The RFID system is a contactless automatic identification system that identifies tags attached on goods through radio frequency communication. This system is expected to supplant barcode systems, the contact reading technique that is most widely used at present. The RFID system can be applied in a variety of areas. Among those, Ari Juels proposed an environment to prove that a pair of tags has been scanned simultaneously. And he presented a "yoking proof" protocol for this. But the yoking-proof protocol is vulnerable to replay attack. Although modified yoking-proof protocols for alleviating this drawback have been proposed, they are not immune to replay attack, either. In this paper, we analyze problems of existing yoking-proof protocols and present a new protocol, which will make replay attack difficult, based on this analysis. We have also extend this protocol so that it can provide yoking proofs for a tag group, including a multiple number of tags.