<s>
Rambutan	B-Algorithm
is	O
a	O
family	O
of	O
encryption	O
technologies	O
designed	O
by	O
the	O
Communications-Electronics	O
Security	O
Group	O
(	O
CESG	O
)	O
,	O
the	O
technical	O
division	O
of	O
the	O
United	O
Kingdom	O
government	O
's	O
secret	O
communications	O
agency	O
,	O
GCHQ	O
.	O
</s>
<s>
Unlike	O
CESG	O
's	O
Red	B-Algorithm
Pike	I-Algorithm
system	O
,	O
Rambutan	B-Algorithm
is	O
not	O
available	O
as	O
software	O
:	O
it	O
is	O
distributed	O
only	O
as	O
a	O
self-contained	O
electronic	O
device	O
(	O
an	O
ASIC	O
)	O
which	O
implements	O
the	O
entire	O
cryptosystem	O
and	O
handles	O
the	O
related	O
key	O
distribution	O
and	O
storage	O
tasks	O
.	O
</s>
<s>
Rambutan	B-Algorithm
is	O
not	O
sold	O
outside	O
the	O
government	O
sector	O
.	O
</s>
<s>
Technical	O
details	O
of	O
the	O
Rambutan	B-Algorithm
algorithm	O
are	O
secret	O
.	O
</s>
<s>
Security	O
researcher	O
Bruce	O
Schneier	O
describes	O
it	O
as	O
being	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
(	O
linear-feedback	B-Architecture
shift	I-Architecture
register	I-Architecture
)	O
based	O
cryptosystem	O
with	O
5	O
shift	B-General_Concept
registers	I-General_Concept
each	O
of	O
around	O
80	O
bits	O
,	O
and	O
a	O
key	O
size	O
of	O
112	O
bits	O
.	O
</s>
<s>
RAMBUTAN-I	O
communications	O
chips	O
(	O
which	O
implement	O
a	O
secure	O
X.25	B-Protocol
based	O
communications	O
system	O
)	O
are	O
made	O
by	O
approved	O
contractors	O
Racal	O
and	O
Baltimore	O
Technologies/Zergo	O
Ltd	O
.	O
CESG	O
later	O
specified	O
RAMBUTAN-II	O
,	O
an	O
enhanced	O
system	O
with	O
backward	O
compatibility	O
with	O
existing	O
RAMBUTAN-I	O
infrastructure	O
.	O
</s>
<s>
The	O
RAMBUTAN-II	O
chip	O
is	O
a	O
64-pin	O
quad	B-Algorithm
ceramic	I-Algorithm
pack	I-Algorithm
chip	O
,	O
which	O
implements	O
the	O
electronic	O
codebook	O
,	O
cipher	O
block	O
chaining	O
,	O
and	O
output	O
feedback	O
operating	B-Algorithm
modes	I-Algorithm
(	O
each	O
in	O
64	O
bits	O
)	O
and	O
the	O
cipher	O
feedback	O
mode	O
in	O
1	O
or	O
8	O
bits	O
.	O
</s>
<s>
Schneier	O
suggests	O
that	O
these	O
modes	O
may	O
indicate	O
Rambutan	B-Algorithm
is	O
a	O
block	O
cipher	O
rather	O
than	O
a	O
stream	O
.	O
</s>
<s>
Rambutan	B-Algorithm
operates	O
in	O
three	O
modes	O
:	O
ECB	O
,	O
CBC	O
,	O
and	O
8	O
bit	O
CFB	O
.	O
</s>
