Notes for January 17, 1997

1.	Hello

a.	cs153r account set up to receive project descriptions and homework #1.

2.	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

3.	Use of PKC

a.	Normally used as key interchange system to exchange secret keys (cheap)

b.	Then use secret key system (too expensive to use PKC for this)

4.	RSA

a.	Provides both authenticity and confidentiality

b.	Go through algorithm, examples

5.	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.