Method for checking the authenticity of an electronic module of a modular field device in automation technology

Abstract

The present invention relates to a method for verifying the authenticity of electronic modules of modular field devices in inspection automation technology. A suitable key pair is assigned to each electronic module of the field device, and the suitable key pair confirms the identity of the electronic module. Each key pair consists of a public key and a private key, and the public key of the suitable key pair is stored in a list. The list is assigned to the field device or a unit communicating with the field device. The method includes that when an electronic module is replaced or added, the field device or the unit communicating with the field device checks whether the replaced or added electronic module has a key pair, whether the public key of the replaced or added electronic module is listed in the list of public keys, and whether the electronic module has the correct private key. If the conclusion of the check is affirmative, the replaced or added electronic module is allowed to communicate or interact with the field device or some other electronic module related to the function of the field device.

Description

Technical Field

[0001] The present invention relates to a method for verifying the authenticity of an electronic module of a modular field device in automation technology. Background Art

[0002] Field devices for detecting and / or influencing physical, chemical, or biological process variables are commonly used in process automation as well as in manufacturing automation. Measuring devices are used to detect process variables. These measuring devices are used, for example, for pressure and temperature measurements, conductivity measurements, flow rate measurements, pH measurements, level measurements, etc., and detect the corresponding process variables of pressure, temperature, conductivity, pH value, level, flow rate, etc. Actuator systems are used to influence process variables. Examples of actuators are pumps or valves, which can influence the flow rate of a fluid in a pipeline or the level in a storage tank. In addition to the aforementioned measuring devices and actuators, field devices should also be understood to include remote I / O, radio adapters, or generally devices arranged at the field level. In the context of the present invention, all such devices are referred to as field devices, which are used near a process or a plant and provide or process information related to the process or the plant.

[0003] The corresponding field devices typically consist of multiple electronic modules, such as plug-in modules with circuit boards, sensors with digital connections, etc. If an electronic module is replaced or added, it is not currently checked whether the electronic module is authentic. Currently, visual inspection of the electronic module is usually carried out, and the electronic module is considered authentic only after a positive visual inspection.

[0004] The above process poses a significant safety risk: In principle, since it is impossible to detect any type of electronic module that may have been tampered with, there is a risk in the installation of automation technology that an electronic module that may have been tampered with will be installed. For example, if an electronic module does not meet the requirements for use in a potentially explosive area but is used in such an area, this will definitely endanger lives. Summary of the Invention

[0005] This patent application describes a method for ensuring the authenticity of a module: whether the module is actually the module it purports to be. The main consideration here is to check whether a specific module exists, where the identity is checked and modules of the same design are not automatically accepted. In the applicant's patent application filed simultaneously with this patent application, the authenticity of the manufacturer is checked, that is, whether the electronic module is from the original manufacturer or a trusted third party or supplier. Of course, both methods can also be used simultaneously or sequentially to check the electronic module.

[0006] The object of the present invention is to automatically detect non-authentic electronic modules.

[0007] This object is achieved by a method for verifying the authenticity of electronic modules of modular field devices in automation technology, wherein for each electronic module of the field device, a suitable key pair is assigned, which key pair is used to confirm the identity of the electronic module, wherein each key pair consists of a public key Pk and a private key pk, and wherein the public key of the suitable key pair is stored in a list, wherein the list is assigned to the field device or a unit communicating with the field device, and wherein the method comprises the following method steps:

[0008] - When an electronic module is replaced or added, the field device or a unit communicating with the field device checks:

[0009] - whether the replaced or added electronic module has a key pair, and

[0010] - whether the public key of the replaced or added electronic module is listed in the list of public keys,

[0011] - whether the electronic module has the correct private key;

[0012] - If the conclusion of the check is affirmative, the replaced or added electronic module is allowed to communicate or interact with the field device or some other electronic module related to the function of the field device.

[0013] Therefore, it is checked whether there are those individual modules that should exist according to the module trust list. If an electronic module is replaced or added, the method according to the invention is used for detection. If the electronic module cannot prove its authenticity, integration into the operation is rejected.

[0014] According to the invention, before the field device incorporates the replaced or added electronic module into the communication required for operating the field device, the field device hereby checks whether the public key of the electronic module is included in the list of electronic modules identified as trustworthy. The authenticity of the electronic module is usually checked during the runtime of the field device.

[0015] The key pair assigned to each electronic module is also referred to as the encrypted identity of the electronic module. Symmetric encryption and asymmetric encryption are known in principle. In the case of symmetric encryption, encryption and decryption occur using the same key, while in the case of asymmetric encryption, encryption and decryption occur using two different keys.

[0016] In asymmetric encryption, key pairs based on RSA are typically used, and these key pairs may differ in key length. Currently, RSA keys of 2048 bits in length are already considered necessary; those requiring higher security use key lengths of 3072 or even 4096 bits. However, the increased key length not only has a negative impact on the required memory space but also affects performance, i.e., in the case of asymmetric encryption and decryption, especially in key pair generation. Significantly more efficient than RSA encryption systems based on prime number fields are those using elliptic curves. A number of ECs (elliptic curves) have been established. One of them is curve 25519.

[0017] Preferably, an asymmetric key pair is used in combination with the present invention. Asymmetric encryption methods are considered to be extremely secure because two keys that cannot be derived from each other are used: the public key for encryption and the private key for decryption, and vice versa. The private key always remains in the key generator. Encryption is performed using the private key and decryption is performed using the public key, or vice versa.

[0018] In addition, the following method steps are recommended:

[0019] To check whether the electronic module has the public key of a suitable key pair, the field device or the unit communicating with the field device requests the public key of the replaced or added electronic module and checks whether the public key of the electronic module is stored in a list of public keys classified as trustworthy.

[0020] In addition, a test is performed on whether the electronic module has the private key of a suitable key pair. The challenge / response method is preferably used for this test. The fact that the electronic module transmits a trustworthy public key does not prove that this public key is also the public key associated with the electronic module. Ultimately, the electronic module may also be a forged module using an illegally obtained public key. Therefore, it must be checked whether the electronic module is genuine, i.e., whether the provided public key actually belongs to the electronic module, whether the electronic module has provided the correct public key associated with it, and whether this can also be proven. As described above, the challenge / response method is preferably used for this proof.

[0021] For this purpose, the field device or the electronic component sends an arbitrary message to the replaced or added electronic module with a request for signature creation ("challenge"). The module signs the message and then sends the signature ("response") back to the field device or back to the requesting electronic module. Now, the field device or the requesting electronic module can check whether the electronic module has the correct private key based on the signature.

[0022] This signature is created, for example, by module k applying a hashing method to message m and encrypting the resulting hash value with its private key. The field device decrypts the obtained signature with the public key of the module and compares it with the self-computed hash value of the sent message. Ideally, the two hash values are the same, which proves that: a) the module is authenticated since it has sent the correct public key, and b) this can also be proven since the module possesses the associated private key. By providing this proof, the replaced or added electronic module is considered genuine. Special algorithms (DSA, ECDSA, etc.) are also known for signature creation, however, these special algorithms can ultimately also be used with asymmetric key pairs.

[0023] If the electronic module now does not have a suitable key pair, or only has a key pair based on a different curve or a different cryptographic system, then the electronic module cannot participate in the challenge / response method. If the electronic module has a generator, a remedy may be possible, through which a suitable key pair can be generated; alternatively, the electronic module must have a corresponding interface and key memory so that an externally generated key pair can subsequently be written into the electronic module. However, in both cases, the module must know the applicable / associated operations, for example, encrypting with the private key.

[0024] In summary, especially from the field device, an arbitrary message is sent to the replaced or added electronic module as a challenge for a request to create a signature using the private key. The electronic module signs the message with its private key and returns the signature as a response. The signature is used to check whether the electronic module possesses the private key of a suitable key pair. For asymmetric encryption, any key pair is considered suitable. Key pairs based on RSA or EC are common. A key pair is a tool. Such a key pair is now used by the field device to determine the authenticity of the electronic module.

[0025] In certain cases, "suitable" can be further restricted: both the field device and the electronic module must know the corresponding operations (encryption, decryption) using the key pair. For example, if the field device only knows, for example, EC and only knows RSA for the module, the present invention will not work. If the electronic module has no asymmetric encryption at all, then there is no suitable key pair.

[0026] Some special cases are described below: If the check shows that the replaced or added electronic module has no key pair, then it is checked whether a key pair can be generated or provided for the electronic module,

[0027] wherein, in the case of the key pair being provided or generated by another electronic module, the key pair is passed to the replaced or added electronic module.

[0028] Furthermore, it is proposed in combination with the present invention that replaced or added electronic modules without a suitable key pair or for which a suitable key pair cannot be generated are still excluded from communication.

[0029] If the check shows that the replaced or added electronic module has a key pair, but the public key of the key pair is not stored in the list even though the electronic module appears to be genuine, then once an authorized person has confirmed the trustworthiness of the electronic module, the public key of the generated key pair is assigned to the list of electronic modules classified as trustworthy.

[0030] In the case where a suitable key pair can be generated for an electronic module, if an authorized person confirms the trustworthiness of the electronic module, the public key of the key pair is also stored in the list of electronic modules classified as trustworthy. In this way, the list can grow and contain the public keys of multiple electronic modules. Of course, when replacing a module, it is convenient to delete the public key of the replaced module from the module trust list.

[0031] If an electronic module does not have a suitable key pair, or only has a key pair based on another curve or another cryptographic system, then the electronic module cannot participate in the challenge / response method. To generate a suitable key pair, the electronic module must have a generator through which such a (suitable) key pair can be generated, or the electronic module must have an interface and a key memory so that an externally generated key pair can be written into the electronic module. However, in both cases, the electronic module must be aware of the applicable / associated prerequisites and operations (e.g., encrypting with the private key).

[0032] It is stipulated that during the production process or during service use, each electronic module is provided with a suitable key pair by the original manufacturer or a third party authorized by the original manufacturer; furthermore, the public key of the suitable key pair is stored in the list of electronic modules classified as trustworthy at the corresponding time point. During or after the production process, due to a module being replaced or added, a trustworthy person will inform the field device that the replaced or added electronic module is considered trustworthy. In this case, the field device incorporates the public key of the electronic module into its module trust list MTL.

[0033] When replacing an electronic module, the public key of the replaced electronic module is deleted from the list of electronic modules classified as trustworthy.

[0034] As already mentioned above, a check or test on whether the electronic module is genuine can be performed during the ongoing operation of the field device.

[0035] It has also been mentioned that in combination with the present invention, instead of the public key of the electronic module, a derivative (e.g., a hash value) or some other independent and unique identifier can be used. Description of the Drawings

[0036] The present invention will be explained in more detail with reference to the following drawings. Shown in the drawings are:

[0037] Figure 1 is a schematic diagram of a field device that is suitable for performing the method according to the present invention and has a plurality of electronic modules, and

[0038] Figure 2 is a flowchart depicting the method according to the present invention with different developments. Detailed Description of the Invention

[0039] Figure 1 is a schematic diagram of a field device FG that has a plurality of electronic modules Mk and is suitable for performing the method according to the present invention. In the shown case, the field device FG has three electronic modules Mk, where k = 1, 2, 3. A suitable key pair Pk, pk is assigned to each electronic module Mk of the field device FG, where k = 1, 2, 3. Such a suitable key pair Pk, pk is a prerequisite for the associated electronic module Mk to be able to confirm its authenticity. Each key pair Pk, pk consists of a public key Pk and a private key pk. In addition, the public key Pk of the suitable key pair Pk, pk is stored in a list MTL, where this list MTL is assigned to the field device FG or a unit U communicating with the field device FG. MTL is an abbreviation for Module Trust List. This list contains the public keys Pk of the electronic modules Mk classified as trustworthy. Only when the inspection step for the method according to the present invention and / or its further embodiments is positively evaluated, is the replaced or newly added electronic module Mk functionally integrated into the field device FG.

[0040] A separate key pair Q, q consisting of a public key Q and a private key q is also assigned to the field device. The field device FG can, if necessary, send the public key Q to one or more electronic modules Mk, for example, to determine a secret consensus between the field device FG and the electronic module Mk and use it (or its derivative) as a symmetric key for encrypted communication (keyword: "DiffieHellman", replacement of the public key). In addition, it is possible that not only must the electronic module Mk prove its identity to the field device FG, but also the field device FG must prove its identity to the electronic module Mk. For example, if the electronic module Mk has stored a lot of sensitive (secret) data, then this electronic module may only be able to transfer this data to one field device or only to a specific field device FG. For this purpose, each electronic module Mk will have to have a stored field device trust list, in which the public keys of the field devices FGk classified as trustworthy are listed.

[0041] Figure 2Shows a flow chart describing the method according to the invention with different developments.

[0042] For example, below program point 10, a new electronic module Mk (e.g., Mod3new) is inserted to replace electronic module Mod3; alternatively, a new module Mk, e.g., electronic module Mod4, is newly added. At program point 20, it is checked whether the new electronic module Mk has a suitable key pair Pk, pk. If it has a suitable key pair, at program point 30 it is checked whether the public key Pk of the replaced or added electronic module Mk is listed in the MTL list of public keys Pk. If the test result is positive, at program point 40 it is checked whether the new electronic module Mk has the correct private key pk. If this check result is positive, the replaced or added electronic module Mk is allowed to communicate or interact with the field device FG or with some other electronic module Mk (related to the function of the field device FG). This check terminates at program point 60. This check may also be performed by a separate unit. This is not shown separately in Figure 2 It is not shown separately.

[0043] To check whether the electronic module Mk has the public key Pk of the suitable key pair Pk, pk determined at program point 30, the field device FG or the unit U communicating with the field device FG requests the public key Pk of the replaced or added electronic module Mk and checks whether the public key Pk of the electronic module Mk is stored in the list MTL.

[0044] The check (program point 40) on whether the electronic module Mk also has the correct private key pk of the suitable key pair Pk, pk is performed by a challenge / response method. For this purpose, in particular, the field device FG sends an arbitrary message m to the replaced or added electronic module Mk as a challenge for a request to create a signature using the existing private key pk. The electronic module Mk signs the message m with its private key pk and returns the signature as a response. This signature is used to check whether the electronic module Mk has the correct private key pk of the suitable key pair Pk, pk. This is the case if the encrypted and decrypted message m is again the message m.

[0045] Now consider what may happen if the check result at program point 20, 30, or 40 is negative.

[0046] If the check at program point 20 shows that the electronic module Mk does not have a suitable key pair Pk, pk, then check whether a key pair Pk, pk can be generated or provided for the electronic module Mk (program point 70). If the key pair Pk, pk can be provided or generated by the field device FG or another electronic module Mk (program point 80), then the key pair Pk, pk is passed to the replaced or added electronic module Mk. The replaced or added module Mk itself may also generate a suitable key pair Pk, pk. For this purpose, suitable technical prerequisites must be available. Once the authorized person has confirmed the trustworthiness of the electronic module Mk, the public key Pk is stored in the list MTL.

[0047] In the case where the electronic module Mk does not have a suitable key pair Pk, pk or a suitable key pair Pk, pk cannot be generated for the electronic module Mk (program point 70), then the electronic module Mk remains excluded from the communication. Optionally, an error message is generated stating that the electronic module Mk does not have a suitable key pair Pk, pk (program point 90).

[0048] If the public key Pk of the replaced or added module Mk is not included in the list MTL (program point 30) and the authorized user has not confirmed the trustworthiness of the electronic module Mk, then an error message is issued stating that the electronic module Mk is not trustworthy (program point 120). The field device FG does not integrate the replaced or added module into the communication.

[0049] If the challenge / response test at program point 40 shows that the electronic module does not possess the correct private key pk, then an error message is generated at program point 130 stating that the electronic module Mk is not authentic.

[0050] The method according to the invention can reliably prove the correct identity of the electronic module Mk. Fake modules can be eliminated.

Claims

1. A method for verifying the authenticity of an electronic module of a modular field device in automation technology, wherein, a suitable key pair (Pk, pk) is assigned to each electronic module of the field device, the suitable key pair confirming the identity of the electronic module, wherein each key pair (Pk, pk) consists of a public key and a private key, and wherein the public key of the suitable key pair (Pk, pk) is stored in a list, wherein the list is assigned to the field device or a unit communicating with the field device, where k = 1, 2,..., n, and wherein the method comprises the following method steps: When an electronic module is replaced or added, the field device or a unit communicating with the field device checks: whether the replaced or added electronic module has a key pair (Pk, pk), and whether the public key of the replaced or added electronic module is listed in the list of public keys, whether the electronic module has the correct private key; If the conclusion of the check is affirmative, the replaced or added electronic module is allowed to communicate or interact with the field device or some other electronic module related to the function of the field device; If the check shows that the replaced or added electronic module does not have a key pair (Pk, pk), it is checked whether a key pair (Pk, pk) can be generated or provided for the electronic module, wherein, in the case where the key pair (Pk, pk) is provided or generated by another electronic module, the key pair (Pk, pk) is passed to the replaced or added electronic module.

2. The method according to claim 1, the method comprising the following method steps: In order to check whether the electronic module has the public key of the suitable key pair (Pk, pk), the field device or a unit communicating with the field device requests the public key of the replaced or added electronic module and checks whether the public key of the electronic module is stored in the list.

3. The method according to claim 1 or 2, the method comprising the following method steps: The test regarding whether the electronic module has the private key of the suitable key pair (Pk, pk) is performed by a challenge / response method.

4. The method according to claim 3, the method comprising the following method steps: An arbitrary message is sent to the replaced or added electronic module as a challenge for a request to create a signature using the private key; The electronic module signs the message with its private key and returns the signature as a response; The signature is used to check whether the electronic module has the private key of the suitable key pair (Pk, pk).

5. The method according to claim 4, wherein, the field device sends an arbitrary message to the replaced or added electronic module as a challenge for a request to create a signature using the private key.

6. The method according to claim 1, the method comprising the following method steps: In the case where the electronic module does not have a suitable key pair (Pk, pk) or a suitable key pair (Pk, pk) cannot be generated for the electronic module, the electronic module remains excluded from communication.

7. The method according to claim 1 or 2, wherein the method comprises the following method steps: If the check shows that the replaced or added electronic module has a key pair (Pk, pk), but the public key of the key pair (Pk, pk) is not stored in the list, then if the authorized person confirms the trustworthiness of the electronic module, the public key of the generated key pair (Pk, pk) is assigned to the list.

8. The method according to claim 1 or 2, wherein the method comprises the following method steps: In the case where a suitable key pair (Pk, pk) can be generated for the electronic module, if the authorized person confirms the trustworthiness of the electronic module, the public key of the key pair (Pk, pk) is stored in the list.

9. The method according to claim 1 or 2, wherein the method comprises the following method steps: During the production process or during service use, each of the electronic modules is provided with a suitable key pair (Pk, pk) by the original manufacturer or a third party authorized by the original manufacturer, and the public key of the suitable key pair (Pk, pk) is stored in the list.

10. The method according to claim 1 or 2, wherein the method comprises the following method steps: When replacing an electronic module, the public key of the replaced electronic module is deleted from the list.

11. The method according to claim 3, wherein the method comprises the following method steps: The check and the test are performed during the ongoing operation of the field device.

12. The method according to claim 1 or 2, wherein the method comprises the following method steps: Instead of the public key of the electronic module, a derivative or some other independent and unique identifier is used.

13. The method according to claim 12, wherein, the derivative is a hash value.

Images