# An SSI-Based Solution to Support Lawful Interception
## 1 Introduction  
Lawful interception (LI) is a procedure in which the content of communications among private individuals or organizations is collected and provided to agents authorized by the law [1]. Besides ethical and legal issues [2, 3], which are outside the scope of this paper, researchers focused their attention on the technical aspects of the LI procedure. An LI procedure involves three actors: the Network Operator (NO), which physically intercepts data; the Law Enforcement Monitoring Facility (LEMF), which collects, stores, and analyzes these data; the Law Enforcement Agency (LEA), which accesses the data kept by the LEMF for legal purposes. The literature includes several proposals and standards regarding both the physical interception of data performed by the NO [4; 5; 6] and the provision of these data to the LEMF, such as CALEA [7], 3 GPP TS 33.108 [8], ITU-T Y.2770 [9]. Among them, ETSI TS 101 671 V3.15.1, published in June 2018, is the most recent and used technical standard in LI [10]. It has been developed by the European Telecommunications Standards Institute and provides guidelines for implementing the interfaces and processes required for LI, ensuring compliance with legal and regulatory frameworks while maintaining the integrity and privacy of intercepted data. Three Handover interfaces are defined to govern communication between the NO and the LEMF. Moreover, data types specifying the handling of intercepted information as well as mechanisms to ensure the confidentiality and integrity of intercepted data are defined. ETSI TS 101 671 serves as a foundational framework for lawful interception across jurisdictions, promoting interoperability and standardization while addressing privacy and ethical considerations. However, to the best of our knowledge, the interaction between the LEMF and the LEA is not explicitly addressed in ETSI TS 101 671 or other standards. This leads to the adoption of different practices across countries [11; 12], mostly based on manual, non-secure processes, which can cause security and efficiency concerns, including increased risks of errors, delays, and data integrity violations. This issue becomes even more critical in cross-border investigations, where the LEA may delegate access to intercepted data to an External Agency (EA). Without standardized authentication and authorization mechanisms, an EA can retain access beyond the authorized period or an insider within the agency could extract sensitive information without detection. These vulnerabilities expose lawful interception systems to potential data leaks, unauthorized disclosures, and operational inefficiencies. In this paper, we aim to cover the above gap by adopting the Self-Sovereign Identity (SSI) paradigm [13; 14; 15; 16]. SSI is a new paradigm that empowers people to own and control their data without relying on centralized entities. SSI provides several advantages over alternative approaches such as federated identity management (FIM) and authentication based on Public Key Infrastructure (PKI). Unlike FIM, which relies on trusted third parties (e.g., Google or Facebook) to authenticate users, or PKI-based solutions, which require certificate authorities to manage certificates, SSI is a decentralized approach that eliminates bottlenecks and single points of failure. The privacy-preserving nature of SSI allows users to selectively disclose only the necessary information without revealing their full identity. This is in accordance with the minimization principle of GDPR. In contrast, FIM and PKI solutions require continuous involvement of identity providers, and privacy concerns may arise from honest but curious providers that legitimately participate in the users' authentications but also have the ability to infer sensitive information from the observed user behaviors. Another advantage of SSI is its interoperability and portability. PKI requires multiple certificates for different services, and FIM systems need pre-established agreements between providers, limiting their portability.