Which technique retrieves an item from a service without revealing which item is retrieved?

• A. Big Data
• B. Passwordless Authentication
• C. Private Information Retrieval (PIR)
• D. Cryptocurrency

Answer: (C)

Private Information Retrieval is the concept being tested. It describes methods that let you fetch a specific item from a service without revealing to the service which item you retrieved. In a normal retrieval, the query exposes the exact item you want, so the service can learn your target. PIR uses cryptographic techniques to blind the query or to distribute the retrieval across multiple servers, so the server(s) can return the correct item without learning which one you asked for. There are two common forms: information-theoretic PIR, which needs several non-colluding servers, and computational PIR, which relies on cryptographic hardness to protect the privacy with a single server. The result is the requested item, while the privacy of the query remains intact. This idea isn’t about handling large data sets (Big Data), authentication methods without passwords (Passwordless Authentication), or digital currencies (Cryptocurrency).