<s>
The	O
GOST	B-Algorithm
hash	B-Algorithm
function	I-Algorithm
,	O
defined	O
in	O
the	O
standards	O
GOST	B-Algorithm
R	I-Algorithm
34.11-94	I-Algorithm
and	O
GOST	B-Algorithm
34.311-95	I-Algorithm
is	O
a	O
256-bit	O
cryptographic	B-Algorithm
hash	I-Algorithm
function	I-Algorithm
.	O
</s>
<s>
It	O
was	O
initially	O
defined	O
in	O
the	O
Russian	O
national	O
standard	O
GOST	B-Algorithm
R	I-Algorithm
34.11-94	I-Algorithm
Information	O
Technology	O
–	O
Cryptographic	O
Information	O
Security	O
–	O
Hash	B-Algorithm
Function	I-Algorithm
.	O
</s>
<s>
The	O
equivalent	O
standard	O
used	O
by	O
other	O
member-states	O
of	O
the	O
CIS	O
is	O
GOST	B-Algorithm
34.311-95	I-Algorithm
.	O
</s>
<s>
This	O
function	O
must	O
not	O
be	O
confused	O
with	O
a	O
different	O
Streebog	B-Algorithm
hash	B-Algorithm
function	I-Algorithm
,	O
which	O
is	O
defined	O
in	O
the	O
new	O
revision	O
of	O
the	O
standard	O
GOST	B-Algorithm
R	I-Algorithm
34.11-2012	I-Algorithm
.	O
</s>
<s>
The	O
GOST	B-Algorithm
hash	B-Algorithm
function	I-Algorithm
is	O
based	O
on	O
the	O
GOST	B-Algorithm
block	I-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
GOST	B-Algorithm
processes	O
a	O
variable-length	O
message	O
into	O
a	O
fixed-length	O
output	O
of	O
256	O
bits	O
.	O
</s>
<s>
The	O
input	O
message	O
is	O
broken	O
up	O
into	O
chunks	O
of	O
256-bit	O
blocks	O
(	O
eight	O
32-bit	O
little	O
endian	O
integers	O
)	O
;	O
the	O
message	O
is	O
padded	B-Algorithm
by	O
appending	O
as	O
many	O
zeros	O
to	O
it	O
as	O
are	O
required	O
to	O
bring	O
the	O
length	O
of	O
the	O
message	O
up	O
to	O
256	O
bits	O
.	O
</s>
<s>
Each	O
block	O
is	O
processed	O
by	O
the	O
step	O
hash	B-Algorithm
function	I-Algorithm
,	O
where	O
,	O
,	O
are	O
a	O
256-bit	O
blocks	O
.	O
</s>
<s>
The	O
is	O
the	O
desired	O
value	O
of	O
the	O
hash	B-Algorithm
function	I-Algorithm
of	O
the	O
message	O
M	O
.	O
</s>
<s>
—	O
Initial	O
256-bit	O
value	O
of	O
the	O
hash	B-Algorithm
function	I-Algorithm
,	O
determined	O
by	O
user	O
.	O
</s>
<s>
The	O
step	O
hash	B-Algorithm
function	I-Algorithm
maps	O
two	O
256-bit	O
blocks	O
into	O
one	O
:	O
.	O
</s>
<s>
After	O
the	O
keys	O
generation	O
,	O
the	O
enciphering	O
of	O
is	O
done	O
using	O
GOST	B-Algorithm
28147-89	I-Algorithm
in	O
the	O
mode	O
of	O
simple	O
substitution	O
on	O
keys	O
.	O
</s>
<s>
On	O
the	O
last	O
step	O
,	O
the	O
shuffle	O
transformation	O
is	O
applied	O
to	O
,	O
S	O
and	O
m	O
using	O
a	O
linear-feedback	B-Architecture
shift	I-Architecture
register	I-Architecture
.	O
</s>
<s>
In	O
the	O
result	O
,	O
the	O
intermediate	O
hash	B-Algorithm
value	O
is	O
obtained	O
.	O
</s>
<s>
First	O
we	O
define	O
the	O
ψ	O
function	O
,	O
doing	O
LFSR	B-Architecture
on	O
a	O
256-bit	O
block	O
:	O
</s>
<s>
There	O
are	O
two	O
commonly	O
used	O
sets	O
of	O
initial	O
parameters	O
for	O
GOST	B-Algorithm
R	O
34.11	O
94	O
.	O
</s>
<s>
Although	O
the	O
GOST	B-Algorithm
R	O
34.11	O
94	O
standard	O
itself	O
does	O
n't	O
specify	O
the	O
algorithm	O
initial	O
value	O
and	O
S-box	B-Algorithm
of	O
the	O
enciphering	O
transformation	O
,	O
but	O
uses	O
the	O
following	O
"	O
test	O
parameters	O
"	O
in	O
the	O
samples	O
sections	O
.	O
</s>
<s>
The	O
CryptoPro	O
S-box	B-Algorithm
comes	O
from	O
"	O
production	O
ready	O
"	O
parameter	O
set	O
developed	O
by	O
CryptoPro	O
company	O
,	O
it	O
is	O
also	O
specified	O
as	O
part	O
of	O
RFC	O
4357	O
,	O
section	O
11.2	O
.	O
</s>
<s>
In	O
2008	O
,	O
an	O
attack	O
was	O
published	O
that	O
breaks	O
the	O
full-round	O
GOST	B-Algorithm
hash	B-Algorithm
function	I-Algorithm
.	O
</s>
<s>
The	O
paper	O
presents	O
a	O
collision	B-Algorithm
attack	I-Algorithm
in	O
2105	O
time	O
,	O
and	O
first	O
and	O
second	O
preimage	O
attacks	O
in	O
2192	O
time	O
(	O
2n	O
time	O
refers	O
to	O
the	O
approximate	O
number	O
of	O
times	O
the	O
algorithm	O
was	O
calculated	O
in	O
the	O
attack	O
)	O
.	O
</s>
<s>
The	O
256-bit	O
(	O
32-byte	O
)	O
GOST	B-Algorithm
hashes	B-Algorithm
are	O
typically	O
represented	O
as	O
64-digit	O
hexadecimal	O
numbers	O
.	O
</s>
<s>
Even	O
a	O
small	O
change	O
in	O
the	O
message	O
will	O
,	O
with	O
overwhelming	O
probability	O
,	O
result	O
in	O
a	O
completely	O
different	O
hash	B-Algorithm
due	O
to	O
the	O
avalanche	O
effect	O
.	O
</s>
<s>
Two	O
samples	O
coming	O
from	O
the	O
GOST	B-Algorithm
R	I-Algorithm
34.11-94	I-Algorithm
standard	O
:	O
</s>
<s>
GOST	B-Algorithm
algorithm	O
with	O
CryptoPro	O
S-box	B-Algorithm
generates	O
different	O
set	O
of	O
hash	B-Algorithm
values	O
.	O
</s>
