Overview of AES Encryption Answers 1. What is a critical factor that determines the security of an encryption algorithm? A. The experience of the developer B. The number of encryption rounds used C. The strength of the encryption key D. The complexity of the algorithm structure Answer: The strength of the encryption key (C) The security of any encryption algorithm is heavily reliant on the security of the key. 2. How many rounds does the AES algorithm use with a 256-bit key? A. 16 rounds B. 14 rounds C. 10 rounds D. 12 rounds Answer: 14 rounds (B) A 256-bit key in AES utilizes 14 rounds. 3. In which of the following sectors is AES not commonly used? A. Financial transactions B. Government communications C. Personal smartphone applications D. Manufacturing operations Answer: Manufacturing operations (D) AES is widely used in securing sensitive data in various sectors, but not typically in manufacturing operations. 4. What effect does increasing the key size have on the AES algorithm? A. Reduces the encryption time B. Makes the algorithm less efficient C. Decreases the number of rounds D. Improves the algorithm’s resistance to attacks Answer: Improves the algorithm’s resistance to attacks (D) Longer key sizes lead to more rounds, which enhances the security and resistance to attacks. 5. Which statement accurately describes AES's strength against attacks? A. It relies solely on its algorithm structure to ensure security. B. Rigorous security analysis has shown its resistance to various attacks. C. Its security is guaranteed by the length of the key used. D. It has never been attacked successfully. Answer: Rigorous security analysis has shown its resistance to various attacks. (B) AES has proven resistant to various attacks based on rigorous security analysis. 6. What is the primary characteristic of AES as a symmetric-key encryption algorithm? A. AES uses a variable-length key for encryption. B. AES encrypts data using public keys. C. AES is a block cipher that operates on fixed-size blocks. D. AES utilizes a stream cipher for encrypting data. Answer: AES is a block cipher that operates on fixed-size blocks. (C) AES is specifically designed to encrypt data in fixed-size blocks, distinguishing it as a block cipher. 7. What size of blocks does AES use for encryption? A. 512 bits B. 256 bits C. 128 bits D. 64 bits Answer: 128 bits (C) AES operates exclusively on 128-bit blocks of data during the encryption process. 8. Which transformation is NOT part of the AES round operations? A. Mix columns B. Shift rows C. Swap blocks D. Byte substitution Answer: Swap blocks (C) AES consists of byte substitution, shift rows, and mix columns, but does not include a swap blocks operation. 9. How does the key schedule in AES contribute to the algorithm's security? A. It creates unique round keys for each round of encryption. B. It combines the plaintext with the key directly. C. It generates keys of a single fixed length. D. It prevents any changes to the key once selected. Answer: It creates unique round keys for each round of encryption. (A) The key schedule generates unique round keys that enhance the security through the avalanche effect. 10. Which operation is omitted in the last round of AES encryption? A. Key addition B. Shift rows C. Byte substitution D. Mix columns Answer: Mix columns (D) In the final round of AES encryption, the mix columns operation is skipped, unlike the other rounds. 11. What is the role of the S-box in AES? A. To shift rows of the state matrix. B. To mix the key with the plaintext. C. To encrypt the final output. D. To substitute values in the state matrix. Answer: To substitute values in the state matrix. (D) The S-box is crucial for the byte substitution process, replacing values in the state matrix during encryption. 12. In the decryption process of AES, what is done with the round keys? A. They are reused from the encryption key directly. B. They are not necessary for decryption. C. They are generated in the same order as encryption. D. They are derived in reverse order of encryption. Answer: They are derived in reverse order of encryption. (D) The decryption process requires the round keys to be derived in reverse order to correctly invert the encryption operations. 13. What does the avalanche effect ensure in the context of AES? A. Small key changes do not affect the output. B. The ciphertext remains unchanged regardless of key alterations. C. All changes in the plaintext lead to the same output. D. Small changes in the key do not translate to similar changes in ciphertext. Answer: Small changes in the key do not translate to similar changes in ciphertext. (D) The avalanche effect guarantees that even small modifications in the encryption key produce significant changes in the resulting ciphertext.