1. ACM International Collegiate Programming Contest Banff Springs, Alberta April 6 – 10, 2008 Sep. 22 (local) Oct. 6 (Oswego – preliminary) Nov. 10 (RIT – regional final) stefanko@cs.rochester.edu Sep. 11, CBS 601, 4:15pm

3. Office hours Instructor office hours (CSB 620) Monday 12noon-1pm Thursday - after class TA office hours (CSB 728) Monday 4pm - 5pm Wednesday 4pm - 5pm Problem sessions Friday 8am – 9am, CSB 601

4. Homework #1 1) you should receive email saying which parts do you need to solve (A,C,I) 2) if you do not receive the email by today evening – send me email 3) has to be typeset on a computer, turn in 2 copies by Sep. 20

5. Quiz #1 – Number Theory and Cryptography Sep 6 Sep 11 Sep 13 Sep 18 pages 1-44

6. Cryptography ALICE BOB EVE

7. ALICE BOB EVE Cryptography – private key K=secret key y=encode(x,K)x’=decode(y,K)

8. ALICE BOB EVE Cryptography – public key A= public key B= private key y=ENCODE(x,A) x=DECODE(y,B)

9. Cryptography – public key - RSA 1. pick two large primes p,q, let N=pq 2. pick e such that gcd(e,p-1)=1, gcd(e,q-1)=1 3. find d such that e.d  1 mod (p-1)(q-1) 4. announce e,N, keep p,q,d secret ENCODE(x) = x e mod N DECODE(y) = y d mod N