– Break a message into blocks
– Apply block cipher on the blocks
– Is that it?
Electronic Code Book(ECB)
(M1==M3) -> (C1==C3)
Lack the basic protection against integrity attacks on the ciphertext at message level(i.e., multiple cipher blocks)
Without additional integrity protection
cipher block substitution and rearrangement attacks
fabrication of specific information
Protecting Message Integrity
Only send last block of CBC(CBC residue) alog with the plaintext
Any modification in plaintext rsult in a CBC residue computed by the receiver to be different from the CBC residue from sender
Ensures integrity
simply sending all CBC blocks(for confidentiality) replicating last CBC block(for integrity) does not work
Should use two separate secret keys: one for encryption and the other for generating residue(two encryption passes)
Or, CBC(message|hash of message)
