Which principle states that a cryptosystem should be secure even if the algorithm is public, and only the key must remain secret?

• A. Encryption
• B. Kerckhoffs's Principle
• C. Cipher
• D. Plaintext

Answer: (B)

Security relies on the key being kept secret, even when everyone knows the method used to encrypt. This idea is Kerckhoffs's Principle: a cryptosystem should remain secure if the algorithm is public and only the key remains secret. By making the algorithm open to analysis, its weaknesses can be found and fixed, while the actual protection comes from the secrecy and strength of the key. For example, RSA relies on a publicly known algorithm, with security resting on the difficulty of factoring large numbers and the secrecy of the private key. The other terms describe parts of the process or data, not the principle about keeping cryptographic security tied to the key rather than the obscurity of the algorithm.