HMAC provides a way to both encrypt a communication and authenticate its origin.

This relies on a shared pair of secret keys between all the parties

The function computing the tag deterministic: the same (message, key) tuple will always produce the same output. However, even if the message is public, knowing the key is required in order to be able to compute a valid tag. Therefore, the key should remain confidential. The tag, however, can be public.

The following keyed message authentication codes are availabled:

• Sel.HMAC.SHA256
• Sel.HMAC.SHA512
• Sel.HMAC.SHA512_256 (truncated HMAC-SHA-512)