code: func (c *ServerContext) DecryptMessage(msg []byte, seqno uint32) (uint32, []byte, error) {
  	return decryptMessage(c.sctxt, msg, seqno)
  }
docs: // DecryptMessage uses the established server context to decrypt a message
  // using the provided sequence number.
  // It returns the quality of protection flag and the decrypted message in addition to any error.