Notes for January 16, 1998

1. Greetings and felicitations!
   1. Reading: Pfleeger, pp. 21-46; Garfinkel & Spafford, pp. 139-159, 175-179
2. Puzzle of the day
   1. Look for things the size of the shell ...
3. Long key generation
   1. 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.)
   2. Enigma/rotor systems; wheels, 3 rotors and a reflecting one. Go through it; UNIX uses this for crypt(1) command.
   3. Perfect secrecy: when the probability of computing the plaintext message is the same whether or not you have the ciphertext

   4. Only cipher with perfect secrecy: one-time pads; C=AZPR; is that DOIT or DONT?
4. Breaking UNIX crypt(1)
   1. Purely statistical attack is possible (me) but it takes gobs of ciphertext

   2. Known plaintext attack: that's Reeds and Weinberger's attack, with a nice suggestion by Bob Morris

5. DES
   1. Go through the algorithm