Method for executing a polymorphic machine code of a predetermined function by a microprocessor

A polymorphic machine code of a predetermined function, this polymorphic machine code comprising instructions executable by a microprocessor which, when executed by this microprocessor, causes:

• a) the acquisition of a numerical value capable of varying, from one execution to another of the same polymorphic machine code, then
• b) the generation, according to the numerical value acquired, of a first and, alternately, a second instruction stream, these first and second instruction streams each being capable of performing the predetermined function when they are executed by the microprocessor, each of these instruction streams being formed of a succession of basic blocks, each basic block starting at a branch address and ending with a branch instruction to a branch address of another basic block, these first and second instruction streams being distinguished from each other by at least one instruction opcode or a different operand or a different literal value or a different number of instructions,
• c) the recording of the generated instruction stream in a main memory, then
• d) the execution of the generated instruction stream that has just been recorded,
• before step c):
• for each branch address at which a basic block starts, the microprocessor automatically adds into the generated instruction stream a renewal instruction capable, when executed by the microprocessor, of triggering, immediately after the branching to this branch address, the renewal of an initialization vector of a stream decryption module with a specific value associated with this branch address, then
• a stream encryption module, parameterized by an initialization vector, encrypts the instruction stream as it is generated in the course of this encryption each basic block is encrypted using the specific value of the initialization vector associated with the branch address at which it starts,
• during step c), only the instruction stream thus encrypted is recorded in the main memory, and
• during step d), each time an encrypted instruction of the instruction stream is loaded from the main memory for being executed, this instruction is first decrypted by the decryption module, then transferred, without passing through the main memory, to an arithmetic and logic unit of the microprocessor, then executed by this arithmetic and logic unit, in the course of this step d), the added renewal instructions are executed as they are encountered in the instruction stream.

An electronic apparatus capable of executing a polymorphic machine code of a predetermined function, this apparatus comprising a microprocessor programmed for performing the following steps:

• a) acquisition of a numerical value capable of varying, from one execution to another of the same polymorphic machine code, then
• b) generation, according to the numerical value acquired, of a first and, alternately, a second instruction stream, these first and second instruction streams each being capable of performing the predetermined function when they are executed by the microprocessor, each of these instruction streams being formed of a succession of basic blocks, each basic block starting at a branch address and ending with a branch instruction to a branch address of another basic block, these first and second instruction streams being distinguished from each other by at least one instruction opcode or a different operand or a different literal value or a different number of instructions,
• c) recording of the generated instruction stream in a main memory, then
• d) execution of the generated instruction stream that has just been recorded,
• wherein the microprocessor is also programmed for performing the following steps:
• before step c):
• for each branch address at which a basic block starts, the microprocessor automatically adds into the generated instruction stream a renewal instruction capable, when executed by the microprocessor, of triggering, immediately after the branching to this branch address, the renewal of an initialization vector of a stream decryption module with a specific value associated with this branch address, then
• a stream encryption module, parameterized by an initialization vector, encrypts the instruction stream as it is generated, in the course of this encryption each basic block is encrypted using the specific value of the initialization vector associated with the branch address at which it starts,
• during step c), only the instruction stream thus encrypted is recorded in the main memory, and
• during step d), each time an encrypted instruction of the instruction stream is loaded from the main memory for being executed, this instruction is first decrypted by the decryption module, then transferred, without passing through the main memory, to an arithmetic and logic unit of the microprocessor, then executed by this arithmetic and logic unit, in the course of this step d), the added renewal instructions are executed as they are encountered in the instruction stream.