Evaluating Time-Bounded Defense Against RRC Relay in 5G Broadcast Messages

As 5G and future generations of mobile networks aim to provide faster and more secure wireless connections, 5G broadcast messages remain unprotected. Hence, a user device cannot verify the identity of a base station before establishing the connection and starting the registration procedure. This long-existing loophole enables various types of fake base station (FBS) attacks. To protect end-users from these attacks, a practical solution is to introduce a digital signature for these broadcast messages. However, an FBS may also have the ability to relay a digitally signed broadcast message from a benign base station to bypass the protection. Considering that a relayed message needs extra time to reach a user device, a time-bounded defense mechanism can be used on top of the digital signature to offer replay protection. Although previous work proposed such a solution, none have implemented it or evaluated it against relay attacks. Hence, to evaluate the performance of our proposed digital signature scheme and the time-bounded defense, we implemented the solution against relay attacks using an open-source 5G system. Our results show that the overhead introduced is acceptable and that the time-bounded defense is effective against relay attacks.