Cryptography and
Network Security
Chapter 1
Roadmap
 Cryptographic




algorithms and protocols
Symmetric ciphers
Asymmetric encryption
Data integrity: hash functions
Authentication
 Mutual
Trust
 Computer Security
 Network Security
Computer Security
 Need
for Security
 NIST definition of 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)
This definition introduces 3
key objectives:
 Confidentiality:
Data confidentiality, Privacy.
 Integrity:
Data Integrity, System Integrity.
 Availability
Key Security Concepts
Additional Concepts: Authenticity, Accountability
Examples of Security
Violations
 Capturing
a file(by C) during transmission
from A to B
 Message Interception
 Faking source identity
 Delaying the message
 Deny having sent the message
Levels of Impact
 can
define 3 levels of impact from a
security breach



Low
Moderate
High
Examples of Security
Requirements
– student grades
 integrity – patient information
 availability – authentication service
 confidentiality
Computer Security Challenges
not simple
2. must consider potential attacks
3. procedures used counter-intuitive
4. involve algorithms and secret info
5. must decide where to deploy mechanisms
6. battle of wits between attacker / admin
7. not perceived on benefit until fails
8. requires regular monitoring
9. too often an after-thought
10. regarded as impediment to using system
1.
OSI Security Architecture
X.800 “Security Architecture for OSI”
defines a systematic way of defining and
providing security requirements.
 ITU-T
 For
us it provides a useful, if abstract,
overview of concepts we will study
Aspects of Security
 consider



security attack
security mechanism
security service
 note


3 aspects of information security:
terms
threat – a potential for violation of security
attack – an assault on system security, a
deliberate attempt to evade security services
Passive Attacks
Release of Message Contents
Active Attacks
Active Attacks
(b)Replay
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 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
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
2828:
“a processing or communication service
provided by a system to give a specific kind of
protection to system resources”
Security Services (X.800)

Authentication - assurance that communicating
entity is the one claimed


peer-entity
data origin authentication

Access Control - prevention of the
unauthorized use of a resource

Data Confidentiality –protection of data from
unauthorized disclosure
•
•
•
•
Connection Confidentiality
Connectionless Confidentiality
Selective-Field Confidentiality
Traffic-Flow Confidentiality
 Data
•
•
•
•
•
Integrity:
Connection Integrity with Recovery
Connection Integrity without Recovery
Selective-Field Connection Integrity
Connectionless Integrity
Selective-Field Connectionless Integrity
 Non-Repudiation
- protection against
denial by one of the parties in a
communication
•
•
Nnrepudiation, Origin
Nonrepudiation, Destination
Security Mechanism
 Method
or technique used to provide
security.
 Feature
designed to detect, prevent, or
recover from a security attack
 No
single mechanism will support all
security services required
Security Mechanisms (X.800)
 specific security mechanisms:
 Encipherment (reversible, irreversible), 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
Service
Peer Entity
Authentication
Data Origin
Authentication
Access Control
Confidentiality
Traffic Flow
Confidentiality
Data Integrity
Nonrepudiation
Availability
Mechanism
Digital Access
Data
Encipherment Signature Control Integrity
Authentication Traffic Routing
Exchange
Notariza
Padding Control
tion
Service
Mechanism
Digital Access
Encipherment Signature Control Integrity
Peer Entity
Authentication
Y
Y
Data Origin
Authentication
Y
Y
Access Control
Y
Traffic Flow
Confidentiality
Y
Data Integrity
Y
Availability
Authentication Traffic Routing
Exchange
Notariza
Padding Control
tion
Y
Y
Confidentiality
Nonrepudiation
Data
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Attack
Service
Release of
Traffic
Message
Contents
Analysis
Masquerade
Peer Entity
Authentication
Y
Data Origin
Authentication
Y
Y
Access Control
Confidentiality
Traffic Flow
Confidentiality
Y
Y
Data Integrity
Nonrepudiation
Y
Replay
Modification of
Denial of
Messages
Service
Attack
Mechanism
Encipherment
Digital Signature
Access Control
Data Integrity
Authentication
Exchange
Traffic Padding
Routing Control
Notarization
Release of
Traffic
Message
Contents
Analysis
Masquerade
Replay
Modification of
Denial of
Messages
Service
Exercises
1. An organization wants protection against passive
attacks. As a security manager of the organization which
security services would you recommend for your
organization? Justify your answer.
2. Consider a database management system used by a
departmental store. Give examples of confidentiality,
integrity, availability, and authenticity requirements
associated with the system. In each case indicate the
degree of importance of the requirement.
3. An organization has a server in which some manual are
kept. It also provides some applications. The organization
wants the manuals to be viewed by all the employees
whenever required by them. However project managers
can modify the contents of the manuals. For this they must
first request the admin. If the admin is confirmed that it is
only the concerned project manager making a request he
grants permission to make changes to the concerned
manual. What type of security services must be present to
enable these activities in the organization?
4. Consider an implanted medical device that monitors
and records data about a patient’s health and stores
the information locally. To access the data, authorized
personnel must transmit a PIN to the implanted
device, and once authorized, electronically request
specific portions of the data. Give examples of
confidentiality, integrity and availability requirements
associated with the system, and in each indicate the
degree of importance of the requirement.
Model for Network Security
Model for Network Security
using this model requires us to:

1.
2.
3.
4.
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
Model for Network Access
Security
Model for Network Access
Security
using this model requires us to:

1.
2.
select appropriate gatekeeper functions to
identify users
implement security controls to ensure only
authorised users access designated
information or resources
Summary
 topic
roadmap & standards organizations
 security concepts:

confidentiality, integrity, availability
 X.800
security architecture
 security attacks, services, mechanisms
 models for network (access) security
The art of war teaches us to rely not on the
likelihood of the enemy's not coming, but
on our own readiness to receive him; not
on the chance of his not attacking, but
rather on the fact that we have made our
position unassailable.
—The Art of War, Sun Tzu
 Text
Book:
1. William Stallings - Cryptography and
Network Security: Principles and Practice,
Prentice Hall, 5th edition, 2010.
 Reference
Book:
1. Behrouz A. Forouzan and Debdeep
Mukhopadhyay - Cryptography and Network
Security, McGraw Hill, 2nd Edition, 2008.