DE102023108678A1 - Method for signing or decrypting data with a cryptographic key and computer program product and device therefor - Google Patents

Abstract

The invention relates to a method for signing and/or decrypting data (18) with a cryptographic key (20, 20a, 20b). The method comprises receiving (40) a request (42) to generate at least one key (20, 20a, 20b) for signing or decrypting data (18), detecting (43) an indicator (34), selecting (44) at least one physical property (30a, 30b, 30c, 30d) of at least one component (26a, 26b, 26c, 26d) of a device (10) depending on the indicator (34), generating (46) at least one key (20, 20a, 20b) depending on the selected physical property (30a, 30b, 30c, 30d) and signing (48) and/or decrypting the data (18) depending on the at least one key (20, 20a, 20b).The invention further relates to a computer program product and a device (10).

Description

The invention relates to signing and/or decrypting data with a cryptographic key. The invention also relates to a device for signing and/or decrypting data with a cryptographic key and a computer program product for carrying out the method on the device.

It is generally known from the prior art to link data with a signature, namely a digital signature. The signature, namely an electronic or digital signature, can be used to uniquely identify a signer or signature creator and to check the integrity of the signed data. To sign, for example, in asymmetric cryptographic procedures, a sender or signer creates a signature using a private key for the data to be signed. The signature is added to the data. A recipient of the data and the signature can use a previously received public key from the sender to check whether the signature and the data clearly originate from the sender.

Instead of or in addition to adding the signature, data can also be encrypted and decrypted using keys, especially cryptographic keys. To encrypt, the previously mentioned asymmetric cryptographic method, which is also called asymmetric encryption method, can be used to encrypt data with a recipient's public key, which the recipient can then decrypt with his or her private key.

Devices that are designed for signing or decrypting carry a key, in particular a private key, for signing or decrypting, usually in a memory that is often particularly protected against being read by unauthorized persons. This ensures that a key, in particular the private key, cannot be used by unauthorized persons to sign or decrypt data. Protecting a memory against being read by others is, however, very complex and complete protection of the key is difficult to implement. For this reason, it is desirable to avoid storing secret keys as much as possible.

A method that makes it possible to dispense with the storage of secret keys is based on the use of so-called "physical unclonable functions", i.e. physically non-copyable functions, which are also called PUFs for short. PUFs of this type are hardware structures in a semiconductor that serve to enable the semiconductor to be clearly identified and to use them to secure keys for cryptographic processes. Accordingly, a PUF represents a unique individual feature that is linked to a physical object, for example a device for signing or decrypting.

In detail, physical properties of a component, such as a semiconductor, are used to generate a secret key only when it is needed. For example, a charge decay curve of a capacitor is recorded and starting values for generating a complex key are extracted from the temporal course of the charge decay. Alternatively, the charge decay curve can be converted into digital information, such as a bit sequence, and used as a key itself. The use of "physically unclonable functions" thus makes it possible to dispense with storing the key, since it can be deleted immediately after being used for signing or decrypting and regenerated at any time.

It should be noted that states or progressions of physical properties of hardware structures usually change over time. Physical properties used, such as the switch-on state of a sensor to generate a key, can therefore be changed by the aging of the sensor or by cosmic radiation. A device that uses a preselected hardware structure or component to generate a key generates keys after a certain period of time that differ from the keys originally generated with the same hardware structure or component. If such a deviation occurs, a private key generated from the hardware structure changes in the example of an asymmetric cryptography method. Data to be decrypted or signed with a private key that was encrypted with a previously valid public key or whose integrity is to be checked with a previously valid public key can no longer be decrypted or signed to determine integrity with the changed private key. It is therefore necessary to distribute a public key that corresponds to the new private key.

Such a new distribution of keys is impractical and data already encrypted with old public keys can no longer be decrypted because an old private key cannot be reconstructed. In addition, the change in a physical property may not occur during a transition period. deterministic. The change between an old and a new key is difficult to predict and it can even happen that the new key switches back to the old key during the transition period.

Accordingly, during a transition period in which a physical property of a component changes from an original or previous state to a changed state depending on external influences, such as temperature, the same physical property of the component can temporarily lead to the generation of an original key and temporarily to the generation of a changed key. Unambiguous decryption or verification of the signature is then no longer possible. For a user, using the hardware structure to generate the key is therefore impractical or even impossible, especially during the transition period of the physical property of the hardware structure.

The invention is therefore based on the task of addressing the problems of the prior art. In particular, a way is to be found to sign or decrypt data using a key generated from a PUF, taking into account a state of the PUF in transition, i.e. a changing physical property of a component. In any case, an alternative to what is known from the prior art is to be found.

The invention relates to a method for signing and/or decrypting data with a cryptographic key according to claim 1.

Accordingly, the invention relates to a method for signing and/or decrypting data with a cryptographic key. A cryptographic key corresponds, for example, to a bit sequence, preferably with a predefined length.

According to the invention, the method firstly comprises receiving a request to generate at least one cryptographic key for signing or decrypting data. A request can, for example, be a request within a device that is generated automatically. An example of such a request is the start of an application with which data is to be decrypted. Another request can be a general start, i.e. a booting up or booting of a device with which data can be signed or decrypted. However, a request can also be received from a user interface. Receiving a request can therefore be viewed as a trigger to start a signature or decryption process.

The next step is to capture an indicator. The indicator may include data read from a memory location, data generated in the device, or data also received from a user interface. A physical property is then selected depending on the indicator.

A physical property is linked to at least one component of a device. Accordingly, a physical property of at least one component is selected. The physical property describes, for example, a measurable physical behavior of the component or of several components that have this physical property in common, preferably during predefined circumstances.

A physical property of at least one component includes, for example, a temporal discharge curve of a capacitor. The predefined circumstances can, for example, correspond to a predefined charge state of the capacitor, from which the charge curve is measured. Furthermore, a physical property can include any other temporal behavior of a component. In the case of several first components, for example different resistors, the physical property can correspond to the resistance values of each of the resistors or to a mathematical combination of the resistance values. Preferably, a physical property of at least one component corresponds to a "physically unclonable function".

A special feature is that the physical property is selected depending on the indicator. Preferably, several physical properties are predefined, whereby one or more physical properties of the predefined physical properties are selected depending on the indicator for the further process.

In a further step, at least one key is then generated depending on the at least one physical property and data is then signed and/or decrypted depending on the at least one key.

By selecting the physical property depending on the indicator, it is possible to use several different to provide physical properties for generating a key and to select these depending on the indicator. This means that, for example, as soon as it is determined that a physical property, namely preferably a PUF, has changed and thus a key generated from it differs from the previously generated key, a different physical property can be selected by simply changing the indicator.

For example, after receiving a request to generate the key, a reference file can be provided in the device and signed with the generated key. A previously stored public key can then be used to check whether the signature is valid. If the signature is invalid, this indicates that the key for signing no longer corresponds to the previously generated key. The indicator can then be changed, for example, to select a different physical property and avoid non-deterministic behavior during key generation.

According to a first embodiment, a set with several, in particular more than two or exactly two, physical properties of one or more components is selected depending on the indicator. The set therefore preferably corresponds to one of several predefined sets. Each of the sets comprises several physical properties, which are also preferably predefined for the respective set.

Preferably, several physical properties are selected, each of which is assigned to at least one component. The components that are assigned to a physical property are preferably not assigned to another physical property. Furthermore, at least one key is generated depending on each of the selected physical properties. In addition, the data is signed and/or decrypted with each of the generated keys.

For example, according to the last-mentioned embodiment, a set is selected depending on the indicator that generates a key depending on the two discharge curves based on its physical properties, each of which corresponds to a discharge curve of a component. The file is then signed and/or decrypted with both keys. If one of the keys fails or is invalid because one of the underlying physical properties has changed, the physical property of the other component is stable with sufficient probability. The second key thus remains valid and a signature can then be verified with a corresponding public key.

Decryption with at least one of the generated keys is therefore successful. A recipient of the data can therefore still check the signature with the other key or decrypt the data even if one key fails. The probability of a complete failure increases accordingly with the number of selected physical properties in a set.

When we refer here and in the following to an invalid key or a key that fails, we mean a key that is generated from a physical property of a component, but which differs from a key that was previously generated using the physical property of the component due to a change in the state of the physical property.

Even if a key fails or becomes invalid, i.e. if the physical properties of a component have changed, data can be encrypted, decrypted or signed at any time.

According to a specific embodiment of the embodiment described above, at least two physical properties are selected in step c). A first physical property of the two physical properties corresponds to a physical property of at least one first component. A second physical property of the two physical properties corresponds to a physical property of at least one second component that differs from the first component.

According to a further embodiment, at least three physical properties are selected in step c). A first physical property of the three physical properties corresponds to a physical property of at least one first component and one second component. A second physical property of the three physical properties corresponds to a physical property of at least one second and one third component. A third physical property of the three physical properties corresponds to a physical property of at least one third and one first component.

Each of three keys is based on the physical properties of at least two components.

A change in the behavior of a component therefore leads to the failure of two keys. However, this is accepted in order to enable a comparatively higher bit depth of the keys, i.e. the number of bits in each of the keys, with comparatively few components. A device that, for example, only provides a small number of components for generating keys can be used to generate keys that are as long as possible. However, by using three physical properties and thus three keys, the failure of a component, i.e. a change in the physical properties, has no effect on at least one of the keys. This one of the three keys remains valid.

According to a further embodiment, the indicator displays a set of several sets to be selected. The sets are preferably predefined. Each set comprises a plurality of physical properties. The physical properties of each set are preferably also predefined. At least one physical property of each selectable set differs from a physical property of another set. For example, if a first set comprises the physical properties A, B and C, another set comprises the physical properties B, C and D. Yet another set comprises the physical properties C, D and E.

This ensures that in the event of a key failure, i.e. a key that can be assigned to a set via a physical property becoming invalid, a previous set can be replaced by selecting another set that does not contain the physical property for generating the failed key. By adjusting the indicator, a complete set with assigned valid keys can be obtained again.

By selecting a new set, the group of physical properties is expanded to include physical properties that have not yet been used. No identical sets exist.

According to a further embodiment, the sets of physical properties have a sequence. One or more sets following a previous set in the sequence each comprise at least one physical property that is identical to the previous set. An identical physical property thus leads to the generation of an identical key as long as a state of the physical property does not change. Accordingly, for example, a first set of the sets comprises the physical property A and the physical property B, a second set following in the sequence comprises the physical property B and the physical property C. A further second set following the first set comprises, for example, the physical property A and the physical property C. A third set following in the sequence comprises the physical property C and the physical property D.

By specifying the order, it is possible to select a new set in the sequence with the indicator in which all keys can again be considered valid. In addition, backward compatibility with data that would have to be decrypted with a key that has become invalid is made possible, since the following set also includes at least one physical property with which a previously valid key is generated. The new set thus generates at least one key to decrypt data that would have to be decrypted with the keys of a previous set. If, for example, key A from the first set becomes invalid, it is possible to switch to the second set. Set two contains keys B and C according to this example. If key B in the first set were to fail, the system would switch to the second set, which contains keys A and C.

According to a further embodiment, a state or a time indication is monitored and recorded. A time indication includes, for example, a point in time, in particular a date or a period of time. A state can be the monitoring of the physical properties of a currently valid set. A state can also correspond to a decay of atoms or a gas discharge. Monitoring a state can, for example, correspond to a measurement by a Geiger counter integrated into the device, which monitors the decay of atoms to be observed in a component whose physical property is being monitored. The Geiger counter can also be used to measure, i.e. monitor, cosmic radiation.

According to this embodiment, if a stored or storeable criterion comparable to the time or the state remains unfulfilled, a previous value of the indicator is retained. The indicator therefore remains constant during each run of the method. The same set of physical properties is implemented when repeating the steps according to the invention after receiving a request to generate at least one key up to signing or decrypting the file.

This means that an identical set or the identical physical properties are always selected. This is done according to this embodiment until the criterion is met. In the event that the criterion is met, the indicator, i.e. preferably its value, is changed. This selects a set that differs from the previously selected set. Preferably, a set is selected that corresponds to a set following the previously selected set in a sequence of sets.

A criterion may be an expiration time, such as an expiration date, reaching a time period, detecting the device having a changing physical property, or detecting that the device has been exposed to a certain amount of cosmic radiation.

An automatic change of the rates depending on the indicator thus occurs depending on the time or a state and a criterion.

A state can also be the verification of the signature, which, as already mentioned above, is carried out using the signed reference file and the public stored key. The criterion is then the validity or invalidity of the signature.

A comparison of the state or the time with a criterion thus describes the independent recognition by the device that there is a need to generate a new key. This recognition can be achieved by detecting changed hardware structures, i.e. the physical properties, with the device, for example through measured values and reaching tolerance limits.

According to the embodiment, a renewal of the keys is thus possible in an event- or time-dependent manner without a user of a device having to ensure that the keys are renewed in a timely manner.

According to a further embodiment, several criteria are stored and after each of the criteria is fulfilled by the state or the time specification, a set with the indicator is selected that differs from one of the or all of the sets that were selected before the respective criterion was fulfilled. The indicator is therefore preferably changed to a value that it has not yet assumed. Different sets correspond to sets with at least one different physical property.

This allows for continuous renewal of keys, excluding sets that have already been used.

According to a particular embodiment, a control instance is provided that detects a change in a physical property. This can happen, for example, if the device's own public key, which is stored in the device, changes. This applies in the case that the device's own public key is generated depending on its own private key, which in turn is generated depending on the physical property. A comparison of a stored and a newly generated public key then shows the change in the physical property. The control instance can then preferably adapt the indicator or check whether a changed physical property is so stable that it can continue to be used to generate a key without changing the indicator.

According to a further embodiment, after detecting a change in a physical property, the control instance issues at least one new public key, which is generated depending either on the changed physical property with the same indicator or on another physical property selected by a changed indicator.

According to a further embodiment, the indicator and/or the criterion changes each time the steps according to the invention are run through, from receiving a request to generate at least one key to signing and/or decrypting the data depending on the at least one key. In particular, in the case where sets have a sequence and consecutive sets each contain an identical physical property and a changed physical property, a sequence of the encrypted or signed data can thus be identified.

For example, if a first set contains the physical properties A and B, a second set contains the physical properties B and C, and a third set contains the physical properties C and D, the first time the procedure is run, the files are signed with the first set, i.e. with keys from the physical properties A and B. When the procedure is run again, data is signed with the second set, i.e. with the keys generated from the physical properties B and C. This continues, so that a recipient of the data from one run can only decrypt this data if he is also the recipient of the data from the previous run.

According to a further embodiment, the indicator corresponds to a command or a command, which is preferably received from a user interface. The at least one physical property is therefore selected depending on the command or command. In particular, a set of physical properties dependent on the command or command is selected. Preferably, the command or command is used to select a set of physical properties that corresponds to one of several predefined sets of physical properties.

Accordingly, a user of an internal monitoring control of the device, which monitors the state of the physical properties, for example, or another application, can select a set of predefined physical properties using a command or instruction. Preferably, the sets are predefined and are made available for selection. This makes it possible for a user not to have to select physical properties themselves. In the case of a key that is no longer valid, the user or an application can select the other set that enables keys to be generated that are valid for a new period of time by specifying a command or instruction with which a different set can be selected.

According to a further embodiment, the indicator comprises a password or is selected depending on a password. The password is, for example, a character string or corresponds to biometric data. A password made up of biometric data is also called a biometric password and can correspond to a fingerprint or the like. Depending on the password, one of several sets, which in particular correspond to predefined sets, is selected. The several sets preferably each comprise several physical properties with which an electronic key can be generated.

Alternatively, depending on the password, at least one physical property can be predefined and selected after predefinition. The password itself thus serves to specify the indicator so that it contains information about which physical properties are to be used to generate one or more keys. According to a further alternative, at least one of several predefined physical properties is selected depending on the password.

Accordingly, several passwords can be specified that do not themselves serve to generate the electronic key. Rather, the passwords are each directly assigned to one of several sets of physical properties or physical properties. When a user enters a password, for example, he or she selects a physical property linked to this password using the indicator, protected by the password, in order to generate the electronic key from it.

This makes key generation even more secure.

According to a further embodiment, the at least one key that is generated depending on the at least one physical property comprises one or more key pairs of an asymmetric encryption method. Accordingly, the data is signed depending on the asymmetric key pair in such a way that first a hash of the file to be signed is formed and this hash is signed with each of the private keys of the generated key pairs. The results of the signing, namely the signature and preferably also the respective public key of the key pairs, are shown in metadata of the data. Alternatively, only the result of the signing, i.e. the encrypted or signed hash, can be shown as the signature, with the public keys being transmitted separately.

This makes it possible to easily sign data and transfer the signed data using a single file that contains metadata. The method is therefore preferably used for signing media such as images.

According to a further embodiment, at least one of the public keys of a key pair is signed with at least one private key of a further key pair before being stored in the metadata of the data, in particular of a media file such as an image. The private key of the further key pair is preferably a private key of a key that can be generated identically from a current set and a set that is different from the current set. The set that is different from the current set is preferably a previous set in the sequence.

Thus, when a new public key is generated by or depending on a new set of physical properties, this new public key is previously signed with the previous private key. This can prevent or at least counteract the inclusion of such public keys in the metadata. that do not originate from the actual user who signs the file.

According to a further embodiment, a plurality of physical properties is selected depending on the indicator, wherein a plurality comprises, for example, at least 10 or at least 20 or at least 50 physical properties. Accordingly, a plurality of keys are generated from the physical properties.

The state then represents the proportion or number of valid and invalid keys. Furthermore, a criterion is met if a predefined proportion of the plurality of keys is recognized as invalid. Otherwise, the criterion remains unmet. Once the criterion is met, a new indicator is then provided with which a new plurality of physical properties is selected. The predefined proportion corresponds, for example, to a proportion of 5%, 10% or 20%.

Accordingly, data is signed or decrypted with the plurality of keys generated from the plurality of physical properties until a check in the device detects that a predefined proportion of this plurality of keys becomes invalid. Only after this predefined proportion is exceeded is a new plurality of physical properties selected by the indicator, so that from that point on, data is signed or decrypted with a plurality of new keys that are considered valid.

Furthermore, the invention relates to a computer program product comprising instructions which, when executed on a processor of a computer unit, cause the processor to carry out the method according to one of the aforementioned embodiments. A computer unit is preferably a device or a part of a device, the device corresponding, for example, to a computer, a tablet, a mobile phone or the like.

The invention also includes a device for signing or decrypting data with a cryptographic key. The device is designed to carry out a method according to one of the aforementioned embodiments. The device is preferably a mobile device, such as a laptop or a mobile phone or tablet. Furthermore, the device can also correspond to any stationary computer.

The device preferably comprises a plurality of components, namely electronic components, such as hardware structures, which may be analog structures or digital structures. According to a particular embodiment, the device itself may be an analog structure which is configured to carry out the method.

• 1 eine Vorrichtung gemäß einem Ausführungsbeispiel zum Ausführen des Verfahrens,
• 2 Schritte eines Ausführungsbeispiels des Verfahrens,
• 3 Schritte eines bevorzugten Ausführungsbeispiels des Verfahrens,
• 4 ein weiteres Ausführungsbeispiel eines Auswahlschritts,
• 5 ein zweites Ausführungsbeispiel eines Schritts zum Erfassen eines Indikators,
• 6 ein drittes Ausführungsbeispiel eines Schritts zum Erfassen eines Indikators und
• 7 ein viertes Ausführungsbeispiel eines Schritts zum Erfassen eines Indikators.

Further embodiments are apparent from the exemplary embodiments explained in more detail in the figures. Here:

• 1 a device according to an embodiment for carrying out the method,
• 2 Steps of an embodiment of the method,
• 3 Steps of a preferred embodiment of the method,
• 4 another embodiment of a selection step,
• 5 a second embodiment of a step for detecting an indicator,
• 6 a third embodiment of a step for detecting an indicator and
• 7 a fourth embodiment of a step for detecting an indicator.

1 shows a device 10 for signing and/or decrypting data with a cryptographic key. For this purpose, the device comprises a memory 12 in which, for example, data to be signed is stored. This data can correspond, for example, to media data, such as image data, which originates from an image sensor of a camera.

The device 10 also includes a microcontroller unit 14, which includes, for example, a processor and other modules required for data processing. A crypto module 16 is provided in the microcontroller unit 14 in order to sign data 18 received from the memory 12 in accordance with a key 20. After being signed by the device 10, the data 18 can be output at an interface 22 with the signature 23. Encrypted data can also be received via the interface 22, which can be fed to the crypto module 16 in order to decrypt it with the key 20.

The key 20 is determined using a key generator 24 depending on a physical property of one or more components 26a, 26b, 26c, 26d of the device 10. Accordingly, the device 10 comprises the multiple components 26a, 26b, 26c, 26d. The components 26a, 26b, 26c, 26d correspond, for example, to sensors, other memory modules, digital hardware structures or circuits, and analog electrical components.

The microcontroller unit 14 can, for example, send a trigger signal 28 to one or more of the components 26a, 26b, 26c, 26d, so that each of the components 26a, 26b, 26c, 26d or at least one or more selected components 26a, 26b, 26c, 26d send a signal, which is in particular an analog signal. The signal indicates a physical property 30a, 30b, 30c, 30d of the respective component 26a, 26b, 26c, 26d. The key 20 can be determined depending on the physical property 30a, 30b, 30c, 30d, which is fed to the key generator 24.

Furthermore, a decision maker 32 is provided which receives an indicator 34 with which one or more of the received physical properties 30a, 30b, 30c, 30d are selected and, after the selection, fed to the key generator 24.

2 shows steps according to an embodiment of the method that can be used with the 1 illustrated device 10. In a step 40, a request 42 to generate at least one key 20 for signing or decrypting data 18 is received. In step 43, an indicator 34 is then detected. Furthermore, in step 44, at least one physical property 30a, 30b, 30c, 30d of at least one component 26a, 26b, 26c, 26d of the device 10 is selected depending on the indicator 34. In step 46, at least one key 20 is then generated depending on the at least one selected physical property 30a, 30b, 30c, 30d and in step 48 the data 18 is signed depending on the at least one key 20.

3 shows a special embodiment of steps 44, 46, 48 of 2 According to this embodiment, in step 44, two physical properties 30a, 30b are selected depending on the indicator 34. Depending on the selected physical properties 30a, 30b, two keys 20a, 20b are generated in step 46 and in step 48 the data 18 is signed with both keys 20a, 20b. Accordingly, step 48 outputs a signed file 50 which has the data 18 itself and a first signature 52a and a second signature 52b in metadata 21. The first signature 52a was generated with the first key 20a and the second signature 52b was generated with the second key 20b.

4 shows a further embodiment of the selection step 44, in which the physical properties 30a, 30b, 30c, 30d are assigned to several sets 54a, 54b, 54c. Depending on the indicator 34, one of the sets 54a, 54b, 54c is now selected and output for step 46. Step 46, which is not shown here, generates a key 20a, 20b for decrypting or signing the data 18 depending on the physical properties 30a, 30b, 30c, 30d of the selected set 54a, 54b, 54c.

The sets 54a, 54b, 54c are, for example, assigned to a sequence 56, wherein the set 54a corresponds to a set 58 that is previous in the sequence, the set 54b corresponds to a set 60 that is next in the sequence, and the set 54c corresponds to a further set 62 that is next in the sequence. The indicator 34 can, for example, in this case assume the values "1", "2" or "3". In the case of an indicator 34 that assumes the value "1", the previous set 58 is selected. In the case that the indicator assumes the value "2", the next set 60 is selected, and in the case that the indicator assumes the value "3", the next set 62 is selected.

5 shows an embodiment in which the indicator 34 is detected in step 43 by receiving a value, for example value “1”, “2” or “3” from a user interface 64 as a command 65 of the device 10.

In 6 an alternative detection of the indicator 34 is shown according to a further embodiment. Here, in a step 43 for detecting the indicator, a state 66 or a time specification 68 is compared with a criterion 70 in a sub-step 72. The indicator 34 has a start value 74 which corresponds, for example, to the value "1" and is read from a memory 75. This start value 74 is output as indicator 34 by a selection step 77 as long as the criterion 70 is recognized as not fulfilled in the sub-step 72. If the criterion 70 is fulfilled, the indicator 34 is increased or adjusted in the selection step and output as a new indicator 34. The new indicator 34 is again saved as start value 74.

After the increase, the indicator 34 assumes the value "2", for example, so that from this point on, the indicator 34 has the value "2". Preferably, after an indicator 34 has been changed, all previously selected indicators 34 are saved so that, for example, indicators 34 cannot assume a value after a change that corresponds to a previous value each time the method is run. Preferably, indicators 34 that were already used before criteria 70 were met are therefore not reused.

7 shows, according to another embodiment, the selection of one or more physical properties 30a, 30b, 30c, 30d depending on an indicator 34 which is generated depending on a password 76. The password 76 is fed to a decoder 78 in this alternative embodiment of step 43 and depending on the output of the decoder 78 in the selection step 77 an indicator 34 corresponding to the result of the decoding is selected for selecting one or more corresponding sets 54a, 54b, 54c of physical properties 30a, 30b, 30c, 30d in order to generate one or more keys 20a, 20b therefrom.

list of reference symbols

10

device

12

memory

14

microcontroller unit

16

crypto module

18

Data

20

Key

20a

first key

20b

second key

21

metadata

22

interface

23

signature

24

key generator

26a

component

26b

component

26c

component

26d

component

28

trigger signal

30a

physical property

30b

physical property

30c

physical property

30 days

physical property

32

decision-makers

34

indicator

40

Receive Request

42

request

43

Capture Indicator

44

Selecting at least one physical property

46

Generate Key

48

Signing Data

50

signed file

52a

first signature

52b

second signature

54a

Sentence

54b

Sentence

54c

Sentence

56

Series

58

previous sentence

60

subsequent sentence

62

further subsequent sentence

64

user interface

65

command

66

Condition

68

time indication

70

criterion

72

Compare event or time with criterion

74

starting value

75

memory

76

password

77

selection step

78

decoder

Claims (15)

Method for signing and/or decrypting data (18) with a cryptographic key (20, 20a, 20b), comprising the steps: a) receiving (40) a request (42) to generate at least one key (20, 20a, 20b) for signing or decrypting data (18), b) detecting (43) an indicator (34), c) selecting (44) at least one physical property (30a, 30b, 30c, 30d) of at least one component (26a, 26b, 26c, 26d) of a device (10) depending on the indicator (34), d) generating (46) at least one key (20, 20a, 20b) depending on the selected physical property (30a, 30b, 30c, 30d) and e) signing (48) and/or decrypting the data (18) depending on the at least one key (20, 20a, 20b). procedure according to claim 1 , wherein depending on the indicator (34) in step c) a set (54a, 54b, 54c) with several, in particular two, physical properties (30a, 30b, 30c, 30d) is selected, wherein in step d) a key (20, 20a, 20b) is generated depending on each of the selected physical properties (30a, 30b, 30c, 30d) and in step e) the data (18) are signed and/or decrypted with each of the generated keys (20, 20a, 20b). procedure according to claim 1 or 2 , wherein in step c) at least three physical properties (30a, 30b, 30c, 30d) are selected, wherein a first physical property (30a, 30b, 30c, 30d) of the three physical properties (30a, 30b, 30c, 30d) corresponds to a physical property (30a, 30b, 30c, 30d) of at least one first component (26a, 26b, 26c, 26d) and one second component (26a, 26b, 26c, 26d), a second physical property (30a, 30b, 30c, 30d) of the three physical properties (30a, 30b, 30c, 30d) corresponds to a physical property (30a, 30b, 30c, 30d) of at least one second and one third component (26a, 26b, 26c, 26d) and a third physical property (30a, 30b, 30c, 30d) of the three physical properties (30a, 30b, 30c, 30d) corresponds to a physical property (30a, 30b, 30c, 30d) of at least the third and the first component (26a, 26b, 26c, 26d). Method according to one of the Claims 1 until 3 , wherein the indicator (34) indicates a set to be selected from a plurality of, in particular predefined sets (54a, 54b, 54c), each comprising a plurality of, in particular predefined physical properties (30a, 30b, 30c, 30d), wherein at least one physical property (30a, 30b, 30c, 30d) of each set (54a, 54b, 54c) differs from a physical property (30a, 30b, 30c, 30d) of every other set (54a, 54b, 54c). procedure according to claim 4 , wherein the sets (54a, 54b, 54c) of physical properties (30a, 30b, 30c, 30d) have a sequence (56) and in the sequence (56) one or more sets (54a, 54b, 54c) following a previous set (54a, 54b, 54c) each comprise at least one physical property (30a, 30b, 30c, 30d) identical to the previous set (54a, 54b, 54c). Method according to one of the preceding claims, wherein a state (66) or a time indication (68), comprising a point in time, in particular a date, or a period of time is monitored or recorded, wherein in the event that a stored or storeable criterion (70) comparable to the time indication (68) or the state (66), in particular an expiration date (70) or an expiration period, remains unfulfilled, an indicator is specified for recording, which remains constant and is selected with the same set (54a, 54b, 54c) when repeating steps a) to e), and wherein in the event that the criterion (70) is fulfilled, an indicator is specified for recording, which is changed compared to the constant indicator and with which a set (54a, 54b, 54c) different from the previously selected set (54a, 54b, 54c), preferably one in the sequence of sets (54a, 54b, 54c) the following set (54a, 54b, 54c) is selected in step c). procedure according to claim 6 , wherein a plurality of criteria (70) are stored and, after each of the criteria (70) is fulfilled by the state or the time indication, a set (54a, 54b, 54c) is selected which differs from one of the or all of the sets (54a, 54b, 54c) which were selected before the respective criterion (70) was fulfilled. Method according to one of the preceding claims, wherein the indicator (34) and/or the criterion (70) changes during each run of steps a) to e). Method according to one of the preceding claims, wherein the indicator (34) comprises a command or an instruction (65) to select in step c) at least one property (30a, 30b, 30c, 30d) or dependent set (54a, 54b, 54c) of physical properties (30a, 30b, 30c, 30d), in particular from a plurality of predefined sets (54a, 54b, 54c) of physical properties (30a, 30b, 30c, 30d), dependent on the command or instruction (65). Method according to one of the Claims 1 until 9 , wherein the indicator (34) comprises a password (76), in particular a character string or biometric data, or is generated depending on a password and, depending on the password (76), one of several sets (54a, 54b, 54c), which in particular correspond to predefined sets (54a, 54b, 54c), is selected or, depending on the password (76), at least one physical property (30a, 30b, 30c, 30d) is predefined and/or selected. Method according to one of the preceding claims, wherein the at least one key comprises at least one key pair of an asymmetric encryption method and in step e) a hash of the data to be signed is signed with the or each of the private keys of the generated key pairs, wherein the results of the signing and preferably the respective public key of the key pairs are represented as signatures in metadata of the data. procedure according to claim 11 , where at least one or all of the public keys of a key pair in the metadata additionally is signed with at least one private key of a further key pair and stored in the metadata after signing, wherein the private key of the further key pair is preferably a private key of a key that can be generated identically from a current set and a set different from the current set, in particular a set that is previous in the sequence. Method according to one of the preceding claims, wherein in step c) a plurality of physical properties (30a, 30b, 30c, 30d) and in step e) a plurality of keys are generated from the physical properties (30a, 30b, 30c, 30d), wherein a state represents a monitoring of the validity and invalidity of the keys and wherein a criterion (70) is met if a predefined proportion of the plurality of keys is recognized as invalid and the criterion (79) otherwise remains unmet. Computer program product comprising instructions which, when executed on a processor of a computer unit, cause the processor to carry out the method according to one of the Claims 1 until 13 to execute. Device (10) for signing and/or decrypting data with a cryptographic key, wherein the device is designed to implement a method according to one of the Claims 1 until 13 to execute.

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