Bsc CSIT Semester 5 – Cryptography – Unit 2. Symmetric Ciphers

Explain the single round operation in DES. Describe the F function in DES.

Define CIA triad. State the encryption process of double and triple DES. What is the task of S-Box in DES ? Discuss with an example.

Define Galois field with an example. Explain any two modes of block cipher encryption. Deterimine the quadratic residues of 7.

llustrate the concept of security policy and mechanism with an example. Differentiate between block cipher and stream cipher. Explain the process of key expansion in AES.

How encryption is done using IDEA algorithm.

Write down the encryption and decryption process at 2-DES and 3-DES. Explain the Fiestal cipher structure. Divide 5x2 + 4x + 6 by 2x + 1 over GF(7).

Let us consider the 4 bits key set as {1100, 1010, 0000, 1111, 0101, 1001} and input text as {1011, 1110, 1011, 1000}. Now trace the first full round operation of IDEA algorithm.

Describe the different modes of block cipher.

Describe the Fiestel Cipher structure. Given the key {2B, 7E, 15, 16, 28, AE, D2, A6, AB, F7, 97, 66, 01, 02, 03, 04}, compute the first 4 byte of next key after first iteration, using the following S-Box in AES.

Explain any two modes of block cipher encryption.

Decrypt the ciphertext “HI” using Hill Cipher where the key is [5/4 3/3].