Information Technology Reference
In-Depth Information
a)
B
c)
A
b)
B
A
A
B
32
32
Crypt
(e)
+
32
G
r
T
r
G
r
T
r
Crypt
(e)
32
>>>8
A'
96
(
A
'
,
e
1
)
E
S
32;96
A'
(
A
'
,
e'
)
Crypt
(e)
E
S
32;96
96
B'
(
B'
,
e
2
)
E
S
32;96
Fi
na
l
transformation
>>>8
96
e
1,2
=
e
1,2
(
e
,
r
)
e'
=
e'
(
e
,
r
)
Fig. 6.
Firmware-suitable ciphers: a
−
SCO-2, b
−
SCO-3, c
−
outline of encryption
Ta b l e 3 .
SCO-2 and SCO-3: Specification of the switching bits and round subkeys
e
=
1
∗
e
=
1
∗∗
Round
e
=
0
e
=
0
e
=
1
e
e
r
G
r
T
r
G
r
T
r
G
r
T
r
e
1
e
2
e
1
e
2
1
Q
1
Q
2
Q
2
Q
3
Q
2
Q
3
1
0
1
0
1
1
2
Q
3
Q
4
Q
4
Q
1
Q
1
Q
4
0
0
0
1
0
0
3
Q
3
Q
2
Q
2
Q
3
Q
3
Q
2
1
1
1
0
0
0
4
Q
4
Q
1
Q
1
Q
4
Q
4
Q
1
0
1
0
1
0
0
5
Q
4
Q
3
Q
1
Q
3
Q
3
Q
1
1
0
1
1
1
1
6
Q
1
Q
2
Q
2
Q
4
Q
4
Q
2
1
1
1
0
1
1
7
Q
4
Q
3
Q
3
Q
4
Q
4
Q
3
0
1
0
0
0
0
8
Q
4
Q
2
Q
2
Q
1
Q
1
Q
2
0
0
0
1
0
0
9
Q
3
Q
1
Q
3
Q
4
Q
4
Q
3
1
0
1
0
1
1
10
Q
4
Q
1
Q
1
Q
4
Q
4
Q
1
1
1
1
0
0
0
11
Q
3
Q
2
Q
2
Q
3
Q
3
Q
2
1
0
1
1
1
1
12
Q
1
Q
4
Q
4
Q
3
Q
3
Q
4
0
1
0
1
0
0
FT
Q
2
Q
3
Q
1
Q
2
Q
1
Q
2
-
-
-
-
-
-
=(
,
,
,
)
SCO-3 (b) working with the 128-bit key
Q
. The generalized en-
cryption scheme of the both ciphers is represented in Fig. 6(c). The FT in SCO-2 is
performed as swapping subblocks and performing two XOR operations:
A
:
Q
1
Q
2
Q
3
Q
4
=
⊕
A
G
13
and
B
:
=
B
⊕
T
13
. In SCO-3 the FT is performed as follows:
A
:
=
A
−
32
G
13
and
B
:
=
−
n
”) denote addition (subtraction) modulo 2
n
.Table3presents
the key scheduling and specification of the switching bits for SCO-2 and SCO-3. The
ciphers use identical key scheduling for encryption, however for decryption SCO-2 and
SCO-3 use different key scheduling. Key scheduling marked with token
B
+
32
T
13
,where“
+
n
”(“
∗
(
∗∗
) corre-
sponds to SCO-3 (SCO-2).
