Dr. Bhavani Thuraisingham

1. Cyber Security Lecture for July 2, 2010 Security Architecture and Design Dr. Bhavani Thuraisingham

2. Outline • Computer Architecture • Operating System • System Architecture • Security Architecture • Security Models • Security Models of Operation • System Evaluation Methods • Open Vs Closed Systems • Some security threats

3. Computer Architecture Components • Central Processing Unit (CPU) • Registers • Memory Units • Input/output Processors • Single Processor • Multi-Processor • Multi-Core Architecture • Grids and Clouds

4. Operating Systems • Memory Management • Process management • File Management • Capability Domains • Virtual Machines

5. System Architecture • The software components that make up the system • Middleware • Database management • Networks • Applications

6. Security Architecture • Security critical components of the system • Trusted Computing Base • Reference Monitor and Security Kernel • Security Perimeter • Security Policy • Least Privilege

7. Trusted Computing Base • The trusted computing base (TCB) of a computer system is the set of all hardware, firmware, and/or software components that are critical to its security, in the sense that bugs or vulnerabilities occurring inside the TCB might jeopardize the security properties of the entire system. By contrast, parts of a computer system outside the TCB must not be able to misbehave in a way that would leak any more privileges than are granted to them in accordance to the security policy. • The careful design and implementation of a system's trusted computing base is paramount to its overall security. Modern operating systems strive to reduce the size of the TCB so that an exhaustive examination of its code base (by means of manual or computer-assisted software audit or program verification) becomes feasible.

8. Reference Monitor and Security Kernel • In operating systems architecture, a reference monitor is a tamperproof, always-invoked, and small-enough-to-be-fully-tested-and-analyzed module that controls all software access to data objects or devices (verifiable). • The reference monitor verifies that the request is allowed by the access control policy. • For example, Windows 3.x and 9x operating systems were not built with a reference monitor, whereas the Windows NT line, which also includes Windows 2000 and Windows XP, was designed to contain a reference monitor, although it is not clear that its properties (tamperproof, etc.) have ever been independently verified, or what level of computer security it was intended to provide.

9. Security Models • Bell and LaPadula (BLP) Confidentiality Model • Biba Integrity Model (opposite to BLP) • Clark Wilson Integrity Model • Other Models • information Flow Model • Non Interference Model • Graham Denning Model • Harrison-Ruzzo-Ullman Model • Lattice Model

10. Bell and LaPadula • A system state is defined to be "secure" if the only permitted access modes of subjects to objects are in accordance with a security policy. To determine whether a specific access mode is allowed, the clearance of a subject is compared to the classification of the object (more precisely, to the combination of classification and set of compartments, making up the security level) to determine if the subject is authorized for the specific access mode. The clearance/classification scheme is expressed in terms of a lattice. The model defines two mandatory access control (MAC) rules and one discretionary access control (DAC) rule with three security properties: • The Simple Security Property - a subject at a given security level may not read an object at a higher security level (no read-up). • The *-property (read "star"-property) - a subject at a given security level must not write to any object at a lower security level (no write-down). The *-property is also known as the Confinement property. • The Discretionary Security Property - use of an access matrix to specify the discretionary access control.

11. Biba • In general, preservation of data integrity has three goals: • Prevent data modification by unauthorized parties • Prevent unauthorized data modification by authorized parties • Maintain internal and external consistency (i.e. data reflects the real world) • Biba security model is directed toward data integrity (rather than confidentiality) and is characterized by the phrase: "no read down, no write up". This is in contrast to the Bell-LaPadula model which is characterized by the phrase "no write down, no read up". • The Biba model defines a set of security rules similar to the Bell-LaPadula model. These rules are the reverse of the Bell-LaPadula rules: • The Simple Integrity Axiom states that a subject at a given level of integrity must not read an object at a lower integrity level (no read down). • The * (star) Integrity Axiom states that a subject at a given level of integrity must not write to any object at a higher level of integrity (no write up).

12. Clark Wilson Model • The Clark-Wilson integrity model provides a foundation for specifying and analyzing an integrity policy for a computing system. • The model is primarily concerned with formalizing the notion of information integrity. • Information integrity is maintained by preventing corruption of data items in a system due to either error or malicious intent. • An integrity policy describes how the data items in the system should be kept valid from one state of the system to the next and specifies the capabilities of various principals in the system. • The model defines enforcement rules and certification rules. • The model’s enforcement and certification rules define data items and processes that provide the basis for an integrity policy. The core of the model is based on the notion of a transaction.

13. Clark Wilson Model • A well-formed transaction is a series of operations that transition a system from one consistent state to another consistent state. • In this model the integrity policy addresses the integrity of the transactions. • The principle of separation of duty requires that the certifier of a transaction and the implementer be different entities. • The model contains a number of basic constructs that represent both data items and processes that operate on those data items. The key data type in the Clark-Wilson model is a Constrained Data Item (CDI). An Integrity Verification Procedure (IVP) ensures that all CDIs in the system are valid at a certain state. Transactions that enforce the integrity policy are represented by Transformation Procedures (TPs). A TP takes as input a CDI or Unconstrained Data Item (UDI) and produces a CDI. A TP must transition the system from one valid state to another valid state. UDIs represent system input (such as that provided by a user or adversary). A TP must guarantee (via certification) that it transforms all possible values of a UDI to a “safe” CDI

14. Clark Wilson Model • At the heart of the model is the notion of a relationship between an authenticated principal (i.e., user) and a set of programs (i.e., TPs) that operate on a set of data items (e.g., UDIs and CDIs). The components of such a relation, taken together, are referred to as a Clark-Wilson triple. The model must also ensure that different entities are responsible for manipulating the relationships between principals, transactions, and data items. As a short example, a user capable of certifying or creating a relation should not be able to execute the programs specified in that relation. • The model consists of two sets of rules: Certification Rules (C) and Enforcement Rules (E). The nine rules ensure the external and internal integrity of the data items. To paraphrase these: • C1—When an IVP is executed, it must ensure the CDIs are valid. C2—For some associated set of CDIs, a TP must transform those CDIs from one valid state to another. Since we must make sure that these TPs are certified to operate on a particular CDI, we must have E1 and E2.

15. Clark Wilson Model • E1—System must maintain a list of certified relations and ensure only TPs certified to run on a CDI change that CDI. E2—System must associate a user with each TP and set of CDIs. The TP may access the CDI on behalf of the user if it is “legal.” This requires keeping track of triples (user, TP, {CDIs}) called “allowed relations.” • C3—Allowed relations must meet the requirements of “separation of duty.” We need authentication to keep track of this. • E3—System must authenticate every user attempting a TP. Note that this is per TP request, not per login. For security purposes, a log should be kept. • C4—All TPs must append to a log enough information to reconstruct the operation. When information enters the system it need not be trusted or constrained (i.e. can be a UDI). We must deal with this appropriately. • C5—Any TP that takes a UDI as input may only perform valid transactions for all possible values of the UDI. The TP will either accept (convert to CDI) or reject the UDI. Finally, to prevent people from gaining access by changing qualifications of a TP: • E4—Only the certifier of a TP may change the list of entities associated with that TP

16. Security Modes of Operation • Dedicated • Systems High • Compartmented • Multilevel • Trust and Assurance

17. Secure System Evaluation: TCSEC • Trusted Computer System Evaluation Criteria (TCSEC) is a United States Government Department of Defense (DoD) standard that sets basic requirements for assessing the effectiveness of computer security controls built into a computer system. The TCSEC was used to evaluate, classify and select computer systems being considered for the processing, storage and retrieval of sensitive or classified information. • The TCSEC, frequently referred to as the Orange Book, is the centerpiece of the DoD Rainbow Series publications. Initially issued in 1983 by the National Computer Security Center (NCSC), an arm of the National Security Agency, and then updated in 1985,. • TCSEC was replaced by the Common Criteria international standard originally published in 2005.

18. Secure System Evaluation: TCSEC • Policy: The security policy must be explicit, well-defined and enforced by the computer system. There are two basic security policies: • Mandatory Security Policy - Enforces access control rules based directly on an individual's clearance, authorization for the information and the confidentiality level of the information being sought. Other indirect factors are physical and environmental. This policy must also accurately reflect the laws, general policies and other relevant guidance from which the rules are derived. • Marking - Systems designed to enforce a mandatory security policy must store and preserve the integrity of access control labels and retain the labels if the object is exported. • Discretionary Security Policy - Enforces a consistent set of rules for controlling and limiting access based on identified individuals who have been determined to have a need-to-know for the information.

19. Secure System Evaluation: TCSEC • Accountability: Individual accountability regardless of policy must be enforced. A secure means must exist to ensure the access of an authorized and competent agent which can then evaluate the accountability information within a reasonable amount of time and without undue difficulty. There are three requirements under the accountability objective: • Identification - The process used to recognize an individual user. • Authentication - The verification of an individual user's authorization to specific categories of information. • Auditing - Audit information must be selectively kept and protected so that actions affecting security can be traced to the authenticated individual. • The TCSEC defines four divisions: D, C, B and A where division A has the highest security. Each division represents a significant difference in the trust an individual or organization can place on the evaluated system. Additionally divisions C, B and A are broken into a series of hierarchical subdivisions called classes: C1, C2, B1, B2, B3 and A1.

20. Secure System Evaluation: TCSEC • Assurance: The computer system must contain hardware/software mechanisms that can be independently evaluated to provide sufficient assurance that the system enforces the above requirements. By extension, assurance must include a guarantee that the trusted portion of the system works only as intended. To accomplish these objectives, two types of assurance are needed with their respective elements: • Assurance Mechanisms : Operational Assurance: System Architecture, System Integrity, Covert Channel Analysis, Trusted Facility Management and Trusted Recovery • Life-cycle Assurance : Security Testing, Design Specification and Verification, Configuration Management and Trusted System Distribution

21. Secure System Evaluation: ITSEC • The Information Technology Security Evaluation Criteria (ITSEC) is a structured set of criteria for evaluating computer security within products and systems. The ITSEC was first published in May 1990 in France, Germany, the Netherlands, and the United Kingdom based on existing work in their respective countries. Following extensive international review, Version 1.2 was subsequently published in June 1991 by the Commission of the European Communities for operational use within evaluation and certification schemes. • Levels E1 – E6

22. Secure System Evaluation: Common Criteria • The Common Criteria for Information Technology Security Evaluation (abbreviated as Common Criteria or CC) is an international standard (ISO/IEC 15408) for computer security certification. • Common Criteria is a framework in which computer system users can specify their security functional and assurance requirements, vendors can then implement and/or make claims about the security attributes of their products, and testing laboratories can evaluate the products to determine if they actually meet the claims. In other words, Common Criteria provides assurance that the process of specification, implementation and evaluation of a computer security product has been conducted in a rigorous and standard manner. • Levels: EAL 1 – EAL 7 (Evaluation Assurance Levels)

23. Certification and Accreditation • Certification and Accreditation (C&A) is a process for implementing information security. It is a systematic procedure for evaluating, describing, testing and authorizing systems prior to or after a system is in operation. • Certification is a comprehensive assessment of the management, operational, and technical security controls in an information system, made in support of security accreditation, to determine the extent to which the controls are implemented correctly, operating as intended, and producing the desired outcome with respect to meeting the security requirements for the system. • Accreditation is the official management decision given by a senior agency official to authorize operation of an information system and to explicitly accept the risk to agency operations (including mission, functions, image, or reputation), agency assets, or individuals, based on the implementation of an agreed-upon set of security controls.

24. Open vs. Closed System • Open systems allow users to reuse, edit, manipulate, and contribute to the system development • Open source software is an example of Open systems • Licensed to the public • Freeware is also an example of Open systems • Closed system permits users the system as it is

25. Some Security Threats • Buffer Overflow • Maintenance Hooks • Time of check / Time of use attacks