<s>
It	O
describes	O
what	O
is	O
known	O
as	O
a	O
Vigenère	B-Algorithm
cipher	I-Algorithm
,	O
a	O
well-known	O
scheme	O
in	O
cryptography	O
.	O
</s>
<s>
While	O
Carroll	O
calls	O
this	O
cipher	O
"	O
unbreakable	O
,	O
"	O
Kasiski	O
had	O
already	O
published	O
in	O
1863	O
a	O
volume	O
describing	O
how	O
to	O
break	O
such	O
ciphers	O
and	O
Charles	O
Babbage	O
had	O
secretly	O
found	O
ways	O
to	O
break	O
polyalphabetic	B-Algorithm
ciphers	I-Algorithm
in	O
the	O
previous	O
decade	O
during	O
the	O
Crimean	O
War	O
.	O
</s>
<s>
The	O
piece	O
begins	O
with	O
a	O
tabula	B-Algorithm
recta	I-Algorithm
.	O
</s>
