code: func (c *Conversation) dhKeyMessage() ([]byte, error) {
  	c.initAKE()
  
  	// TODO: where does this 40 come from?
  	y, err := c.randMPI(make([]byte, 40)[:])
  
  	if err != nil {
  		return nil, err
  	}
  
  	c.setSecretExponent(y)
  	wipeBigInt(y)
  
  	return c.serializeDHKey(), nil
  }
docs: // dhKeyMessage = alice = y
  // Alice -- DH Key --------------> Bob