An access control model based on the security evaluation of subject and object was proposed. At first, some important concepts and their relationships, such as user (subject) security degree, resource (object) security degree, user security level, resource security level, and operation level were defined. Then a formula to qualify the condition that the user must satisfy when he accessed a certain system resource by a certain operation was provided from the angle of security. The object security degree was decided by the security evaluation value of the device that the accessed resource lied in, which equaled the weighting sum of the evaluation values of the threat, the vulnerability and the environment security. The user security degree was decided by five factors, such as the security of physical device used by the user, compliance of the use of the resources, the history behavior of the user, the evaluation of the user by a third party, and the identity certificate class. The methods to compute the values of these five factors were discussed and the subject security degree was equal to the weighting sum. At last, the proposed access control model based on the security evaluation of subject and object was verified in practical application. The statistics of experiment showed that, compared with the access control system depended on firewall and IDS, the total number and severity of security events of the system based on the proposed access control model decrease obviously.
