Stream Encryption

EE September 1987 STREAM ENCRYPTION by B.P. McArdle One of the evils peculiar to the computerized world is hacking- the unlawful accessing of computers. One way of effectively combatting this nefarious activity is encrypting the data. Encryption is the process that turns data into secret form. The original data is known as the plaintext or cleartext and the encrypted data as the cipher- text. If the plaintext is P and the ciphertext is C, the encryption operation is described by Ex [P] =C [1] where K is a parameter called the key which is used to vary E. The effect of a change of key is to generate a different C for the same P. The user chooses a par- ticular key from a set of poss- ible keys (K) and encrypts the plaintext. The ciphertext is stored or transmitted over a channel as illustrated in Fig. 1 to a receiver. The receiving oper- ator must know the particular key in use to enable him to recover the plaintext with the inverse or decryption operation Aci (0= r3K(c)=P [2] Ex...