  Vajda and Buttyan (VB) proposed a set of five lightweight RFID authentication
protocols. Defend, Fu, and Juels (DFJ) did cryptanalysis on two of them - XOR
and SUBSET. To the XOR protocol, DFJ proposed repeated keys attack and nibble
attack. In this paper, we identify the vulnerability existed in the original
VB's successive session key permutation algorithm. We propose three
enhancements to prevent DFJ's attacks and make XOR protocol stronger without
introducing extra resource cost.

Cryptography and Security