Zero Round-Trip Time for the Extended Access Control Protocol

The Extended Access Control (EAC) protocol allows to create a shared cryptographic key between a client and a server. While originally used in the context of identity card systems and machine readable travel documents, the EAC protocol is increasingly adopted as a universal solution to secure transactions or for attribute-based access control with smart cards. Here we discuss how to enhance the EAC protocol by a so-called zero-round trip time (0RTT) mode. Through this mode the client can, without further interaction, immediately derive a new key from cryptographic material exchanged in previous executions. This makes the 0RTT mode attractive from an efficiency viewpoint such that the upcoming TLS 1.3 standard, for instance, will include its own 0RTT mode. Here we show that also the EAC protocol can be augmented to support a 0RTT mode. Our proposed EAC+0RTT protocol is compliant with the basic EAC protocol and adds the 0RTT mode smoothly on top. We also prove the security of our proposal according to the common security model of Bellare and Rogaway in the multi-stage setting.