In a Running Key cipher, the keyword is the text of a predetermined book or passage. For example, if the chossed book was "A Tale of Two Cities" by Charles Dickens, then the keyword would be
It was the best of times, it was the worst of times...
Enciphering and deciphering the message is performed using the exact same method as the Vigeńere Cipher.
If the predetermined passage is a string of random letters that is only used once and then discarded, this is similar to a One-time Pad.
