The present invention relates to a process and a system for data transmission. Authentication data and an electronic key are generated, whereby the electronic key is stored as assigned to the authentication data. At least part of the electronic key is transmitted by means of an authentication module of the central module to a communications terminal. Asynchronously to that, data are encrypted into encrypted data by means of an encryption module and by means of at least part of the electronic key. The encrypted data are transmitted between a central module and a communications terminal. The encrypted data are decrypted by means of a decryption module and by means of at least part of the electronic key.