The invention provides a general and flexible mechanism for a secure access control on a computer. Cryptographic checksums are applied for the identification of a program to another program. These cryptographic checksums are generated automatically for the programs. Each program has its program-specific identifier which can be regarded as a substantially unique value or name. Such a program-specific identifier can be used to verify the validity of one program to another program. Mutual trust relationships between different programs can therewith be set up easily.