I am using HKDF with an IKM and salt, the OKM is used as the key for an HMAC operation. The HMAC algorithm is authenticating messages in a communications system
The salt is the concatenation of 2 nonces, 1 drawn drawn by each of the communicating nodes and can be found by any one observing the communications system
Messages are sent as:
message || sequence number || HMAC(key, sequence number || message)
My question is this: Is it safe to use the OKM directly as the key for the message HMAC or should I perform some other operation on the OKM before using it?