<s>
Phelix	B-Algorithm
is	O
a	O
high-speed	O
stream	B-Algorithm
cipher	I-Algorithm
with	O
a	O
built-in	O
single-pass	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
(	O
MAC	O
)	O
functionality	O
,	O
submitted	O
in	O
2004	O
to	O
the	O
eSTREAM	O
contest	O
by	O
Doug	O
Whiting	O
,	O
Bruce	O
Schneier	O
,	O
Stefan	O
Lucks	O
,	O
and	O
Frédéric	O
Muller	O
.	O
</s>
<s>
Phelix	B-Algorithm
uses	O
a	O
256-bit	O
key	O
and	O
a	O
128-bit	O
nonce	O
,	O
claiming	O
a	O
design	O
strength	O
of	O
128	O
bits	O
.	O
</s>
<s>
Phelix	B-Algorithm
is	O
optimised	O
for	O
32-bit	O
platforms	O
.	O
</s>
<s>
The	O
authors	O
state	O
that	O
it	O
can	O
achieve	O
up	O
to	O
eight	O
cycles	O
per	O
byte	O
on	O
modern	O
x86-based	O
processors	O
.	O
</s>
<s>
FPGA	O
Hardware	O
performance	O
figures	O
published	O
in	O
the	O
paper	O
"	O
Review	O
of	O
stream	B-Algorithm
cipher	I-Algorithm
candidates	O
from	O
a	O
low	O
resource	O
hardware	O
perspective	O
"	O
are	O
as	O
follows	O
:	O
</s>
<s>
Phelix	B-Algorithm
is	O
a	O
slightly	O
modified	O
form	O
of	O
an	O
earlier	O
cipher	O
,	O
Helix	O
,	O
published	O
in	O
2003	O
by	O
Niels	O
Ferguson	O
,	O
Doug	O
Whiting	O
,	O
Bruce	O
Schneier	O
,	O
John	O
Kelsey	O
,	O
Stefan	O
Lucks	O
,	O
and	O
Tadayoshi	O
Kohno	O
;	O
Phelix	B-Algorithm
adds	O
128	O
bits	O
to	O
the	O
internal	O
state	O
.	O
</s>
<s>
Phelix	B-Algorithm
's	O
design	O
was	O
largely	O
motivated	O
by	O
Muller	O
's	O
differential	O
attack	O
.	O
</s>
<s>
Phelix	B-Algorithm
was	O
selected	O
as	O
a	O
Phase	O
2	O
Focus	O
Candidate	O
for	O
both	O
Profile	O
1	O
and	O
Profile	O
2	O
by	O
the	O
eSTREAM	O
project	O
.	O
</s>
<s>
The	O
authors	O
of	O
Phelix	B-Algorithm
classify	O
the	O
cipher	O
as	O
an	O
experimental	O
design	O
in	O
its	O
specifications	O
.	O
</s>
<s>
The	O
authors	O
advise	O
that	O
Phelix	B-Algorithm
should	O
not	O
be	O
used	O
until	O
it	O
had	O
received	O
additional	O
cryptanalysis	O
.	O
</s>
<s>
Phelix	B-Algorithm
was	O
not	O
advanced	O
to	O
Phase	O
3	O
,	O
largely	O
because	O
of	O
Wu	O
and	O
Preneel	O
's	O
key-recovery	O
attack	O
noted	O
below	O
that	O
becomes	O
possible	O
when	O
the	O
prohibition	O
against	O
reusing	O
a	O
nonce	O
is	O
violated	O
.	O
</s>
<s>
The	O
first	O
cryptanalytic	O
paper	O
on	O
Phelix	B-Algorithm
was	O
a	O
chosen-key	B-General_Concept
distinguishing	I-General_Concept
attack	I-General_Concept
,	O
published	O
in	O
October	O
2006	O
.	O
</s>
<s>
Doug	O
Whiting	O
has	O
reviewed	O
the	O
attack	O
and	O
notes	O
that	O
while	O
the	O
paper	O
is	O
clever	O
,	O
the	O
attack	O
unfortunately	O
relies	O
on	O
incorrect	O
assumptions	O
concerning	O
the	O
initialisation	O
of	O
the	O
Phelix	B-Algorithm
cipher	O
.	O
</s>
<s>
A	O
second	O
cryptanalytic	O
paper	O
on	O
Phelix	B-Algorithm
titled	O
"	O
Differential	O
Attacks	O
against	O
Phelix	B-Algorithm
"	O
was	O
published	O
on	O
26	O
November	O
2006	O
by	O
Hongjun	O
Wu	O
and	O
Bart	O
Preneel	O
.	O
</s>
<s>
The	O
paper	O
shows	O
that	O
if	O
the	O
cipher	O
is	O
used	O
incorrectly	O
(	O
nonces	O
reused	O
)	O
,	O
the	O
key	O
of	O
Phelix	B-Algorithm
can	O
be	O
recovered	O
with	O
about	O
237	O
operations	O
,	O
234	O
chosen	O
nonces	O
and	O
238.2	O
chosen	O
plaintext	O
words	O
.	O
</s>
<s>
The	O
authors	O
of	O
the	O
differential	O
attack	O
express	O
concern	O
that	O
each	O
plaintext	O
word	O
affects	O
the	O
keystream	B-Algorithm
without	O
passing	O
through	O
(	O
what	O
they	O
consider	O
to	O
be	O
)	O
sufficient	O
confusion	O
and	O
diffusion	O
layers	O
.	O
</s>
<s>
They	O
claim	O
this	O
is	O
an	O
intrinsic	O
weakness	O
in	O
the	O
structure	O
of	O
Helix	O
and	O
Phelix	B-Algorithm
.	O
</s>
<s>
The	O
authors	O
conclude	O
that	O
they	O
consider	O
Phelix	B-Algorithm
to	O
be	O
insecure	O
.	O
</s>
