In class exercises, November 11, 2014.

We'll work the problem on the last slide of the lecture.  

Note:  This is also an exercise in RA 5!

Recap:

   A wishes to send 500Kb message to B.
   Readable only by B.
   Authenticated as coming from A.
   A and B do not share a private key, but do share a public key.

   Public key encryption rate:    1Kbps
   Symmetric key encryption rate: 1Mbps
   Hash algorithm: 256 bit hash,  100Kbps

   Goal: Message encryption/decryption totals less than 15 seconds.

1) First, suppose we just use the B public key to encrypt m
   Outside of performance, is that enough?

2) Could slide 29 help us our here?  What are the (possible) problems?

2) How long does does public key encryption take? 
  
3) Ok, public key encryption is too slow.  
   How long does symmetric encryption take?

4) Can slide 30 help us out here?  (What do we need to add to 
   address the problem requirements?)

5) What all do we need to send?

6) How long does the encryption take?