In this letter, we propose a privacy-preserving authentication protocol with RSA cryptosystem in an RFID environment. For both overcoming the resource restriction and strengthening security, our protocol uses only modular exponentiation with exponent three at RFID tag side, with the padded random message whose length is greater than one-sixth of the whole message length.

In this letter we propose a new mode for block ciphers which uses an unknown random block as feedback. We show that the successful differential/linear cryptanalyses of DES under the mode require at least the complexity of the exhaustive key search. We also present the processing overhead of our scheme compared to that of ECB mode.