Abstract -GSM suffers from various security weaknesses: Just recently, Barkan, Biham and Keller presented a ciphertext-only attack on the GSM encryption algorithm AY2 which recovers the encryption key from a few dozen milliseconds of encrypted traffic within less than a second. Furthermore, it is well-known that it is possible to mount a man-in-the-middle attack in GSM during authentication which allows an attacker to make a victim mobile station authenticate itself to a fake base station which in turn forwards the authentication traffic to the real network, thus impersonating the victim mobile station to a real network and vice versa. In this paper we discuss the impact of GSM encryption attacks, that recover the encryption key, and the man-in-themiddle attack on the security of networks, which employ UMTS and GSM base stations simultaneously. We suggest to protect UMTS connections from GSM attacks by integrating an additional authentication and key agreement on intersystem handovers between GSM and UMTS. Keywords -UMTS, GSM, security, handover, attack I. INTRODUCTION Mobile telephony in general and in Europe in particular is on the move from 2G to 3G, i.e., GSM to UMTS networks. As long as UMTS is not in operation on a large scale, both GSM and UMTS technologies will coexist and have to interoperate. I.e., during the transition phase there will be areas with GSM coverage only, areas with UMTS coverage only and areas with both UMTS and GSM coverage. In order to facilitate the transition from GSM to UMTS, the UMTS standard allows subscribers to roam between UMTS and GSM base stations depending on what is available at their current location. Thus, subscribers can access network services such as, for example, initiating phone calls independently of their location. Furthermore, the standard allows for session handovers from GSM to UMTS base stations and vice versa. This even tighter form of interoperation between UMTS and GSM enables a subscriber to stay connected while moving. In order to allow for interoperation between the two technologies, the UMTS standard implements mechanism to
In UMTS the encryption reaches further than GSM, into the backbone network, and namely the Radio Network Controller which is located between the base station and the Mobile Switching Center REF .
On the impact of GSM encryption and man-in-the-middle attacks on the security of interoperating GSM/UMTS networks
2004 IEEE 15th International Symposium on Personal, Indoor and Mobile Radio Communications (IEEE Cat. No.04TH8754)
2004 IEEE 15th International Symposium on Personal, Indoor and Mobile Radio Communications (IEEE Cat. No.04TH8754)
Computer Science