Input:
psk - a secret key. It may be present. If not present this value shall be the empty octet string, ∅.
(k 1, k 2, …, k n) - n-tuple of octet strings containing shared secrets k i, exchanged through a hybrid key exchange, see
Figure 4.
MA, MB - octet string of a pair of exchanged messages in establishment of the shared secrets k i.
context - octet string context set by the instance of the key exchange transaction - this may include a transcript of
additional exchanged messages.
label - an octet string that specifies a separation of use for the application or instance of the key-exchange. Any labels
used in the key exchange should not be provided as an argument to the same hash function for another purpose in the
application.
length - the length in octets of the derived key material key_material.
Process:
1) Form secret = psk || k1 || k 2 || … || k n.
2) Set f_context = f(context, MA, MB), where f is a context formatting function.
3) key_material = KDF(secret, label, f_context, length).
4) Return key_material.
Output:
key_material - derived key material.