http://www.geocities.com/Hollywood/8702/cypher.html
Many spies and diplomats have used the Vernam cipher throughout the 20th
century. The key, rather than consisting of decimal digits, can be a long
random sequence of the binary digits 0 and 1, and the additions and
subtractions would be carried out in base 2 by machine, rather than in
base 10 by hand. Nevertheless, the key must still be hand-carried from
the place where it is generated to the places where it will be used, and
it must be assiduously guarded during all phases of delivery and storage
to prevent it from falling into the hands of an adversary.
From Software, Security and Computer Science:
Cryptology
