CSCI-6960H08 Cryptography and Network Security

---

Modified: Thu, Jan 22, 2004

Q1
Consider the characteristics of advanced symmetric block ciphers
as given in Section 6.4 of Stallings.
Evaluate any 5 of the following block ciphers:
 IDEA, CAST-128, CAST-256, RC5, RC6, Blowfish, Twofish, Rijndael
with respect to the characteristics.  
i.e. this question just screams for a table!

Q2
Evaluate subkey generation for both encryption and decryption for
each of the following block ciphers:
 IDEA, CAST-128, CAST-256, RC5, RC6, Blowfish, Twofish, Rijndael

How much work is involved? How much memory storage? On-line versus 
off-line? Pre-computed keys versus "on-the-fly" key generation.

Q3 
Assuming you have a file that needs to be encrypted/decrypted in the 
ECB mode of operation.  Evaluate the RC6, Blowfish, or Rijndael 
encryption/decryption algorithm(s) for parallel operation assuming 
that you have a parallel processor of the type:
a) SIMD (single instruction multiple data) array processor.
b) n-stage pipeline processor, or a
c) MIMD (multiple instruction multiple data)

Q4
We wish to generate a uniformly distributed stream of bits b(i) for i= 0
to 2^32 -1 where the probability {b(i)=0} = probability {b(i)=1} =  0.5 .
We will call that stream of b(i) bits the "one-time" pad AND we would
like to generate a new pad each and every day.

Case (a):  given a physical or natural source of truely random numbers, 
producing a stream of more than 2^32 random numbers, but the probability 
{b(i)=0} does not equal the probability {b(i)=1}; For example, we could 
have a camera (64-shades of grey) pointed at on coming traffic of 
Interstate 91.

or

Case (b): given a physical or natural source of just one truely random 
64-bit number (one-a-day truely random number source). For example, one 
or more strings of daily Lotto numbers from one or more U.S. States.

For each case, (a) and (b) describe how you would create your random
"one-time pad" of 2^32 - 1 bits and for each case,  what are the 
chances that the resulting bit sequences satisfies the next-bit test 
(un-correlated bit stream)