A method is described for authenticating a portable object that includes a processor and a memory. The memory contains at least one code defining operations capable of being executed by the portable object, as well as a one-way function. The method comprises an authentication of the portable object which includes sending the portable object an order so that the latter executes a calculation of a result by applying to the one way function at least part of the code. This result enters into the implementation of a given operation, the operation being performed successfully only when the portable object is authentic.