Elastic-Tweak: A Framework for Short Tweak Tweakable Block Cipher Avik Chakraborti1, Nilanjan Datta2, Ashwin Jha2, Cuauhtemoc Mancillas Lopez3, Mridul Nandi2, Yu Sasaki1 1 NTT Secure Platform Laboratories, Japan 2 Indian Statistical Institute, Kolkata, India 3 Computer Science Department, CINVESTAV-IPN, Mexico
[email protected], nilanjan isi
[email protected],
[email protected],
[email protected],
[email protected],
[email protected] Abstract. Tweakable block cipher (TBC), a stronger notion than stan- dard block ciphers, has wide-scale applications in symmetric-key schemes. At a high level, it provides flexibility in design and (possibly) better security bounds. In multi-keyed applications, a TBC with short tweak values can be used to replace multiple keys. However, the existing TBC construction frameworks, including TWEAKEY and XEX, are designed for general purpose tweak sizes. Specifically, they are not optimized for short tweaks, which might render them inefficient for certain resource constrained applications. So a dedicated paradigm to construct short- tweak TBCs (tBC) is highly desirable. In this paper, we present a ded- icated framework, called the Elastic-Tweak framework (ET in short), to convert any reasonably secure SPN block cipher into a secure tBC. We apply the ET framework on GIFT and AES to construct efficient tBCs, named TweGIFT and TweAES. We present hardware and software results to show that the performance overheads for these tBCs are minimal. We perform comprehensive security analysis and observe that TweGIFT and TweAES provide sufficient security without any increase in the number of block cipher rounds when compared to GIFT and AES.