UNIT-1

Introduction:
•​ The Process of Protecting information is called as Information security, means
securing the data that is made available on network.
•​ The mainly information security provides availability, privacy and integrity.
•​ The generic name for the collection of tools designed to protect data and to thwart
hackers is computer security.
•​ Hackers use their technological skills to break into computer systems and access
confidential information. Hackers are people, who make a living from break through
information security systems. People within the company also try to hack the systems,
this is the biggest threat to information security.
•​ Network Security measures are needed to protect data during data transmission, the
term network security is somewhat misleading, because virtually all business,
government and academic organizations interconnect their data processing equipment
with a collection of interconnected networks, such a collection is often referred to as
an internet and the term internet security is used.

The need for security:

•​ Security provider privacy for your data means no other party can view your data.
•​ Security is required because the widespread use of data processing equipment, the
security of information felt to be valuable to an organization.

•​ Network Security measures are needed to protect data during their transmission.
Following are the examples of security violations:
•​ User A transmits a sensitive information file to User B. The Unauthorized User C is
able to monitor the transmission and capture a copy of the file during its transmission.
•​ A message is sent from a customer to a stock broker with instructions for various
transactions, subsequently the investments lose value and the customer denies sending
the message.
•​ While transmitting the message between two users, the unauthorized user intercepts
the message, alters its contents to add or delete entries, and then forwards the message
to destination user.

OSI Security Architecture:

•​ The International Telecommunication Union Telecommunication (ITU-T)
recommendation X.800, Security Architecture for OSI, defines such a Systematic
approach.
 •​ The OSI Security architecture is useful to manager as a way of organizing the task of
providing Security.
•​ It mainly focuses on security attacker, mechanisms and Services
1)​ Security attack: Any action that compromises the security information owned by an
organization.
2)​ Security mechanism: A process that is designed to detect, prevent or recover from a
security attack.
3)​ 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.

Security Attacks:
There are four general categories of attacks.
1) Interruption: An Asset of the system is destroyed or becomes unavailable. This is a threat
to availability.
eg: cutting of communication line
2) Interception : An unauthorized party gain access to an asset. This is a threat to Secrecy.
eg: wiretapping to capture data in a network.
3) Modification : An Unauthorized party not only gains access but tampers with an asset.
This is a threat to integrity.
eg: changing values in a data file
4) Fabrication: This is also a threat to integrity. An unauthorized party inserts counter fit
objects into the System.
Eg: Addition of records to a file
Attack: Any action that compromises the security of information owned by an organization.
Security attacks are of two types:
1.​ Passive attacks
2.​ Active attacks
1. Passive attacks:
Passive 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
1.​ Release of message contents
2.​ Traffic analysis

1.​ Release of message contents:

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 content of these transmissions.

2) Traffic analysis:
Mask the contents of message so that opponents could not extract the information from
the message. Encryption is used for masking.

Active Attack: Active attacks involve some modification of the data stream or the
creation of a false stream.
Active attacks can be sub divided into four categories.
1)​ masquerade: It takes place when one entity pretends to be a different entity
 Eg: 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.Interruption attacks are called as masquerade attacks.

2)​ Replay: It involves the passive capture of a data unit and its subsequent
retransmission to produce an unauthorized effect.

3)​ Modification of message: It involves some change to the original message. It

produces an unauthorized effect.

4) Denial of service: It prevents or inhibits the normal use or management of communication

facilities. Fabrication causes denial of service attacks.
•​ Another form of denial service is the disruption of an entire network, either by
disabling the network or by overloading it with messages so as to degrade
performance.
Security Approaches:
•​ An organization can take several approaches to implement its security model.
•​ The various approaches are
1. No Security : In this simplest case, the approach could be a decision to implement no
security at all
2. Security through obscurity: In this model, a system is secure simply because nobody
knows about its existence and contents. This approach cannot work for too long as there are
many ways an attacker can come to know about it.
3. Host Security: In this scheme, the security for each host is enforced individually. This is a
very safe approach, but the trouble is
•​ That it cannot scale well. The complexity and diversity of modern organizations
makes the task even harder.
4.Network Security: Host Security is tough to achieve as organization grow is become
more diverse. In this, the focus is to control network access to various hosts and their
services, rather than individual host security. This is a very efficient and scalable model.

Security services:
•​ A Security Service is a service that provides security for data that transferring from
source system to destination system.
•​ X.800 divides security services into different categories.
1.​ Authentication: Authentication means identifying origin of message correctly and it
should ensured that identity is not false.
​ ​ The authentication service is concerned with assuring that a communication is
authentic. In public & private computer network, authentication is commonly done through
the use of login, passwords.
​
•​ Two specific authentication services are defined in X.800
 •​ Peer entity authentication: It used in association with a logical connection to
provide confidence in the identity of the entities connected.
•​ Data origin authentication : It does not provide protection against the duplication or
modification of data units. This type of service supports applications like electronic
mail where there are no prior
Interactions between the communicating entities.
2.Access control: It is the ability to limit and control the access to host systems and
applications via communication links. To achieve this, each entity trying to gain access must
first be identified, or authenticated, so that access rights can be tailored to the individual.
3. Data Confidentiality: It is the protection of transmitted data from passive attacks with the
respect to the content of a data transmission, several levels of protection can be identified.
•​ The other aspect of confidentiality is the protection of traffic flow from analysis.
•​ This requires that an attacker not be able to observe the source & destination,
frequency, length or other characteristics of the traffic on a communications facility.
•​ Confidentiality is classified into
i.​ Connection confidentiality: The protection of all user data on a connection
ii.​ Connectionless confidentiality: The protection of all user data in a single data
block
iii.​ Selective field confidentiality : The confidentiality of selected fields within the
user data on a connection or in a single data block.
iv.​ Traffic flow confidentiality : The protection of the information that might be
derived from observation of traffic flows.
4.Data Integrity: message that is sent through network cannot be modifiable by other party.
•​ Integrity means data that is sent through the secure channel is not altered or tampered
by others.
•​ Altering of message means message may be deleted, edited or new message may be
added or delay the transmission etc.
•​ Integrity ensures that message received is as it is sent.
•​ Modification causes loss of message integrity.
•​ Data integrity can be classified as
i.​ Connection integrity with recovery
ii.​ Connection integrity without recovery
iii.​ Selective field connection integrity
iv.​ Connectionless integrity
v.​ Selective field connectionless integrity
5.Non-repudiation: Once the transaction is completed through secure channel further sender
or receiver cannot deny the transmission
 •​ Non-repudiation prevents either sender or receiver from denying a transmitted
message.
•​ When a message is received, the sender can prove that the alleged receiver in fact
received the message.
6. Availability: A variety of attacks can result in the loss of or reduction in availability.
X.800 treats availability as a property to be associated with various security services.
•​ An availability service is one that protects a system to ensure its availability.

Security Mechanisms:
•​ To ensure the security we have some mechanisms.
1) Specific security mechanisms: It may be incorporated into the appropriate protocol layer
in order to provide some of the OSI Security services
a) Encipherment:
•​ The data will be hidden by cipher.
•​ The sender will convert the data into a unreadable format means sender hides the data.
•​ When the receiver, receives the data which is in unreadable that is converted into
readable format.
b) Digital signature:
•​ Some special identity which is used for authentication.
•​ It is like a thumbnail and stamp.
•​ It is also used to Integrity of data.
c) Access control:
•​ Restricting the permissions to several levels.
•​ In any organization, upto what extent of permissions can be given to a particular
persons.
d) Authentication Exchange:
•​ Declaring the user as an authenticated user by comparing the username and password
with the data that we are having in database. Ex: login Instagram.
e) Traffic Padding:
•​ We have to add extra bits in the beginning or in the middle or in the ending in order to
confuse the observer or hacker.
f) Routing control:
 •​ Enabler selection of particular physically secure routes for certain data and allows
routing changes, especially when a breach of security is suspended.
g) Notarization:
•​ The use of a trusted third party to assure certain properties of a data exchange.
2.Pervasive security mechanisms: Mechanisms that are not specific to any particular OSI
security service or protocol layer.
a) Trusted functionality:
•​ That which is perceived to be correct with respect to some criteria
b) Event detection :
•​ Detection of security relevant events
c) Security label :
•​ The marking bound to resource that names or designates the security attributes of that
resource.
d) Security recovery:
•​ Deals with requests from mechanisms, such as event handling and management
functions and takes recovery actions.

A Model for Network Security:

•​ A message is to be transferred from source to destination across some sort of internet.
Both the sides must Co-operate for the exchange of the data.
•​ A logical information channel is established by defining a route through the internet
from source to destination.
•​ All the techniques for providing security have two components.
1.​ A security related transformation on the information to be sent.
2.​ Some Secret information shared by the two principles, it is hoped, unknown to the
opponent.
 •​ A trusted third party is needed to achieve secure transmission.
Basic tasks in designing a particular security service:
1.​ Design an algorithm for performing the security related transformation.
2.​ Generate the secret information to be used with the algorithm.
3.​ Develop methods for the distribution and sharing of the secret information.
4.​ Specify a protocol to be used by the two principles that makes use of the Security
algorithm.
•​ Another type of unwanted access is the placement in a computer system of logic that
exploits vulnerabilities in the system & that can affect application programs as well as
utility programs. Programs can present two kinds of threats.
1.​ Information access threats: Intercept or modify data on behalf of users who should
not have access to that data.
2.​ Service threats: Exploit Service flows in computer to inhibit use by legitimate user

Cryptography Concepts and Techniques:

Introduction:
Cryptography: Cryptography means secret writing, is the science of converting a message
into a coded form that hides the information contained in the message. We encrypt a message
before its transmission ,so that can eavesdropper may not get the information contained in the
message.
There are many ways of carrying out encryption , These are called cryptography or
ciphers.
Plain Text and Cipher Text:
Plain Text: This is the original message or data that is fed into algorithm as input.
Cipher Text: This is the Scrambled message produced as output. It depends on the Plain text
and the Secret Key. For a given message, two different keys will produced.
Encryption : The process of converting plain text into Cipher text is Known as encryption.
Decryption : The process of converting cipher text into plain text is known as decryption.
A cryptography system consists of two components
1.​ A Set of complementary algorithms, encryption algorithm(E) and decryption
algorithm(D).
2.​ Cipher key(K)
Cryptographic Systems are generally classified along three independent dimensions
1.​ The type of operations used for transforming plain text to cipher text: All
encryption algorithms are based on two general principles.
i)​ Substitution
ii)​ Transposition
i)​ Substitution: It means replacing a symbol of the plain text with another symbol
Eg: COMPUTER--- DPNQVUFS
ii) Transposition: It means rearranging the order of appearance of the symbols of the
message.
Eg: COMPUTER- CMUEOPTR
2. The number of keys used: If both sender and receiver use the same key, the system is
referred to as Symmetric, Single key or Conventional encryption.
If the sender and receiver each use a different key, the system is referred to as Symmetric
, two key or public key encryption.
3) The way in which the plain text is processed:
 A block cipher processes the input one block of elements at a time, producing an output
block for each input block. A Stream cipher processes the input elements continuously ,
Producing output one element at a time, as it goes along.
There are two general approaches to attacking a conventional encryption scheme.
1)​ Cryptanalysis:
It is the art of deciphering an encrypted message without complete Knowledge of the key
required for decryption. An attempted cryptanalysis is called a cryptanalytic attack.
Cryptanalytic Attacks:
A Cryptanalyst can attack a Cryptosystem in several ways.
The following are the various type of attacks.

Substitution Techniques:
A Substitution Technique is one in which the letters of plain text are replaced by other letters
or by number or symbols.
The Various substitution Techniques are:
1)​ Caeser Cipher:
•​ Letters are replaced by other letters.
•​ The earlier known and simplest method used be Julius Caeser.
•​ Replacing each letter of the alphabet with the letter standing three places further down
the alphabet.

Algorithm:
For each plaintext letter ‘p’, substitute the ciphertext letter ‘C’.
C=E(p,k)mod 26= (p+k) mod 26
P=D(C,k)mod 26=(C-k) mod 26
Ex: Let key K=3
 word= NEW
N=>m=12, C=(12+3) mod 26=15=>P
E=>m=4, C=(4+3) mod 26=7=>H
W=>m=22, C=(22+3) mod 26=25=>Z
•​ Caeser cipher is also Known as additive cipher or shift ciphers
2) Monoalphabetic substitution cipher:
•​ In monoalphabetic substitution, the relationship between a symbol in the plain text
to a symbol in the cipher text is always one-to-one.
•​ After sender and receiver agreed to a single key , that key is used to encrypt each
letter in the plain text or decrypt each letter in the cipher text.
•​ A better solution is to create a mapping between each plain text character and the
corresponding cipher text character.
•​ An example key for monoalphabetic substitution cipher

Eg:Message is machine
Plain text: machine
Cipher text:PDFKLQH
3) Playfair cipher:
•​ Aka Playfair square or Wheatstone-Playfair cipher.
•​ Manual symmetric encryption technique.
•​ The first literal digraphs substitution cipher.
•​ Invented in 1854 by Charles Wheatstone.
•​ Bore the name of Lord Playfair for promoting its use.
The Playfair Cipher Encryption Algorithm: ​
The Algorithm consists of 2 steps: ​

1)​ Generate the key Square(5×5): ​

The key square is a 5×5 grid of alphabets that acts as the key for encrypting the
plaintext. Each of the 25 alphabets must be unique and one letter of the alphabet
(usually J) is omitted from the table (as the table can hold only 25 alphabets). If the
plaintext contains J, then it is replaced by I. ​
 The initial alphabets in the key square are the unique alphabets of the key in the order
in which they appear followed by the remaining letters of the alphabet in order.

Ex: key is Monarchy

2) Algorithm to encrypt the plain text: The plaintext is split into pairs of two letters
(digraphs). If there is an odd number of letters, a Z is added to the last letter. ​
For example:
PlainText: "instruments" ​
After Split: 'in' 'st' 'ru' 'me' 'nt' 'sz'
i) Pair cannot be made with same letter. Break the letter in single and add a bogus
letter to the previous letter.
Plain Text: “hello”
After Split: ‘he’ ‘lx’ ‘lo’
Here ‘x’ is the bogus letter.
ii) If the letter is standing alone in the process of pairing, then add an extra bogus
letter with the alone letter
Plain Text: “helloe”
AfterSplit: ‘he’ ‘lx’ ‘lo’ ‘ez’
Here ‘z’ is the bogus letter.
Rules for Encryption:
1) If both the letters are in the same column: Take the letter below each one (going back to
the top if at the bottom).​
For example: ​

Diagraph: "me“ ​
Encrypted Text: cl ​
Encryption: ​
m -> c​
e -> l
2)​ If both the letters are in the same row: Take the letter to the right of each one (going
back to the leftmost if at the rightmost position).​
For example:

Diagraph: "st"​
Encrypted Text: tl​
Encryption: ​
s -> t​
t -> l
3) If neither of the above rules is true: Form a rectangle with the two letters and
take the letters on the horizontal opposite corner of the rectangle.
For example:
 Diagraph: "nt"​
Encrypted Text: rq​
Encryption: ​
n -> r​
t -> q
For example:
Plain Text: "instruments“
Keyword: Monarchy
After split: in st ru me nt sz

Encrypted Text: gatlmzclrqtx

4) Hill Cipher:
•​ The hill cipher takes a mathematical approach to Multi-letter substitution.
•​ A numerical value assigned to each letter of the alphabet.
•​ Ex: Integers 0 through 25 - A through Z
Hill Algorithm:
Encryption:
Here C:Cipher E:Encryption K:Key P:Plain text

Hill Cipher example:

Plaintext: ACT
Key: GYBNQKURP
•​ We have to encrypt the message ‘ACT’ (n=3).The key is ‘GYBNQKURP’ which can
be written as the nxn matrix:Here G-> 6 number, Y->24 number,B->1 number so…on

•​ The message ‘ACT’ is written as vector:Here A->0 number,C->2 number,T->19

number
The enciphered vector is given as:

MOD 26

MOD 26

•​ Here 15->P,14->O,7->H, so cipher text is POH

5) Polyalphabetic Cipher:
•​ To improve on the simple monoalphabetic technique.
i)Vigenere Cipher:
•​ It consists of the 26 Caesar ciphers with shifts of 0 through 25.
Encryption process:

Decryption process :
Example:
Key : deceptivedeceptivedeceptive
Plaintext : wearediscoveredsaveyourself
Ciphertext :ZICVTWQNGRZGVTWAVZHCQYGLMG

Key 3 4 2 4 15 19 8 21 4 3 4 2 4 15

PT 2 4 0 17 4 3 8 18 2 14 21 4 17 4
2

CT 2 8 2 21 19 22 16 13 6 17 25 6 21 19
5

Ke 1 8 2 4 3 4 2 4 1 1 8 2 4
y 9 1 5 9 1
PT 3 1 0 2 4 2 1 2 1 1 4 1 5
8 1 4 4 0 7 8 1
CT 2 0 2 2 7 2 1 2 6 1 1 6 9
2 1 5 6 4 1 2

ii)One Time Pad:

•​ Improvement to the vigenere cipher.
•​ It yields the ultimate in Security.
•​ Random key that is as long as the message.
•​ The Key need not be repeated.
•​ In addition, the key is to be used to encrypt and decrypt a single message and then is
discarded.
•​ Each new message requires a new key of the same length as the new message
Two Fundamental Difficulties:
•​ The practical problem of making large quantities of random keys.
 •​ Even more daunting is the problem of key distribution and protection.
•​ Because of these difficulties, the one-time pad is of limited utility and is useful
primarily for low-bandwidth channels requiring very high security.
Ex:Input: Message = HELLO,
Key = MONEY
Output: Cipher – TSYPM,
Message – HELLO
Explanation:
Part 1: Plain text to Ciphertext
Plain text — H E L L O = 7 4 11 11 14
Key — M O N E Y = 12 14 13 4 24
Plain text + key = 19 18 24 15 38
Cipher – TSYPM

Transposition Techniques :
•​ In transposition Techniques, the letters of plain text remain same, but their original
sequence is changed in symmetric way.
i) Rail Fence Technique:
•​ The plaintext is written down as a sequence of diagonals and then read off as a
sequence of rows.
Example:
Encipher the message “ Vignan is the best” with a rail fence of depth 2
•​ Plaintext: Vignan is the best
•​ Depth: 2

V g a i T e e t

i n n s h b s

•​ Ciphertext:VGAITEETINNSHBS
ii) Row Column Transposition:
•​ A More Complex Scheme.
•​ Create Rectangle box.
 •​ Write : Row by Row
•​ Read :Column by Column
Example: Encrypt the message “ Guard leaves at fifteen hours”
•​ Plaintext: Guard leaves at fifteen hours
•​ Key : 5263174

5 2 6 3 1 7 4
G U A R D L E

A V E S A T F

I F T E E N H

O U R S X Y Z

Ciphertext: DAEXUVFURSESEFHZGAIOAETRLTNY

Steganography:
•​ The technique of hiding message in another message or picture or audio/sound or
video or any another source is known as steganography.
•​ Example for Steganography:
1)​ Image Steganography: Hide message in a message without disturbing the picture.
2)​ Audio Steganography: Hide message in an audio stream without effecting the actual
sound
3)​ Video Steganography: Hide message in a video
4)​ Invisible ink: number of substances can be used for writing but leave no visible trace
until heat or some chemical is applied to the paper.
5)​ Pin Punctures: Small pin punctures on selected letters are ordinarily not visible
unless the paper is held up in front of a light.