Que.________________ is a cipher formed out of substitution where for a given key-value the cipher alphabet for every plain text remains fixed all through the encryption procedure.
Que.In Playfair cipher, at first, a key table is produced. That key table is a 5 by 5 grid of alphabets which operates as the key to encrypt the plaintext.
Que.In _____________ a sequence of actions is carried out on this block after a block of plain-text bits is chosen for generating a block of cipher-text bits.