Abstract. Recent emergence of RFID tags capable of performing public key operations motivates new RFID applications, including electronic travel documents, identification cards and payment instruments. In this context, public key certificates form the cornerstone of the overall system security. In this paper, we argue that one of the prominent challenges is how to handle revocation and expiration checking of RFID reader certificates. This is an important issue considering that these high-end RFID tags are geared for applications such as e-documents and contactless payment instruments. Furthermore, the problem is unique to public keybased RFID systems, since a passive RFID tag has no clock and thus cannot use (time-based) off-line methods. In this paper, we address the problem of reader certificate expiration and revocation in PKI-Based RFID systems. We begin by observing an important distinguishing feature of personal RFID tags used in authentication, access control or payment applicat...