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Security Models and Architecture

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Presentation on theme: "Security Models and Architecture"— Presentation transcript:

1 Security Models and Architecture
CISSP Exam Preparation Bernie Eydt

2 Overview Basic concepts The Models Bell-LaPadula (BLP) Biba
Clark-Wilson Chinese Wall Systems Evaluation

3 Basic Concepts

4 Terminology 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 policy

5 Types 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.

6 Information 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 users

7 Access Control Models

8 Models Bell-LaPadula Biba Clark-Wilson Chinese Wall
Good brief summary on Harris p.247

9 Bell-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.

10 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 computers

11 Biba 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 useless

12 Clark-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)

13 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 transformation

14 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 duties

15 Clark-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.

16 Chinese Wall Focus 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 behavior

17 Systems Evaluation

18 Trusted Computer System Evaluation (TCSEC)
Criteria published in the Orange Book Officially replaced by Common Criteria Four Levels A Verified protection A1 Verified design B Mandatory protection B1 Labeled Security B2 Structured Protection B3 Security Domains C Discretionary protection C1 Discretionary security C2 Controlled access D Minimal security

19 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)

20 Common 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)

21 Common Criteria – Evaluation Assurance Levels
Evaluation Assurance Levels - Overview Define a scale for measuring the criteria for the evaluation of PPs (Protection Profiles) and STs (Security Targets) Constructed using components from the assurance families Organization Seven hierarchically ordered EALs in a uniformly increasing scale of assurance Bullet Slides On bullet slides without photos or graphs, text is centered on slide. Subtitles are 28 pt. Arial.

22 CC EALs - Reference Level Short Title US TCSEC EAL 7
Formally verified design and tested A1 EAL 6 Semi-formally verified design and tested B3 EAL 5 Semi-formally designed and tested B2 EAL 4 Methodically designed, tested and reviewed B1 C2 EAL 3 Methodically tested and checked EAL 2 Structurally tested C1 EAL 1 Functionally tested Higher Assurance Lower Assurance

23 CC EALs – Summary 1-3 EAL 1 - Functionally tested
“Applicable where some confidence in correct operation is required, but the threats to security are not viewed as serious” EAL 2 - Structurally tested “Applicable where developers or users require a low to moderate level of independently assured security” EAL 3 - Methodically tested and checked “Applicable where the requirement is for a moderate level of independently assured security”

24 CC EALs – Summary 4-5 EAL 4 - Methodically designed, tested and reviewed “Applicable where developers or users require a moderate to high level of independently assured security” EAL 5 - Semi-formally designed and tested “Applicable where the requirement is for a high level of independently assured security”

25 CC EALs – Summary 6-7 EAL 6 - Semi-formally verified design and tested
“Applicable to the development of specialised TOEs (Targets of Evaluation), for high risk situations ” EAL 7 - Formally verified design and tested “Applicable to the development of security TOEs for application in extremely high risk situations

26 CC EALs - Web References
Common Web Site Main page Formal specification document Introductory overviews introductory_overviews/index.html

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