Abstract: Provided is an execution system including a central processing unit (CPU), a system memory (SM) storing a genuine program (cGC) having ciphered instructions (Cl) stored at determined addresses. A secure agent component (SAC) is dedicated to the protection of the execution of the cGC. The SAC comprises a signature register (SR) storing an instruction flow signature depending on previously executed instructions and a ciphering/deciphering module. A new instruction flow signature is determined depending on instruction and on an instruction flow signature of the previous instruction in the instruction flow of the cGC before storing this new instruction flow signature in the signature register (SR). Other embodiments disclosed.