Abstract: A secure ID authentication system for authenticating over a multi-channel cellular radio network a response from a user module comprising a SIM card to a request from an application programming interface (API) to authenticate a transaction, in which; a request is sent to an identity application server (IAS) holding a database of user module ID information; the IAS transmits the request over a first channel of the cellular network as a class 2 SMS message to the SIM card; the SIM card causes the request to be displayed on the user module; when a response is entered, the user module encrypts the response and associated data and transmits the encrypted data over a second channel of the cellular network to an over-the-air (OTA) gateway to the IAS; and the IAS decrypts the data and transmits the response to the API.