1 Mehrdad Nourani Network Security. 2 Network Security Essentials Session 02.

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Mehrdad Nourani

Network SecurityNetwork Security

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Network Security Essentials

Session 02Session 02

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Security Issues: Past & Present

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Security in Early Days

• In the early days of data processing, the security of information was provided primarily by physical and administrative means:

—Computer buildings, floors, rooms were guarded and alarmed to prevent outsides from intruding and disrupting operations.

—The focus was on physical break-ins, the theft of computer equipment, and the physical theft or destruction of disk packs, tape reels, punch cards, or other media.

—Insiders were kept at bay and access was limited to a small set of computer professionals.

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Information Security

• The requirements of information security within organizations have undergone two major changes:

—The introduction of shared systems such as time-shared and/or systems that can be accessed over the public telephone or data network.

—The introduction of distributed systems and the use of networks and communications facilities for carrying data between terminal user and computer and between computer and computer.

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Computer vs. Network Security

• Computer security is the generic term for a collection of tools designed to protect data and to thwart hackers.

• Network security is the security measures that are needed to protect data during their transmission.

• In most systems, the boundaries between computer security and network security are blurred since most, if not all, of today’s systems are distributed in nature.

—Networking is a core part of today’s environment.

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Examples of Security Violations

• User A transmits a sensitive file to user B; User C intercepts the file and captures a part or all of it.

• An employee is fired without warning. The personnel manager sends a message to invalidate the employee’s account. The employee intercepts the message and then retrieves some sensitive information.

• A message is sent from a customer to a stockbroker with instructions for a transaction; the investment loses value and the customer denies sending the message.

• …

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Different Aspects of Security

• Security attack: Any action that compromises the security of information owned by an organization.

• Security mechanism: A mechanism that is designed to detect, prevent, or recover from a security attack.

• Security service: A service that enhances the security of the data processing systems and the information transfers of an organization.—A system designed to counter security attacks.

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Information Integrity and Cheating

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Information Integrity Functions

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Reasons for Cheating (1)

• 1. Gain unauthorized access to information.• 2. Impersonate another user to shift responsibility

or else to use the other’s license for the purpose of:—a. Originating fraudulent information—b. Modifying legitimate information—c. Using fraudulent identity to gain unauthorized access—d. Fraudulently authorizing transactions or endorsing

them

• 3. Disavow responsibility or liability for information the cheater did originate

• 4. Claim to have received from some other user information that the cheater created (i.e., fraudulent attribution of responsibility or liability).

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Reasons for Cheating (2)

• 5. Claim to have sent to a receiver (at a specified time) information that was not sent (or was sent at a different time)

• 6. Either disavow receipt of information that was in fact received, or claim a false time of receipt.

• 7. Enlarge cheater’s legitimate license (for access, origination, distribution, etc.)

• 8. Modify (without authority to do so) the license of others (fraudulently enroll others, restrict, or enlarge existing licenses, etc.)

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Reasons for Cheating (3)

• 9. Conceal the presence of some information (a covert communication) in other information (the overt communication)

• 10. Insert self into a communication link between other users as an active (undetected) relay point.

• 11. Learn who accesses which information (sources, files, etc.) and when the accesses are made even if the information itself remains concealed (e.g., a generalization of traffic analysis from communications channels to databases, software, etc.)

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Reasons for Cheating (4)

• 12. Impeach an information integrity protocol by revealing information the cheater is supposed to (by terms of the protocol) keep secret

• 13. Pervert the function software, typically by adding a covert function

• 14. Cause others to violate a protocol by means of introducing incorrect information

• 15. Undermine confidence in a protocol by causing apparent failures in the system

• 16. Prevent communication among other users, in particular, surreptitious interference to cause authentic communication to be rejected as unauthentic

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Goal of Network Security

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Internet Security

• Our focus is on Internet Security• It consists of measures to deter, prevent, detect,

and correct security violations that involve the transmission of information

• We need systematic way to define requirements• Consider three aspects of information security:

—security attack—security mechanism—security service

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Security Attacks

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Security Attack

• Any action that compromises the security of information owned by an organization

• Information security is about how to prevent attacks, or failing that, to detect attacks on information-based systems

• Should include a wide range of attacks• Can focus of generic types of attacks• Note: often threat & attack mean same

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Categories of Security Attacks

• Interruption—Attack on availability

• Interception—Attack on confidentiality

• Modification—Attack on integrity

• Fabrication—Attack on authenticity

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Normal Flow

• Normal Flow is the flow of information from an information source, such as a file, or a region of main memory, to a destination, such as another file or user.

InformationSource

InformationDestination

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Interruption

• An asset of the system is destroyed or becomes unavailable or unusable.—This is an attack on availability.

• Examples: The destruction of hardware, the cutting of a communication line, or the disabling of the file management system.

InformationSource

InformationDestination

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Interception

• An unauthorized party gains access to an asset.—This is an attack on confidentiality.

• The unauthorized party could be a person, a program, or a computer.

• Examples: Wiretapping to capture data in a network and the unauthorized copying of files or programs.

InformationSource

InformationDestination

UnauthorizedParty

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Modification

• An authorized party not only gains access to but tampers with an asset.—This is an attack on integrity.

• Examples: Changing values in a data file, altering a program so that it performs differently, or modifying the content of messages being transmitted in a network.

InformationSource

InformationDestination

UnauthorizedParty

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Fabrication

• An authorized party inserts counterfeit objects into the system.—This is an attack on authenticity.

• Examples: The insertion of spurious (fake) messages in a network or the addition of records to a file.

InformationSource

InformationDestination

UnauthorizedParty

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Passive Attacks

• Passive attacks eavesdrop or monitor the transmission.

• Goal: To obtain transmitted information• Two types of passive attacks:

—1. Release of contents: A telephone conversation, an electronic mail message, or confidential information.

—2. Traffic analysis: Using the location and identities of hosts and the frequency and length of messages to determine the type of communication taking place.

• Passive attacks are difficult to detect since they do not involve any alteration of data.

• The emphasis is on prevention rather than detection.

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Active Attacks

• Active attacks may modify of the data stream or create a false stream.

• Four Types of active attacks:—1. Masquerade: takes place when one entity pretends to

be a different entity. This form usually includes one of the other forms of active attack.

—2. Replay: involves the passive capture of a data unit and its subsequent retransmission to produce an unauthorized effect.

—3. Modification: occurs when an unauthorized party gains access to and tampers with an asset. This is an attack on integrity.

—4. Denial of service: prevents or inhibits the normal use or management of communications facilities.

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Security Mechanisms

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Method and Procedure

• A mechanism that is designed to detect, prevent, or recover from a security attack

• No single mechanism that will support all functions required

• However, one particular element underlies many of the security mechanisms in use: cryptographic techniques

• Hence, we will cover this area

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Mechanisms Explain Details

• specific security mechanisms:—digital signatures, access controls, data integrity,

authentication exchange, traffic padding, routing control, notarization

• pervasive security mechanisms:—trusted functionality, security labels, event detection,

security audit trails, security recovery

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Security Services

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Importance of Security Service

• Is something that enhances the security of the data processing systems and the information transfers of an organization

• Intended to counter security attacks• Makes use of one or more security mechanisms

to provide the service• Replicates functions normally associated with

physical documents—E.g. have signatures, dates; need protection from

disclosure, tampering, or destruction; be notarized or witnessed; be recorded or licensed

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Security Services

• Confidentiality is the protection of transmitted data from passive attacks.

• Authentication is concerned with assuring that a communication is authentic.

• Integrity assures that messages are received as sent.—A connection-oriented integrity service should assure

that there are no duplicates, insertions, deletions, modifications, reordering, or replays.

—A connectionless integrity service deals only with an individual message.

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Security Services (cont.)

• Non-Repudiation prevents either the sender or receiver from denying a transmitted message.

• Access Control is the ability to limit and control the access to host systems and applications via communications links.

• Availability is the ability to prevent the loss or a reduction in availability of elements of a distributed system.

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Network Security Model

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Requirement of the Security Model

• Design a suitable algorithm for the security transformation

• Generate the secret information (keys) used by the algorithm

• Develop methods to distribute and share the secret information

• Specify a protocol enabling the principals to use the transformation and secret information for a security service

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Operation of the Model

• A message is presented to be transferred from one party to another across some sort of internet.

• The two parties (principals) in the transaction must cooperate for the exchange to take place.

• A logical information channel is established by defining a route through the internet from source to destination using a communications protocol such as TCP/IP.

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Components of the Model

• Security is an issue when it is necessary to protect the transmission from an opponent.

• All techniques for providing security have two components:—1. A security-related transformation on the information

to be sent—2. Some secret information share by the two principles

and hopefully unknown to opponent.

• Additionally, in some cases a trusted third party may be used for distributing the secret information or arbitrating disputes between the two parties over authenticity.

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Network Access Security Model

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Requirement of the Security Model

• Select appropriate gatekeeper functions to identify users

• Implement security controls to ensure only authorised users access designated information or resources

• Trusted computer systems can be used to implement this model

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Internet Standards

• Internet Society is responsible for the development and publication of standards for use over the Internet.

• Internet Society is a professional membership organization.

• Internet Society is involved in Internet development and standardization.

• Internet Society is the coordinating committee for Internet design, engineering, and management.

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Organizations to Review Standards

• Internet Society consists of three organizations:

—1. Internet Architecture Board (IAB) which is responsible for defining the overall architecture of the Internet.

—2. Internet Engineering Task Force (IETF) which is the protocol development arm of the Internet.

—3. Internet Engineering Steering Group (ISEG) which is responsible for technical management of OETF activities and the Internet standard process.

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Request For Comments (RFC)

• RFCs are the Internet Standards• RFC is developed and published by the Internet

Engineering Task Force (IETF)• Approved by the Internet Engineering Steering

Group (IESEG).• To become a standard, the RFC must …

—Be stable and well-understood—Be technically competent—Have multiple, independent, and interoperable

implementations with substantial operational experience.

—Enjoy significant public support—Be recognizably useful in some or all parts of the

Internet