Notes for January 15, 1997

1.	Hello

a.	Would it help to put out code for using getpwnam and getgrent? Gene will discuss 
this program in section, too.

2.	Puzzle of the day

a.	No right answer, but there are better places to look than others. Išll ask this one 
periodically to see how your knowledge is changing.

3.	Breaking UNIX crypt(1)

a.	Purely statistical attack is possible (me) but it takes gobs of ciphertext

b.	Known plaintext attack: thatšs Reeds and Weinbergeršs attack, with a nice sugges-
tion by Bob Morris

4.	Public-Key Cryptography

a.	Basic idea: 2 keys, one private, one public

b.	Cryptosystem must satisfy: (a), given public key, CI to get private key; (b) cipher 
withstands chosen plaintext attack; (c) encryption, decryption computationally fea-
sible [note: commutativity NOT required]

c.	Benefits: can give confidentiality or authentiction or both