<s>
well	O
known	O
and	O
popular	O
cipher	O
RC4	B-Algorithm
designed	O
by	O
Ron	O
Rivest	O
.	O
</s>
<s>
VMPC	O
is	O
a	O
modification	O
of	O
the	O
RC4	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
The	O
core	O
of	O
the	O
cipher	O
is	O
the	O
VMPC	O
function	O
,	O
a	O
transformation	O
of	O
n-element	O
permutations	B-Algorithm
defined	O
as	O
:	O
</s>
<s>
According	O
to	O
computer	O
simulations	O
the	O
average	O
number	O
of	O
operations	O
required	O
to	O
recover	O
from	O
for	O
a	O
16-element	O
permutation	B-Algorithm
is	O
about	O
211	O
;	O
for	O
64-element	O
permutation	B-Algorithm
,	O
about	O
253	O
;	O
and	O
for	O
a	O
256-element	O
permutation	B-Algorithm
,	O
about	O
2260	O
.	O
</s>
<s>
The	O
VMPC	O
function	O
is	O
used	O
in	O
an	O
encryption	O
algorithm	O
–	O
the	O
VMPC	O
stream	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
Where	O
256-element	O
permutation	B-Algorithm
and	O
integer	O
value	O
are	O
obtained	O
from	O
the	O
encryption	O
password	O
using	O
the	O
VMPC-KSA	O
(	O
Key	O
Scheduling	O
Algorithm	O
)	O
.	O
</s>
