Devices and methods for executing instructions in an automatic and secure manner include a security processor having at least a read-only memory, a random access memory, a computer capable of performing cryptographic functions, a monotonic counter management unit associated with one or more monotonic counters, is such that it does not include any other storage memory, meaning that the security processor does not store any program or external data, a public key allowing at least one initial enrolled administrator to be authenticated is stored before the first use of same in its read-only memory, its random access memory is capable of loading a set of data and instructions that can be authenticated by a public key cryptographic module, the execution by the computer, after the authentication of same, of certain instructions, increments one of the monotonic counters.