Q. A typical combination lock (A) requires three turns between 1 and 40. Assume that we
have a special combination lock (B) that requires five turns between 1 and 10.
Which lock is more secure? Explain?
Q Why it is the norm to publish the encryption algorithms and do not keep them secret?
Q Why AES is more secure than DES?
Q Assume we have the following encryption algorithm:
 Algorithm A: Caesar-based cipher: Divide the string into 4 bit long blocks and
replace each block with another block K positions away with wrap around.
 Algorithm B: Monoalphabetic-based cipher: arbitrary map one block with
another block.
1. If you have a cipher text C, how many trials are needed (in the worst case) to find
the plain text assuming Algorithm A is the encryption Algorithm?
2. Repeat 1. of Algorithm B is the encryption Algorithm.
Q. Describe how Bob can authenticate himself to Alice by sending her only one message
using:
1. Secrete Key Cryptography.
2. Public Key Cryptography.
3. A Message Digest Algorithm.
Q. Explain why UNIX requires its users to authenticate themselves by sending their
password in plain text?
Q. Explain how to use a MD algorithm as a symmetric encryption algorithm?
Q Dr. Wahab used the simple crypt program of assignment #1 to encrypt his
grade sheet for this class. Assume he keeps the grade sheet sorted
alphabetically by last name and he uses a 4-character key. Describe how
some of you may be able to decipher the grade sheet.
Q. In Generating RSA keys we use the command:
> openssl genrsa -out rsaprivatekey.pem -des3 1024
What is 1024?
What is –des3?
Q. In DES, assume the we have the following data block:
FF00 0000 0000 0000
What is the result of the initial permutation in HEX?
Q In DES, assume the key is: FF00 0000 0000 0000
what is the value of C0 in binary.
Q. In DES, assume that input to one round is all 0s and the key of that round is all 1s.
What is the value of the first 40 bits (in HEX) of the output of that round?
Q.In AES-128: What the result of applying MixColumn to that column of all 1s?