A method for confirming identity of a physical unit (M) in an open, wireless telecommunications network, having the following steps: storing a secret identity (SIMEI) and an open identity (IMEI) in memory in the physical unit (M); receiving an identity request (IR) with a first parameter (CHv) from the testing device (P) at the physical unit (M); generating an electronic signature (SIGt) by means of a first cryptographic function (F3) from the secret identity (SIMEI) and at least the first parameter (CHv) in the physical unit (M), and sending the generated electronic signature (SIGt) and the open identity (IMEI) to a testing device (P); wherein the identity of the physical unit (M) is confirmed if the electronic signature (SIGt) matches a corresponding electronic signature (SIGv) generated by the testing device by application of a first cryptographic function to the secret identity (SIMEI).