Introduction
to
Cryptography and
Network Security
Dr. Bimal Kumar Meher
Associate Professor. Dept. of CSE
Silicon Institute of Technology
What is Information Security?
Information security (InfoSec), is the practice
of defending information from
unauthorized access,
disclosure,
disruption,
modification,
inspection,
recording,
destruction.
Who needs Information Security?
Government,
Military,
Corporations,
Financial institutions,
Hospitals
Private businesses
They have a great deal of
confidential information about their employees,
customers, products, research and financial status.
Books for this Course
Text Books:
Cryptography and Network Security:
Principles and Practice- William Stallings, PHI.
Network Security:Charlie Kaufman, Radia
Perlman, Mike Spencier, PHI
Reference Book:
Cryptography and Network Security- B.A.
Forouzan & D. Mukhopadhyay, McGraw Hill
Special Indian Edition.
Introduction
Security goals or attributes called C I A Triad
Three aspects of Security
Security attacks
Security services
Security mechanisms
To introduce two techniques, Cryptography and
Steganography to implement security mechanisms
C I A Triad
C I A
Confidentiality
• Confidentiality is to maintain secrecy of the
information from any unintended/unauthorized
person or process.
• Probably the most common aspect of information
security.
Message
Now my Acc.
Balance 2Lac.
Sender Receiver
EVE
Eavesdropper
Integrity
• Information needs to be changed whenever
there is a need.
• Integrity means that changes need to be done
only by authorized entities and through
authorized mechanisms.
Message Message
I am fine I am not fine
Sender Receiver
EVE
Attacker
Availability
• The information created and stored by an
organization needs to be available to authorized
entities only.
• It is the most essential attribute for the critical
information which are stored remotely.
Message
I need your
help urgently
Sender Receiver
EVE
Attacker
Three Aspects of Security
Security Attacks: Any action that
compromises the security of data owned
by an organisation
Security Services: It ensures the security
of the data and its transfer by using some
of the security mechanisms.
Security Mechanisms: Processes those
are designed to detect, prevent, or recover
from a security attack.
Security Attacks
The three goals of security-Confidentiality,
Integrity, and Availabilitycan be threatened by
security attacks.
1. Attacks on Confidentiality
2. Attacks on Integrity
3. Attacks on Availability
All these attacks can be broadly classified as
either Active or Passive attacks
Taxonomy of attacks with relation
to security goals
Attacks on Confidentiality
Snooping refers to unauthorized access to or
interception of data.
Traffic analysis refers to obtaining some specific
type of information by monitoring online traffic.
Attacks on Integrity
Modification means that the attacker intercepts the
message and changes it.
Masquerading or spoofing happens when the
attacker impersonates somebody else.
Attacks on Integrity
Replaying means the attacker obtains a copy
of a message sent by a user and later tries to replay
it.
Repudiation means that sender of the message
might later deny that he has sent the message; the
receiver of the message might later deny that he has
received the message.
Attacks on Availability
Denial of service (DoS) is a very powerful attack,
which may slow down or totally interrupt the service
of a system.
An attacker in DoS typically floods the targeted
machine (Server) with so many superfluous requests
that, the machine remains busy in servicing them;
As a result all legitimate requests from other systems
are prevented from servicing.
DDoS: More sophisticated attack using many
attack sources
Example of DoS Attack
Source: Cloudflare Inc. US
Active vs Passive Attacks
Active attack may change the data or harm the
system.
Passive attack is not to change the data or
harm the system, but to obtain the information.
So it harms the sender and receiver of the message.
Active vs Passive
Eve
Eve
Active vs Passive Attacks(contd…)
Which one is difficult to detect?
Security Services
Peer-Entity Auth.
Data Origin Auth.
Access Control
Security
Confidentiality
Services
Data Integrity
Nonrepudiation
Availability
Security Mechanism
Relation between Services and Mechanisms
Mechanisms
Enciph Digital Access Data Auth. Traffic Routing Notari
Services erment Sign. Control Integrity Exch. Pad. Control zation
Peer-Entity Auth.
Data Origin Auth.
Access Control
Confidentiality
Data Integrity
Nonrepudiation
Availability
Security Implementation Techniques
• Mechanisms discussed in the previous
sections are only theoretical recipes to
implement security.
• The actual implementation of security goals
needs some techniques.
• Two techniques mostly used: Cryptography
and Steganography.
Cryptography
• Cryptography, a word with Greek origin, means
“secret writing.”
• Now this term is used as the science and art of
transforming messages to make them secure and
immune to attacks.
Cryptography(contd…)
• Although Cryptography, earlier referred to
encryption/decryption, but now it is
defined as three distinct mechanisms:
• Symmetric key Encipherment
• Asymmetric key Encipherment
• Hashing
Symmetric Key Encipherment
Also called Symmetric key cryptography
Or Secret Key Cryptography
The sender of the message uses some predefined
algorithm and a shared secret key for encryption.
The receiver uses the same shared secret key for
decryption.
It is something like Alice puts the message in a
box and locks the box using a key whose duplicate
key is available with Bob who can open the box
and takes the message from the box.
Example: Decrypt: uknkeqp, qgjgaml
Asymmetric Key Encipherment
Also called Public key encipherment
Or public key cryptography
Unlike symmetric, it uses two keys
They are named as: public key & private key
To send a message to Bob, Alice first encrypts the
message by using Bob’s public key.
To decrypt the message, Bob uses his own private
key.
The algorithm used here is more complex than the
previous one.
Hashing
It is a process by which a fixed length message
digest is created out of a variable length
message.
It is much smaller than the message to be sent.
This is essential in
Data integrity
Digital signature
Authentication
THE REST OF YOUR SYLLABUS
The rest of your text book is divided into four parts.
Part One: Symmetric-Key Encipherment
Part Two: Asymmetric-Key Encipherment
Part Three: Integrity, Authentication, and Key Management
Part Four: Network Security
