Method for checking the authenticity of electronic modules (Mk) of a modular field device in automation technology where each electronic module (Mk with k = 1, 2,... n) of the field device has a suitable key pair (Pk, pk with k = 1, 2....n) is assigned, which confirms the identity of the electronic module (Mk), wherein each key pair (Pk, pk) consists of a public key (Pk) and a private key (pk), and wherein the public keys (Pk) of the suitable key pairs (Pk, pk) are stored in a list, wherein the list to the field device or one with the field device communicating unit, the method comprising the following method steps: - When replacing or adding an electronic module (Mk), the field device or the unit communicating with the field device checked: - whether the replaced or added electronic module (Mk) has a key pair (Pk, pk), and - whether the public key (Pk) of the replaced or added electronic module is included in the list of public keys (Pk), - whether the electronic module (Mk) is in possession of the correct private key(pk), whereby a challenge-response procedure is used to test whether the electronic module (Mk) is in possession of the private key (pk) of the suitable key pair (Pk, pk), - a communication or interaction of the field device concerning the functionality of the replaced or added electronic module (Mk) with the field device or another electronic module (Mk) is permitted if the check is completed with a positive result, - If the check shows that the replaced or added electronic module (Mk) does not have a key pair (Pk, pk), the system checks whether a key pair (Pk, pk) can be generated or provided for the electronic module (Mk), wherein, in the event that the key pair (Pk, pk) is provided or generated by a further electronic module (Mk), the key pair (Pk, pk) is transferred to the replaced or added electronic module (Mk). where each electronic module (Mk with k = 1, 2,... n) of the field device has a suitable key pair (Pk, pk with k = 1, 2....n) is assigned, which confirms the identity of the electronic module (Mk), wherein each key pair (Pk, pk) consists of a public key (Pk) and a private key (pk), and wherein the public keys (Pk) of the suitable key pairs (Pk, pk) are stored in a list, wherein the list to the field device or one with the field device communicating unit, the method comprising the following method steps: - When replacing or adding an electronic module (Mk), the field device or the unit communicating with the field device checked: - whether the replaced or added electronic module (Mk) has a key pair (Pk, pk), and - whether the public key (Pk) of the replaced or added electronic module is included in the list of public keys (Pk), - whether the electronic module (Mk) is in possession of the correct private key(pk), whereby a challenge-response procedure is used to test whether the electronic module (Mk) is in possession of the private key (pk) of the suitable key pair (Pk, pk), - a communication or interaction of the field device concerning the functionality of the replaced or added electronic module (Mk) with the field device or another electronic module (Mk) is permitted if the check is completed with a positive result, - If the check shows that the replaced or added electronic module (Mk) does not have a key pair (Pk, pk), the system checks whether a key pair (Pk, pk) can be generated or provided for the electronic module (Mk), wherein, in the event that the key pair (Pk, pk) is provided or generated by a further electronic module (Mk), the key pair (Pk, pk) is transferred to the replaced or added electronic module (Mk). - When replacing or adding an electronic module (Mk), the field device or the unit communicating with the field device checked: - whether the replaced or added electronic module (Mk) has a key pair (Pk, pk), and - whether the public key (Pk) of the replaced or added electronic module is included in the list of public keys (Pk), - whether the electronic module (Mk) is in possession of the correct private key(pk), whereby a challenge-response procedure is used to test whether the electronic module (Mk) is in possession of the private key (pk) of the suitable key pair (Pk, pk), - whether the replaced or added electronic module (Mk) has a key pair (Pk, pk), and - whether the public key (Pk) of the replaced or added electronic module is included in the list of public keys (Pk), - whether the electronic module (Mk) is in possession of the correct private key(pk), whereby a challenge-response procedure is used to test whether the electronic module (Mk) is in possession of the private key (pk) of the suitable key pair (Pk, pk), - a communication or interaction of the field device concerning the functionality of the replaced or added electronic module (Mk) with the field device or another electronic module (Mk) is permitted if the check is completed with a positive result, - If the check shows that the replaced or added electronic module (Mk) does not have a key pair (Pk, pk), the system checks whether a key pair (Pk, pk) can be generated or provided for the electronic module (Mk), wherein, in the event that the key pair (Pk, pk) is provided or generated by a further electronic module (Mk), the key pair (Pk, pk) is transferred to the replaced or added electronic module (Mk).