Lawful Intercept Handling of Protected Services
Offering communication services with end-to-end (E2E) cryptographic protection is becoming more desirable and more common. 3GPP-defined services (such as those of the IMS framework) have so far largely relied on trustworthy network infrastructure, complemented by strong cryptographic access security and hop-by-hop protection in the core and service domains. However, also here, E2E protected services are gaining attractivity. Indeed, the solution defined in TS 33.535, Authentication and Key Management for Applications based on 3GPP credentials in the 5G System (AKMA), can be leveraged as a basis for protecting basically any IP-based service provided to a UE (an ME with USIM-credentials). While this trend is both natural and desirable from a user privacy point of view, it creates problems related to regulatory obligations for CSPs to provide Lawful Interception (LI). The problems are particularly emphasised in roaming scenarios, where each of two different CSPs in distinct jurisdictions might independently need to provide LI without reliance on co-operation by the other CSP and/or law enforcement in the other jurisdiction.
The currently dominant approach to tackle these issues has been to simply not activate the protection (encryption) when it potentially conflicts with LI requirements. Going forward, this is most likely not a sustainable solution. For example, it potentially exposes the traffic to any 3rd party and, moreover, it typically also results in data integrity being disabled, while the issues are predominantly tied to data confidentiality.
The present document provides a technical study on how to enable protected services without negative consequences for LI. The CSP’s LI obligation to provide communication with the encryption removed only applies when the CSP also provides the technical means enabling the protection (e.g. key management), and therefore the scope is limited to that use case.