Unlinkability, the property that prevents an adversary recognizing whether outputs are from the same user, is an important concept in RFID. Although hash-based schemes can provide unlinkability by using a low-cost hash function, existing schemes are not scalable since the server needs O(N) hash calculations for every ID matching, where N is the number of RFID devices. Our solution is the K-steps ID matching scheme, which can reduce the number of hash calculations on the server to O(logN). In this paper, we explain the protocol, describe a test implementation, and discuss the application of this scheme to practical RFID systems. We also compare the scheme with other hash-based schemes from various viewpoints.