<s>
In	O
cryptography	O
,	O
Skipjack	B-Algorithm
is	O
a	O
block	O
cipher	B-Application
—	O
an	O
algorithm	O
for	O
encryption	O
—	O
developed	O
by	O
the	O
U.S.	O
National	O
Security	O
Agency	O
(	O
NSA	O
)	O
.	O
</s>
<s>
Skipjack	B-Algorithm
was	O
proposed	O
as	O
the	O
encryption	O
algorithm	O
in	O
a	O
US	O
government-sponsored	O
scheme	O
of	O
key	O
escrow	O
,	O
and	O
the	O
cipher	B-Application
was	O
provided	O
for	O
use	O
in	O
the	O
Clipper	O
chip	O
,	O
implemented	O
in	O
tamperproof	O
hardware	O
.	O
</s>
<s>
Skipjack	B-Algorithm
is	O
used	O
only	O
for	O
encryption	O
;	O
the	O
key	O
escrow	O
is	O
achieved	O
through	O
the	O
use	O
of	O
a	O
separate	O
mechanism	O
known	O
as	O
the	O
Law	O
Enforcement	O
Access	O
Field	O
(	O
LEAF	O
)	O
.	O
</s>
<s>
Moreover	O
,	O
their	O
report	O
gave	O
some	O
insight	O
into	O
the	O
(	O
classified	O
)	O
history	O
and	O
development	O
of	O
Skipjack	B-Algorithm
:	O
</s>
<s>
In	O
March	O
2016	O
,	O
NIST	O
published	O
a	O
draft	O
of	O
its	O
cryptographic	O
standard	O
which	O
no	O
longer	O
certifies	O
Skipjack	B-Algorithm
for	O
US	O
government	O
applications	O
.	O
</s>
<s>
Skipjack	B-Algorithm
uses	O
an	O
80-bit	O
key	O
to	O
encrypt	O
or	O
decrypt	O
64-bit	O
data	O
blocks	O
.	O
</s>
<s>
It	O
is	O
an	O
unbalanced	B-Algorithm
Feistel	I-Algorithm
network	I-Algorithm
with	O
32	O
rounds	O
.	O
</s>
<s>
A	O
truncated	O
differential	O
attack	O
was	O
also	O
published	O
against	O
28	O
rounds	O
of	O
Skipjack	B-Algorithm
cipher	B-Application
.	O
</s>
<s>
A	O
claimed	O
attack	O
against	O
the	O
full	O
cipher	B-Application
was	O
published	O
in	O
2002	O
,	O
but	O
a	O
later	O
paper	O
with	O
attack	O
designer	O
as	O
a	O
co-author	O
clarified	O
in	O
2009	O
that	O
no	O
attack	O
on	O
the	O
full	O
32	O
round	O
cipher	B-Application
was	O
then	O
known	O
.	O
</s>
<s>
An	O
algorithm	O
named	O
Skipjack	B-Algorithm
forms	O
part	O
of	O
the	O
back-story	O
to	O
Dan	O
Brown	O
's	O
1998	O
novel	O
Digital	O
Fortress	O
.	O
</s>
<s>
In	O
Brown	O
's	O
novel	O
,	O
Skipjack	B-Algorithm
is	O
proposed	O
as	O
the	O
new	O
public-key	B-Application
encryption	I-Application
standard	O
,	O
along	O
with	O
a	O
back	O
door	O
secretly	O
inserted	O
by	O
the	O
NSA	O
(	O
"	O
a	O
few	O
lines	O
of	O
cunning	O
programming	O
"	O
)	O
which	O
would	O
have	O
allowed	O
them	O
to	O
decrypt	O
Skipjack	B-Algorithm
using	O
a	O
secret	O
password	O
and	O
thereby	O
"	O
read	O
the	O
world	O
's	O
email	O
"	O
.	O
</s>
<s>
When	O
details	O
of	O
the	O
cipher	B-Application
are	O
publicly	O
released	O
,	O
programmer	O
Greg	O
Hale	O
discovers	O
and	O
announces	O
details	O
of	O
the	O
backdoor	O
.	O
</s>
<s>
Additionally	O
,	O
in	O
the	O
Half-Life	B-Application
2	I-Application
modification	O
Dystopia	B-Application
,	O
the	O
"	O
encryption	O
"	O
program	O
used	O
in	O
cyberspace	O
apparently	O
uses	O
both	O
Skipjack	B-Algorithm
and	O
Blowfish	B-Algorithm
algorithms	O
.	O
</s>
