Practical‐time related‐key attack on Hummingbird‐2. Issue 6 (1st November 2015)

• Record Type: Journal Article
• Authors: Shi, Zhenqing; Zhang, Bin; Feng, Dengguo
• Is Part Of: IET information security. Volume 9:Issue 6(2015)
• Page Start: 321
• Page End: 327
• Publication Date: 2015-11-01
• Subjects: divide and conquer methods -- cryptography; practical‐time related‐key attack -- Hummingbird‐2 -- lightweight cipher -- MAC functionality -- cryptographic notion -- combination points -- differential equation -- internal state bits -- divide and conquer strategy -- cryptographic S‐boxes; Computer security -- Periodicals; Cryptography -- Periodicals; Computer networks -- Security measures -- Periodicals; Database security -- Periodicals; 005.8
• DOI: 10.1049/iet-ifs.2014.0424
• Languages: English
• ISSNs: 1751-8709

Abstract

Abstract : Hummingbird‐2, designed by Engels et al ., is a lightweight cipher with built‐in MAC functionality. In this study, the authors examine the security of Hummingbird‐2 in the related‐key model. First, the authors define a new cryptographic notion of an S ‐box, called combination points, based on its differential equation, and demonstrate some properties of combination points. A potential application of the new notion is to recover some partial input of an S ‐box, and the authors show this on Hummingbird‐2 by recovering some internal state bits. Then, by carefully studying the differential distributions of the S ‐boxes, a set of key dependent S ‐boxes can be derived and be used to recover the subkey word of Hummingbird‐2. At last, by the divide and conquer strategy, all the 128 key bits can be recovered with a complexity of 2 40, which is much lower than that (2 64 ) of the attack at FSE 2013. The attack has been fully implemented on a PC and the secret key has been recovered in a few hours. The results provide some new insights into the design of cryptographic S‐boxes.