CS 772/872


                          Assignment #2


            Due Midnight, Thursday  Oct. 14, 2004

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Part 1: 

 
Q1:
A. Show the result, in HEX,  of the first round of DES to  encrypt a
message M (all 1s)  with a key K(all 0s). 
B. Repeat 1  if the most significant bit of M is changed to  0.

Q2:
Repeat Q1  using AES-128.

Q3: 
In DES, a key K is called a weak key if for any message m: K{m} = K[m]
i.e., encrypting m with K is the same as decrypting m with K.
For example in DES a weak key  is either:

    * all 1s 
    * all 0s 
    * half 0s and half 1s
    * half 1s and half 0s

Assume a weak key is used in  the Output Feedback Mode (OFB), describe
the relationship between the resulting cipher blocks if  the input data
to be encrypted is all 1s.



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Part 2: This is based on openssl
<http://www.cs.odu.edu/%7Ecs772/fall04/lectures/introduction_openssl.htm>
   (it is installed at: /usr/local/ssl/bin/openssl)

    * For this assignment use the  public/private keypair  created
      during assignmnet# 1.

    * Let passwd.txt  contains a password Y of your choice. 

Encrypt passwd.txt  using: cs772_rsapublickey.pem
<http://www.cs.odu.edu/%7Ecs772/fall04/public_keys/cs772_rsapublickey.pem> 
and then base64-decode the file to produce:  passwd.base64.

    * Let a2.zip  is a zip file containing   the relevant files of  your
      solution to   Part1 <#Part1>.

    * Sign the message digest of  a2.zip  using your private key and
      call the resulting file: a2_zip_mdsignature.

Encode this file to produce:  a2_zip_mdsignature.base64.

    * Encrypt a2.zip  using your password  Y and let a2_zip.base64  is
      the encrypted base64 encoded file.
    * Create one file called <login>_all.zip that contains:

    * a2_zip.base64
    * a2_zip_mdsignature.base64
    * passwd.base64     

    * Finally, submit <login>_all.zip to cs772 under the directory
      Assignment  #2

             
AbdelWahab