ITPEC FE Morning April 2021 Question 38
Which of the following is an encryption method that can be used for encrypting data managed in a database using the same key for encryption and decryption?
Explanation
AES — a symmetric (common key) cipher, using one key both to encrypt and to decrypt.
AES (Advanced Encryption Standard) is a block cipher with keys of 128, 192 or 256 bits. Symmetric ciphers are fast, which is why they encrypt large amounts of stored data such as database contents; the same key must be kept secret by everyone who decrypts.
Answer (a)
Why not others:
- •(b) PKI — the public key infrastructure of certificate authorities and certificates that binds public keys to owners; it is not a cipher
- •(c) RSA — a public key cipher: data encrypted with one key of a pair is decrypted with the other
- •(d) SHA-256 — a hash function; it produces a fixed 256-bit digest and cannot be decrypted at all
Key rule: Same key for both directions means symmetric (AES, DES); a key pair means public key (RSA, elliptic curve); no way back means a hash (SHA).
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