Technical Field
The present disclosure generally relates to electronic circuits and, more specifically, to microcontrollers or processing units manipulating encrypted information (data, instructions, addresses, etc.). The present disclosure more specifically relates to the protection of such a processing against fault-injection attacks.
Description of the Related Art
In many applications, processing units, for example, central processing units (CPU) of microcontrollers, manipulate information which are stored in encrypted fashion in volatile or non-volatile memories external to the processing unit or exchanged in encrypted fashion with other circuits or functions.
Since it is encrypted in the memories, the information is protected. However, to be processed, be it data, addresses, or instructions, the information should be decrypted by the processing unit. The processing results are, before being output by the processing unit (to be stored or communicated to another function), encrypted by the processing unit.
The fact for the information to be manipulated in non-encrypted fashion by the processing unit is a weakness in the protection.
To attempt overcoming this problem, it has already been provided to use an additional processing unit having the function of executing in parallel the same operations as the main processing unit, and of comparing certain results provided by the two processing units. In case of a divergence, this means that the main processing unit has been submitted to an attack, typically a fault injection, and the system may react, for example, by blocking the communication of the information to the outside.
However, in case of a fault injection on the verification elements or of multiple faults, these solutions appear to be insufficient.
There thus is a need to improve the protection of encrypted information during the unencrypted execution thereof by a processing unit.
The subject matter discussed in the Background section is not necessarily prior art and should not be assumed to be prior art merely as a result of its discussion in the Background section. Along these lines, the recognition of one or more problems in the prior art discussed in the Background section and the subject matter associated therewith should not be treated as prior art unless expressly stated to be prior art. Instead, the discussion in the Background section encompassing one or more recognized problems in the prior art should be treated as part of the inventor's approach to the particular problem, which in and of itself may also be inventive.