According to one aspect, a system-on-a-chip is proposed which includes a memory storage, a computation circuit, a comparison circuit, and a validation circuit. The memory storage is configured to store an external software module. The computation circuit is configured to compute several modified software modules from the external software module and compute check values by iteration until obtaining a final check value. Each check value is computed at least from a given modified software module and a check value previously computed, starting with a predefined initial check value. The comparison circuit is configured to compare the final check value to an expected value stored in the system-on-a-chip. The validation circuit is configured to validate the external software module when the final check value is equal to the expected value.