Notes for January 21, 1998

1. Greetings and felicitations!
   1. Reading: Pfleeger, pp. 91-118
2. Puzzle of the day
   1. Fun stuff
3. DES
   1. Go through the algorithm
4. Public Key Cryptography
   1. Basic idea: 2 keys, one private, one public
   2. Cryptosystem must satisfy:
      • given public key, CI to get private key;
      • cipher withstands chosen plaintext attack; and
      • encryption, decryption computationally feasible [note: commutativity NOT required]
   3. Benefits: can give confidentiality or authentiction or both
5. Use of public key cryptosystem
   1. Normally used as key interchange system to exchange secret keys (cheap)
   2. Then use secret key system (too expensive to use PKC for this)