A method is used to restore the security of a secure assembly such as a chip card, after the contents of its second memory zone have been read by a third party. The method is for generating a security key implemented by a secure module comprising a central unit, a first conditional access memory zone and at least one second memory zone containing all or part of the user program. The method includes reading of all or part of the second memory zone, and generation of at least one root key based on all or part of the second zone data and on at least one item of secret information stored in the first memory zone.