1. Process to protect, using at least one blank unit ( 60 ) including at least memorization means ( 15 ) and processing means ( 16 ), a vulnerable software ( 2 v ) against its unauthorized usage, said vulnerable software ( 2 v ) being produced from a source ( 2 vs ) and working on a data processing system ( 3 ), said protection process comprising: during a protection phase (P): creating a protected software ( 2 p ): by choosing, in the source of the vulnerable software ( 2 vs ), at least one conditional branch, by choosing at least one portion of the source of the vulnerable software ( 2 vs ) containing at least one chosen conditional branch, by producing a source of the protected software ( 2 ps ) from the source of the vulnerable software ( 2 vs ), by modifying at least one chosen portion of the source of the vulnerable software ( 2 vs ) to obtain at least one modified portion of the source of the protected software ( 2 ps ), this modification being such that during the execution of the protected software ( 2 p ): a first execution part ( 2 pes ) is executed in the data processing system ( 3 ) and a second execution part ( 2 peu ) is executed in a unit ( 6 ), obtained from the blank unit ( 60 ) after upload of information, and the second execution part ( 2 peu ) executes at least the functionality of at least one chosen conditional branch and puts at the data processing system ( 3 )'s disposal, a piece of information enabling the first execution part ( 2 pes ), to carry on its execution at the chosen spot, and by producing: a first object part ( 2 pos ) of the protected software ( 2 p ), from the source of the protected software ( 2 ps ), said first object part ( 2 pos ) being such that during the execution of the protected software ( 2 p ), appears a first execution part ( 2 pes ) which is executed in the data processing system ( 3 ) and whose at least a portion takes into account a result obtained from executing the at least one chosen conditional branch in the unit ( 6 ), and a second object part ( 2 pou ) of the protected software ( 2 p ), said second object part ( 2 pou ) being such that, after upload to the blank unit ( 60 ) and during the execution of the protected software ( 2 p ), appears the second execution part ( 2 peu ) by means of which each chosen conditional branch is executed, and uploading the second object part ( 2 pou ) to the blank unit ( 60 ), with the intention of obtaining the unit ( 6 ), and during a usage phase (U) during which the protected software ( 2 p ) is executed: in the presence of the unit ( 6 ) and each time a portion of the first execution part ( 2 pes ) imposes it, executing the functionality of a conditional branch in the unit ( 6 ), so that said portion is executed correctly and that, consequently, the protected software ( 2 p ) is completely functional, and in the absence of the unit ( 6 ) and in spite of the request by a portion of the first execution part ( 2 pes ) to execute the functionality of a conditional branch in the unit ( 6 ), not being able to fulfill said request correctly, so that at least said portion is not executed correctly and that consequently, the protected software ( 2 p ) is not completely functional, wherein during the protection phase (P): defining: as instructions set, an instructions set whose at least some instructions work with registers and use at least one operand with the intention of returning a result, constructing exploitation means enabling the unit ( 6 ) to execute elementary functions of a set, the execution of said elementary functions being triggered by execution in the data processing system ( 3 ), of elementary commands, for at least some of the instructions working with registers: a part (PF) defining the functionality of the instruction, and a part defining the expected chaining for the execution of the instructions and including bits fields corresponding to: an identification field of the instruction (CII), and for each operand of the instruction: a flag field (CD k ), and an expected identification field (CIP k ) of the operand, for each register belonging to the exploitation means and used by the instructions set, a generated identification field (CIG v ) in which is automatically memorized the identification of the last instruction which has returned its result in said register, as detection means ( 17 ), means enabling, during the execution of an instruction, for each operand, when the flag field (CD k ) imposes it, to check the equality of the generated identification field (CIG v ) corresponding to the register used by said operand, and the expected identification field (CIP k ) of the origin of said operand, and as coercion means ( 18 ), means enabling to modify the result of the instructions, if at least one of the checked equalities is false.