of privacy. The evolution of the definition over releases reflects the growing complexity of networks and the need to cover new identity types, such as those used in IMS and 5G.