Method for detecting anomalies suggesting a manipulation during a secure starting operation of a software-controlled device
A method for recognizing anomalies suggesting a manipulation during a secure booting operation of a software-controlled device comprises, inter alia, checking operating parameters of system components necessary for the operation of a microprocessor, checking a flag indicating an improperly concluded booting operation, and signature-based authenticity checking of software to be loaded or software components to be loaded. In the case of multistage booting operations, counter values assigned to a respective stage are compared with associated reference values. In the event of a fault, each check can output a signal on the basis of which, optionally together with further signals, the type of an attack can be recognized, so that specific countermeasures can be initiated.
1 . A method for recognizing a type of an attack on a secure booting operation of a microprocessor-controlled device, comprising:
reading out at least one operating parameter from at least one system component necessary for an operation of the microprocessor, and comparing the at least one operating parameter read out with corresponding stored reference values, wherein, if the comparison shows a difference, a first signal, which signals a recognized side channel attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated,
checking a state of a flag that is set during an as yet unsuccessfully concluded booting operation, wherein, if the flag is set, a second signal, which signals a recognized fault injection attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated, wherein, if the flag is not set, the flag is set after the check,
calculating a hash value or a checksum over at least one block of a software or software component, and comparing with a hash value or checksum stored for a same at least one block of the software or software component during a preceding booting operation, or calculating an authentication code of software to be loaded or a software component to be loaded, and comparing the calculated authentication code with the authentication code of the preceding booting operation read out from a memory, wherein, if the comparison shows a difference, a third signal, which signals a recognized attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated,
calculating, if not already done previously, an authentication code of software to be loaded or a software component to be loaded, and comparing the calculated authentication code with a reference code read out from a memory, wherein, if the comparison shows a difference, a fourth signal, which signals a recognized fault injection attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated,
replacing the authentication code of the preceding booting operation read out from the memory with the authentication code calculated for the current booting operation, and deleting the flag that is set during an as yet unsuccessfully concluded booting operation.
2 . The method as claimed in claim 1 , additionally comprising, if the booting operation is of multistage design:
comparing a current stage of a multistage booting operation with a reference value assigned to this stage, wherein, if the comparison shows a difference, a fifth signal, which signals a recognized fault injection attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated, and wherein otherwise the execution of the booting operation and the loading of subsequent stages are continued until a last stage of the booting operation indicated by the corresponding reference value has been loaded.
3 . The method as claimed in claim 1 , additionally comprising:
storing unique time information at a beginning and/or after successful conclusion of the booting operation,
comparing, for each new booting operation, present time information with a time information stored during a previous booting operation, wherein, if the comparison shows a difference which is less than a predefined value, a sixth signal, which signals a recognized attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated.
4 . The method as claimed in claim 1 , additionally comprising:
storing unique time information at a beginning and/or after successful conclusion of the booting operation,
comparing, for each new booting operation, a number of preceding rebooting operations within a predefined time with a permissible maximum value, wherein, if the number of preceding rebooting operations is above the permissible maximum value, a sixth signal, which signals a recognized attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated.
5 . The method as claimed in claim 4 , wherein the beginning and/or the successful conclusion of a booting operation are/is ascertained on a basis of a power consumption that is typical of these events.
6 . The method as claimed in claim 4 , wherein the beginning of a booting operation is determined on a basis of a reset signal output by a microprocessor.
7 . The method as claimed in claim 4 , additionally comprising:
monitoring the allocation of at least one system resource of a first device during the booting operation, and
comparing a number of allocations of a same system resource to a same process within a predetermined second time period with a maximum value predefined for this system resource, wherein, if the number of allocations of the same system resource to the same process exceeds the predefined maximum value, a seventh signal, which signals a recognized attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated.
8 . A device comprising at least one processor, volatile and nonvolatile memory and at least one further system component necessary for the operation of the microprocessor, which are communicatively connected to one another via one or more data lines or one or more data buses, wherein computer program instructions are retrievably stored in the nonvolatile memory and, when the instructions are executed by the at least one processor, configure the device to carry out a method comprising:
reading out at least one operating parameter from at least one system component necessary for an operation of the microprocessor, and comparing the at least one operating parameter read out with corresponding stored reference values, wherein, if the comparison shows a difference, a first signal, which signals a recognized side channel attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated,
checking a state of a flag that is set during an as yet unsuccessfully concluded booting operation, wherein, if the flag is set, a second signal, which signals a recognized fault injection attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated, wherein, if the flag is not set, the flag is set after the check,
calculating a hash value or a checksum over at least one block of a software or software component, and comparing with a hash value or checksum stored for a same at least one block of the software or software component during a preceding booting operation, or calculating an authentication code of software to be loaded or a software component to be loaded, and comparing the calculated authentication code with the authentication code of the preceding booting operation read out from a memory, wherein, if the comparison shows a difference, a third signal, which signals a recognized attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated,
calculating, if not already done previously, an authentication code of software to be loaded or a software component to be loaded, and comparing the calculated authentication code with a reference code read out from a memory, wherein, if the comparison shows a difference, a fourth signal, which signals a recognized fault injection attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated,
replacing the authentication code of the preceding booting operation read out from the memory with the authentication code calculated for the current booting operation, and deleting the flag that is set during an as yet unsuccessfully concluded booting operation.
9 . The device of claim 8 , wherein the method further comprises:
comparing a current stage of a multistage booting operation with a reference value assigned to this stage, wherein, if the comparison shows a difference, a fifth signal, which signals a recognized fault injection attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated, and wherein otherwise the execution of the booting operation and the loading of subsequent stages are continued until a last stage of the booting operation indicated by the corresponding reference value has been loaded.
10 . The device of claim 8 , wherein the method further comprises:
storing unique time information at a beginning and/or after successful conclusion of the booting operation,
comparing, for each new booting operation, present time information with a time information stored during a previous booting operation, wherein, if the comparison shows a difference which is less than a predefined value, a sixth signal, which signals a recognized attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated.
11 . The device of claim 8 , wherein the method further comprises:
storing unique time information at a beginning and/or after successful conclusion of the booting operation,
comparing, for each new booting operation, a number of preceding rebooting operations within a predefined time with a permissible maximum value, wherein, if the number of preceding rebooting operations is above the permissible maximum value, a sixth signal, which signals a recognized attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated.
12 . The device of claim 11 , wherein the beginning and/or the successful conclusion of a booting operation are/is ascertained on a basis of a power consumption that is typical of these events.
13 . The device of claim 11 , wherein the beginning of a booting operation is determined on a basis of a reset signal output by a microprocessor.
14 . The device of claim 11 , wherein the method further comprises:
monitoring the allocation of at least one system resource of a first device during the booting operation, and
comparing a number of allocations of a same system resource to a same process within a predetermined second time period with a maximum value predefined for this system resource, wherein, if the number of allocations of the same system resource to the same process exceeds the predefined maximum value, a seventh signal, which signals a recognized attack and a failed booting operation, is output and the method is ended and the further booting operation is terminated.