A method for protecting embedded system software and embedded system

The invention pertains to a software protection method that finds particular utility in embedded systems. The protection is based on authentication carried out entirely by means of hardware. A system includes a security circuit integrated on the same microcircuit with a processor. As the system is started, the security circuit reads (404) from the program memory certain portions of the program code and calculates (405) in accordance with a certain algorithm one or more identifiers. Secret code stored in the security circuit is used as operands in the calculation. The identifiers calculated are compared (406) to correct ones and system use is enabled (408) only if the identifiers match. For further protection it is possible to use a program memory circuit which has a component-specific identification code and to check (403) and use as operand (405) said identification code. The security circuit may also be used to decrypt an entirely encrypted program. The method makes the misuse of embedded system software considerably more difficult than in known systems. In addition, compared to software-based authentication, the protection uses less system resources.