<s>
A	O
stream	B-Algorithm
cipher	I-Algorithm
is	O
a	O
symmetric	B-Algorithm
key	I-Algorithm
cipher	B-Application
where	O
plaintext	O
digits	O
are	O
combined	O
with	O
a	O
pseudorandom	B-Error_Name
cipher	B-Application
digit	O
stream	O
(	O
keystream	B-Algorithm
)	O
.	O
</s>
<s>
In	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
,	O
each	O
plaintext	O
digit	O
is	O
encrypted	O
one	O
at	O
a	O
time	O
with	O
the	O
corresponding	O
digit	O
of	O
the	O
keystream	B-Algorithm
,	O
to	O
give	O
a	O
digit	O
of	O
the	O
ciphertext	O
stream	O
.	O
</s>
<s>
Since	O
encryption	O
of	O
each	O
digit	O
is	O
dependent	O
on	O
the	O
current	O
state	O
of	O
the	O
cipher	B-Application
,	O
it	O
is	O
also	O
known	O
as	O
state	O
cipher	B-Application
.	O
</s>
<s>
The	O
pseudorandom	B-Error_Name
keystream	B-Algorithm
is	O
typically	O
generated	O
serially	O
from	O
a	O
random	O
seed	B-Algorithm
value	I-Algorithm
using	O
digital	O
shift	B-General_Concept
registers	I-General_Concept
.	O
</s>
<s>
The	O
seed	B-Algorithm
value	I-Algorithm
serves	O
as	O
the	O
cryptographic	O
key	O
for	O
decrypting	O
the	O
ciphertext	O
stream	O
.	O
</s>
<s>
Stream	B-Algorithm
ciphers	I-Algorithm
represent	O
a	O
different	O
approach	O
to	O
symmetric	B-Algorithm
encryption	I-Algorithm
from	O
block	O
ciphers	B-Application
.	O
</s>
<s>
Block	O
ciphers	B-Application
operate	O
on	O
large	O
blocks	O
of	O
digits	O
with	O
a	O
fixed	O
,	O
unvarying	O
transformation	O
.	O
</s>
<s>
This	O
distinction	O
is	O
not	O
always	O
clear-cut	O
:	O
in	O
some	O
modes	B-Algorithm
of	I-Algorithm
operation	I-Algorithm
,	O
a	O
block	O
cipher	B-Application
primitive	O
is	O
used	O
in	O
such	O
a	O
way	O
that	O
it	O
acts	O
effectively	O
as	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
Stream	B-Algorithm
ciphers	I-Algorithm
typically	O
execute	O
at	O
a	O
higher	O
speed	O
than	O
block	O
ciphers	B-Application
and	O
have	O
lower	O
hardware	O
complexity	O
.	O
</s>
<s>
However	O
,	O
stream	B-Algorithm
ciphers	I-Algorithm
can	O
be	O
susceptible	O
to	O
security	O
breaches	O
(	O
see	O
stream	B-Algorithm
cipher	I-Algorithm
attacks	O
)	O
;	O
for	O
example	O
,	O
when	O
the	O
same	O
starting	O
state	O
(	O
seed	O
)	O
is	O
used	O
twice	O
.	O
</s>
<s>
Stream	B-Algorithm
ciphers	I-Algorithm
can	O
be	O
viewed	O
as	O
approximating	O
the	O
action	O
of	O
a	O
proven	O
unbreakable	O
cipher	B-Application
,	O
the	O
one-time	B-Algorithm
pad	I-Algorithm
(	O
OTP	O
)	O
.	O
</s>
<s>
A	O
one-time	B-Algorithm
pad	I-Algorithm
uses	O
a	O
keystream	B-Algorithm
of	O
completely	O
random	O
digits	O
.	O
</s>
<s>
The	O
keystream	B-Algorithm
is	O
combined	O
with	O
the	O
plaintext	O
digits	O
one	O
at	O
a	O
time	O
to	O
form	O
the	O
ciphertext	O
.	O
</s>
<s>
However	O
,	O
the	O
keystream	B-Algorithm
must	O
be	O
generated	O
completely	O
at	O
random	O
with	O
at	O
least	O
the	O
same	O
length	O
as	O
the	O
plaintext	O
and	O
cannot	O
be	O
used	O
more	O
than	O
once	O
.	O
</s>
<s>
This	O
makes	O
the	O
system	O
cumbersome	O
to	O
implement	O
in	O
many	O
practical	O
applications	O
,	O
and	O
as	O
a	O
result	O
the	O
one-time	B-Algorithm
pad	I-Algorithm
has	O
not	O
been	O
widely	O
used	O
,	O
except	O
for	O
the	O
most	O
critical	O
applications	O
.	O
</s>
<s>
A	O
stream	B-Algorithm
cipher	I-Algorithm
makes	O
use	O
of	O
a	O
much	O
smaller	O
and	O
more	O
convenient	O
key	O
such	O
as	O
128	O
bits	O
.	O
</s>
<s>
Based	O
on	O
this	O
key	O
,	O
it	O
generates	O
a	O
pseudorandom	B-Error_Name
keystream	B-Algorithm
which	O
can	O
be	O
combined	O
with	O
the	O
plaintext	O
digits	O
in	O
a	O
similar	O
fashion	O
to	O
the	O
one-time	B-Algorithm
pad	I-Algorithm
.	O
</s>
<s>
The	O
keystream	B-Algorithm
is	O
now	O
pseudorandom	B-Error_Name
and	O
so	O
is	O
not	O
truly	O
random	O
.	O
</s>
<s>
The	O
proof	O
of	O
security	O
associated	O
with	O
the	O
one-time	B-Algorithm
pad	I-Algorithm
no	O
longer	O
holds	O
.	O
</s>
<s>
It	O
is	O
quite	O
possible	O
for	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
to	O
be	O
completely	O
insecure	O
.	O
</s>
<s>
A	O
stream	B-Algorithm
cipher	I-Algorithm
generates	O
successive	O
elements	O
of	O
the	O
keystream	B-Algorithm
based	O
on	O
an	O
internal	O
state	O
.	O
</s>
<s>
This	O
state	O
is	O
updated	O
in	O
essentially	O
two	O
ways	O
:	O
if	O
the	O
state	O
changes	O
independently	O
of	O
the	O
plaintext	O
or	O
ciphertext	O
messages	O
,	O
the	O
cipher	B-Application
is	O
classified	O
as	O
a	O
synchronous	O
stream	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
By	O
contrast	O
,	O
self-synchronising	O
stream	B-Algorithm
ciphers	I-Algorithm
update	O
their	O
state	O
based	O
on	O
previous	O
ciphertext	O
digits	O
.	O
</s>
<s>
In	O
a	O
synchronous	O
stream	B-Algorithm
cipher	I-Algorithm
a	O
stream	O
of	O
pseudorandom	B-Error_Name
digits	O
is	O
generated	O
independently	O
of	O
the	O
plaintext	O
and	O
ciphertext	O
messages	O
,	O
and	O
then	O
combined	O
with	O
the	O
plaintext	O
(	O
to	O
encrypt	O
)	O
or	O
the	O
ciphertext	O
(	O
to	O
decrypt	O
)	O
.	O
</s>
<s>
In	O
the	O
most	O
common	O
form	O
,	O
binary	O
digits	O
are	O
used	O
(	O
bits	O
)	O
,	O
and	O
the	O
keystream	B-Algorithm
is	O
combined	O
with	O
the	O
plaintext	O
using	O
the	O
exclusive	O
or	O
operation	O
(	O
XOR	O
)	O
.	O
</s>
<s>
This	O
is	O
termed	O
a	O
binary	O
additive	O
stream	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
In	O
a	O
synchronous	O
stream	B-Algorithm
cipher	I-Algorithm
,	O
the	O
sender	O
and	O
receiver	O
must	O
be	O
exactly	O
in	O
step	O
for	O
decryption	O
to	O
be	O
successful	O
.	O
</s>
<s>
Moreover	O
,	O
because	O
of	O
this	O
property	O
,	O
synchronous	O
stream	B-Algorithm
ciphers	I-Algorithm
are	O
very	O
susceptible	O
to	O
active	O
attacks	O
:	O
if	O
an	O
attacker	O
can	O
change	O
a	O
digit	O
in	O
the	O
ciphertext	O
,	O
they	O
might	O
be	O
able	O
to	O
make	O
predictable	O
changes	O
to	O
the	O
corresponding	O
plaintext	O
bit	O
;	O
for	O
example	O
,	O
flipping	O
a	O
bit	O
in	O
the	O
ciphertext	O
causes	O
the	O
same	O
bit	O
to	O
be	O
flipped	O
in	O
the	O
plaintext	O
.	O
</s>
<s>
Another	O
approach	O
uses	O
several	O
of	O
the	O
previous	O
N	O
ciphertext	O
digits	O
to	O
compute	O
the	O
keystream	B-Algorithm
.	O
</s>
<s>
Such	O
schemes	O
are	O
known	O
as	O
self-synchronizing	B-Algorithm
stream	I-Algorithm
ciphers	I-Algorithm
,	O
asynchronous	O
stream	B-Algorithm
ciphers	I-Algorithm
or	O
ciphertext	O
autokey	O
(	O
CTAK	O
)	O
.	O
</s>
<s>
The	O
idea	O
of	O
self-synchronization	O
was	O
patented	O
in	O
1946	O
and	O
has	O
the	O
advantage	O
that	O
the	O
receiver	O
will	O
automatically	O
synchronise	O
with	O
the	O
keystream	B-Algorithm
generator	O
after	O
receiving	O
N	O
ciphertext	O
digits	O
,	O
making	O
it	O
easier	O
to	O
recover	O
if	O
digits	O
are	O
dropped	O
or	O
added	O
to	O
the	O
message	O
stream	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
self-synchronising	O
stream	B-Algorithm
cipher	I-Algorithm
is	O
a	O
block	O
cipher	B-Application
in	O
cipher	B-Application
feedback	O
(	O
CFB	O
)	O
mode	B-Algorithm
.	O
</s>
<s>
Binary	O
stream	B-Algorithm
ciphers	I-Algorithm
are	O
often	O
constructed	O
using	O
linear-feedback	B-Architecture
shift	I-Architecture
registers	I-Architecture
(	O
LFSRs	B-Architecture
)	O
because	O
they	O
can	O
be	O
easily	O
implemented	O
in	O
hardware	O
and	O
can	O
be	O
readily	O
analysed	O
mathematically	O
.	O
</s>
<s>
The	O
use	O
of	O
LFSRs	B-Architecture
on	O
their	O
own	O
,	O
however	O
,	O
is	O
insufficient	O
to	O
provide	O
good	O
security	O
.	O
</s>
<s>
Various	O
schemes	O
have	O
been	O
proposed	O
to	O
increase	O
the	O
security	O
of	O
LFSRs	B-Architecture
.	O
</s>
<s>
Because	O
LFSRs	B-Architecture
are	O
inherently	O
linear	O
,	O
one	O
technique	O
for	O
removing	O
the	O
linearity	O
is	O
to	O
feed	O
the	O
outputs	O
of	O
several	O
parallel	O
LFSRs	B-Architecture
into	O
a	O
non-linear	O
Boolean	O
function	O
to	O
form	O
a	O
combination	O
generator	O
.	O
</s>
<s>
Normally	O
LFSRs	B-Architecture
are	O
stepped	O
regularly	O
.	O
</s>
<s>
One	O
approach	O
to	O
introducing	O
non-linearity	O
is	O
to	O
have	O
the	O
LFSR	B-Architecture
clocked	O
irregularly	O
,	O
controlled	O
by	O
the	O
output	O
of	O
a	O
second	O
LFSR	B-Architecture
.	O
</s>
<s>
Such	O
generators	O
include	O
the	O
stop-and-go	O
generator	O
,	O
the	O
alternating	B-Algorithm
step	I-Algorithm
generator	I-Algorithm
and	O
the	O
shrinking	B-Algorithm
generator	I-Algorithm
.	O
</s>
<s>
An	O
alternating	B-Algorithm
step	I-Algorithm
generator	I-Algorithm
comprises	O
three	O
LFSRs	B-Architecture
,	O
which	O
we	O
will	O
call	O
LFSR0	O
,	O
LFSR1	O
and	O
LFSR2	O
for	O
convenience	O
.	O
</s>
<s>
The	O
initial	O
state	O
of	O
the	O
three	O
LFSRs	B-Architecture
is	O
the	O
key	O
.	O
</s>
<s>
The	O
stop-and-go	O
generator	O
(	O
Beth	O
and	O
Piper	O
,	O
1984	O
)	O
consists	O
of	O
two	O
LFSRs	B-Architecture
.	O
</s>
<s>
One	O
LFSR	B-Architecture
is	O
clocked	O
if	O
the	O
output	O
of	O
a	O
second	O
is	O
a	O
1	O
,	O
otherwise	O
it	O
repeats	O
its	O
previous	O
output	O
.	O
</s>
<s>
This	O
output	O
is	O
then	O
(	O
in	O
some	O
versions	O
)	O
combined	O
with	O
the	O
output	O
of	O
a	O
third	O
LFSR	B-Architecture
clocked	O
at	O
a	O
regular	O
rate	O
.	O
</s>
<s>
The	O
shrinking	B-Algorithm
generator	I-Algorithm
takes	O
a	O
different	O
approach	O
.	O
</s>
<s>
Two	O
LFSRs	B-Architecture
are	O
used	O
,	O
both	O
clocked	O
regularly	O
.	O
</s>
<s>
If	O
the	O
output	O
of	O
the	O
first	O
LFSR	B-Architecture
is	O
1	O
,	O
the	O
output	O
of	O
the	O
second	O
LFSR	B-Architecture
becomes	O
the	O
output	O
of	O
the	O
generator	O
.	O
</s>
<s>
If	O
the	O
first	O
LFSR	B-Architecture
outputs	O
0	O
,	O
however	O
,	O
the	O
output	O
of	O
the	O
second	O
is	O
discarded	O
,	O
and	O
no	O
bit	O
is	O
output	O
by	O
the	O
generator	O
.	O
</s>
<s>
Another	O
approach	O
to	O
improving	O
the	O
security	O
of	O
an	O
LFSR	B-Architecture
is	O
to	O
pass	O
the	O
entire	O
state	O
of	O
a	O
single	O
LFSR	B-Architecture
into	O
a	O
non-linear	O
filtering	O
function	O
.	O
</s>
<s>
For	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
to	O
be	O
secure	O
,	O
its	O
keystream	B-Algorithm
must	O
have	O
a	O
large	O
period	O
,	O
and	O
it	O
must	O
be	O
impossible	O
to	O
recover	O
the	O
cipher	B-Application
's	O
key	O
or	O
internal	O
state	O
from	O
the	O
keystream	B-Algorithm
.	O
</s>
<s>
Cryptographers	O
also	O
demand	O
that	O
the	O
keystream	B-Algorithm
be	O
free	O
of	O
even	O
subtle	O
biases	O
that	O
would	O
let	O
attackers	O
distinguish	O
a	O
stream	O
from	O
random	O
noise	O
,	O
and	O
free	O
of	O
detectable	O
relationships	O
between	O
keystreams	B-Algorithm
that	O
correspond	O
to	O
related	O
keys	O
or	O
related	O
cryptographic	O
nonces	O
.	O
</s>
<s>
As	O
with	O
other	O
attacks	O
in	O
cryptography	O
,	O
stream	B-Algorithm
cipher	I-Algorithm
attacks	O
can	O
be	O
certificational	O
so	O
they	O
are	O
not	O
necessarily	O
practical	O
ways	O
to	O
break	O
the	O
cipher	B-Application
but	O
indicate	O
that	O
the	O
cipher	B-Application
might	O
have	O
other	O
weaknesses	O
.	O
</s>
<s>
Securely	O
using	O
a	O
secure	O
synchronous	O
stream	B-Algorithm
cipher	I-Algorithm
requires	O
that	O
one	O
never	O
reuse	O
the	O
same	O
keystream	B-Algorithm
twice	O
.	O
</s>
<s>
That	O
generally	O
means	O
a	O
different	O
nonce	O
or	O
key	O
must	O
be	O
supplied	O
to	O
each	O
invocation	O
of	O
the	O
cipher	B-Application
.	O
</s>
<s>
Application	O
designers	O
must	O
also	O
recognize	O
that	O
most	O
stream	B-Algorithm
ciphers	I-Algorithm
provide	O
not	O
authenticity	O
but	O
privacy	O
:	O
encrypted	O
messages	O
may	O
still	O
have	O
been	O
modified	O
in	O
transit	O
.	O
</s>
<s>
Short	O
periods	O
for	O
stream	B-Algorithm
ciphers	I-Algorithm
have	O
been	O
a	O
practical	O
concern	O
.	O
</s>
<s>
For	O
example	O
,	O
64-bit	B-Device
block	O
ciphers	B-Application
like	O
DES	B-Algorithm
can	O
be	O
used	O
to	O
generate	O
a	O
keystream	B-Algorithm
in	O
output	O
feedback	O
(	O
OFB	O
)	O
mode	B-Algorithm
.	O
</s>
<s>
Some	O
applications	O
using	O
the	O
stream	B-Algorithm
cipher	I-Algorithm
RC4	B-Algorithm
are	O
attackable	O
because	O
of	O
weaknesses	O
in	O
RC4	B-Algorithm
's	O
key	O
setup	O
routine	O
;	O
new	O
applications	O
should	O
either	O
avoid	O
RC4	B-Algorithm
or	O
make	O
sure	O
all	O
keys	O
are	O
unique	O
and	O
ideally	O
unrelated	O
(	O
such	O
as	O
generated	O
by	O
a	O
well-seeded	O
CSPRNG	B-Algorithm
or	O
a	O
cryptographic	B-Algorithm
hash	I-Algorithm
function	I-Algorithm
)	O
and	O
that	O
the	O
first	O
bytes	O
of	O
the	O
keystream	B-Algorithm
are	O
discarded	O
.	O
</s>
<s>
The	O
elements	O
of	O
stream	B-Algorithm
ciphers	I-Algorithm
are	O
often	O
much	O
simpler	O
to	O
understand	O
than	O
block	O
ciphers	B-Application
and	O
are	O
thus	O
less	O
likely	O
to	O
hide	O
any	O
accidental	O
or	O
malicious	O
weaknesses	O
.	O
</s>
<s>
Stream	B-Algorithm
ciphers	I-Algorithm
are	O
often	O
used	O
for	O
their	O
speed	O
and	O
simplicity	O
of	O
implementation	O
in	O
hardware	O
,	O
and	O
in	O
applications	O
where	O
plaintext	O
comes	O
in	O
quantities	O
of	O
unknowable	O
length	O
like	O
a	O
secure	O
wireless	B-General_Concept
connection	I-General_Concept
.	O
</s>
<s>
If	O
a	O
block	O
cipher	B-Application
(	O
not	O
operating	O
in	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
mode	B-Algorithm
)	O
were	O
to	O
be	O
used	O
in	O
this	O
type	O
of	O
application	O
,	O
the	O
designer	O
would	O
need	O
to	O
choose	O
either	O
transmission	O
efficiency	O
or	O
implementation	O
complexity	O
,	O
since	O
block	O
ciphers	B-Application
cannot	O
directly	O
work	O
on	O
blocks	O
shorter	O
than	O
their	O
block	O
size	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
128-bit	O
block	O
cipher	B-Application
received	O
separate	O
32-bit	O
bursts	O
of	O
plaintext	O
,	O
three	O
quarters	O
of	O
the	O
data	O
transmitted	O
would	O
be	O
padding	B-Algorithm
.	O
</s>
<s>
Block	O
ciphers	B-Application
must	O
be	O
used	O
in	O
ciphertext	B-Algorithm
stealing	I-Algorithm
or	O
residual	B-Algorithm
block	I-Algorithm
termination	I-Algorithm
mode	B-Algorithm
to	O
avoid	O
padding	B-Algorithm
,	O
while	O
stream	B-Algorithm
ciphers	I-Algorithm
eliminate	O
this	O
issue	O
by	O
naturally	O
operating	O
on	O
the	O
smallest	O
unit	O
that	O
can	O
be	O
transmitted	O
(	O
usually	O
bytes	O
)	O
.	O
</s>
<s>
Another	O
advantage	O
of	O
stream	B-Algorithm
ciphers	I-Algorithm
in	O
military	O
cryptography	O
is	O
that	O
the	O
cipher	B-Application
stream	O
can	O
be	O
generated	O
in	O
a	O
separate	O
box	O
that	O
is	O
subject	O
to	O
strict	O
security	O
measures	O
and	O
fed	O
to	O
other	O
devices	O
such	O
as	O
a	O
radio	O
set	O
,	O
which	O
will	O
perform	O
the	O
XOR	O
operation	O
as	O
part	O
of	O
their	O
function	O
.	O
</s>
<s>
ChaCha	O
is	O
becoming	O
the	O
most	O
widely	O
used	O
stream	B-Algorithm
cipher	I-Algorithm
in	O
software	O
;	O
others	O
include	O
:	O
</s>
<s>
RC4	B-Algorithm
,	O
</s>
<s>
A5/1	B-Algorithm
,	O
</s>
<s>
A5/2	B-Algorithm
,	O
</s>
<s>
FISH	B-Algorithm
,	O
</s>
<s>
ISAAC	B-Algorithm
,	O
</s>
<s>
MUGI	B-Algorithm
,	O
</s>
<s>
Panama	B-Algorithm
,	O
</s>
<s>
Phelix	B-Algorithm
,	O
</s>
<s>
Pike	B-Algorithm
,	O
</s>
<s>
Salsa20	B-Algorithm
,	O
</s>
<s>
SEAL	B-Algorithm
,	O
</s>
<s>
SOBER	B-Algorithm
,	O
</s>
<s>
SOBER-128	B-Algorithm
,	O
</s>
<s>
WAKE	B-Algorithm
.	O
</s>
<s>
StreamcipherCreationdate	O
Speed(cycles per byte )	O
(	O
bits	O
)	O
AttackEffectivekey-length	O
Initialization	B-Algorithm
vector	I-Algorithm
InternalstateBest	O
known	O
ComputationalcomplexityA5/1198954	O
or	O
64	O
(	O
in	O
2G	O
)	O
22	O
(	O
in	O
2G	O
)	O
64Active	O
KPA	O
ORKPA	O
time	O
–	O
memory	O
tradeoff	O
~	O
2	O
seconds	O
OR239.91A5/219895411464	O
?	O
Active4.6	O
milliseconds	O
Achterbahn-128/8020061	O
(	O
hardware	O
)	O
80/12880/128297/351Brute	O
force	O
for	O
frame	O
lengths	O
L	O
≤	O
244	O
.	O
</s>
<s>
2128	O
for	O
L	O
≤	O
244.CryptMT2005	O
Variable	O
up	O
to	O
19968	O
19968	O
(	O
2008	O
)	O
(	O
2008	O
)	O
Crypto-1Pre-1994	O
48	O
16	O
48	O
Active	O
KPA	O
(	O
2008	O
)	O
40	O
ms	O
OR248	O
(	O
2008	O
)	O
E0	B-Algorithm
(	O
cipher	B-Application
)	O
Pre-1999	O
Variable(usually 128 )	O
4	O
132	O
KPA	O
(	O
2005	O
)	O
238	O
(	O
2005	O
)	O
FISH1993VariableKnown-plaintext	O
attack211Grain	O
Pre-20048064160Key	O
derivation243HC-256	O
Pre-20044	O
(	O
WP4	O
)	O
25625665536ISAAC19962.375	O
(	O
W64-bit	O
)	O
–	O
4.6875	O
(	O
W32-bit	O
)	O
8	O
–	O
8288( usually	O
40	O
–	O
256	O
)	O
8288(2006 )	O
First-roundweak-internal-state-derivation4.67	O
×101240	O
(	O
2001	O
)	O
MICKEYPre-2004	O
80	O
Variable	O
(	O
0	O
to	O
80	O
)	O
200	O
Differential	O
Fault	O
Attack	O
(	O
2013	O
)	O
232.5	O
(	O
2013	O
)	O
MUGI1998	O
–	O
20021281281216	O
(	O
2002	O
)	O
~	O
282PANAMA19982256128	O
?	O
1216	O
?	O
Hash	B-Algorithm
collisions	O
(	O
2001	O
)	O
282Phelix	O
Pre-2004	O
up	O
to	O
8	O
(	O
Wx86	O
)	O
256	O
+	O
a	O
128-bit	O
nonce128	O
?	O
Differential	O
(	O
2006	O
)	O
237Pike1994Variable	O
(	O
2004	O
)	O
(	O
2004	O
)	O
Py	B-Algorithm
Pre-20042.68	O
–	O
2048	O
?	O
</s>
<s>
)	O
648320Cryptanalytic	O
theory	O
(	O
2006	O
)	O
275Rabbit2003-Feb3.7(WP3 )	O
–	O
9.7(WARM7 )	O
12864512	O
(	O
2006	O
)	O
(	O
2006	O
)	O
RC419877	O
WP58	O
–	O
2048( usually	O
40	O
–	O
256	O
)	O
RC4	B-Algorithm
does	O
not	O
take	O
an	O
IV	O
.	O
</s>
<s>
United	O
States	O
National	O
Security	O
Agency	O
documents	O
sometimes	O
use	O
the	O
term	O
combiner-type	B-Algorithm
algorithms	I-Algorithm
,	O
referring	O
to	O
algorithms	O
that	O
use	O
some	O
function	O
to	O
combine	O
a	O
pseudorandom	B-Algorithm
number	I-Algorithm
generator	I-Algorithm
(	O
PRNG	O
)	O
with	O
a	O
plaintext	O
stream	O
.	O
</s>
