312-50V10 · Question #32
Alice encrypts her data using her public key PK and stores the encrypted data in the cloud. Which of the following attack scenarios will compromise the privacy of her data?
The correct answer is D. Alice also stores her private key in the cloud, and Harry breaks into the cloud server as before. Asymmetric encryption with a public key protects data only as long as the corresponding private key remains secret. Storing the private key alongside encrypted data in the same location eliminates that protection.
Question
Alice encrypts her data using her public key PK and stores the encrypted data in the cloud. Which of the following attack scenarios will compromise the privacy of her data?
Options
- ANone of these scenarios compromise the privacy of Alice's data
- BAgent Andrew subpoenas Alice, forcing her to reveal her private key. However, the cloud server
- CHacker Harry breaks into the cloud server and steals the encrypted data
- DAlice also stores her private key in the cloud, and Harry breaks into the cloud server as before
How the community answered
(45 responses)- A2% (1)
- B7% (3)
- C11% (5)
- D80% (36)
Why each option
Asymmetric encryption with a public key protects data only as long as the corresponding private key remains secret. Storing the private key alongside encrypted data in the same location eliminates that protection.
Scenario D does compromise Alice's privacy, making this choice factually incorrect.
In this scenario the cloud server does not hold the private key, so even if Alice is compelled to reveal her key the server-side encrypted data is not independently accessible to an attacker without both elements together.
Stealing only the encrypted ciphertext does not compromise privacy because without Alice's private key the data cannot be decrypted.
If Alice stores her private key in the cloud alongside the encrypted data, an attacker who breaches the cloud server obtains both artifacts. With the private key and the ciphertext in hand, Harry can trivially decrypt all of Alice's data, fully compromising her privacy. The encryption provides no protection when the key needed to reverse it is equally accessible.
Concept tested: Public key encryption and private key confidentiality
Source: https://learn.microsoft.com/en-us/azure/security/fundamentals/encryption-overview
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