Kuznyechik

Kuznyechik
General
Designers	InfoTeCS JSC^[1]
First published	2015
Certification	GOST, and FSS
Cipher detail
Key sizes	256 bits Feistel network
Block sizes	128 bits
Structure	Substitution-permutation network
Rounds	10
Best public cryptanalysis
A meet-in-the-middle attack on 5 rounds.^[2]

Kuznyechik (Russian: 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^[3] and also in RFC 7801.

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 (/kʊznˈɛtʃɪk/). 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.^[4]

The standard GOST R 34.12-2015 defines the new cipher in addition to the old GOST block cipher (now called Magma) one and does not declare the old cipher obsolete.^[5]

Kuznyechik is based on a substitution-permutation network, though the key schedule employs a Feistel network. The first block cipher with a mixed structure.

Designations

$\mathbb F$ — Finite field $GF(2^{8})$ $x^{8}+x^{7}+x^{6}+x+1$ .

$Bin_{8}:\mathbb {Z} _{p}\rightarrow V_{8}$ — $\mathbb {Z} _{p}$ ( $p=2^{8}$ )

${Bin_{8}}^{-1}:V_{8}\rightarrow \mathbb {Z} _{p}$ — $Bin_{8}$ .

$\delta :V_{8}\rightarrow \mathbb {F}$ — $\mathbb F$ .

$\delta ^{-1}:\mathbb {F} \rightarrow V_{8}$ — $\delta$

Description

For encryption, decryption and key generation, the following functions:

$Add_{2}[k](a)=k\oplus a$ , где $k$ , $a$ — двоичные строки вида $a=a_{15}||$ … $||a_{0}$ ( $||$ — symbol Concatenation strings).

$N(a)=S(a_{15})||$ … $||S(a_{0}).~~N^{-1}(a)$ — обратное к $N(a)$ преобразование.

$G(a)=\delta (a_{15},$ … $,a_{0})||a_{15}||$ … $||a_{1}.$

$G^{-1}(a)$ — обратное к $G(a)$ преобразование, причём $G^{-1}(a)=a_{14}||a_{13}||$ … $||a_{0}||\delta (a_{14},a_{13},$ … $,a_{0},a_{15}).$

$H(a)=G^{16}(a)$ , где $G^{16}$ — композиция преобразований $G^{15}$ и $G$ и т. д.

$F[k](a_{1},a_{0})=(HNAdd_{2}[k](a_{1})\oplus a_{0},a_{1}).$

The nonlinear transformation

Non-linear transformation is given by substituting S = Bin₈ S' Bin₈⁻¹.

Значения подстановки S' заданы в виде массива S' = (S'(0), S'(1), …, S'(255)):

$S'=(252,238,221,17,207,110,49,22,251,196,250,218,35,197,4,77,233,$ $119,240,219,147,46,153,186,23,54,241,187,20,205,95,193,249,24,101,$ $90,226,92,239,33,129,28,60,66,139,1,142,79,5,132,2,174,227,106,143,$ $160,6,11,237,152,127,212,211,31,235,52,44,81,234,200,72,171,242,42,$ $104,162,253,58,206,204,181,112,14,86,8,12,118,18,191,114,19,71,156,$ $183,93,135,21,161,150,41,16,123,154,199,243,145,120,111,157,158,178,$ $177,50,117,25,61,255,53,138,126,109,84,198,128,195,189,13,87,223,$ $245,36,169,62,168,67,201,215,121,214,246,124,34,185,3,224,15,236,$ $222,122,148,176,188,220,232,40,80,78,51,10,74,167,151,96,115,30,0,$ $98,68,26,184,56,130,100,159,38,65,173,69,70,146,39,94,85,47,140,163,$ $165,125,105,213,149,59,7,88,179,64,134,172,29,247,48,55,107,228,136,$ $217,231,137,225,27,131,73,76,63,248,254,141,83,170,144,202,216,133,$ $97,32,113,103,164,45,43,9,91,203,155,37,208,190,229,108,82,89,166,$ $116,210,230,244,180,192,209,102,175,194,57,75,99,182).$

Linear transformation

$\gamma$ : $\gamma (a_{15},$ … $,a_{0})=\delta ^{-1}~(148*\delta (a_{15})+32*\delta (a_{14})+133*\delta (a_{13})+16*\delta (a_{12})+$ $194*\delta (a_{11})+192*\delta (a_{10})+1*\delta (a_{9})+251*\delta (a_{8})+1*\delta (a_{7})+192*\delta (a_{6})+$ $194*\delta (a_{5})+16*\delta (a_{4})+133*\delta (a_{3})+32*\delta (a_{2})+148*\delta (a_{1})+1*\delta (a_{0})),$

operations of addition and multiplication are carried out in the field $\mathbb F$ .

Key generation

key generation algorithm uses iterative constant $C_{i}=H(Bin_{128}(i))$ , i=1,2,…32. Sets the shared key $K=k_{255}||$ … $||k_{0}$ .

Iterated keys

$K_{1}=k_{255}||$ … $||k_{128}$

$K_{2}=k_{127}||$ … $||k_{0}$

$(K_{2i+1},K_{2i+2})=F[C_{8(i-1)+8}]$ … $F[C_{8(i-1)+1}](K_{2i+1},K_{2i}),i=1,2,3,4.$

Encryption algorithm

$E(a)=Add_{2}[K_{10}]HNAdd_{2}[K_{9}]$ … $HNAdd_{2}[K_{3}]HNAdd_{2}[K_{1}](a),$ where a — 128-bit string.

Decryption algorithm

$D(a)=Add_{2}[K_{1}]H^{-1}N^{-1}Add_{2}[K_{2}]$ … $H^{-1}N^{-1}Add_{2}[K_{9}]H^{-1}N^{-1}Add_{2}[K_{10}](a).$

Cryptanalysis

Riham AlTawy and Amr M. Youssef describe a meet-in-the-middle attack on the 5-round reduced Kuznyechik which allows to recover the key with time complexity of 2¹⁴⁰, memory complexity of 2¹⁵³, and data complexity of 2¹¹³.^[2]

Alex Biryukov, Leo Perrin, and Aleksei Udovenko published a paper in which they show that the S-Boxes of Kuznyechik and Streebog were not created pseudo-randomly but using a hidden algorithm which they were able to reverse engineer.^[6]

Riham AlTawy, Onur Duman, and Amr M. Youssef published two fault attacks on Kuznyechik which show the importance of protecting the implementations of the cipher.^[7]

Software use

Kuznyechik cipher use in the VeraCrypt

References

↑ http://tc26.ru/standard/draft/PR_GOSTR-bch_v4.zip
1 2 Riham AlTawy and Amr M. Youssef (2015-04-17). "A Meet in the Middle Attack on Reduced Round Kuznyechik" (PDF).
↑ http://tc26.ru/en/standard/gost/GOST_R_34_12_2015_ENG.pdf National Standard of the Russian Federation GOST R 34.12–2015 (English Version)
↑ https://mjos.fi/doc/rus/gh_ctcrypt.pdf Low-Weight and Hi-End: Draft Russian Encryption Standard
↑ http://www.itsec.ru/articles2/crypto/gost-r-chego-ozhidat-ot-novogo-standarta GOST R 34.12–2015: what to expect from a new standard? (Russian only)
↑ Alex Biryukov, Leo Perrin, and Aleksei Udovenko (2016-02-18). "Reverse-Engineering the S-Box of Streebog, Kuznyechik and STRIBOBr1 (Full Version)" (PDF).
↑ Riham AlTawy, Onur Duman, and Amr M. Youssef (2015-04-17). "Fault Analysis of Kuznyechik" (PDF).

Block ciphers (security summary)

Common algorithms	AES Blowfish DES (Internal Mechanics, Triple DES) Serpent Twofish

Less common algorithms	Camellia CAST-128 IDEA RC2 RC5 RC6 SEED ARIA Skipjack TEA XTEA

Other algorithms	3-Way Akelarre Anubis BaseKing BassOmatic BATON BEAR and LION CAST-256 Chiasmus CIKS-1 CIPHERUNICORN-A CIPHERUNICORN-E CLEFIA CMEA Cobra COCONUT98 Crab Cryptomeria/C2 CRYPTON CS-Cipher DEAL DES-X DFC E2 FEAL FEA-M FROG G-DES GOST Grand Cru Hasty Pudding cipher Hierocrypt ICE IDEA NXT Intel Cascade Cipher Iraqi KASUMI KeeLoq KHAZAD Khufu and Khafre KN-Cipher Kuznyechik Ladder-DES Libelle LOKI (97, 89/91) Lucifer M6 M8 MacGuffin Madryga MAGENTA MARS Mercy MESH MISTY1 MMB MULTI2 MultiSwap New Data Seal NewDES Nimbus NOEKEON NUSH PRESENT Q RC6 REDOC Red Pike S-1 SAFER SAVILLE SC2000 SHACAL SHARK Simon SM4 Speck Spectr-H64 Square SXAL/MBAL Threefish Treyfer UES Xenon xmx XXTEA Zodiac

Design	Feistel network Key schedule Lai-Massey scheme Product cipher S-box P-box SPN Avalanche effect Block size Key size Key whitening (Whitening transformation)

Attack (cryptanalysis)	Brute-force (EFF DES cracker) MITM (Biclique attack, 3-subset MITM attack) Linear (Piling-up lemma) Differential (Impossible Truncated Higher-order) Differential-linear Distinguishing (Known-key) Integral/Square Boomerang Mod n Related-key Slide Rotational Timing XSL Interpolation Partitioning Davies' Rebound Weak key Tau Chi-square Time/memory/data tradeoff

Standardization	AES process CRYPTREC NESSIE

Utilization	Initialization vector Mode of operation Padding

Cryptography

History of cryptography Cryptanalysis Outline of cryptography

Symmetric-key algorithm Block cipher Stream cipher Public-key cryptography Cryptographic hash function Message authentication code Random numbers Steganography

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