A team must encrypt multi-gigabyte backups nightly with minimal CPU overhead. Which approach best fits?

• A. AES encryption in CTR mode
• B. Digital signature
• C. Hash-based MAC (HMAC)
• D. Public-key encryption for the entire backup

Answer: (B)

To protect a multi‑gigabyte backup efficiently, you want a way to verify that the backup hasn’t been tampered with and that it came from a trusted source, without paying the heavy cost of encrypting every byte with public‑key cryptography. A digital signature achieves this by signing a compact digest (hash) of the backup data with a private key. During restore, you verify that signature with the corresponding public key. This approach keeps CPU overhead low because the expensive public‑key operation is applied to a small digest rather than the entire large dataset, while still providing strong integrity and authenticity guarantees.

In contrast, encrypting the entire backup with a public‑key or with a heavy mode of operation would incur much higher CPU costs for large data. A hash-based message authentication code (HMAC) provides integrity as well but requires a shared secret and does not offer non‑repudiation. A pure encryption approach would protect confidentiality but is typically more resource-intensive for large volumes of data. In practice, you’d often combine the two: encrypt the backup with a fast symmetric cipher for confidentiality and sign the ciphertext to ensure integrity and authenticity; however, among the given options, the digital signature best fits the goal of minimizing CPU overhead while ensuring the data’s integrity and provenance.