Data Security (CY-503 (C)) - Important Questions

Explain the principle behind symmetric and asymmetric encryption. Describe the process of secure message authentication using hash functions with a relevant example.

Give the ciphertext 'ZICVTWQNGRZGVTWAVZHCQYGLMGJ'; decrypt it using the Caesar cipher with a shift of 17. Show each step clearly.

Explain how public-key cryptography can be used for digital signatures. Why are digital signatures considered a crucial aspect of secure communication?

Discuss RC4 encryption algorithm. Considering a 5-bit RC4 key, generate the first 3 bytes of any pseudo-random key stream.

Summarize the public key cryptographic principles. Explain RSA algorithm for given example, where $p=3$ and $q=11$.

Explain with an example how encryption and decryption is performed in AES?

Describe the steps to find the message digest using SHA-512 algorithm. What is the order of finding the messages which have the same message digest?

Explain cipher block modes of operation (ECB, CBC, CFB, OFB) with merits and demerits.

Explain how PGP provides authentication and confidentiality; draw the PGP message format.

Discuss Message Authentication Codes / HMAC and their role in message integrity and authentication.

Explain Data Encryption Standard (DES). Describe its structure and key scheduling. Discuss the weaknesses of DES.

Differentiate between block and stream ciphers (or explain block vs stream cipher properties).

Explain core information theory concepts used in cryptography such as entropy and redundancy. Define Shannon entropy using $H(X) = -\sum_i p_i \log_2 p_i$ and compute it for a source with given symbol probabilities.