BAKSHEESH: Similar Yet Different From GIFT (and ZORRO)

We propose a lightweight block cipher named BAKSHEESH, which draws inspiration from GIFT (CHES'17). BAKSHEESH runs for 35 rounds, which is 12.5 per cent fewer rounds compared to GIFT-128 whilst maintaining the same security claims against classical attacks. However, we also present an alternate (but equivalent) angle of BAKSHEESH that follows the heritage of ZORRO (CHES'13). In the GIFT heritage version, BAKSHEESH uses a 4-bit SBox that has a non-trivial Linear Structure (LS). In the alternate ZORRO heritage specification, it employs a 3-bit SBox and realises a partial non-linear layer. BAKSHEESH is suitable for efficient hardware and software implementations, and also offers an edge on side channel countermeasures and other niche applications. For instance, our study on the threshold implementation shows that BAKSHEESH offers a few-fold advantage over other lightweight ciphers. We therefore create a new paradigm of lightweight ciphers through adequate deliberation on the design choice and solidify it with appropriate security analysis and ample implementation/benchmark.