Which principle states that security should rely on the secrecy of the key rather than the secrecy of the algorithm?

• A. Kerckhoffs's principle
• B. Security by obscurity
• C. One-time pad property
• D. Diffie-Hellman assumption

Answer: (A)

Relying on the secrecy of the key rather than the secrecy of the algorithm means cryptographic strength comes from keeping the key secret and using a well-analyzed, openly available algorithm. If everyone knows how the system works but the key remains unknown and properly protected, the system stays secure. This approach lets cryptographers publicly study and improve the algorithm, while security depends on protecting the key, not hiding the method itself.

In practice, this is why widely used algorithms like AES are published and scrutinized. The confidence in their security comes from the strength of the key and proper key management, not from concealing how the algorithm operates. If the algorithm were kept secret and leaked, security could collapse even if the method itself is strong, because a single exposure could reveal the key or the method of encryption.

Security by obscurity—which tries to hide the algorithm alone—fails as a reliable strategy because once the secrecy is breached, the entire system can fall apart. The other options touch on different ideas: the one-time pad property relates to perfect secrecy under strict conditions (true randomness and one-time use of the key) but does not articulate the general principle about algorithm openness; and the Diffie-Hellman assumption concerns the hardness of a mathematical problem, not how secrecy is achieved in cryptosystems.