Data and Network Security

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What is Computer Security?

• The protection afforded to an automated information system in order to attain the applicable objectives of preserving the integrity, availability and confidentiality of information system resources (includes hardware, software, firmware, information/data, and telecommunications) is called Computer Security.

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What is Computer Security? • For some Computer Security is controlling access to

hardware, software and data of a computerized system.• A large measure of computer security is simply keeping the

computer system's information secure. • In broader terms, computer security can be thought of as

the protection of the computer and its resources against accidental or intentional disclosure of confidential data, unlawful modification of data or programs, the destruction of data, software or hardware.

• Computer security also includes the denial of use of one’s computer facilities for criminal activities including computer related fraud and blackmail.

• Finally, computer security involves the elimination of weaknesses or vulnerabilities that might be exploited to cause loss or harm.

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The Need for Computer Security

• Why the need for Computer Security?– The value of computer assets and services

• What is the new IT environment?– Networks and distributed applications/services– Electronic Commerce (E-commerce, E-business)

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The Value of Computer Assets and Services

• Most companies use electronic information extensively to support their daily business processes.

• Data is stored on customers, products, contracts, financial results, accounting etc.

• If this electronic information were to become available to competitors or to become corrupted, false or disappear, what would happen? What would the consequences be? Could the business still function?

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Network Security Issues• “The network is the computer”

• Proliferation of networks has increased security risks much more.

• Sharing of resources increases complexity of system.• Unknown perimeter (linked networks), unknown path.• Many points of attack.• Computer security has to find answers to network security

problems.• Hence today the field is called Computer and Network

Security.

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Computer Security Requirements

• Secrecy• Integrity• Availability• Authenticity• Non-repudiation• Access control

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Secrecy (Confidentiality)

• Secrecy requires that the information in a computer system only be accessible for reading by authorized parties.

• This type of access includes:– Printing– Displaying– Other forms of disclosure, including simply revealing the

existing of an object

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Integrity

• Integrity requires that the computer system asset can be modified only by authorized parties.

• Modification includes:– Writing– Changing– Changing status– Deleting and – Creating

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More About Integrity

• Integrity: In lay usage, information has integrity when it is timely, accurate, complete, and consistent. However, computers are unable to provide or protect all of these qualities. Therefore, in the computer security field, integrity is often discussed more narrowly as having two data integrity and system integrity.

• “Data integrity is a requirement that information and programs are changed only in a specified and authorized manner.”

• System integrity is a requirement that a system “performs its intended function in an unimpaired manner, free from deliberate or inadvertent unauthorized manipulation of the system.”

• The definition of integrity has been, and continues to be, the subject of much debate among computer security experts.

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Availability

• Availability requires that computer system assets are available to authorized parties.

• Availability is a requirement intended to assure that systems work promptly and service is not denied to authorized users.

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Authenticity• Authenticity means that parties in a information services

can ascertain the identity of parties trying to access information services.

• Also means that the origin of the message is certain.• Therefore two types:

– Principal Authentication– Message Authentication

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Non-repudiation• Originator of communications can’t deny it later.• Without non-repudiation you could place an order for 1

million dollars of equipment online and then simply deny it later.

• Or you could send an email inviting a friend to the dinner and then disclaim it later.

• Non-repudiation associates the identity of the originator with the transaction in a non-deniable way.

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Access Control• Unauthorized users are kept out of the system.• Unauthorized users are kept out of places on the

system/disk.• Typically makes use of Directories or Access Control Lists

(ACLs) or Access Control Matrix• Objects: Resources that need to be protected• Subjects: Entities that need access to resources• Rights: Permissions• Each entry is a triple <subject, object, rights>

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Type of Attacks/Threats in Computer Systems

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• A threat is a danger which could affect the security (confidentiality, integrity, availability) of assets, leading to a potential loss or damage.

• Interruption• Interception• Modification• Fabrication

Type of Attacks in Computer Systems

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Normal Flow of Information

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Interruption

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

• Examples include destruction of a piece of hardware, such as a hard disk, the cutting of a communication link, or the disabling of the file management system.

• DOS - Denial of Service Attacks have become very well known.

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Interruption

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Interception

• Information disclosure/information leakage• 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 include:

– wiretapping to capture data in a network– the illicit copying of files or programs

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Interception

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Modification• Modification is integrity violation.• An unauthorized party not only gains access to but tampers with an asset.• This is an attack on the integrity.• Examples include changing values in a data file, altering a program so that

it performs differently, and modifying the content of a message being transmitted in a network.

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Modification

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Fabrication

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

• Examples include the insertion of spurious messages in a network or the addition of records to a file.

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Fabrication

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Classification of Attacks

• Computer Security attacks can be classified into two broad categories:– Passive Attacks can only observe communications or

data.– Active Attacks can actively modify communications or

data. Often difficult to perform, but very powerful. Examples include• Mail forgery/modification• TCP/IP spoofing/session hijacking

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Passive Attacks and Active Attacks

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Passive Attacks and Active Attacks

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Passive Attacks• Eavesdropping on or monitoring of transmission.• The goal of the opponent is to obtain information that is being

transmitted.• Two types:

– Release-of-message contents– Traffic Analysis

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Release-of-message Contents

• Opponent finds out the contents or the actual messages being transmitted.

• How to protect?– Encryption– Steganography

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Traffic Analysis

• More subtle than release-of-message contents.• Messages may be kept secret by masking or encryption but

…• The opponent figures out information being carried by the

messages based on the frequency and timings of the message.

• How to protect?– Data/Message Padding– Filler Sequences

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Passive Attacks Problems

• Difficult to detect because there is no modification of data.• Protection approach should be based on prevention rather

than detection.

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Active Attacks

• Active attacks involve some sort of modification of the data stream or the creation of a false stream.

• Four sub-categories:– Masquerade– Replay– Modification of Messages– Denial of service

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Masquerade

• An entity pretends to be another.• For the purpose of doing some other form of attack.• Example a system claims its IP address to be what it is not,

IP spoofing.• How to protect?

– Principal/Entity Authentication

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Replay

• First passive capture of data and then its retransmission to produce an unauthorized effect.

• Could be disastrous in case of critical messages such as authentication sequences, even if the password were encrypted.

• How to protect?– Time stamps– Sequence Numbers

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Modification of Messages

• Some portion of a legitimate message is altered or messages are delayed or reordered to produce an unauthorized effect.

• How to protect?– Message Authentication Codes– Chaining

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Denial of Service - DOS• Prevents the normal use or management of communication

facilities.• Such attacks have become very common on the Internet

especially against web servers.• On the Internet remotely located hackers can crash the

TCP/IP software by exploiting known vulnerabilities in various implementations.

• One has to constantly look out for software updates and security patches to protect against these attacks.

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Problems with Active Attacks

• Easy to detect but difficult to prevent.• Efforts are directed to quickly recover from disruption or

delays.• Good thing is that detection will have a deterrent effect.

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How Threats Affect Computer Systems

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HARDWARE

SOFTWARE

DATA

Interception (Theft)

Interruption (Denial of Service)

Interception (Eavesdropping

)

Interruption (Loss)

Interception (Theft)

Interruption (Deletion)

Modification (Malicious Code)

FabricationModification

A Model for Network Security

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Security Protocols

• A protocol is a series of steps, involving two or more parties, designed to accomplish a task.– Every one involved in a protocol must know the protocol

and all of the steps to follow in advance.– Everyone involved in the protocols must agree to follow

it.– The protocol must be unambiguous; each step must be

well defined and there must be no chance of misunderstanding.

– The protocol must be complete; there must be a specified action for every possible situation.

– It should not be possible to do more or learn more than what is specified in the protocol.

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Security Protocol Layers

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The further down you go, the more transparent it is

The further up you go, the easier it is to deploy

Application

Presentation

Session

Transport

Netw ork

Datalink

Physical

Application

Presentation

Session

Transport

Netw ork

Datalink

Physical

Email - S/M IM E

SSL

IPSec

PPP - ECP

PHYSICAL NETW ORKEncrypting

NICEncrypting

NIC

Security Services Provided by Security Protocols

• Access control: Protects against unauthorized use.• Authentication: Provides assurance of someone's identity.• Confidentiality: Protects against disclosure to

unauthorized identities.• Integrity: Protects from unauthorized data alteration.• Non-repudiation: Protects against originator of

communications later denying it.

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Security Mechanisms• Three basic building blocks are used:

– Encryption is used to provide confidentiality, can provide authentication and integrity protection.

– Digital signatures are used to provide authentication, integrity protection, and non-repudiation.

– Checksums/hash algorithms are used to provide integrity protection, can provide authentication.

• One or more security mechanisms are combined to provide a security service/protocol.

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Services, Mechanisms, Algorithms

• A typical security protocol provides one or more security services (authentication, secrecy, integrity, etc.)

• Services are built from mechanisms.• Mechanisms are implemented using algorithms.

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SSL

Signatures Encryption Hashing

DSA RSA RSA DES SHA1 MD5

Services (Security Protocols)

Mechanisms

Algorithms

Services, Mechanisms, Algorithms

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Security Protocols (Services)

Standards-based Security ProtocolsProprietary Security

Protocols

SSL IPSecPrivateWi

reBig Brother

Mechanisms

Encryption Signature HashingKey

Exchange

Algorithms

Symmetric

Asymmetric

Asymmetric

Symmetric

MD-5SHA-1

Diffie-HellmanDES

AESRSAECC

DSARSA

DESMAC

Encryption and Security

• Encryption is a key enabling technology to implement computer security.

• But Encryption is to security like bricks are to buildings.• In the next module we will study encryption in detail.

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Computer security is based on eight major elements:

1. Computer security should support the mission of the organization.

2. Computer security is an integral element of sound management.

3. Computer security should be cost-effective.4. Computer security responsibilities and accountability should

be made explicit.5. System owners have computer security responsibilities

outside their own organizations.6. Computer security requires a comprehensive and integrated

approach.7. Computer security should be periodically reassessed.8. Computer security is constrained by societal factors.

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Typical Security Solutions and Technologies

• Physical security• Encryption• Access control• Automatic call back• Node authentication• Differentiated access rights• Antivirus software• Public Key Infrastructure• Firewalls

• User authentication• Passwords and

passphrases• Challenge-response

systems• Token or smart cards• Exchange of secret

protocol• Personal characteristics -

Biometrics

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THANK YOU!

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