code: func (h finishedHash) clientSum(masterSecret []byte) []byte {
  	if h.version == VersionSSL30 {
  		return finishedSum30(h.clientMD5, h.client, masterSecret, ssl3ClientFinishedMagic[:])
  	}
  
  	out := make([]byte, finishedVerifyLength)
  	h.prf(out, masterSecret, clientFinishedLabel, h.Sum())
  	return out
  }
docs: // clientSum returns the contents of the verify_data member of a client's
  // Finished message.