Authentication and authorization Access control consists of two steps, authentication and authorization. Subject Do operation Reference monitor Object Source Makes an access request Request Guard Resources memory printers files nodes Computer System Security and Management Access Control

Access operations There is two access modes: Observe – look at the contents of an object Example application level: select * from table (sql) or SNMP get operation Alter – change the content of an object Example application level: delete from table (sql) or SNMP set operation In Linux there is three different access attributes: Read (r), Write, (w) and execute (e). And three different access groups: Owner, groups and others For example: -rw-r--r-- 1 root root 221 Dec hosts The owner of the file hosts, root, has read and write access. Groups has read access and others has read access Computer System Security and Management Access Control

Administrative access rights Meaning of read, write and execute operations: read – reading from file and list directories contents write – writing to file and create or rename a file in the directory execute – executing a (program) file and search the directory Operations for manipulating a subject’s access rights is called grant and revoke when the subject’s rights are modified by some other party. Example root changes the ownership of a file: chown nobody:nobody /tmp/script.sh When the owner changes his own access right operation is called assert and deny. Computer System Security and Management Access Control

Access Control Lists An ACL corresponds to a column of the access control matrix and states who may access a given object. ACL for process.c Bill: read, write; ACL for lists.c Alice: execute; Bill: write; Linux access control model is based on simple ACLs. Active Directory, AD, in Windows server uses ACL. AD uses GPO, Group Policy, to grant access to object like applications or printers to groups. Computer System Security and Management Access Control

Intermediate controls Group and negative permissions: Group1 in AD has access to a network disk meanwhile Group2 hasn’t. Privileges: root access in Linux. To grant root access in Mac os X we can use the command sudo, but we need a password. Role-Based Access Control: RBAC. In Linux root has the highest privilege or admin user in windows. Computer System Security and Management Access Control