<s>
In	O
cryptography	O
,	O
the	O
Rip	B-Algorithm
van	I-Algorithm
Winkle	I-Algorithm
cipher	I-Algorithm
is	O
a	O
provably	O
secure	O
cipher	B-Application
with	O
a	O
finite	O
key	O
,	O
assuming	O
the	O
attacker	O
has	O
only	O
finite	O
storage	O
.	O
</s>
<s>
The	O
cipher	B-Application
requires	O
a	O
broadcaster	O
(	O
perhaps	O
a	O
numbers	O
station	O
)	O
publicly	O
transmitting	O
a	O
series	O
of	O
random	O
numbers	O
.	O
</s>
<s>
The	O
sender	O
encrypts	O
a	O
plaintext	O
message	O
by	O
XORing	B-Application
it	O
with	O
the	O
random	O
numbers	O
,	O
then	O
holding	O
it	O
some	O
length	O
of	O
time	O
T	O
.	O
</s>
<s>
As	O
soon	O
as	O
the	O
receiver	O
gets	O
the	O
encrypted	O
message	O
,	O
he	O
XORs	B-Application
it	O
with	O
the	O
random	O
numbers	O
he	O
remembers	O
were	O
transmitted	O
T	O
ago	O
,	O
to	O
recover	O
the	O
original	O
plaintext	O
message	O
.	O
</s>
<s>
Ueli	O
Maurer	O
says	O
the	O
original	O
Rip	B-Algorithm
van	I-Algorithm
Winkle	I-Algorithm
cipher	I-Algorithm
is	O
completely	O
impractical	O
,	O
but	O
it	O
motivated	O
a	O
new	O
approach	O
to	O
provable	O
security	O
.	O
</s>
