[eid5775]9https://www.rfc-editor.org/errata/eid5775)
It is not clear how to derive CMK[j]
This is related to Errata 5770, and the fix is similar.
Since we have:
CMK[j] = last 20 octets of IMCK[j]
The definition of CMK[0] is clear. It just needs to be written down.
CMK[0] = last 20 octets of IMCK[0]
This matches the implementations.