<s>
Kuznyechik	B-Algorithm
(	O
,	O
literally	O
"	O
grasshopper	B-Application
"	O
)	O
is	O
a	O
symmetric	O
block	O
cipher	O
.	O
</s>
<s>
It	O
is	O
defined	O
in	O
the	O
National	O
Standard	O
of	O
the	O
Russian	O
Federation	O
GOST	B-Algorithm
R	I-Algorithm
34.12-2015	I-Algorithm
and	O
also	O
in	O
RFC	O
7801	O
.	O
</s>
<s>
The	O
name	O
of	O
the	O
cipher	O
can	O
be	O
translated	O
from	O
Russian	O
as	O
grasshopper	B-Application
,	O
however	O
,	O
the	O
standard	O
explicitly	O
says	O
that	O
the	O
English	O
name	O
for	O
the	O
cipher	O
is	O
Kuznyechik	B-Algorithm
(	O
)	O
.	O
</s>
<s>
The	O
designers	O
claim	O
that	O
by	O
naming	O
the	O
cipher	O
Kuznyechik	B-Algorithm
they	O
follow	O
the	O
trend	O
of	O
difficult	O
to	O
pronounce	O
algorithm	O
names	O
set	O
up	O
by	O
Rijndael	B-Algorithm
and	O
Keccak	B-Algorithm
.	O
</s>
<s>
The	O
standard	O
GOST	B-Algorithm
R	I-Algorithm
34.12-2015	I-Algorithm
defines	O
the	O
new	O
cipher	O
in	O
addition	O
to	O
the	O
old	O
GOST	B-Algorithm
block	I-Algorithm
cipher	I-Algorithm
(	O
now	O
called	O
Magma	O
)	O
as	O
one	O
and	O
does	O
not	O
declare	O
the	O
old	O
cipher	O
obsolete	O
.	O
</s>
<s>
Kuznyechik	B-Algorithm
is	O
based	O
on	O
a	O
substitution	B-Algorithm
–	I-Algorithm
permutation	I-Algorithm
network	I-Algorithm
,	O
though	O
the	O
key	B-Algorithm
schedule	I-Algorithm
employs	O
a	O
Feistel	B-Algorithm
network	I-Algorithm
.	O
</s>
<s>
Riham	O
AlTawy	O
and	O
Amr	O
M	O
.	O
Youssef	O
describe	O
a	O
meet-in-the-middle	O
attack	O
on	O
the	O
5-round	O
reduced	O
Kuznyechik	B-Algorithm
which	O
enables	O
recovery	O
of	O
the	O
key	O
with	O
a	O
time	O
complexity	O
of	O
2140	O
,	O
memory	O
complexity	O
of	O
2153	O
,	O
and	O
data	O
complexity	O
of	O
2113	O
.	O
</s>
<s>
Alex	O
Biryukov	O
,	O
Leo	O
Perrin	O
,	O
and	O
Aleksei	O
Udovenko	O
published	O
a	O
paper	O
in	O
which	O
they	O
show	O
that	O
the	O
S-boxes	B-Algorithm
of	O
Kuznyechik	B-Algorithm
and	O
Streebog	B-Algorithm
were	O
not	O
created	O
pseudo-randomly	O
but	O
by	O
using	O
a	O
hidden	O
algorithm	O
which	O
they	O
were	O
able	O
to	O
reverse	O
engineer	O
.	O
</s>
<s>
Later	O
Leo	O
Perrin	O
and	O
Aleksei	O
Udovenko	O
published	O
two	O
alternative	O
decompositions	O
of	O
the	O
S-box	B-Algorithm
and	O
proved	O
its	O
connection	O
to	O
the	O
S-box	B-Algorithm
of	O
the	O
Belarusian	O
cipher	O
BelT	O
.	O
</s>
<s>
The	O
authors	O
of	O
the	O
paper	O
note	O
that	O
while	O
the	O
reason	O
for	O
using	O
such	O
a	O
structure	O
remains	O
unclear	O
,	O
generating	O
S-boxes	B-Algorithm
by	O
a	O
hidden	O
algorithm	O
contradicts	O
the	O
concept	O
of	O
nothing-up-my-sleeve	O
numbers	O
which	O
could	O
prove	O
that	O
no	O
weaknesses	O
were	O
intentionally	O
introduced	O
in	O
their	O
design	O
.	O
</s>
<s>
Riham	O
AlTawy	O
,	O
Onur	O
Duman	O
,	O
and	O
Amr	O
M	O
.	O
Youssef	O
published	O
two	O
fault	B-General_Concept
attacks	I-General_Concept
on	O
Kuznyechik	B-Algorithm
which	O
show	O
the	O
importance	O
of	O
protecting	O
the	O
implementations	O
of	O
the	O
cipher	O
.	O
</s>
<s>
VeraCrypt	B-Operating_System
(	O
a	O
fork	O
of	O
TrueCrypt	B-Application
)	O
included	O
Kuznyechik	B-Algorithm
as	O
one	O
of	O
its	O
supported	O
encryption	O
algorithms	O
.	O
</s>
