Method for encrypting data on a field device, and method for decrypting data on a field device

Abstract

The invention relates to a method for encrypting data (D) on a field device (1) used in automation technology, said method comprising: - providing a field device (1) having a first key memory (10), a data memory (20), a communication interface (30), and a computing unit (40), the first key memory (10) having a first master key (MK1) and the communication interface (30) being designed to receive data (D); - deriving a data encryption key (DEK) from the first master key (MK1); - receiving data (D) via the communication interface (30); - encrypting the data (D) with the data encryption key (DEK) and storing the encrypted data (D*) in the data memory (20); - deriving a first key encryption key (KEK1) from the first master key (MK1); - encrypting the data encryption key (DEK) using the first key encryption key (KEK1) and storing the encrypted data encryption key (DEK*) in the data memory (20).

Description

[0001] Method for encrypting data on a field device and method for decrypting data on a field device

[0002] The invention relates to a method for encrypting data on a field device and a method for decrypting data on a field device.

[0003] Field devices used in industrial plants are already known from the state of the art. Field devices are widely used in process automation technology as well as in manufacturing automation technology. Field devices essentially refer to all devices used close to the process and that provide or process-relevant information. Field devices are used to record and / or influence process variables. Measuring devices or sensors are used to record process variables. These are used, for example, for pressure and temperature measurement, conductivity measurement, flow measurement, pH measurement, level measurement, etc. and record the corresponding process variables such as pressure, temperature, conductivity, pH value, level, flow, etc. Actuators are used to influence process variables.These include, for example, pumps or valves that can influence the flow of a fluid in a pipe or the fill level in a container. In addition to the previously mentioned measuring devices and actuators, field devices also include remote I / Os, wireless adapters, and generally devices located at the field level.

[0004] A large number of such field devices are produced and distributed by the Endress+Hauser Group.

[0005] In modern industrial plants, field devices are usually connected to higher-level units via communication networks such as fieldbuses (Profibus®, Foundation® Fieldbus, HART®, etc.). These higher-level units are usually control systems (DCS) or control units, such as a PLC (programmable logic controller). The higher-level units are used, among other things, for process control, process visualization, process monitoring and for commissioning the field devices. The measured values ​​recorded by the field devices, particularly sensors, are transmitted via the respective bus system to one (or possibly several) higher-level units. In addition, data transmission from the higher-level unit to the field devices via the bus system is also required, particularly for the configuration and parameterization of field devices and for controlling actuators.

[0006] Field devices designed to meet cybersecurity requirements typically have a central security component, a so-called Field Device Authentication Module (FDAM). Sensitive data, such as logbooks, account databases, keys, certificates, and interface configurations, are stored encrypted in this FDAM. This data is encrypted using a key generated from a master key stored in the field device's memory chip. Since this master key is unique for each memory chip produced, the encrypted data is bound to this key.

[0007] However, decrypting the data becomes problematic if the master key cannot be read due to a defect in the memory chip. In such a case, the encrypted data on the field device is permanently lost.

[0008] It is therefore an object of the invention to provide a method which allows data to be encrypted in an accessible and secure manner.

[0009] This object is achieved according to the invention by a method for encrypting data on a field device of automation technology according to claim 1.

[0010] The method according to the invention comprises:

[0011] Providing a field device with a first key memory, a data memory, a communication interface and a computing unit, wherein the first key memory has a first master key and the communication interface is suitable for receiving data,

[0012] Deriving a data protection key from the first master key,

[0013] Receiving data via the communication interface,

[0014] Encrypting the data with the data protection key and storing the encrypted data in the data storage,

[0015] Deriving a first key protection key from the first master key, encrypting the data protection key with the first key protection key and

[0016] Storing the encrypted data protection key in the data storage,

[0017] Reading in a secret via the communication interface and generating a second salt by the computing unit, wherein the second salt is stored in the data memory, generating a second key protection key based on the secret and the second salt,

[0018] Encrypting the data protection key with the second key protection key and storing the encrypted data protection key in the data store.

[0019] The method according to the invention enables data to be securely encrypted while remaining accessible, even if an originally used master key becomes inaccessible, for example, because the memory chip in which the master key is persistently stored is defective. The method according to the invention thus enables a user to access the encrypted data in the field device at any time, even if the master key is destroyed, simply by entering a so-called secret, e.g., a password. It is even possible for the defective memory chip to be replaced with a new memory chip with a different master key, and for this different master key to ultimately be used to decrypt the data.

[0020] According to one embodiment of the invention, the secret is a QR code, a file or a manual password entry.

[0021] According to one embodiment of the invention, when generating the second key protection key, a second verification information is created by the computing unit and is stored on the data storage device, wherein the computing unit is suitable for checking, using the second verification information, whether the second key protection key is suitable for decrypting the encrypted data protection key.

[0022] According to one embodiment of the invention, the second verification information comprises a hash created by the computing unit using the second string and the secret.

[0023] The above-mentioned object is further achieved by a method for decrypting data encrypted by the inventive method on a field device according to claim 5.

[0024] The method according to the invention comprises:

[0025] Reading the secret into the computing unit via the communication interface and reading the second salt from the data memory into the computing unit,

[0026] Generating the second key protection key based on the secret and the second salt by the computing unit, wherein the second key protection key is suitable for decrypting the encrypted data protection key,

[0027] Decrypting the encrypted data protection key using the second key protection key by the computing unit so that the data protection key is obtained,

[0028] Decrypting the encrypted data using the data protection key by the processing unit so that the data is obtained,

[0029] Reading the data from the data storage by the computing unit.

[0030] According to one embodiment of the invention, the method further comprises:

[0031] Reading the second verification information from the data memory by the computing unit, checking the second key protection key using the second verification information by the computing unit to determine whether the second key protection key is suitable for decrypting the encrypted data protection key.

[0032] According to one embodiment of the invention, the method further comprises:

[0033] Inserting a second key memory with a second master key into the field device, deriving a third key protection key from the second master key, encrypting the data protection key with the third key protection key to obtain an encrypted data protection key,

[0034] Storing the encrypted data protection key in the data store.

[0035] According to one embodiment of the invention, the first key memory is repaired so that the first master key is reusable, and the computing unit uses the first master key to derive the first key protection key, to decrypt the encrypted data protection key with the first key protection key, to decrypt the encrypted data with the data protection key.

[0036] The invention is explained in more detail with reference to the following description of the figures. Figure 1 shows a schematic representation of a field device for implementing a method according to the invention.

[0037] The field device 1 of automation technology, schematically illustrated in Figure 1, is suitable for executing the method according to the invention on the field device 1. The field device 1 comprises a first key memory 10, a data memory 20, a communication interface 30, and a processing unit 40.

[0038] The first key memory 10 is preferably a microcontroller-internal memory. The first key memory 10 is preferably a persistent memory, i.e., with NAND and NOR gates. The first key memory 10 has a first master key MK1. The first master key MK1 is permanently assigned to the first key memory 10. This means that the first master key MK1 is unique and inseparable from the first key memory 10. The first key memory 10 is preferably physically separated from the data memory 20, so that if the first key memory 10 becomes defective, the data memory 20 continues to function.

[0039] The communication interface 30 is suitable for receiving data D. This data D includes, for example, account data, keys, certificates, firmware updates, QR codes, manual password entries, or even measurement data from a sensor. The communication interface 30 naturally has the user interface necessary for the respective data transmission, e.g., an input unit for manual password entry, a USB port for data transmission via USB, a Wi-Fi antenna for data transmission via Wi-Fi, a camera or scanner or display for transmitting QR codes, etc.

[0040] The computing unit 40 is preferably implemented as a microcontroller and has a volatile memory. The following describes in detail the method according to the invention for securely storing data D in the field device 1 described above.

[0041] First, the field device 1 described above is prepared. This means that the field device 1 is ready for use and, for example, data D for the field device 1 is available at the communication interface 30.

[0042] A data protection key DEK is then derived from the first master key MK1 by the processing unit 40. The data key DEK is stored, for example, in the volatile memory of the processing unit 40 for further operations. This allows the first master key MK1 to be accessed only once after each restart of the field device 1. This allows operations that require the data key DEK to be performed more quickly and simultaneously saves energy. The data key DEK is ideally a symmetric key. This means that it can be used to encrypt and decrypt data.

[0043] Next, data D is received via the communication interface 30. As described above, this may be, for example, a firmware update or an access code for activating a paid software module.

[0044] The data D is then encrypted with the data protection key DEK and the encrypted data D* is stored in the data storage 20. At this point, it should be noted that encrypted objects are marked with an asterisk in the following text and in the figures for easier understanding.

[0045] Furthermore, a first key protection key KEK1 is derived from the first master key MK1. The first key protection key KEK1 is suitable, as its name suggests, for protecting a key, i.e., for encrypting it. The first key protection key KEK1 is particularly suitable for encrypting and decrypting the data key DEK. Preferably, the computing unit 40 generates a so-called first salt ST1 associated with the first key protection key KEK1 and a first piece of verification information VI1 associated with the first key protection key KEK1 for the first key protection key KEK1 derived from the first master key MK1. The first salt ST1 and the first piece of verification information VI1 are stored in the data memory 20.Likewise, a first derivation algorithm associated with the first key protection key KEK1, which was used to create the first verification information VI1, is preferably stored with the first verification information VI1 in the data storage 20. This is followed by encryption of the data protection key DEK using the first key protection key KEK1, and storage of the encrypted data protection key DEK* in the data storage 20.

[0046] In the following, a data protection key DEK encrypted with a specific key protection key KEK1, KEK2, KEK3 is marked with a number of asterisks corresponding to the key number, so that it is clear with which key protection key KEK1, KEK2, KEK3 the encrypted data protection key DEK*, DEK**, DEK*** can be decrypted.

[0047] Next, a so-called secret SC is read in via the communication interface 30. The secret SC is preferably a QR code, a file, or a manual password entry. The secret SC is presented, entered, or provided by a user at the communication interface 30, so that the secret SC can be read in at the communication interface 30.

[0048] Likewise, a second salt ST2 is generated by the computing unit 40, wherein the second salt ST2 is stored in the data memory 20. The second salt ST2 is suitable for use by the computing unit 40 together with the secret SC to generate a key.

[0049] A second key protection key (KEK2) is then generated based on the entered secret (SC) and the second salt (ST2). This has the advantage that the second key protection key (KEK2) can be recreated at any time using the secret (SC) and the second salt (ST2), independent of the first master key (MK1).

[0050] When generating a key protection key KEK1, KEK2, KEK3, a piece of verification information VI1, VI2, VI3 that is individual for this key protection key is preferably created by the computing unit 40 and stored on the data storage device 20. The computing unit 40, with the aid of the verification information VI1, VI2, VI3, is suitable for checking whether a key protection key KEK1, KEK2, KEK3 is suitable for decrypting the data protection key DEK*, DEK**, DEK*** encrypted with the respective key protection key KEK1, KEK2, KEK3. This check is carried out by a checker VR, also called a validator (see Figure 1). The verification information VI1, VI2, VI3 preferably comprises a so-called hash, which was created by the computing unit 40 using the salt ST1, ST2, ST2 and the secret SC (if this was used to create the key protection key).When creating the hash, a predetermined algorithm AL1, AL2, AL3 was preferably applied and generated using a so-called key derivation function (KDF). Preferably, the respective algorithm AL1, AL2, AL3 used is also stored in the data memory 20 together with the verification information VI1, VI2, VI3. According to one embodiment of the method, a corresponding second verification information VI2 is created for the second key protection key KEK2.

[0051] The data protection key DEK is then encrypted using the second key protection key KEK2 and the encrypted data protection key DEK** is stored in the data storage 20.

[0052] Next, a method for reading data securely stored by the method described above, i.e., the encrypted data D*, is described when the first key memory 10 of the field device 1 is defective, so that the first master key MK1 is unusable.

[0053] First, the secret SC is read into the computing unit 40 via the communication interface 30. To do this, a user must provide the secret SC, for example, enter it manually if it is a password, or, as described above, present it if it is a QR code.

[0054] The salt ST is also read from the data memory 20 into the computing unit 40. Since the second salt ST2 was stored unencrypted in the data memory 20, it is possible to use it directly.

[0055] Next, the second key protection key KEK2 is generated based on the secret SC and the second salt ST2 by the computing unit 40. The second key protection key KEK2 is suitable for decrypting the encrypted data protection key DEK**.

[0056] Optionally, the second verification information VI2 is read from the data memory 20 by the computing unit 40 and the second key protection key KEK2 is checked using the second verification information VI2 by the computing unit 40 to determine whether the second key protection key KEK2 is suitable for decrypting the encrypted data protection key DEK**.

[0057] The encrypted data protection key DEK** is then decrypted by the computing unit 40 using the second key protection key KEK2. The data protection key DEK is thus obtained.

[0058] The encrypted data D* is then decrypted by the computing unit 40 using the data protection key DEK. The data D is thus readable.

[0059] Finally, the data D are read from the data memory 20 by the computing unit 40. According to one embodiment of the method, the defective first key memory 10, i.e., the memory chip or microcontroller of the field device 1, is replaced or supplemented by a second key memory 11, i.e., a new memory chip. The second key memory 11 has a second master key MK2, which is different from the first master key MK1. When a defective first key memory 10 is replaced, the first master key MK1 is lost. In order to avoid having to enter the secret SC every time the field device 1 is restarted in order to gain access to the data D as described above, the second master key MK2 is used to generate a third key protection key KEK3.The third key protection key KEK3 is used to encrypt the data protection key DEK (in a sense, a copy thereof) and store it in the data memory 20 (see Figure 1, DEK***). Thus, the computing unit 40 can generate the third key protection key KEK3 itself with each restart using the second master key MK2 and use it to decrypt the encrypted data protection key DEK***. As mentioned above, a third salt ST3 and a third piece of verification information VI3 are preferably generated here as well and stored in the data memory 20 together with a third algorithm AL3, which was used to generate the third salt ST3 and the verification information VI3.

[0060] In the event that the first key memory 10 is repaired so that the first master key MK1 is reusable, the computing unit 40 is adapted to use the first master key MK1 to derive the first key protection key KEK1, to decrypt the encrypted data protection key DEK* with the first key protection key KEK1, to decrypt the encrypted data D* with the data protection key DEK.

[0061] List of reference symbols

[0062] I Field device

[0063] 10 first key storage

[0064] II second key storage

[0065] 20 data storage

[0066] 30 Communication interface

[0067] 40 computing units

[0068] D Data

[0069] D* encrypted data

[0070] H Hash

[0071] SC Secret

[0072] KDF key derivation

[0073] VR auditor

[0074] AL1 first algorithm

[0075] AL2 second algorithm

[0076] AL2 third algorithm

[0077] ST 1 first salt

[0078] ST2 second salt

[0079] ST3 third salt

[0080] VI1 first verification information

[0081] VI2 second verification information

[0082] VI3 third verification information

[0083] MK1 first master key

[0084] MK2 second master key

[0085] DEK data protection key

[0086] DEK* data protection key encrypted with the first key protection key

[0087] DEK** Data protection key encrypted with the second key protection key

[0088] DEK*** Data protection key encrypted with the third key protection key

[0089] KEK1 first key protection key

[0090] KEK2 second key protection key

[0091] KEK3 third key protection key

Claims

Patent claims 1 . Method for encrypting data (D) on a field device (1 ) of automation technology, comprising: Providing a field device (1) with a first key memory (10), a data memory (20), a communication interface (30), and a computing unit (40), wherein the first key memory (10) has a first master key (MK1), and the communication interface (30) is suitable for receiving data (D), deriving a data protection key (DEK) from the first master key (MK1), receiving data (D) via the communication interface (30), encrypting the data (D) with the data protection key (DEK), and storing the encrypted data (D*) in the data memory (20), deriving a first key protection key (KEK1) from the first master key (MK1), encrypting the data protection key (DEK) with the first key protection key (KEK1), and storing the encrypted data protection key (DEK*) in the data memory (20), Reading in a secret (SC) via the communication interface (30) and generating a second salt (ST2) by the computing unit (40), wherein the second salt (ST2) is stored in the data memory (20), Generating a second key protection key (KEK2) based on the secret (SC) and the second salt (ST2), Encrypting the data protection key (DEK) by the second key protection key (KEK2) and storing the encrypted data protection key (DEK**) in the data memory (20).

2. Method according to claim 1, wherein the secret (SC) is a QR code, a file or a manual password entry.

3. Method according to claim 1 or 2, wherein, when generating the second key protection key (KEK2), a second verification information (VI2) is created by the computing unit (40) and stored on the data memory (20), wherein the computing unit (40) is suitable, with the aid of the second verification information (VI2), for checking whether the second key protection key (KEK2) is suitable for decrypting the encrypted data protection key (DEK**).

4. The method according to claim 3, wherein the second verification information (VI2) comprises a hash (H) which was created by the computing unit (40) using the second salt (ST2) and the secret (SC).

5. A method for decrypting data (D*) encrypted by a method according to one of the preceding claims on a field device (1), comprising: Reading the secret (SC) into the computing unit (40) via the communication interface (30) and reading the second salt (ST2) from the data memory (20) into the computing unit (40), Generating the second key protection key (KEK2) based on the secret (SC) and the second salt (ST2) by the computing unit (40), wherein the second key protection key (KEK2) is suitable for decrypting the encrypted data protection key (DEK**), Decrypting the encrypted data protection key (DEK**) using the second key protection key (KEK2) by the computing unit (40) so that the data protection key (DEK) is obtained, Decrypting the encrypted data (D*) using the data protection key (DEK) by the computing unit (40) so that the data (D) is obtained, Reading the data (D) from the data memory (20) by the computing unit (40).

6. The method according to claim 5, wherein the method further comprises: Reading the second verification information (VI2) from the data memory (20) by the computing unit (40), Checking the second key protection key (KEK2) using the second verification information (VI2) by the computing unit (40) whether the second key protection key (KEK2) is suitable for decrypting the encrypted data protection key (DEK**).

7. The method according to any one of claims 5 to 6, wherein the method further comprises: inserting a second key memory (11) with a second master key (MK2) into the field device (1), Deriving a third key protection key (KEK3) from the second master key (MK2), encrypting the data protection key (DEK) by the third key protection key (KEK3) so that an encrypted data protection key (DEK***) is obtained, storing the encrypted data protection key (DEK***) in the data memory (20).

8. The method according to claim 7, wherein the first key memory (10) is repaired so that the first master key (MK1) is reusable, and the computing unit (40) uses the first master key (MK1) to derive the first key protection key (KEK1) to decrypt the encrypted data protection key (DEK*) with the first key protection key (KEK1) to decrypt the encrypted data (D*) with the data protection key (DEK).

Images