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Cryptography and Network Security�Chapter 1

Fifth Edition

of William Stallings

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�Security: is ensuring the (Secrecy) confidentiality, data integrity and availability of components of computing system.�

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Cryptographic algorithms and protocols can be grouped into four main areas:

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Definitions

Network Security - measures to protect data during their transmission
Internet Security - measures to protect data during their transmission over a collection of interconnected networks

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The field of network and �Internet security consists of:�

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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)

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Key Security Concepts

These three concepts form what is often referred to as the CIA triad The three concepts embody the fundamental security objectives for both data and for information and computing services. FIPS PUB 199 provides a useful characterization of these three objectives in terms of requirements and the definition of a loss of security in each category:

• Confidentiality (covers both data confidentiality and privacy): preserving authorized restrictions on information access and disclosure, including means for protecting personal privacy and proprietary information. A loss of confidentiality is the unauthorized disclosure of information.

• Integrity (covers both data and system integrity): Guarding against improper information modification or destruction, and includes ensuring information non-repudiation and authenticity. A loss of integrity is the unauthorized modification or destruction of information.

• Availability: Ensuring timely and reliable access to and use of information. A loss of availability is the disruption of access to or use of information or an information system.

Although the use of the CIA triad to define security objectives is well established, some in the security field feel that additional concepts are needed to present a complete picture. Two of the most commonly mentioned are:

• Authenticity: The property of being genuine and being able to be verified and trusted; confidence in the validity of a transmission, a message, or message originator.

• Accountability: The security goal that generates the requirement for actions of an entity to be traced uniquely to that entity.

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Levels of Impact

can define 3 levels of impact from a security breach

Low
Moderate
High

We can define three levels of impact on organizations or individuals should there be a breach of security (i.e., a loss of confidentiality, integrity, or availability). These levels are defined in FIPS PUB 199:

• Low: The loss could be expected to have a limited adverse effect on organizational operations, organizational assets, or individuals. A limited adverse effect means that, for example, the loss of confidentiality, integrity, or availability might (i) cause a degradation in mission capability to an extent and duration that the organization is able to perform its primary functions, but the effectiveness of the functions is noticeably reduced; (ii) result in minor damage to organizational assets; (iii) result in minor financial loss; or (iv) result in minor harm to individuals.

• Moderate: The loss could be expected to have a serious adverse effect on organizational operations, organizational assets, or individuals. A serious adverse effect means that, for example, the loss might (i) cause a significant degradation in mission capability to an extent and duration that the organization is able to perform its primary functions, but the effectiveness of the functions is significantly reduced; (ii) result in significant damage to organizational assets; (iii) result in significant financial loss; or (iv) result in significant harm to individuals that does not involve loss of life or serious, life-threatening injuries.

• High: The loss could be expected to have a severe or catastrophic adverse effect on organizational operations, organizational assets, or individuals. A severe or catastrophic adverse effect means that, for example, the loss might (i) cause a severe degradation in or loss of mission capability to an extent and duration that the organization is not able to perform one or more of its primary functions; (ii) result in major damage to organizational assets; (iii) result in major financial loss; or (iv) result in severe or catastrophic harm to individuals involving loss of life or serious life threatening injuries.

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Goals of computer security

• To protect computer assets from:

– Human errors, natural disasters, physical and electronic maliciousness.

• Confidentiality, Integrity, Availability

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Confidentiality� ( Secrecy, Privacy).

Data confidentiality

Assures that private or confidential information is not made available or disclosed to unauthorized individuals

Privacy

Assures that individuals control or influence what information related to them may be collected and stored and by whom and to whom that information may be disclosed

(Ensuring that the system is only accessible by authorized parties.)

This definition introduces three key objectives (goals) that are at the heart of computer

security:

• Confidentiality: This term covers two related concepts:

Data confidentiality: Assures that private or confidential information is

not made available or disclosed to unauthorized individuals.

Privacy: Assures that individuals control or influence what information

related to them may be collected and stored and by whom and to whom

that information may be disclosed.

•Integrity: This term covers two related concepts:

Data integrity: Assures that information and programs are changed only in

a specified and authorized manner.

System integrity: Assures that a system performs its intended function in

an unimpaired manner, free from deliberate or inadvertent unauthorized

manipulation of the system.

• Availability: Assures that systems work promptly and service is not denied to

authorized users

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Integrity

Data integrity

Assures that information and programs are changed only in a specified and authorized manner

System integrity

Assures that a system performs its intended function in an unimpaired manner, free from deliberate or inadvertent unauthorized manipulation of the system

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Availability

• Assures that systems work promptly and service is not denied to authorized users

Ensuring that authorized parties are not

denied access to information and resources

• Ensuring that the computer works when it

is supposed to work and that it works the

way it should.

(access to computing resources without difficulties.)

.

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Other goals

Non-repudiation

– Prevents either sender or receiver from denying a transmitted message.

--- when a msg is sent, the receiver can prove that the sender is sent that message.

Legitimate use

– Ensuring that resources are not used by

unauthorized parties or in unauthorized ways.

– Examples:

Printer and disk quotas.
Spam-filters in E-mail servers..

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Kinds of Security breaches�

Exposure: . A form of possible loss or a harm in computing system . Examples :

Unauthorized disclosure of data ,modification of data or Denial legitimate access to computing.

Vulnerability: is a weakness in the security system that might be exploited to cause a data loss or harm.

• Attack: an assault on system security, a deliberate attempt to evade security services.

NOTE: Violate the security policy of a system.

(Attempt to exploit a vulnerability.).

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�Threat��

Threat:- a potential for violation of security

Physical threats - weather, natural disaster, bombs, power etc.

Human threats - stealing, trickery, spying, sabotage, accidents.

Software threats - viruses, Trojan horses, logic bombs.

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Network Security

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Network Security

Normal Flow:

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Network Security

Four types of possible attacks are:
Interruption: services or data become unavailable, unusable, destroyed, and so on, such as lost of file, denial of service, etc.

Cut wire lines,

Jam wireless signals,

Drop packets,

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2. Interception: an unauthorized subject has gained access to an object, such as stealing data, overhearing others communication, etc.

Wiring, eavesdrop

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3. Modification: unauthorized changing of data or tempering with services, such as alteration of data, modification of messages, etc.

intercept

Replaced info

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4. Fabrication: additional data or activities are generated that would normally no exist, such as adding a password to a system, replaying previously send messages, etc.

Also called impersonation

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Security Trends

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OSI Security Architecture� . OSI : Open System Interconnection� . ITU : International Telecommunication Union

ITU-T X.800 “Security Architecture for OSI”
defines a systematic way of defining and providing security requirements
for us it provides a useful, if abstract, overview of concepts we will study

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Aspects of Security

consider 3 aspects of information security:

security attack
security mechanism
security service

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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
can focus of generic types of attacks

passive
active

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Passive Attacks�A passive attack attempts to learn or make use of information from the system but does not affect system resources�

A useful means of classifying security attacks, used both in X.800 and RFC 2828, is in terms of passive attacks and active attacks. A passive attack attempts to learn or make use of information from the system but does not affect system resources.

Passive attacks are in the nature of eavesdropping on, or monitoring of, transmissions. The goal of the opponent is to obtain information that is being transmitted. Two types of passive attacks are:

+ release of message contents - as shown above in Stallings Figure 1.2a here

+ traffic analysis - monitor traffic flow to determine location and identity of communicating hosts and could observe the frequency and length of messages being exchanged

These attacks are difficult to detect because they do not involve any alteration of the data.

Are difficult to detect because they do not involve any alteration of the data.

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Passive Attacks

Two types of passive attacks are:

The release of message contents
Traffic analysis

Are in the nature of eavesdropping on, or monitoring of, transmissions
Goal of the opponent is to obtain information that is being transmitted

Passive attacks (Figure 1.1) are in the nature of eavesdropping on, or monitoring

of, transmissions. The goal of the opponent is to obtain information that is being

transmitted. Two types of passive attacks are the release of message contents and

traffic analysis.

The release of message contents is easily understood. A telephone conversation,

an electronic mail message, and a transferred file may contain sensitive or

confidential information. We would like to prevent an opponent from learning the

contents of these transmissions.

A second type of passive attack, traffic analysis , is subtler. Suppose that we

had a way of masking the contents of messages or other information traffic so that

opponents, even if they captured the message, could not extract the information

from the message. The common technique for masking contents is encryption. If we

had encryption protection in place, an opponent might still be able to observe the

pattern of these messages. The opponent could determine the location and identity

of communicating hosts and could observe the frequency and length of messages

being exchanged. This information might be useful in guessing the nature of the

communication that was taking place.

Passive attacks are very difficult to detect, because they do not involve any

alteration of the data. Typically, the message traffic is sent and received in an apparently

normal fashion, and neither the sender nor receiver is aware that a third party

has read the messages or observed the traffic pattern. However, it is feasible to prevent

the success of these attacks, usually by means of encryption. Thus, the emphasis

in dealing with passive attacks is on prevention rather than detection.

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Active Attacks�An active attack attempts to alter system resources or affect their operation

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Active Attacks

Involve some modification of the data stream or the creation of a false stream
Difficult to prevent because of the wide variety of potential physical, software, and network vulnerabilities
Goal is to detect attacks and to recover from any disruption or delays caused by them

Active attacks (Figure 1.1b) involve some modification of the data stream or the

creation of a false stream and can be subdivided into four categories: masquerade,

replay, modification of messages, and denial of service.

A masquerade takes place when one entity pretends to be a different entity

(path 2 of Figure 1.1b is active). A masquerade attack usually includes one of the

other forms of active attack. For example, authentication sequences can be captured

and replayed after a valid authentication sequence has taken place, thus enabling an

authorized entity with few privileges to obtain extra privileges by impersonating an

entity that has those privileges.

Replay involves the passive capture of a data unit and its subsequent retransmission

to produce an unauthorized effect (paths 1, 2, and 3 active).

Modification of messages simply means that some portion of a legitimate

message is altered, or that messages are delayed or reordered, to produce an

unauthorized effect (paths 1 and 2 active). For example, a message meaning “Allow

John Smith to read confidential file accounts ” is modified to mean “Allow Fred

Brown to read confidential file accounts. ”

The denial of service prevents or inhibits the normal use or management of

communications facilities (path 3 active). This attack may have a specific target; for

example, an entity may suppress all messages directed to a particular destination

(e.g., the security audit service). Another form of service denial is the disruption

of an entire network, either by disabling the network or by overloading it with

messages so as to degrade performance.

Active attacks present the opposite characteristics of passive attacks. Whereas

passive attacks are difficult to detect, measures are available to prevent their success.

On the other hand, it is quite difficult to prevent active attacks absolutely

because of the wide variety of potential physical, software, and network vulnerabilities.

Instead, the goal is to detect active attacks and to recover from any disruption

or delays caused by them. If the detection has a deterrent effect, it may also

contribute to prevention.

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Security Service

enhance security of data processing systems and information transfers of an organization
intended to counter security attacks
using one or more security mechanisms
Often use replicates functions normally associated with physical documents

which, for example, have signatures, dates; need protection from disclosure, tampering, or destruction; be notarized or witnessed; be recorded or licensed

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Security Services

X.800:

“a service provided by a protocol layer of communicating open systems, which ensures adequate security of the systems or of data transfers”

RFC(Request for comment) 4949 :

“a processing or communication service provided by a system to give a specific kind of protection to system resources”

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Security Services (X.800)

Authentication - assurance that the communication is authenticated.

There are two specific authentication services defined in X.800:

Peer entity authentication:- Provides for the corroboration of the entity of a peer entity in association.
Data origin authentication:- provides for the corroboration of the source of a data units.

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Security Services (X.800)

Access Control - prevention of the unauthorized use of a resources and applications.
Data Confidentiality –protection of data from unauthorized disclosure(from passive attacks).
Data Integrity - assurance that data received is as sent by an authorized entity.
No modifications allowed from unauthorized users.
Non-Repudiation - protection against denial by one of the parties in a communication.

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Security Mechanism

feature designed to detect, prevent, or recover from a security attack
no single mechanism that will support all services required
however one particular element underlies many of the security mechanisms in use:

cryptographic techniques

hence our focus on this topic

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Security Mechanisms (X.800)

specific security mechanisms:

encipherment, 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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Model for Network Security

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Model for Network Security

using this model requires us to:

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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Model for Network Access Security

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Model for Network Access Security

using this model requires us to:

select appropriate gatekeeper functions to identify users
implement security controls to ensure only authorised users access designated information or resources

trusted computer systems may be useful to help implement this model

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Summary

have considered:

definitions for:

computer, network, internet security

X.800 standard
security attacks, services, mechanisms
models for network (access) security