Using Block Ciphers

a. Incorrect use of block ciphers

 - In pictures

b. Eavesdropping security: CBC mode

c. Use cases: how to choose an IV
 - Single use key: no IV needed (IV = 0)
 - Multi use key: use a fresh random IV for every message
 - In pictures

d. Eavesdropping security: CTR mode

e. Performance

f. Warning
 - Eavesdropping security is insufficient for most applications
 - Needs also to defend against active attacks
 - CBC and CTR modes are insecure against active attacks