- Greetings and Felicitations!
- Puzzle of the Day
- Long key generation
- Running-key cipher: M=THETREASUREISBURIED; K=THESECONDCIPHERISAN; C=MOILVGOFXTMXZFLZAEQ; wedge is that (plaintext,key) letter pairs are not random (T/T, H/H, E/E, T/S, R/E, A/O, S/N, etc.)
- Enigma/rotor systems; wheels, 3 rotors and a reflecting one. Go through it; UNIX uses this for crypt(1) command.
- Perfect secrecy: when the probability of computing the plaintext message is the same whether or not you have the ciphertext
- Only cipher with perfect secrecy: one-time pads; C=AZPR; is that DOIT or DONT?

- DES
- Go through the algorithm

- Public-Key Cryptography
- Basic idea: 2 keys, one private, one public
- Cryptosystem must satisfy:
- given public key, CI to get private key;
- cipher withstands chosen plaintext attack;
- encryption, decryption computationally feasible [note: commutativity not required]

- Benefits: can give confidentiality or authentication or both

Send email to cs153@csif.cs.ucdavis.edu.

Department of Computer Science

University of California at Davis

Davis, CA 95616-8562