Forgery and Subkey Recovery on CAESAR Candidate iFeed

Abstract. iFeed is a blockcipher-based authenticated encryption design by Zhang, Wu, Sui, and Wang and a first round candidate to the CAESAR competition. iFeed is claimed to achieve confidentiality and authenticity in the nonce-respecting setting, and confidentiality in the nonce-reuse setting. Recently, Chakraborti et al. published forgeries on iFeed in the RUP and nonce-reuse settings. The latter attacks, however, do not invalidate the iFeed designers’ security claims. In this work, we consider the security of iFeed in the nonce-respecting setting, and show that a valid forgery can be constructed after only one encryption query. Even more, the forgery leaks both subkeys EK (0128 ) and EK (PMN 1), where K is the secret key and PMN the nonce used for the authenticated encryption. Furthermore, we show how at the price of just one additional forgery one can learn EK (P∗ ) for any freely chosen plaintext P∗ . These design weaknesses allow one to decrypt earlier iFeed encryptions ...

• Type: Journal
• Year: 2015
• Where: SACRYPT
• Authors: Willem Schroé, Bart Mennink, Elena Andreeva 0001, Bart Preneel
• Keywords: Cryptology, SACRYPT 2015