91Ó°ÊÓ

If the Cacsar cipher produced KDSSB ELUWKGDB, what is the plaintext message?

Consider a sequence of positive integers \(a_{1}, a_{2}, \ldots, a_{n}\), where \(a_{i+1}>2 a_{i}\) for \(i=1\), \(2, \ldots, n-1 .\) Show that the sequence is superincreasing.

(a) Encipher the message HAPPY DAYS ARE HERE using the autokey cipher with seed \(Q\). (b) Decipher the message BBOT XWBZAWUVGK, which was produced by the autokey cipher with seed \(\mathrm{RX}\).