This document discusses security architecture and models, including differences between commercial and government security requirements. It covers security evaluation criteria, security practices for the Internet, technical platforms in terms of hardware/software, and system security techniques like preventative, detective and corrective controls. The document also describes the layered approach to security architecture.

1. Security Architecture andSecurity Architecture and
ModelsModels

2. Security Architecture and ModelsSecurity Architecture and Models
 Security models in terms of confidentiality, integrity, andSecurity models in terms of confidentiality, integrity, and
information flowinformation flow
 Differences between commercial and government securityDifferences between commercial and government security
requirementsrequirements
 The role of system security evaluation criteria such asThe role of system security evaluation criteria such as
TCSEC, ITSEC, and CCTCSEC, ITSEC, and CC
 Security practices for the Internet (IETF IPSec)Security practices for the Internet (IETF IPSec)
 Technical platforms in terms of hardware, firmware, andTechnical platforms in terms of hardware, firmware, and
softwaresoftware
 System security techniques in terms of preventative,System security techniques in terms of preventative,
detective, and corrective controlsdetective, and corrective controls

3. The Layered ApproachThe Layered Approach

4. The Architectures
 Platform Architecture
 Operating System Software and Utilities
 Central Processing Unit (CPU) States
 Memory Management Overview
 Input/Output Devices
 Storage Devices
• Operating System
 Multitasking - Systems allow a user to perform more than
one computer Task, such as the operation of an application
program at the same time
 Multithreading - The ability of a program or an operating
system process to manage its use by more than one user at
a time and to even manage multiple requests by the same
user without having to have multiple copies of the
programming running in the computer

5. The Architectures Cont…
 Operating System
• Multiprogramming system - System that allows for the
interleaved execution of two or more programs by a processor
• Multiprocessing - The coordinated processing of two or more
programs by a processor that contains parallel processors
 CPU States
• Run - The CPU is executing instructions for the current process
• Wait - The process is waiting for a defined event to occur, such
as retrieving data from a hard disk
• Sleep - The process is suspended and waiting for its next time
slice in the CPU, or a given event to occur such as an alarm
• Masked/interruptible state - Interrupts are implemented to allow
system events to be synchronized. For example, if the masked
bit is not set, the interruption is disabled (masked off)

6. The Architectures Cont…
 MemoryMemory
Random Access Memory (RAM)
 Dynamic Random Access Memory (DRAM)
 Extended Data Output RAM (EDO RAM)
 Synchronous DRAM (SDRAM)
 Double Data Rate SDRAM (DDR SDRAM)
 Burst Extended Data Output DRAM (BEDO DRAM)
Read-Only Memory (ROM)
 Programmable Read-Only Memory (PROM)
 Erasable and Programmable Read-Only Memory (EPROM)
 Electrically Erasable Programmable Read-Only Memory
(EEPROM)
Flash Memory

7. The Architectures Cont…
 StorageStorage
• Primary - Main memory directly accessible to the CPU
• Secondary - Nonvolatile storage medium
• Real - A program is given a definite storage location
in memory
• Virtual - The ability to extend the apparent size of
RAM
• Volatile - RAM
• Nonvolatile – ROM and Secodary storage devices
• Write-Once Read Memory -

8. The Architectures Cont…
 Network Environment - A data communication system allowing a
number of devices to communicate with each other
• Local Environment
• Shared Environment
• Security Environments
• Dedicated security mode -processing of one particular type or
classification of information
• System high-security mode – system hardware/software is only
trusted to provide need-to-know protection between users
• Multi-level security mode - allows two or more classification levels
• Controlled mode - type of multi-level security in which a more limited
amount of trust
• Compartmentalized security mode - process two or more types of
compartmented information
 Enterprise Architecture - Systematically derived and captured
structural descriptions

9. Related DefinitionsRelated Definitions
 Access control - Prevention of unauthorized use orAccess control - Prevention of unauthorized use or
misuse of a systemmisuse of a system
 ACL - Access control listACL - Access control list
 Access Mode - An operation on an object recognized byAccess Mode - An operation on an object recognized by
the security mechanisms - think read, write or executethe security mechanisms - think read, write or execute
actions on filesactions on files
 Accountability- Actions can be correlated to an entityAccountability- Actions can be correlated to an entity
 Accreditation - Approval to operate in a given capacity inAccreditation - Approval to operate in a given capacity in
a given environmenta given environment
 Asynchronous attack - An attack exploiting the timeAsynchronous attack - An attack exploiting the time
lapse between an attack action and a system reactionlapse between an attack action and a system reaction

10. Related Definitions Cont…Related Definitions Cont…
 Audit trail - Records that document actions on or againstAudit trail - Records that document actions on or against
a systema system
 Bounds Checking - Within a program, the process ofBounds Checking - Within a program, the process of
checking for references outside of declared limits. Whenchecking for references outside of declared limits. When
bounds checking is not employed, attacks such as bufferbounds checking is not employed, attacks such as buffer
overflows are possibleoverflows are possible
 Compartmentalization - Storing sensitive data in isolatedCompartmentalization - Storing sensitive data in isolated
blocksblocks
 Configuration Control - management and control ofConfiguration Control - management and control of
changes to a system’s hardware, firmware, software,changes to a system’s hardware, firmware, software,
and documentationand documentation
 confinement - Ensuring data cannot be abused when aconfinement - Ensuring data cannot be abused when a
process is executing a borrowed program and has someprocess is executing a borrowed program and has some
access to that dataaccess to that data

11. Related Definitions Cont…Related Definitions Cont…
 Contamination – Corruption of data of varyingContamination – Corruption of data of varying
classification levelsclassification levels
 Correctness Proof - Mathematical proof of consistencyCorrectness Proof - Mathematical proof of consistency
between a specification and implementationbetween a specification and implementation
 Countermeasure - anything that neutralizes vulnerabilityCountermeasure - anything that neutralizes vulnerability
 Covert Channel - A communication channel that allowsCovert Channel - A communication channel that allows
cooperating processes to transfer information in a waycooperating processes to transfer information in a way
that violates a system’s security policythat violates a system’s security policy
• covert storage channel involves memory shared bycovert storage channel involves memory shared by
processesprocesses
• covert timing channel involves modulation of systemcovert timing channel involves modulation of system
resource usage (like CPU time)resource usage (like CPU time)

12. Related Definitions Cont…Related Definitions Cont…
 Criticality - Importance of system to missionCriticality - Importance of system to mission
 Cycle - One cycle consists of writing a zero, then a 1 inCycle - One cycle consists of writing a zero, then a 1 in
every possible locationevery possible location
 Data Contamination - Deliberate or accidental change inData Contamination - Deliberate or accidental change in
the integrity of datathe integrity of data
 Discretionary Access Control - An entity with accessDiscretionary Access Control - An entity with access
privileges can pass those privileges on to other entitiesprivileges can pass those privileges on to other entities
 Mandatory Access control - Requires that access controlMandatory Access control - Requires that access control
policy decisions are beyond the control of the individualpolicy decisions are beyond the control of the individual
owner of an object (think military security classification)owner of an object (think military security classification)

13. Related Definitions Cont…Related Definitions Cont…
 DoD Trusted Computer System Evaluation CriteriaDoD Trusted Computer System Evaluation Criteria
(TCSEC) - orange book(TCSEC) - orange book
 Firmware - software permanently stored in hardwareFirmware - software permanently stored in hardware
device (ROM, read only memory)device (ROM, read only memory)
 Formal Proof - Mathematical argumentFormal Proof - Mathematical argument
 Hacker/Cracker – Individual who cause DamageHacker/Cracker – Individual who cause Damage
 Logic bomb - An unauthorized action triggered by aLogic bomb - An unauthorized action triggered by a
system statesystem state
 Malicious logic - Evil hardware, software, or firmwareMalicious logic - Evil hardware, software, or firmware
included by malcontents for malcontentsincluded by malcontents for malcontents

14. Related Definitions Cont…Related Definitions Cont…
 Principle of Least Privilege - Every entity grantedPrinciple of Least Privilege - Every entity granted
least privileges necessary to perform assigned tasksleast privileges necessary to perform assigned tasks
 Memory bounds - The limits in a range of storageMemory bounds - The limits in a range of storage
addresses for a protected memory regionaddresses for a protected memory region
 Piggy Back - Unauthorized system via another’sPiggy Back - Unauthorized system via another’s
authorized access (shoulder surfing is similar)authorized access (shoulder surfing is similar)
 Privileged Instructions - Set of instructions generallyPrivileged Instructions - Set of instructions generally
executable only when system is operating inexecutable only when system is operating in
executive stateexecutive state
 Reference Monitor - A security control which controlsReference Monitor - A security control which controls
subjects’ access to resources - an example is thesubjects’ access to resources - an example is the
security kernel for a given hardware basesecurity kernel for a given hardware base

15. Related Definitions Cont…Related Definitions Cont…
 Resource - Anything used while a system is functioningResource - Anything used while a system is functioning
(eg CPU time, memory, disk space)(eg CPU time, memory, disk space)
 Resource encapsulation - Property which statesResource encapsulation - Property which states
resources cannot be directly accessed by subjectsresources cannot be directly accessed by subjects
because subject access must be controlled by thebecause subject access must be controlled by the
reference monitorreference monitor
 Security Kernel - Hardware/software/firmware elementsSecurity Kernel - Hardware/software/firmware elements
of the Trusted Computing Base - security kernelof the Trusted Computing Base - security kernel
implements the reference monitor conceptimplements the reference monitor concept
 Trusted Computing Base - From the TCSEC, the portionTrusted Computing Base - From the TCSEC, the portion
of a computer system which contains all elements of theof a computer system which contains all elements of the
system responsible for supporting the security policy andsystem responsible for supporting the security policy and
supporting the isolation of objects on which thesupporting the isolation of objects on which the
protection is based -follows the reference monitorprotection is based -follows the reference monitor
conceptconcept

16. Related Definitions Cont…Related Definitions Cont…
 TCSEC - Trusted Computer Security Evaluation CriteriaTCSEC - Trusted Computer Security Evaluation Criteria
- Evaluation Guides other than the Orange Book- Evaluation Guides other than the Orange Book
 ITSEC - Information Technology Security EvaluationITSEC - Information Technology Security Evaluation
Criteria (European)Criteria (European)
 CTCPEC - Canadian Trusted Computer ProductCTCPEC - Canadian Trusted Computer Product
Evaluation CriteriaEvaluation Criteria
 CC - Common CriteriaCC - Common Criteria

17. Related Definitions Cont…Related Definitions Cont…
 Trusted SystemTrusted System
• follows from TCBfollows from TCB
• A system that can be expected to meet users’A system that can be expected to meet users’
requirements for reliability, security, effectiveness duerequirements for reliability, security, effectiveness due
to having undergone testing and validationto having undergone testing and validation
 System AssuranceSystem Assurance
• the trust that can be placed in a system, and thethe trust that can be placed in a system, and the
trusted ways the system can be proven to have beentrusted ways the system can be proven to have been
developed, tested, maintained, etc.developed, tested, maintained, etc.

18. TCB Levels (from TCSEC)TCB Levels (from TCSEC)
 D - Minimal protectionD - Minimal protection
 C - Discretionary ProtectionC - Discretionary Protection
• C1 cooperative users who can protect their own infoC1 cooperative users who can protect their own info
• C2 more granular DAC, has individual accountabilityC2 more granular DAC, has individual accountability
 B - Mandatory ProtectionB - Mandatory Protection
• B1 Labeled Security ProtectionB1 Labeled Security Protection
• B2 Structured ProtectionB2 Structured Protection
• B3 Security DomainsB3 Security Domains
 A - Verified ProtectionA - Verified Protection
• A1 Verified DesignA1 Verified Design

19. Related Definitions Cont…Related Definitions Cont…
 Virus - program that can infect other programsVirus - program that can infect other programs
 Worm - program that propagates but doesn’t necessarilyWorm - program that propagates but doesn’t necessarily
modify other programsmodify other programs
 Bacteria or rabbit - programs that replicate themselves toBacteria or rabbit - programs that replicate themselves to
overwhelm system resourcesoverwhelm system resources
 Back Doors - trap doors - allow unauthorized access toBack Doors - trap doors - allow unauthorized access to
systemssystems
 Trojan horse - malicious program masquerading as aTrojan horse - malicious program masquerading as a
benign programbenign program

20. The Security KernelThe Security Kernel

21. General Operating System Protection
 User identification and authentication
 Mandatory access control
 Discretionary access control
 Complete mediation
 Object reuse protection
 Audit
 Protection of audit logs
 Audit log reduction
 Trusted path
 Intrusion detection

22. Network Protection
 Hash totals
 Recording of sequence checking
 Transmission logging
 Transmission error correction
 Invalid login, modem error, lost connections, CPU failure,
disk error, line error, etc.
 Retransmission control

23. The BIG ThreeThe BIG Three
 ConfidentialityConfidentiality
• Unauthorized users cannot access dataUnauthorized users cannot access data
 IntegrityIntegrity
• Unauthorized users cannot manipulate/destroy dataUnauthorized users cannot manipulate/destroy data
 AvailabilityAvailability
• Unauthorized users cannot make system resourcesUnauthorized users cannot make system resources
unavailable to legitimate usersunavailable to legitimate users

24. Security ModelsSecurity Models
Bell-LaPadulaBell-LaPadula
BibaBiba
Clark & WilsonClark & Wilson
Non-interferenceNon-interference
State machineState machine
Access MatrixAccess Matrix
Information flowInformation flow

25. Bell-LaPadulaBell-LaPadula
 A state machine model capturing the confidentialityA state machine model capturing the confidentiality
aspects of access controlaspects of access control

26. Biba Integrity ModelBiba Integrity Model
 The Biba integrity model mathematically describes read
and write restrictions based on integrity access classes
of subjects and objects (Biba used the terms “integrity
level” and “integrity compartments”)

27. Clark & Wilson ModelClark & Wilson Model
 An Integrity Model, like BibaAn Integrity Model, like Biba
 Addresses all 3 integrity goalsAddresses all 3 integrity goals
• Prevents unauthorized users from makingPrevents unauthorized users from making
modificationsmodifications
• Maintains internal and external consistencyMaintains internal and external consistency
• Prevents authorized users from making improperPrevents authorized users from making improper
modificationsmodifications
 T - cannot be Tampered with while being changedT - cannot be Tampered with while being changed
 L - all changes must be LoggedL - all changes must be Logged
 C - Integrity of data is ConsistentC - Integrity of data is Consistent

28. Clark & Wilson Model Cont…Clark & Wilson Model Cont…
 Proposes “Well Formed Transactions”Proposes “Well Formed Transactions”
• perform steps in orderperform steps in order
• perform exactly the steps listedperform exactly the steps listed
• authenticate the individuals who perform the stepsauthenticate the individuals who perform the steps
 Calls for separation of dutyCalls for separation of duty
 Well-formed transaction - The process and data items
can be changed only by a specific set of trusted
programs

29. More ModelsMore Models
 Access matrix model - A state machine model for aAccess matrix model - A state machine model for a
discretionary access control environmentdiscretionary access control environment
 Information flow model - simplifies analysis of covertInformation flow model - simplifies analysis of covert
channelschannels
• A variant of the access control model
• Attempts to control the transfer of information from
one object into another object
• helps to find covert channelshelps to find covert channels

30. More Models Cont…More Models Cont…
 Noninterference model - Covers ways to preventNoninterference model - Covers ways to prevent
subjects operating in one domain from affecting eachsubjects operating in one domain from affecting each
other in violation of security policyother in violation of security policy
 State machine model - Abstract mathematical modelState machine model - Abstract mathematical model
consisting of state variables and transition functionsconsisting of state variables and transition functions
 Chinese Wall Model – provides a model for access rulesChinese Wall Model – provides a model for access rules
in a consultancy business where analysts have to makein a consultancy business where analysts have to make
sure that no conflicts of interest arisesure that no conflicts of interest arise
 Lattice Model - The higher up in secrecy, the moreLattice Model - The higher up in secrecy, the more
constraints on the data; the lower in secrecy, the lessconstraints on the data; the lower in secrecy, the less
constraints on the dataconstraints on the data

31. Certification & AccreditationCertification & Accreditation
 Procedures and judgements to determine the suitabilityProcedures and judgements to determine the suitability
of a system to operate in a target operationalof a system to operate in a target operational
environmentenvironment
 Certification considers system in operationalCertification considers system in operational
environmentenvironment
 Accreditation is the official management decision toAccreditation is the official management decision to
operate a systemoperate a system

32. IPSECIPSEC
 IETF updated 1997, 1998IETF updated 1997, 1998
 Addresses security at IP layerAddresses security at IP layer
 Key goals:Key goals:
• authenticationauthentication
• encryptionencryption
 ComponentsComponents
• IP Authentication Header (AH)IP Authentication Header (AH)
• Encapsulating Security Payload (ESP)Encapsulating Security Payload (ESP)
• Both are vehicles for access controlBoth are vehicles for access control
• Key management via ISAKMPKey management via ISAKMP

33. Network/Host Security ConceptsNetwork/Host Security Concepts
 Security Awareness ProgramSecurity Awareness Program
 CERT/CIRTCERT/CIRT
 Errors of omission vs. correctionErrors of omission vs. correction
 physical securityphysical security
 dial-up securitydial-up security
 Host vs. network security controlsHost vs. network security controls
 WrappersWrappers
 Fault ToleranceFault Tolerance

34. TEMPESTTEMPEST
 Electromagnetic shielding standardElectromagnetic shielding standard
 Mostly for DoD communication EquipmentsMostly for DoD communication Equipments
 Currently not widely usedCurrently not widely used
 See “accreditation” - i.e. acceptance of riskSee “accreditation” - i.e. acceptance of risk

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