OKM = KMAC128(salt | info, IKM, 128, S)

     Where
     
     IKM     = X25519 ECDH secret | sort(HI-my | HI-other)
     salt    = sort(nonce-my | nonce-other)
     info    = sort(DET-my | DET-other)
     S       = the byte string 01001011 | 01000100 | 01000110
                which is the characters "K", "D", and "F"
                in 8-bit ASCII.