Programmable electronic-mechanical reversing flat key interactively communicatable with data processing means

A metal flat key with depressions arranged in the key shank for receiving radially displaceably tumbler pins located in the lock rotor for use as a mechanical key outside and as a mechanical/electronic key inside a closing means with additional electronic means arranged in the lock cylinder includes a casing (2B, 2A, 20, 21) for receiving an electronic assembly (5) and which is fixed to the key shank (1), the casing simultaneously being used as the key grip (2). The casing (2A, 2B, 20, 12) on the casing side to the key shank (1) has a connecting part (12) for receiving electric contacts (4) between grip (2) and key shank (1).