ITPEC FE Morning October 2022 Question 36
When a system with a database is being developed, a security requirement states that the data must be encrypted with a key before being saved to the database, and the same key is required for decryption when the data is being read. Which of the following is an appropriate algorithm that can be used to satisfy the security requirement?
Explanation
AES — encrypting and decrypting with the same key is common-key (symmetric) cryptography, and AES is a symmetric block cipher.
AES encrypts data in 128-bit blocks with a 128, 192 or 256-bit key, and the same key reverses it. That fits the requirement: the application encrypts with the key before saving and decrypts with that key when reading. Symmetric ciphers are also fast, which suits bulk data in a database.
Answer (a)
Why not others:
- •(b) Diffie-Hellman — a key-agreement protocol that lets two parties derive a shared secret over an open channel; it does not encrypt data itself
- •(c) RSA — public-key cryptography: data encrypted with the public key is decrypted with the matching private key, two different keys
- •(d) SHA-256 — a hash function that produces a one-way 256-bit digest; it uses no key and cannot be decrypted
Key rule: Same key → symmetric cipher (AES, DES); key pair → public-key cryptography (RSA, elliptic curve); no way back → hash function (SHA-2, SHA-3).
Security · AI-written, may contain errors
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