Pseudonym

Description

In 3GPP location services (LCS), a pseudonym is a fictitious identity that may be used to conceal the true identity of a target User Equipment (UE) from the requestor and the LCS client. The true identities typically include the Mobile Station International Subscriber Directory Number (MSISDN) and the International Mobile Subscriber Identity (IMSI). By using a pseudonym, the privacy of the subscriber is protected while still allowing location-based services to function. The pseudonym is defined in 3GPP TS 23.271 (Functional stage 2 description of Location Services) and TS 23.273 (5G System Location Services).

The pseudonym is generated and managed by the network, specifically by the LCS server or a dedicated privacy function. When an LCS client requests location information for a target UE, it may use a pseudonym instead of the real identity. The network resolves the pseudonym to the actual identity internally, performs the location procedure, and returns the location result to the client without revealing the true identity. This separation ensures that the LCS client cannot correlate location data with a specific subscriber unless authorized.

The use of pseudonyms is part of a broader privacy framework in 3GPP, which includes mechanisms like temporary identities (e.g., TMSI, GUTI) and user consent requirements. Pseudonyms are particularly relevant for third-party location-based services, such as advertising, social networking, or emergency services, where the client may not need to know the subscriber's real identity. However, the network operator can still map the pseudonym to the real identity for billing, lawful interception, or other authorized purposes.

Pseudonyms can be assigned per LCS client or per service, and they may be changed periodically to prevent long-term tracking. The exact procedures for pseudonym assignment, resolution, and revocation are specified in the relevant 3GPP technical specifications. In 5G, the Location Management Function (LMF) and the Unified Data Management (UDM) play key roles in managing pseudonyms and ensuring privacy.

From an architectural perspective, the pseudonym is an identifier that is used in the Le interface between the LCS client and the LCS server (e.g., GMLC in 4G, LMF in 5G). The LCS client sends a location request containing the pseudonym, and the LCS server translates it to the target UE's identity. The server then interacts with the access network (e.g., RAN, AMF) to obtain the location. The result is returned to the client, again using the pseudonym if necessary. This abstraction layer is crucial for privacy and is a key feature of 3GPP location services.

Overall, the pseudonym is a simple yet powerful concept that balances the need for location-based services with the fundamental right to privacy. It is a mandatory privacy feature in many regulatory frameworks and is supported across generations of 3GPP networks, from Release 6 onwards.

Purpose & Motivation

The pseudonym was introduced to address growing privacy concerns in location-based services. Before its standardization, LCS clients often required the true identity (MSISDN or IMSI) of a target UE to request location information. This exposed sensitive subscriber data to third parties and allowed potential misuse, such as unauthorized tracking or profiling. The pseudonym provides a layer of anonymity, ensuring that the LCS client cannot link location data to a specific individual without explicit authorization.

The motivation also stems from regulatory requirements, such as the EU's ePrivacy Directive and general data protection regulations, which mandate privacy by design. 3GPP responded by defining pseudonyms as part of the LCS architecture in Release 6. This allowed operators to offer location-based services while complying with privacy laws. The pseudonym also facilitates user consent management: the subscriber can authorize a service to use a pseudonym without revealing their true identity.

Furthermore, pseudonyms enable flexible business models. For example, a third-party advertiser can target users based on location without knowing who they are, and the operator can monetize location data without compromising subscriber privacy. The pseudonym can be revoked or changed, giving subscribers control over their privacy. This concept has been carried forward into 5G, where privacy is even more critical due to the proliferation of IoT devices and diverse services.