Security Models and ArchitectureOverviewPowerPoint PresentationTerminologyTypes of Access ControlInformation Flow ModelsSlide 7ModelsBell-LaPadula (BLP) ModelBell-LaPadula Model (Continued)Biba ModelClark-Wilson ModelClark-Wilson Model (Continued)Slide 14Clark-Wilson versus BibaChinese WallSlide 17Trusted Computer System Evaluation (TCSEC)Information Technology Security Evaluation Criteria (ITSEC)Common CriteriaCommon Criteria – Evaluation Assurance LevelsCC EALs - ReferenceCC EALs – Summary 1-3CC EALs – Summary 4-5CC EALs – Summary 6-7CC EALs - Web ReferencesSecurity Models and ArchitectureCISSP Exam PreparationBernie Eydt2OverviewOverview•Basic concepts•The Models–Bell-LaPadula (BLP)–Biba–Clark-Wilson–Chinese Wall•Systems Evaluation3Basic Concepts4TerminologyTerminology•Trusted Computing Base (TCB) – combination of protection mechanisms within a computer system•Subjects / Objects–Subjects are active (e.g., users / programs)–Objects are passive (e.g., files)•Reference Monitor – abstract machine that mediates subject access to objects•Security Kernel – core element of TCB that enforces the reference monitor’s security policy5Types of Access ControlTypes of Access Control•Discretionary Access Control (DAC) – data owners can create and modify matrix of subject / object relationships (e.g., ACLs)•Mandatory Access Control (MAC) – “insecure” transactions prohibited regardless of DAC•Cannot enforce MAC rules with DAC security kernel–Someone with read access to a file can copy it and build a new “insecure” DAC matrix because he will be an owner of the new file.6Information Flow ModelsInformation Flow Models•Pour cement over a PC and you have a secure system•In reality, there are state transitions•Key is to ensure transitions are secure•Models provide rules for how information flows from state to state.•Information flow models do not address covert channels –Trojan horses–Requesting system resources to learn about other users7Access Control Models8ModelsModels•Bell-LaPadula•Biba•Clark-Wilson•Chinese WallGood brief summary on Harris p.2479Bell-LaPadula (BLP) ModelBell-LaPadula (BLP) Model•BLP is formal (mathematical) description of mandatory access control•Three properties:–ds-property (discretionary security) –ss-property (simple security – no “read down”)–*-property (star property – no “write down”)•A secure system satisfies all of these properties•BLP includes mathematical proof that if a system is secure and a transition satisfies all of the properties, then the system will remain secure.10Bell-LaPadula Model (Continued)Bell-LaPadula Model (Continued)•Honeywell Multics kernel was only true implementation of BLP, but it never took hold•DOD information security requirements currently achieved via discretionary access control and segregation of systems rather than BLP-compliant computers11Biba ModelBiba Model•Similar to BLP but focus is on integrity, not confidentiality•Result is to turn the BLP model upside down–High integrity subjects cannot read lower integrity objects (no “read down”)–Subjects cannot move low integrity data to high-integrity environment (no “write up”)•McLean notes that ability to flip models essentially renders their assurance properties useless12Clark-Wilson ModelClark-Wilson Model•Reviews distinction between military and commercial policy–Military policy focus on confidentiality–Commercial policy focus on integrity•Mandatory commercial controls typically involve who gets to do what type of transaction rather than who sees what (Example: cut a check above a certain dollar amount)13Clark-Wilson Model (Continued)Clark-Wilson Model (Continued)•Two types of objects:–Constrained Data Items (CDIs)–Unconstrained Data Items (UDIs)•Two types of transactions on CDIs in model–Integrity Verification Procedures (IVPs)–Transformation Procedures (TPs)•IVPs certify that TPs on CDIs result in valid state•All TPs must be certified to result in valid transformation14Clark-Wilson Model (Continued)Clark-Wilson Model (Continued)•System maintains list of valid relations of the form:{UserID, TP, CDI/UDI}•Only permitted manipulation of CDI is via an authorized TP•If a TP takes a UDI as an input, then it must result in a proper CDI or the TP will be rejected•Additional requirements–Auditing: TPs must write to an append-only CDI (log)–Separation of duties15Clark-Wilson versus BibaClark-Wilson versus Biba•In Biba’s model, UDI to CDI conversion is performed by trusted subject only (e.g., a security officer), but this is problematic for data entry function.•In Clark-Wilson, TPs are specified for particular users and functions. Biba’s model does not offer this level of granularity.16Chinese WallChinese WallFocus is on conflicts of interest.•Principle: Users should not access the confidential information of both a client organization and one or more of its competitors.•How it works–Users have no “wall” initially.–Once any given file is accessed, files with competitor information become inaccessible.–Unlike other models, access control rules change with user behavior17Systems Evaluation18Trusted Computer System Evaluation (TCSEC)Trusted Computer System Evaluation (TCSEC)•Criteria published in the Orange Book•Officially replaced by Common Criteria•Four Levels–A Verified protectionA1 Verified design–BMandatory protectionB1 Labeled SecurityB2 Structured ProtectionB3 Security Domains–C Discretionary protectionC1 Discretionary securityC2 Controlled access–D Minimal security19Information Technology Security Evaluation Criteria (ITSEC)Information Technology Security Evaluation Criteria (ITSEC)•Used primarily in Europe•Target of Evaluation (TOE) is either product or system•Two ratings–Functionality rating (F1 to F10)–Assurance Rating (E0 to E6)•Rough mapping exists between TCSEC and ITSEC (see Harris p.260)20Common CriteriaCommon Criteria•ISO standard evaluation criteria that combines several different criteria, including TCSEC and ITSEC•Participating governments recognize Common Criteria certifications awarded in other nations•Seven Evaluation Assurance Levels (EAL 1-7)•Utilize protection profiles (see Harris p.262)21Evaluation Assurance Levels - OverviewCommon Criteria – Evaluation Assurance LevelsCommon Criteria – Evaluation Assurance Levels•Define a scale for measuring