A method for private wireless communication from a broadcaster to an observer, including determining a maximum time error between broadcaster and observer and defining a time unit T exceeding the maximum time error, and sharing a secret s with the broadcaster and the observer. At the broadcaster, the method includes transmitting a message containing a security code c, and at the observer, receiving the message and assessing its genuineness by comparing the security code c with a value h(s, t120) of a predefined function h for a combination of the secret s and a current epoch t120, wherein the current epoch is an integer multiple of the time unit T.