Running key cipher: Difference between revisions

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{{short description|Type of polyalphabetic substitution cipher}}

{{refimprove|date=March 2016}}

In classical [[cryptography]], the '''running key cipher''' is a type of [[polyalphabetic substitution]] [[cipher]] in which a text, typically from a book, is used to provide a very long [[keystream]]. The earliest description of such a cipher was given in 1892 by French mathematician Arthur Joseph Hermann (better known for founding [[Éditions Hermann]]). Usually, the book to be used would be agreed ahead of time, while the passage to be used would be chosen [[random]]ly for each message and secretly indicated somewhere in the message.

== Example ==