Fichas
Comp Sec
Fichas del conjunto (21)
- 1SubjectProperly authenticated user
- 2Access control methodsAccess Control Matrix
Capabilities
Access Controls Lists - 3Access Control MatrixMatrix indexed by S and O, entry containing P
- 4CapabilitiesRows of ACM. Index by subj, then their P for each O.
implemented by tokens - stored by subj - 5Reference monitor FunctionEnforces Access control Policy
Mediates subj obj access.
Must mediate all to become effective - hence becomes target that must be verified as correct - 6Mode Security LevelUser mode - low clearance (Must call kernel mode to access hardware)
Kernel mode - high clearance (can access hardware)
SuperUser - special user (still user) less restrictions on what kernel mode it can access - 7Access control attacks1. Fool reference Monitor
2. Fool CPU into executing kernel mode code to avoid reference monitor (buffer overrun into kernel mode) - privilege escalation - 8Intermediate controlsLayer between Subjects and objects to make assigning perms easier.
1. Groups
2. Privileges
3. Protection Rings - 9UNIXeach O owned by a UID and GID
Each O has r,w,x flag for user, group, other, in this priority order - 10negative permisssionsadd negative entry to access control structure
need to resolve policy conflicts - 11Privileges & RolesPrivileges(= perms but for RBAC) - rights to execute operations (OS functions)
Roles are intermediate layer between users and operations - 12RBACDefining Roles with privileges and access permissions and assigning users to them
Operations - Obj
Privileges - Perms
Roles - IC
Users - Subj - 13Protections ringsIntermediate layer of HBAC aimed at process and object.
Subjects are processes.
each Process is assigned a num (importance)
Access control decisions compares subject and object number - subj with lower importance access objects with higher. (user proc can call proc in lower ring) - 14Protection Ring ExploitConfused Deputy Problem
what if outer ring calls inner ring to copy inner ring file to outer ring?
Looks like inner ring should be allowed to
Fixed by examining execution history - 15Reference Monitor SecurityReference-validation mechanism must be
1. tamper-proof
2. always invoked
3. verifiable - Must be able to subject it to analysis to ensure correctness. - 16Reference Monitor Implementation1. Hardware AC mechanisms - Gates
2. RM in the Kernel - OS handles requests - Cobra
3.Program in the RM - RM is wrapper around program and interpreter which limits access to wider system. - JAVA Sandbox
4. RM in the program - Program can be transformed to contain RM functionality (AC checks)
Adds complexity to checking integrity and verifying of RM so limits types of programs that it can be applied to - 17Hardware AC mechanism1. memory structures can limit activities - EPROM (Erasable, programable ROM) or WROM (write one only mem) for audit trails
2. Gates - mediate between rings - execution only i.e no copy (beats confused deputy) - 18Clark - Wilson ModelUser programs are IC between S and O(data items)
S are authorised to execute programs
O( data items) are accessible via programs
Focus on Integrity
Effort is in making right programs for IC and using it correctly - 19Clark - Wilson Security MeasuresS have to be identified and authed
O can only be manipulated by a restricted set of programs
S can execute only restricted set of programs
Audit logs must be maintained - continuous verification of system integrity
System must be certified to run properly - at deployment and repeatedly - 20Clark Wilson IntegrityEnforced by
1. Well formed transactions
2. Separation of duties - different people develop test certify and operate the system. Forces collusion to circumvent security - 21Clark Wilson RequirementIntegrity => all manipulations were those for which authorisation was granted.
Requirement is no unauthorised modification of data
1. internal consistency - property of system
2. external consistency - relationship between internal state and external world enforced by audit.
Información
- Descripción
- Fichas sobre Comp Sec, creado por Rish Naik el 17/05/2024.
- Creado por
- Rish Naik
- Visitas
- 5
- Valoración