<s>
ISAAC	B-Algorithm
(	O
indirection	O
,	O
shift	O
,	O
accumulate	O
,	O
add	O
,	O
and	O
count	O
)	O
is	O
a	O
cryptographically	B-Algorithm
secure	I-Algorithm
pseudorandom	I-Algorithm
number	I-Algorithm
generator	I-Algorithm
and	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
designed	O
by	O
Robert	O
J	O
.	O
Jenkins	O
Jr.	O
in	O
1993	O
.	O
</s>
<s>
The	O
generator	O
is	O
ISAAC.	O
"	O
</s>
<s>
The	O
ISAAC	B-Algorithm
algorithm	O
has	O
similarities	O
with	O
RC4	B-Algorithm
.	O
</s>
<s>
It	O
uses	O
an	O
array	B-Data_Structure
of	O
256	O
four-octet	O
integers	O
as	O
the	O
internal	O
state	O
,	O
writing	O
the	O
results	O
to	O
another	O
256	O
four-octet	O
integer	O
array	B-Data_Structure
,	O
from	O
which	O
they	O
are	O
read	O
one	O
at	O
a	O
time	O
until	O
empty	O
,	O
at	O
which	O
point	O
they	O
are	O
recomputed	O
.	O
</s>
<s>
The	O
computation	O
consists	O
of	O
altering	O
i-element	O
with	O
(	O
i⊕128	O
)	O
-element	O
,	O
two	O
elements	O
of	O
the	O
state	O
array	B-Data_Structure
found	O
by	O
indirection	O
,	O
an	O
accumulator	O
,	O
and	O
a	O
counter	O
,	O
for	O
all	O
values	O
of	O
i	O
from	O
0	O
to	O
255	O
.	O
</s>
<s>
ISAAC	B-Algorithm
passes	O
the	O
TestU01	B-Algorithm
empirical	O
randomness	O
test	O
suite	O
.	O
</s>
<s>
This	O
result	O
has	O
had	O
no	O
practical	O
impact	O
on	O
the	O
security	O
of	O
ISAAC	B-Algorithm
.	O
</s>
<s>
The	O
fourth	O
presented	O
(	O
and	O
smallest	O
)	O
set	O
of	O
weak	O
states	O
leads	O
to	O
a	O
highly	O
biased	O
output	O
for	O
the	O
first	O
round	O
of	O
ISAAC	B-Algorithm
and	O
allows	O
the	O
derivation	O
of	O
the	O
internal	O
state	O
,	O
similar	O
to	O
a	O
weakness	O
in	O
RC4	B-Algorithm
.	O
</s>
<s>
He	O
also	O
shows	O
that	O
a	O
previous	O
attack	O
is	O
flawed	O
,	O
since	O
the	O
Paul-Preneel	O
attack	O
is	O
based	O
on	O
an	O
erroneous	O
algorithm	O
rather	O
than	O
the	O
real	O
ISAAC	B-Algorithm
.	O
</s>
<s>
An	O
improved	O
version	O
of	O
ISAAC	B-Algorithm
is	O
proposed	O
,	O
called	O
ISAAC+	O
.	O
</s>
<s>
Many	O
implementations	O
of	O
ISAAC	B-Algorithm
are	O
so	O
fast	O
that	O
they	O
can	O
compete	O
with	O
other	O
high	O
speed	O
PRNGs	O
,	O
even	O
with	O
those	O
designed	O
primarily	O
for	O
speed	O
not	O
for	O
security	O
.	O
</s>
<s>
ISAAC	B-Algorithm
is	O
used	O
in	O
the	O
Unix	O
tool	O
shred	B-Application
to	O
securely	O
overwrite	O
data	O
.	O
</s>
<s>
Also	O
ISAAC	B-Algorithm
algorithm	O
is	O
implemented	O
in	O
Java	O
Apache	O
Commons	O
Math	O
library	O
.	O
</s>
