problem 1: In brief describe the given security goals given by cryptography: confidentiality, integrity, authentication and non-repudiation.

problem 2: State Kirchhoff’s Principle and describe how it relates to the cryptanalysis.

problem 3: Describe the chosen cipher text attack on the encrypted messages.

problem 4: You have intercepted a message encrypted with a Caesar cipher. The ciphertext starts with HWDUYFSFQDXNX and you know the plaintext starts with c. Find out the key and decrypt the message.

problem 5: Use Euclidean’s algorithm to compute the gcd (763, 1729).

problem 6: Construct the Playfair matrix (5 x 5) by using the keyword:

Nuclear Power

Hence decrypt the cipher text

BW   CY   OG   HW   NU

problem 7: Define four kinds of network security threats.