Chapter 5 / 5.10

5.10 REVISION QUESTIONS

1. List and briefly describe the six security services.

1. Briefly describe the encryption/decryption process using such terms as plain text, cipher text, cipher, and key.

1. Briefly explain why simple transformations, such as those used in the Caesar cipher, are not suitable for strong encryption systems.

1. Draw the block diagram of a stream cipher system and briefly describe its operation.

1. Briefly describe how to generate a pseudo-random key stream using a linear shift register.

1. List the desirable properties of an encryption system, briefly explaining each.

1. What is a systematic weakness in an encryption system? What is the impact of systematic weaknesses? How may they arise?

1. What is the basic principle upon which public-key encryption systems rely for their security?

1. Describe briefly the structure of the DES algorithm, including the purpose of the iteration, compression permutation, and left circular shift functions.

1. Describe briefly the structure and operation of Triple DES (3DES).

1. Explain why Triple DES was developed and why it was eventually replaced by AES.

1. List the four primary transformation steps used in AES and briefly describe the purpose of each.

1. Explain how AES achieves both confusion and diffusion within its internal operations.

1. Discuss the advantages of AES over 3DES in terms of performance, key length, and implementation efficiency.

1. Describe how the key length affects the security and computational cost of AES. Which key lengths are recommended for general and long-term applications?

1. Define asymmetric encryption and explain how it differs fundamentally from symmetric encryption.

1. In public-key systems, why can the public key be safely distributed without compromising security?

1. Explain the basic mathematical principle that underpins the security of the RSA algorithm.

1. Describe the process for generating RSA public and private keys, identifying the roles of p, q, n, e, and d.

1. Briefly outline the RSA encryption and decryption operations, referring to the relevant mathematical expressions.

1. Why is RSA unsuitable for encrypting large volumes of data directly? What approach is typically used instead?

1. Define what is meant by a digital signature and explain its role in ensuring authentication and message integrity.

1. Describe the process by which a digital signature is created and verified, identifying the purpose of the message digest.

1. Explain how digital signatures differ from encryption in their use of public and private keys.

1. What is a cryptographic hash function, and why is it important in digital-signature generation?

1. Explain the concept of hybrid encryption and why it is used in modern secure-communications systems.

1. Outline the basic steps of the Diffie–Hellman key-exchange protocol and explain how it enables secure key agreement over an insecure channel.

1. What role do elliptic-curve variants (such as ECDH and ECDSA) play in modern cryptographic systems, and what advantages do they offer?

1. Summarize how digital signatures and key-exchange protocols together provide both authentication and confidentiality in network security.

1. Explain why quantum computing poses a threat to both symmetric and asymmetric encryption systems.

1. List and briefly describe the five main families of post-quantum cryptographic algorithms, noting the mathematical problem on which each is based.

1. Why are lattice-based algorithms such as CRYSTALS-Kyber and CRYSTALS-Dilithium favored in current post-quantum standardization efforts?

1. Describe how hybrid encryption is used during the transition to post-quantum systems and explain its security advantages.

1. Summarize the purpose of the NIST Post-Quantum Cryptography Standardization Project and outline the steps organizations should take to prepare for migration.