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a,c)
e
b,d)
V 1
V 2
V 3
V 4
V 5
V 6
( V , e )
S n ; m
e
X
V'
n
1
1
( e )
P 2 x k ;1
( e )
P 2 x k ;1
( e )
P 2 x k ;1
m
( e )
P m ;1
S n ; m
V
m
k
n
b) : n =32; m = 96
d) : n =64; m = 192
( e )
P 6 k ;1
V' 1
V' 2
V' 3
V' 4
V' 5
V' 6
Y
a) : k = 16
c) : k = 32
Fig. 4. Structure of the boxes P ( e )
96;1 (a), S ( V , e )
32;96 (b), P ( e )
192;1 (c), and S ( V , e )
64;192 (d)
attack [1]. The switchable operation in the ciphers SCO-1, SCO-2, and SCO-3 are used
in a way preventing possibility to define homogeneity of the encryption procedure by
choosing certain types of keys.
Figure 5 presents round encryption function of SCO-1. The 32-bit round subkeys
are denoted as K r , G r ,and T r . Two input data subblocks A and B are of the 32-bit length.
The operational boxes S ( e )
32;96 , S ( e )
32;96 and P ( e )
32;1 have been specified in Section 2.2. The
extension box E forming the controlling vectors is described as follows
V 1 =(
2
×
l 7 ,
l 8 ,
l 1 ,
l 2 ,
l 16 ,
l 15 ,
l 10 ,
l 9 ,
l 5 ,
l 6 ,
l 3 ,
l 4 ,
l 11 ,
l 12 ,
l 13 ,
l 14 )
,
V 2 =(
l 9 ,
l 10 ,
l 11 ,
l 12 ,
l 1 ,
l 2 ,
l 7 ,
l 8 ,
l 13 ,
l 14 ,
l 15 ,
l 16 ,
l 5 ,
l 6 ,
l 3 ,
l 4 )
,
V 3 =(
l 13 ,
l 14 ,
l 15 ,
l 16 ,
l 5 ,
l 6 ,
l 3 ,
l 4 ,
l 1 ,
l 2 ,
l 7 ,
l 8 ,
l 9 ,
l 10 ,
l 11 ,
l 12 )
,
V 4 =(
l 21 ,
l 22 ,
l 29 ,
l 30 ,
l 25 ,
l 26 ,
l 23 ,
l 24 ,
l 31 ,
l 32 ,
l 27 ,
l 28 ,
l 17 ,
l 18 ,
l 19 ,
l 20 )
,
V 5 =(
l 31 ,
l 32 ,
l 27 ,
l 28 ,
l 17 ,
l 18 ,
l 19 ,
l 20 ,
l 29 ,
l 30 ,
l 25 ,
l 26 ,
l 21 ,
l 22 ,
l 23 ,
l 24 )
,
V 6 =(
l 19 ,
l 20 ,
l 23 ,
l 24 ,
l 27 ,
l 28 ,
l 29 ,
l 30 ,
l 21 ,
l 22 ,
l 17 ,
l 18 ,
l 32 ,
l 31 ,
l 25 ,
l 26 )
,
where bits l i corresponds to vector L
=(
l 1 ,
l 2 ,...,
l 32 )
that is input of the E -box and the
. The second-type extension box E used in SCO-1
output vector is V
=(
V 1 ,
V 2 ,...,
V 6 )
is specified as follows: E (
L >>> 16
,where L >>> k
L
)=
E
(
)
denotes rotation of the word
L by k bits:
i
∈{
1
,...,
n
k
}
we have
y i =
x i + k and
i
∈{
n
k
+
1
,...,
n
}
we have
y i =
x i + k n . The extension boxes has been constructed in accordance with the following
criteria:
1. Let X be the input n-bit vector of the box S ( e )
32;96 . Then for all L and i the bit x i
should be permuted depending on six different bits of L.
2. For all i the bit l i should define exactly three bits of V .
The generalized encryption procedure is described as follows.
1. Perform the initial transformation (IT): A :
=
A
G 0 B :
=
B
T 0 ,where A and B
are input 32-bit data subblocks.
2. For rounds r
Using the round subkeys K r , G r ,and T r perform the
round transformation and then swap data subblocks
=
1to8do
{
.
3. Swap data subblocks and perform the final transformation (FT): A :
}
=
A
G 9 ,
B :
=
B
T 9 .
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