Kuznyechik (Russian for 'Grasshopper'; Cyrillic script: Кузнечик) is a symmetric block cipher. It has a block size of 128 bits and key length of 256 bits. It is defined in the National Standard of the Russian Federation GOST R 34.12-2015 and also in RFC 7801. It has received scrutiny for the structure of its S-boxes, which the authors claim were randomly generated. The name of the cipher can be translated from Russian as grasshopper, however, the standard explicitly says that the English name for the cipher is Kuznyechik (). The designers claim that by naming the cipher Kuznyechik they follow the trend of difficult to pronounce algorithm names set up by Rijndael and Keccak. There is also a rumor that the cipher was named after its creators: A. S. Kuzmin, A. A. Nechaev and Company (Russian: Кузьмин, Нечаев и Компания). The standard GOST R 34.12-2015 defines the new cipher in addition to the old GOST block cipher (now called Magma) as one and does not declare the old cipher obsolete. Kuznyechik is based on a substitution–permutation network, though the key schedule employs a Feistel network.
Designations
F {\displaystyle \mathbb {F} } — Finite field G F ( 2 8 ) {\displaystyle GF(2^{8})} x 8 + x 7 + x 6 + x + 1 {\displaystyle x^{8}+x^{7}+x^{6}+x+1} .
B i n 8 : Z p → V 8 {\displaystyle Bin_{8}:\mathbb {Z} _{p}\rightarrow V_{8}} — Z p {\displaystyle \mathbb {Z} _{p}} ( p = 2 8 {\displaystyle p=2^{8}} )
B i n 8 − 1 : V 8 → Z p {\displaystyle {Bin_{8}}^{-1}:V_{8}\rightarrow \mathbb {Z} _{p}} — B i n 8 {\displaystyle Bin_{8}} .
δ : V 8 → F {\displaystyle \delta :V_{8}\rightarrow \mathbb {F} } — F {\displaystyle \mathbb {F} } .
δ − 1 : F → V 8 {\displaystyle \delta ^{-1}:\mathbb {F} \rightarrow V_{8}} — δ {\displaystyle \delta }
Description For encryption, decryption and key generation, the following functions:
A d d 2 [ k ] ( a ) = k ⊕ a {\displaystyle Add_{2}[k](a)=k\oplus a} , where k {\displaystyle k} , a {\displaystyle a} are binary strings of the form a = a 15 | | {\displaystyle a=a_{15}||} ... | | a 0 {\displaystyle ||a_{0}} ( | | {\displaystyle ||} is string concatenation).
N ( a ) = S ( a 15 ) | | {\displaystyle N(a)=S(a_{15})||} ... | | S ( a 0 ) . N − 1 ( a ) {\displaystyle ||S(a_{0}).~~N^{-1}(a)} is a reversed transformation of N ( a ) {\displaystyle N(a)} .
G ( a ) = γ ( a 15 , {\displaystyle G(a)=\gamma (a_{15},} ... , a 0 ) | | a 15 | | {\displaystyle ,a_{0})||a_{15}||} ... | | a 1 . {\displaystyle ||a_{1}.}
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