Transient-steady effect attack on block ciphers

A new Transient-Steady Effect attack on block ciphers called TSE attack is presented in this paper. The concept of transient-steady effect denotes the phenomenon that the output of a combinational circuit keeps a temporal value for a while before it finally switches to the correct value. Unlike most existing fault attacks, our attack does not need a large amount of encryptions to build a statistical model. By injecting a clock glitch to capture the temporal value caused by transientsteady effect, attackers can obtain the information of key from faulty outputs directly. This work shows that AES implementations, which have transient-steady property, are vulnerable to our attack. Experiments are successfully conducted on two kinds of unmasked S-boxes and one kind of masked S-box implemented in serial with FPGA board. After a moderate pre-computation, we need only 1 encryption to recover a key byte of the unmasked S-boxes, and 20 encryptions to recover a key byte of the masked S-box. Furthermore, we investigate the key recover method for parallel unmasked implementation, and discuss a possible attack scenario which may deem WDDL-AES insecure.