Improving Air Interface User Privacy in Mobile Telephony

Abstract

Although the security properties of 3G and 4G mobile networks have significantly improved by comparison with 2G (GSM), significant shortcomings remain with respect to user privacy. A number of possible modifications to 2G, 3G and 4G protocols have been proposed designed to provide greater user privacy; however, they all require significant modifications to existing deployed infrastructures, which are almost certainly impractical to achieve in practice. In this article we propose an approach which does not require any changes to the existing deployed network infrastructures or mobile devices, but offers improved user identity protection over the air interface. The proposed scheme makes use of multiple IMSIs for an individual USIM to offer a degree of pseudonymity for a user. The only changes required are to the operation of the authentication centre in the home network and to the USIM, and the scheme could be deployed immediately since it is completely transparent to the existing mobile telephony infrastructure. We present two different approaches to the use and management of multiple IMSIs.

Defeating the Downgrade Attack on Identity Privacy in 5G

“…Publications proposing cellular network pseudonyms in the same format as IMSI, but with randomized, frequently changing MSIN, include [7][8][9][10]. In Broek et al [7] and Khan and Mitchell [8] the pseudonym's update is embedded in a random challenge, RAND, of AKA. Khan and Mitchell [11] identified a weakness in solutions proposing cellular network pseudonyms in the same format as IMSI, which could be exploited to desynchronize pseudonyms in the UE and the HN.…”

“…(Indeed, if the UE uses pseudonym in IMSI format when it communicates with SN, and the SN does not get the long-term identifier of that UE -for instance, because it was not patched for LI, then the SN has no other choice but to put the UE's pseudonym into the CDR.) For this reason the home network has to consult a log of pseudonym allocations when it maps from UE identifiers in received CDRs to the actual subscribers' data [8,12]. That log includes the following information: (i) the pseudonym, (ii) the IMSI of the subscriber whom the pseudonym is given to, (iii) the time when HN allocated the pseudonym to the subscriber, (iv) the time when the subscriber started using the pseudonym (i.e., the time of the first successful AKA run of that subscriber with the pseudonym), (v) the time when the UE notified that it is no longer using the pseudonym, and (vi) list of SNs that the user has attached with using this pseudonym.…”

“…Hence, even in the unlikely event, where the UE and HN lose synchronization of pseudonyms, the synchronization can be restored because the UE obtains a new LTE pseudonym from the HN simply by connecting to a 5G SN. This paper advances protocol design, beyond what is described in papers [7][8][9][10][11][12], as follows:…”

Retrofitting Mutual Authentication to GSM Using RAND Hijacking

“…As for Dupré, the purpose of the 'special RAND' was completely different to that proposed here. The other published references to the notion appear in papers [4,17,22] that independently propose the use of RAND hijacking for improving the privacy properties of GSM, 3G and 4G networks. As far as the authors are aware, no previous authors have proposed the use of this technique for providing mutual authentication in GSM networks.…”

BVPSMS: A Batch Verification Protocol for End-to-End Secure SMS for Mobile Users

“…However, these protocols do not consider SMS as a communication medium and require additional cost and storage for a group setup. Recently, a solution for user privacy in mobile telephony was proposed using the predefined multiple International Mobile Subscriber Identities (IMSI) for each Universal Subscriber Identity Module (USIM) [40]. However, this solution requires a large storage space, generates a huge overhead for pseudo-identities, and utilizes significant bandwidth for sending IMSIs to each MS.…”