<s>
In	O
the	O
history	O
of	O
cryptography	O
,	O
the	O
Nihilist	B-Algorithm
cipher	I-Algorithm
is	O
a	O
manually	O
operated	O
symmetric	B-Algorithm
encryption	I-Algorithm
cipher	O
,	O
originally	O
used	O
by	O
Russian	O
Nihilists	O
in	O
the	O
1880s	O
to	O
organize	O
terrorism	O
against	O
the	O
tsarist	O
regime	O
.	O
</s>
<s>
Because	O
each	O
symbol	O
in	O
both	O
plaintext	O
and	O
key	O
is	O
used	O
as	O
a	O
whole	O
number	O
without	O
any	O
fractionation	O
,	O
the	O
basic	O
Nihilist	B-Algorithm
cipher	I-Algorithm
is	O
little	O
more	O
than	O
a	O
numerical	O
version	O
of	O
the	O
Vigenère	B-Algorithm
cipher	I-Algorithm
,	O
with	O
multiple-digit	O
numbers	O
being	O
the	O
enciphered	O
symbols	O
instead	O
of	O
letters	O
.	O
</s>
<s>
During	O
World	O
War	O
II	O
,	O
several	O
Soviet	O
spy	O
rings	O
communicated	O
to	O
Moscow	O
Centre	O
using	O
two	O
ciphers	O
which	O
are	O
essentially	O
evolutionary	O
improvements	O
on	O
the	O
basic	O
Nihilist	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
A	O
very	O
strong	O
version	O
was	O
used	O
by	O
Max	O
Clausen	O
in	O
Richard	O
Sorge	O
's	O
network	O
in	O
Japan	O
,	O
and	O
by	O
Alexander	O
Foote	O
in	O
the	O
Lucy	O
spy	O
ring	O
in	O
Switzerland	B-Protocol
.	O
</s>
<s>
In	O
both	O
versions	O
,	O
the	O
plaintext	O
was	O
first	O
converted	O
to	O
digits	O
by	O
use	O
of	O
a	O
straddling	B-Algorithm
checkerboard	I-Algorithm
rather	O
than	O
a	O
Polybius	O
square	O
.	O
</s>
<s>
Shutting	O
down	O
sooner	O
reduces	O
the	O
risk	O
of	O
the	O
operator	O
being	O
found	O
by	O
enemy	O
radio	B-Device
direction	I-Device
finders	I-Device
.	O
</s>
<s>
The	O
standard	O
English	O
straddling	B-Algorithm
checkerboard	I-Algorithm
has	O
28	O
characters	O
and	O
in	O
this	O
cipher	O
these	O
became	O
"	O
full	O
stop	O
"	O
and	O
"	O
numbers	O
shift	O
"	O
.	O
</s>
<s>
The	O
weaker	O
version	O
generated	O
the	O
additive	O
from	O
the	O
text	O
of	O
a	O
novel	O
or	O
similar	O
book	O
(	O
at	O
least	O
one	O
Rote	O
Kapelle	O
member	O
used	O
The	O
Good	O
Soldier	O
Schweik	O
)	O
This	O
text	O
was	O
converted	O
to	O
a	O
digital	O
additive	O
using	O
a	O
technique	O
similar	O
to	O
a	O
straddling	B-Algorithm
checkerboard	I-Algorithm
.	O
</s>
<s>
The	O
ultimate	O
development	O
along	O
these	O
lines	O
was	O
the	O
VIC	B-Algorithm
cipher	I-Algorithm
,	O
used	O
in	O
the	O
1950s	O
by	O
Reino	O
Häyhänen	O
.	O
</s>
<s>
By	O
this	O
time	O
,	O
most	O
Soviet	O
agents	O
were	O
instead	O
using	O
one-time	B-Algorithm
pads	I-Algorithm
.	O
</s>
