1. Cryptography and
Cryptography and
Network Security
Network Security
Chapter 1
Chapter 1
Fourth Edition
Fourth Edition
by William Stallings
by William Stallings
Lecture slides by Lawrie Brown
Lecture slides by Lawrie Brown
2. Chapter 1 – Introduction
Chapter 1 – Introduction
The art of war teaches us to rely not on the
The art of war teaches us to rely not on the
likelihood of the enemy's not coming, but
likelihood of the enemy's not coming, but
on our own readiness to receive him; not
on our own readiness to receive him; not
on the chance of his not attacking, but
on the chance of his not attacking, but
rather on the fact that we have made our
rather on the fact that we have made our
position unassailable.
position unassailable.
—
—The Art of War,
The Art of War, Sun Tzu
Sun Tzu
3. Background
Background
Information Security requirements have changed
Information Security requirements have changed
in recent times
in recent times
traditionally provided by physical and
traditionally provided by physical and
administrative mechanisms
administrative mechanisms
computer use requires
computer use requires automated tools to
automated tools to
protect files and other stored information
protect files and other stored information
use of networks and communications links
use of networks and communications links
requires measures to protect data during
requires measures to protect data during
transmission
transmission
4. Definitions
Definitions
Computer Security
Computer Security -
- generic name for the
generic name for the
collection of tools designed to protect data and
collection of tools designed to protect data and
to thwart hackers
to thwart hackers
Network Security
Network Security -
- measures to protect data
measures to protect data
during their transmission
during their transmission
Internet Security
Internet Security -
- measures to protect data
measures to protect data
during their transmission over a collection of
during their transmission over a collection of
interconnected networks
interconnected networks
5. Aim of Course
Aim of Course
our focus is on
our focus is on Internet Security
Internet Security
which consists of measures to deter,
which consists of measures to deter,
prevent, detect, and correct security
prevent, detect, and correct security
violations that involve the transmission &
violations that involve the transmission &
storage of information
storage of information
7. OSI Security Architecture
OSI Security Architecture
ITU-T X.800 “Security Architecture for OSI”
ITU-T X.800 “Security Architecture for OSI”
defines a systematic way of defining and
defines a systematic way of defining and
providing security requirements
providing security requirements
for us it provides a useful, if abstract,
for us it provides a useful, if abstract,
overview of concepts we will study
overview of concepts we will study
8. Aspects of Security
Aspects of Security
consider 3 aspects of information security:
consider 3 aspects of information security:
security attack
security attack
security mechanism
security mechanism
security service
security service
9. Security Attack
Security Attack
any action that compromises the security of
any action that compromises the security of
information owned by an organization
information owned by an organization
information security is about how to prevent
information security is about how to prevent
attacks, or failing that, to detect attacks on
attacks, or failing that, to detect attacks on
information-based systems
information-based systems
often
often threat
threat &
& attack
attack used to mean same thing
used to mean same thing
have a wide range of attacks
have a wide range of attacks
can focus of generic types of attacks
can focus of generic types of attacks
passive
passive
active
active
12. Security Service
Security Service
enhance security of data processing systems
enhance security of data processing systems
and information transfers of an organization
and information transfers of an organization
intended to counter security attacks
intended to counter security attacks
using one or more security mechanisms
using one or more security mechanisms
often replicates functions normally associated
often replicates functions normally associated
with physical documents
with physical documents
• which, for example, have signatures, dates; need
which, for example, have signatures, dates; need
protection from disclosure, tampering, or
protection from disclosure, tampering, or
destruction; be notarized or witnessed; be
destruction; be notarized or witnessed; be
recorded or licensed
recorded or licensed
13. Security Services
Security Services
X.800:
X.800:
“
“a service provided by a protocol layer of
a service provided by a protocol layer of
communicating open systems, which ensures
communicating open systems, which ensures
adequate security of the systems or of data
adequate security of the systems or of data
transfers”
transfers”
RFC 2828:
RFC 2828:
“
“a processing or communication service
a processing or communication service
provided by a system to give a specific kind of
provided by a system to give a specific kind of
protection to system resources”
protection to system resources”
14. Security Services (X.800)
Security Services (X.800)
Authentication
Authentication -
- assurance that the
assurance that the
communicating entity is the one claimed
communicating entity is the one claimed
Access Control
Access Control -
- prevention of the
prevention of the
unauthorized use of a resource
unauthorized use of a resource
Data Confidentiality
Data Confidentiality –
–protection of data from
protection of data from
unauthorized disclosure
unauthorized disclosure
Data Integrity
Data Integrity -
- assurance that data received is
assurance that data received is
as sent by an authorized entity
as sent by an authorized entity
Non-Repudiation
Non-Repudiation -
- protection against denial by
protection against denial by
one of the parties in a communication
one of the parties in a communication
15. Security Mechanism
Security Mechanism
feature designed to detect, prevent, or
feature designed to detect, prevent, or
recover from a security attack
recover from a security attack
no single mechanism that will support all
no single mechanism that will support all
services required
services required
however
however one particular element underlies
one particular element underlies
many of the security mechanisms in use:
many of the security mechanisms in use:
cryptographic techniques
cryptographic techniques
hence our focus on this topic
hence our focus on this topic
18. Model for Network Security
Model for Network Security
using this model requires us to:
using this model requires us to:
1.
1. design a suitable algorithm for the security
design a suitable algorithm for the security
transformation
transformation
2.
2. generate the secret information (keys) used
generate the secret information (keys) used
by the algorithm
by the algorithm
3.
3. develop methods to distribute and share the
develop methods to distribute and share the
secret information
secret information
4.
4. specify a protocol enabling the principals to
specify a protocol enabling the principals to
use the transformation and secret
use the transformation and secret
information for a security service
information for a security service
20. Model for Network Access
Model for Network Access
Security
Security
using this model requires us to:
using this model requires us to:
1.
1. select appropriate gatekeeper functions to
select appropriate gatekeeper functions to
identify users
identify users
2.
2. implement security controls to ensure only
implement security controls to ensure only
authorised users access designated
authorised users access designated
information or resources
information or resources
trusted computer systems may be useful
trusted computer systems may be useful
to help implement this model
to help implement this model
21. Summary
Summary
have considered:
have considered:
definitions for:
definitions for:
• computer, network, internet security
computer, network, internet security
X.800 standard
X.800 standard
security attacks, services, mechanisms
security attacks, services, mechanisms
models for network (access) security
models for network (access) security
Editor's Notes
#1:Lecture slides by Lawrie Brown for “Cryptography and Network Security”, 4/e, by William Stallings, Chapter 1 “Introduction”.
#2:This quote from the start of Ch0 sets the scene for why we want to study these issues.
#3:The requirements of information security within an organization have undergone two major changes in the last several decades. Before the widespread use of data processing equipment,the security of information felt to be valuable to an organization was provided primarily by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).
Growing computer use implies a need for automated tools for protecting files and other information stored on it. This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be accessed over a public telephone network, data network, or the Internet.
The second major change that affected security is 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. Network security measures are needed to protect data during their transmission.
#4:Here are some key definitions, note boundaries between them are blurred.
#5:Detail the focus of this book/course, which is on Internet Security - being measures to deter, prevent, detect, and correct security violations that involve the transmission & storage of information.
#6:Discuss observed security trends (Stallings section 1.1 & Figure 1.2 above), noting growth in sophistication of attacks contrasting with decrease in skill & knowledge needed to mount an attack.
#7:To assess effectively the security needs of an organization and to evaluate and choose various security products and policies, the manager responsible for security needs some systematic way of defining the requirements for security and characterizing the approaches to satisfying those requirements. This is difficult enough in a centralized data processing environment; with the use of local and wide area networks,the problems are compounded. ITU-T Recommendation X.800, Security Architecture for OSI, defines such a systematic approach. The OSI security architecture is useful to managers as a way of organizing the task of providing security.
#8:The OSI security architecture focuses on security attacks,mechanisms,and services. These can be defined briefly as follows:
• Security attack: Any action that compromises the security of information owned by an organization.
• Security mechanism: A process (or a device incorporating such a process) that is designed to detect, prevent,or recover from a security attack.
• Security service: A processing or communication service that enhances the security of the data processing systems and the information transfers of an organization.The services are intended to counter security attacks, and they make use of one or more security mechanisms to provide the service.
#9:Expand on definition and use of “security attack”, as detailed above.
See Stallings Table 1.1 for definitions of threat and attack.
#10:Have “passive attacks” which attempt to learn or make use of information from the system but does not affect system resources.
By eavesdropping on, or monitoring of, transmissions to:
+ obtain message contents (as shown above in Stallings Figure 1.3a), or
+ monitor traffic flows
Are difficult to detect because they do not involve any alteration of the data.
#11:Also have “active attacks” which attempt to alter system resources or affect their operation.
By modification of data stream to:
+ masquerade of one entity as some other
+ replay previous messages (as shown above in Stallings Figure 1.4b)
+ modify messages in transit
+ denial of service
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.
#12:Consider the role of a security service, and what may be required.
Note both similarities and differences with traditional paper documents, which for example:
have signatures & dates;
need protection from disclosure, tampering, or destruction;
may be notarized or witnessed;
may be recorded or licensed
#13:Also have a couple of definition of “security services” from relevant standards. X.800 defines a security service as a service provided by a protocol layer of communicating open systems, which ensures adequate security of the systems or of data transfers. Perhaps a clearer definition is found in RFC 2828, which provides the following definition: a processing or communication service that is provided by a system to give a specific kind of protection to system resources; security services implement security policies and are implemented by security mechanisms.
#14:This list includes the various "classic" security services which are traditionally discussed.
Note there is a degree of ambiguity as to the meaning of these terms, and overlap in their use.
See Stallings Table 1.2 for details of the 5 Security Service categories and the 14 specific services given in X.800.
#15:Now introduce “Security Mechanism” which are the specific means of implementing one or more security services.
Note these mechanisms span a wide range of technical components, but one aspect seen in many is the use of cryptographic techniques.
#16:Some examples of mechanisms from X.800. Note that the “specific security mechanisms” are protocol layer specific, whilst the “pervasive security mechanisms” are not. We will meet some of these mechanisms in much greater detail later.
See Stallings Table 1.3 for details of these mechanisms in X.800, and Table 1.4 for the relationship between services and mechanisms.
#17:In considering the place of encryption, its useful to use the following two models from Stallings section 1.6.
The first, illustrated in Figure 1.5, models information flowing over an insecure communications channel, in the presence of possible opponents. Hence an appropriate security transform (encryption algorithm) can be used, with suitable keys, possibly negotiated using the presence of a trusted third party.
#18:This general model shows that there are four basic tasks in designing a particular security service, as listed.
#19:The second, illustrated in Figure 1.6, model is concerned with controlled access to information or resources on a computer system, in the presence of possible opponents. Here appropriate controls are needed on the access and within the system, to provide suitable security. Some cryptographic techniques are useful here also.
#20:Detail here the tasks needed to use this model.
Note that trusted computer systems (discussed in Ch 20 can be useful here).
