Two Efficient Fault-Based Attacks on CLOC and SILC

Abstract

CLOC and SILC are two block cipher-based authenticated encryption schemes, submitted to the CAE-SAR competition, that aims to use low area buffer and handle short input efficiently. The designers of CLOC and SILC claimed n 2 -bit integrity security against nonce-reusing adversaries, where n is the blockcipher state size in bits. In this paper, we present single fault-based almost universal forgeries on both CLOC and SILC with only one single bit fault at a fixed position of a specific blockcipher input. In the case of CLOC, the forgery can be done for almost any nonce, associated data and message triplet, except some nominal restrictions on associated data. In the case of SILC, the forgery can be done for almost any associated data and message, except some nominal restrictions on associated data along with a fixed nonce. Both the attacks on CLOC and SILC require several nonce-misusing encryption queries This attack is independent of the underlying block cipher and works on the encryption mode. In this paper, we also validate the proposed fault-based forgery methodology by performing actual fault attacks by electromagnetic pulse injection which shows practicality of the proposed forgery procedure. Next, we provide updated constructions that can resist the fault-based forgery on the mode assuming the underlying block cipher is fault resistant. Finally, we show that, if the underlying block cipher is not fault resistant, then for both CLOC and SILC, the key recovery can be done by injecting fault into the block cipher operations. We have considered the example with AES as the underlying block cipher. We would like to note that our attacks do not violate the designers' claims as our attacks require fault. However, it shows some vulnerability of the schemes when fault is feasible.