CRYSTALS-Kyber is primarily which type of primitive?

• A. Key encapsulation mechanism
• B. Digital signature
• C. Hash function
• D. Symmetric cipher

Answer: (A)

This question tests whether you understand that CRYSTALS-Kyber is a post-quantum public-key primitive used to securely establish a symmetric key. It is a key encapsulation mechanism: the sender uses the recipient’s public key to encapsulate a random secret into a ciphertext, and the recipient uses their private key to decapsulate and recover the same secret. The shared secret can then be fed into a symmetric cipher to encrypt data. It’s not a digital signature, which would provide authentication of origin rather than key exchange; it’s not a hash function, which produces fixed-size digests; and it’s not a symmetric cipher by itself, which would require a previously shared secret rather than a public-key operation to establish it.