Assignment 7

                  revised: 10/19/06

Assigned: 10/3/06
Due: 6:00pm 10/21/06 

Objective: adding encryption (AES) to your ncp client from asnmt 4

Points: 15

Description:

     Add AES CBC encryption to the client program you developed for
     assignment 4.  Use the OpenSSL AES_cbc_encrypt() function to
     encrypt the entire packet structure (e.g., outpkt) just before
     the sendto() and to decrypt the encrypted packet from the server
     right after the recvfrom().  For your 16-byte AES encryption key
     use the MD5 hash of the string aeskey06  (don't include the null
     in the hash).  Your program must calculate the length of the buffer
     needed to hold the encrypted output.  Be sure to use this length
     when sending the buffer to the server.  Verify that the recvfrom()
     returns this length or write an error message and exit.
     For testing with whisper, again use the password  secret06
     For the 16-byte IV, use MD5 to hash the port number as an int in
     network byte order (htonl(port)) with the password
     (don't include the null).

     WARNINGS:
	1. Fix any errors in your client code that were noted in grading for
     	   assignment 4.
	2. Remember, encryption output will usually be bigger than the input
	   so provide a temporary buffer big enough, and you'll need to use
	   a bigger buffer in the recvfrom too
	3. You'll need to reset the IV because AES_cbc_encrypt() modifies
	   the IV
	4. A "bad hmac" from the server may mean your encryption is broken.
	5. All packets from the server will be encrypted.

  You must test your client with the server running on whisper.
  The server is running on port 4322
  Your test results must include an ncp to and from whisper. Include
  in your ANSWERS file the first-byte authenticator values,
  and the value of the data[] field in the response packet you get
  back from whisper.
  whisper will only accept write's to a file called out.tmp and read's
  from a file called in.tmp.  You must use the password  secret06

  Examples
     ncp-aes 4322 secret06 myfile.dat whisper:out.tmp
     ncp-aes 4322 secret06  whisper:in.tmp my.tmp

  Note: the user_authenticator and msg_authenticator should be valid
        from the server on whisper, so check your logic/coding if you
        are getting error codes (not OK) back from the server.

  For your own testing, you may wish to modify ncpd.c to work
  with your client, but the server program will not be graded.
  Your client program must work with the server on whisper.cs.utk.edu


     Don't forget to add required comments to your source code.
     Remember that encryption software is subject to export restrictions.
     See the class policy page.

Place your ANSWERS and source files, Makefile, etc. in a directory and
use 594cns_submit  to submit your results to the TA.