<s>
The	O
GOST	B-Algorithm
block	I-Algorithm
cipher	I-Algorithm
(	O
Magma	O
)	O
,	O
defined	O
in	O
the	O
standard	O
GOST	B-Algorithm
28147-89	I-Algorithm
(	O
RFC	O
5830	O
)	O
,	O
is	O
a	O
Soviet	O
and	O
Russian	O
government	O
standard	O
symmetric	B-Algorithm
key	I-Algorithm
block	O
cipher	O
with	O
a	O
block	O
size	O
of	O
64	O
bits	O
.	O
</s>
<s>
The	O
original	O
standard	O
,	O
published	O
in	O
1989	O
,	O
did	O
not	O
give	O
the	O
cipher	O
any	O
name	O
,	O
but	O
the	O
most	O
recent	O
revision	O
of	O
the	O
standard	O
,	O
GOST	B-Algorithm
R	I-Algorithm
34.12-2015	I-Algorithm
(	O
RFC	O
7801	O
,	O
RFC	O
8891	O
)	O
,	O
specifies	O
that	O
it	O
may	O
be	O
referred	O
to	O
as	O
Magma	O
.	O
</s>
<s>
The	O
GOST	B-Algorithm
hash	I-Algorithm
function	I-Algorithm
is	O
based	O
on	O
this	O
cipher	O
.	O
</s>
<s>
The	O
new	O
standard	O
also	O
specifies	O
a	O
new	O
128-bit	O
block	O
cipher	O
called	O
Kuznyechik	B-Algorithm
.	O
</s>
<s>
GOST	B-Algorithm
28147	O
was	O
a	O
Soviet	O
alternative	O
to	O
the	O
United	O
States	O
standard	O
algorithm	O
,	O
DES	B-Algorithm
.	O
</s>
<s>
GOST	B-Algorithm
has	O
a	O
64-bit	O
block	O
size	O
and	O
a	O
key	O
length	O
of	O
256	O
bits	O
.	O
</s>
<s>
Its	O
S-boxes	B-Algorithm
can	O
be	O
secret	O
,	O
and	O
they	O
contain	O
about	O
354	O
(	O
log2( 16	O
!	O
8	O
)	O
)	O
bits	O
of	O
secret	O
information	O
,	O
so	O
the	O
effective	O
key	O
size	O
can	O
be	O
increased	O
to	O
610	O
bits	O
;	O
however	O
,	O
a	O
chosen-key	O
attack	O
can	O
recover	O
the	O
contents	O
of	O
the	O
S-boxes	B-Algorithm
in	O
approximately	O
232	O
encryptions	O
.	O
</s>
<s>
GOST	B-Algorithm
is	O
a	O
Feistel	B-Algorithm
network	I-Algorithm
of	O
32	O
rounds	O
.	O
</s>
<s>
Its	O
round	O
function	O
is	O
very	O
simple	O
:	O
add	O
a	O
32-bit	O
subkey	O
modulo	O
232	O
,	O
put	O
the	O
result	O
through	O
a	O
layer	O
of	O
S-boxes	B-Algorithm
,	O
and	O
rotate	O
that	O
result	O
left	O
by	O
11	O
bits	O
.	O
</s>
<s>
The	O
S-boxes	B-Algorithm
accept	O
a	O
four-bit	O
input	O
and	O
produce	O
a	O
four-bit	O
output	O
.	O
</s>
<s>
The	O
S-box	B-Algorithm
substitution	O
in	O
the	O
round	O
function	O
consists	O
of	O
eight	O
4	O
×	O
4	O
S-boxes	B-Algorithm
.	O
</s>
<s>
The	O
S-boxes	B-Algorithm
are	O
implementation-dependent	O
,	O
thus	O
parties	O
that	O
want	O
to	O
secure	O
their	O
communications	O
using	O
GOST	B-Algorithm
must	O
be	O
using	O
the	O
same	O
S-boxes	B-Algorithm
.	O
</s>
<s>
For	O
extra	O
security	O
,	O
the	O
S-boxes	B-Algorithm
can	O
be	O
kept	O
secret	O
.	O
</s>
<s>
In	O
the	O
original	O
standard	O
where	O
GOST	B-Algorithm
was	O
specified	O
,	O
no	O
S-boxes	B-Algorithm
were	O
given	O
,	O
but	O
they	O
were	O
to	O
be	O
supplied	O
somehow	O
.	O
</s>
<s>
This	O
led	O
to	O
speculation	O
that	O
organizations	O
the	O
government	O
wished	O
to	O
spy	O
on	O
were	O
given	O
weak	O
S-boxes	B-Algorithm
.	O
</s>
<s>
One	O
GOST	B-Algorithm
chip	O
manufacturer	O
reported	O
that	O
he	O
generated	O
S-boxes	B-Algorithm
himself	O
using	O
a	O
pseudorandom	B-Algorithm
number	I-Algorithm
generator	I-Algorithm
.	O
</s>
<s>
For	O
example	O
,	O
the	O
Central	O
Bank	O
of	O
Russian	O
Federation	O
used	O
the	O
following	O
S-boxes	B-Algorithm
:	O
</s>
<s>
However	O
,	O
the	O
most	O
recent	O
revision	O
of	O
the	O
standard	O
,	O
GOST	B-Algorithm
R	I-Algorithm
34.12-2015	I-Algorithm
,	O
adds	O
the	O
missing	O
S-box	B-Algorithm
specification	O
and	O
defines	O
it	O
as	O
follows	O
.	O
</s>
<s>
The	O
latest	O
cryptanalysis	O
of	O
GOST	B-Algorithm
shows	O
that	O
it	O
is	O
secure	O
in	O
a	O
theoretical	O
sense	O
.	O
</s>
<s>
Since	O
2007	O
,	O
several	O
attacks	O
have	O
been	O
developed	O
against	O
reduced-round	O
GOST	B-Algorithm
implementations	O
and/or	O
weak	O
keys	O
.	O
</s>
<s>
In	O
2011	O
several	O
authors	O
discovered	O
more	O
significant	O
flaws	O
in	O
GOST	B-Algorithm
,	O
being	O
able	O
to	O
attack	O
the	O
full	O
32-round	O
GOST	B-Algorithm
with	O
arbitrary	O
keys	O
for	O
the	O
first	O
time	O
.	O
</s>
<s>
In	O
December	O
2012	O
,	O
Courtois	O
,	O
Gawinecki	O
,	O
and	O
Song	O
improved	O
attacks	O
on	O
GOST	B-Algorithm
by	O
computing	O
only	O
2101	O
GOST	B-Algorithm
rounds	O
.	O
</s>
<s>
Isobe	O
had	O
already	O
published	O
a	O
single	O
key	O
attack	O
on	O
the	O
full	O
GOST	B-Algorithm
cipher	O
,	O
which	O
Dinur	O
,	O
Dunkelman	O
,	O
and	O
Shamir	O
improved	O
upon	O
,	O
reaching	O
2224	O
time	O
complexity	O
for	O
232	O
data	O
and	O
236	O
memory	O
,	O
and	O
2192	O
time	O
complexity	O
for	O
264	O
data	O
.	O
</s>
