a) Consider a substitution cipher where 52 symbols were used instead of 26. In particular, each symbol in the ciphertext is for either a lowercase English letter or an  uppercase letter. Such a modification augments the key space to 52! Does this provide added security compared to a standard substitution cipher? Fully explain why or why not.

 

b) A security expert told you that he has designed a better cipher than AES and DES. "It is an arbitrary reversible substitution cipher for a block size of 128 bits." Analyze the statement quantitatively and qualitatively about why it is or is not practical to implement such a system.