Which of the following encryption types is used in Hash Message Authentication Code (HMAC) for key distribution?

HMAC relies on symmetric key cryptography, where a single shared secret key is distributed between communicating parties and used in conjunction with a hash function (such as SHA-256 or MD5) to produce the authentication code. Both the sender and receiver must possess the same key to compute and validate the HMAC, which is the defining characteristic of symmetric encryption.

Asymmetric encryption uses a public/private key pair and is not used in HMAC; HMAC specifically requires a single shared secret key held by both parties, not separate keys for encryption and decryption.

Ephemeral refers to temporary keys generated for a single session (commonly in Diffie-Hellman key exchange), which describes a key lifecycle property rather than an encryption type used in HMAC.

Permanent is not a recognized encryption type in cryptography; it describes key longevity rather than any encryption algorithm or method used in HMAC operations.