Midori: A Block Cipher for Low Energy

Abstract

In the past few years, lightweight cryptography has become a popular research discipline with a number of ciphers and hash functions proposed. The designers' focus has been predominantly to minimize the hardware area, while other goals such as low latency have been addressed rather recently only. However, the optimization goal of low energy for block cipher design has not been explicitly addressed so far. At the same time, it is a crucial measure of goodness for an algorithm. Indeed, a cipher optimized with respect to energy has wide applications, especially in constrained environments running on a tight power/energy budget such as medical implants.This paper presents the block cipher Midori (The name of the cipher is the Japanese translation for the word Green.) that is optimized with respect to the energy consumed by the circuit per bt in encryption or decryption operation. We deliberate on the design choices that lead to low energy consumption in an electrical circuit, and try to optimize each component of the circuit as well as its entire architecture for energy. An added motivation is to make both encryption and decryption functionalities available by small tweak in the circuit that would not incur significant area or energy overheads. We propose two energy-efficient block ciphers Midori128 and Midori64 with block sizes equal to 128 and 64 bits respectively. These ciphers have the added property that a circuit that provides both the functionalities of encryption and decryption can be designed with very little overhead in terms of area and energy. We compare our results with other ciphers with similar characteristics: it was found that the energy consumptions of Midori64 and Midori128 are by far better when compared ciphers like PRINCE and NOEKEON.

Related-Key Cryptanalysis of Midori

“…Relatedkey cryptanalysis, which was independently introduced by Biham [3] and Knudsen [12], additionally considers the case where the two plaintexts are ciphered † The full specification is presented in [2]. with different keys.…”

“…Lightweight block ciphers follow this trend, and aim at providing energy efficient ways to ensure confidentiality for fixed size block messages. In 2015, the authors of [2] consider the challenging task of minimizing the energy cost for a lightweight block cipher. They proposed a lightweight symmetric block cipher scheme called Midori, composed of two versions Midori64 and Midori128, which respectively cipher 64-and 128-bit message blocks.…”

“…Midori64 and Midori128 [2] are lightweight block ciphers, which respectively cipher 64-bit and 128-bit blocks. While several attack models are discussed by the authors of Midori, the authors made no claims concerning the security of Midori against related-key differential attacks.…”

Practical Low Data-Complexity Subspace-Trail Cryptanalysis of Round-Reduced PRINCE

“…As for the attack on 3 rounds, the idea is to work independently on each column of the key, due to the fact that the columns of M 0 depend on different and independent variables. Initially the attacker guesses 1 column (that is 4 nibbles) of the final key, as for examplek [3], and she uses them to partially decrypt c 1 and c 2 , that is she computes 4 nibbles of s 1 := Rk(c 1 ) and of s 2 := Rk(c 2 ). Note that the attacker cannot guess 4 arbitrary nibbles of the final key but an entire column, since she has to compute the Linear Layer M .…”

“…Starting from [12], in Sect. 3 we investigate the behavior of subspaces in PRINCE. At a high level, we fix a subspace of plaintexts that maintain predictable properties after repeated applications of a key-variant round function.…”