The document discusses network security concepts and algorithms. It introduces network security and defines it as protection of networks from unauthorized access, modification, or disclosure. It then describes common network security concepts like authentication, confidentiality, and data integrity. It also discusses common security attacks like interception, modification, and fabrication. The document also summarizes the RSA and IDEA encryption algorithms, including how keys are generated and how encryption and decryption work.

2. INTRODUCTION
NETWORK is an interconnected collection of
autonomous computers
Two computers are said to be interconnected,
if they are able to exchange information
If one computer can forcibly start or stop or
control another one, then the computers are not
autonomous.

3. A typical Computer Network

4. ADVANTAGE OF NETWORKS
 Information can be send quickly through different
computers and can share data
 For Example, A Company can share files or data
without need to use some external devices to carry the
data.

5. DIS-ADVANTAGE OF NETWORKS
 When we are sending the data between the computers
any other person may watches or modifies confidential
message.
 For Example, some unauthorized user may get access
over the network and may perform any illegal
functions like deleting those data etc…

6. NETWORK SECURITY:-
 To overcome the disadvantage of Networks, we are
giving security to the network that is known as
NETWORK SECURITY.
 Network Security is protection of networks and their
services from unauthorized modification, destruction
or disclosure and provision of assurance that the
network perform its critical functions correctly and
there are no harmful side effects.

7. IMPORTANCE OF SECURITY
 Enforcing data security is top priority for both
governments and businesses worldwide.
 Recent legislation in many countries has set new
standards for protecting customer information.
 There are standards for the security of medical records
and standards for the financial industry regarding
privacy and security of customers’ personal financial
information.

8. TERMINOLOGY IN NETWORK
SECURITY
CRYPTOGRAPHY:-
Study of all encryption and decryption algorithms.
ENCRYPTION:-
 A process of encoding a message so that its meaning is
not obvious.
DECRYPTION:-
• A process of decoding the encoded message i.e it’s the
reverse process of Encryption.

9. TERMINOLOGY IN NETWORK
SECURITY
CRYPTANALYSIS:-
• Without knowing algorithm and key converting cipher
text into plane text.
CRYPTOLOGY:-
• Study of both cryptanalysis and cryptology.

10. DIMENSIONS OF CRYPTOGRAPHY
1.OPERATIONS INVOLVED:-
 TRANSPOSITION:
Sender side:
12345678910
f i l e no. 05 ----> Plaintext
9875 10 32164 ----> Key
0 .o 5 l ifne --------> Ciphertext

11. DIMENSIONS OF CRYPTOGRAPHY
Receiver side:-
12345678910
0.o 5 li f ne -----> Planetext
9875103216 4 -------> Key
1 234 5678910
file no.05---------> Original text

12. DIMENSIONS OF CRYPTOGRAPHY
• SUBSTITUTION:-
Simple Substitution:-
Substitution A B C D E F ……. X Y Z
Table--------> 1 2 3 4 5 6 ……. 24 25 26
Example:-
A C E
1 3 5

13. DIMENSIONS OF CRYPTOGRAPHY
 Substituting a character in plane text by new character
in cipher text is called Substitution.
 Substitution is done by using Substitution table.
 Substitution table should be there at sender and
receiver then only substitution can be done.

14. 2)NO. OF KEYS USED:-
A) Symmetric Key:
It uses single key.
Ex: IDE algorithm

15. b)Asymmetric Key:
It uses Two keys.
Ex: RSA Algorithm.

16. 3.The Way By which Plaintext Is Processed:-
a)Stream-Bit Oriented:
• Data is send as bit by bit.
• Bit= 0 or 1
b)Character Oriented:-
• Data is send character through character.
c)Blocks:-
Data is send through blocks(Group of characters).
Padding:
A string, typically added when the plaintext block is
short. For example, if the block length is 4 bytes and
the cipher requires 16 bytes, then 12 bytes of padding
must be added. The padding string may contain
zeros, alternating zeros and ones, or some other
pattern.

17. Concepts in Network Security
1) AUTHENTICATION:
 Sending the message from authorized person.
 Ex: Sending message from mail
2) CONFIDENTIALITY:
 Unauthorized person (unknown person) cannot know
what is going between two
persons.(Coding/Decoding)
3) NON-REPUTATION:
 Providing third person between two
persons.(Delaying)

18. Concepts in Network Security
4) AVAILABILITY:
 The person is authorized but the person can’t use or
access the data.
5) ACCESS CONTROL:
 The person cannot change or modify the data.
6) DATA INTEGRITY:
 Sender and Receiver receives same message.

19. SECURITY ATTACKS
1) INTERRUPTION:
 Stopping the data while the data is sending to other
person.
 It effects on the concept of Availability.
Sender Receiver
Intruder

20. SECURITY ATTACKS
2) INTERCEPTION:-
 Unknown person hearing the data which is going
between two persons but he cant modifies the data.
It effects the concept of Confidentiality.
Sender Receiver
Intruder

21. SECURITY ATTACKS
3) MODIFICATION:-
 The data which is sending to the receiver , that data ia
changed by the Intruder and sends to Sender receiver.
 This effects the concept of Data-Integrity.
Sender Receiver
Intruder

22. SECURITY ATTACKS
4)FABRICATION:
 While the data is sending to receiver from sender, the
intruder hacks the data and modify or change those
data and send to receiver in the form of sender.
 This effects the concept of Authentication.
Sender Receiver
Intruder

23. SERVICES OF NETWORK SECURITY
1) PASSIVE ATTACK:
 Here Intruder does not modifies the data but they
listens the data.
2) ACTIVE ATTACK:
 Here Intruder changes the data or information.

24. RSA ALGORITHM
by Rivest, Shamir & Adleman of MIT in 1977
best known & widely used public-key scheme
uses large integers (e.g., 1024 bits)
This is Asymmetric key i.e it consists two keys

25. RSA Key Setup
 each user generates a public/private key pair by:
 selecting two large primes at random - p,q
 computing their system modulus n=p*q
-define ø(n)=(p-1)*(q-1)
 selecting at random the encryption key e
 where 1<e<ø(n), gcd(e,ø(n))=1
 solve following equation to find decryption key d
 d*e mod ø(n)=1 and 0≤d≤n
 publish their public encryption key: PU={e,n}
 keep secret private decryption key: PR={d,n}

26. RSA Use
 to encrypt a message M the sender:
 obtains public key of recipient PU={e,n}
 computes: C = Me mod n, where 0≤M<n
 to decrypt the ciphertext C the owner:
 uses their private key PR={d,n}
 computes: M = Cd mod n
 note that the message M must be smaller than the
modulus n (block if needed)

27. RSA Example - Key Setup
1. Select primes: p=17 & q=11
2. Compute n = pq =17 x 11=187
3. Compute ø(n)=(p–1)(q-1)=16 x 10=160
4. Select e: gcd(e,160)=1; choose e=7
5. Determine d: de=1 mod 160 and d < 160 Value
is d=23 since 23x7=161= 10x160+1
6. Publish public key PU={7,187}
7. Keep secret private key PR={23,187}

28. RSA Example - En/Decryption
 sample RSA encryption/decryption is:
 given message M = 88
 encryption:
C = 887 mod 187 = 11
 decryption:
M = 1123 mod 187 = 88

29. IDEA ALGORITHM
 Acronym for IDEA is International Data Encryption
Algorithm
 Designed in 1991 by Swiss Federal Institute of
Technology
 Uses 128-bit key
 IDEA was used as the symmetric cipher in early
versions of the Pretty Good Privacy cryptosystem

30. DESCRIPTION
 In this algorithm, we use 3 operations:
1.XOR
2.MOD ADDITION
3.MOD MULTIPLICATION
 IDEA is a block cipher which uses a 128-bit length key
to encrypt successive 64-bit blocks of plaintext.

31. DESCRIPTION
 The procedure is quite complicated using sub keys
generated from the key to carry out a series of modular
arithmetic and XOR operations on segments of the 64-
bit plaintext block.
 The encryption scheme uses a total of fifty –two 16-bit
sub keys.

32. OPERATIONS
The three operations used in IDEA are:
 Bit-by-bit exclusive-OR of two 16-bit sub- blocks;
denoted as “XOR”.
 Addition of integers modulo 216 where the 16-bit sub-
block is treated as an unsigned integer; the resulting
operation is denoted as “+”.
 Multiplication of integers modulo 216+1 where the 16-
bit sub-block is treated as an unsigned integer except
that the all-zero sub-block is treated as representing
216; the resulting operation is denoted as “x”.

33. DESCRIPTION
These are generated from the 128-bit sub key as follows:
 The 128-bit key is split into eight 16-bit keys which are the first
eight sub keys.
 The digits of the 128-bit key are shifted 25 bits to the left to make
a new key which is split into the next eight 16-bit sub keys
 The second step is repeated until the fifty two sub keys have
been generated.
 The encryption involves modular multiplication with a modules
of ((2^16) + 1) and addition with a modules of (2^16).
 The 64-bit plaintext block is split into four 16-bit segments
which we’ll call x1, x2, x3 and x4.
 The sub keys are z1, z2, z3, z4………z52.

34. The encryption consists of eight rounds with each round involving
the following steps:
 x1 x z1 -- > w1
 x2 + z2 -- >w2
x3 + z3 -- >w3 w1 XOR w9 -- >w11
w3 XOR w9 -- >w12
w2 XOR w10 -- >w13
• w4 XOR w10 -- >w14
• x4 x z4 -- >w4
 w1 XOR w3 -- >w5
 w2 XOR w4 -- >w6
 w5 x z5 -- >w7
 w6 + w7 -- >w8
 w8 x z6 -- > w9
 w7 + w9 -- >w10

36.  The IDEA basic structure is shown in Above Figure.
 After this process the output blocks w12, w13 are exchanged so
that wi11, w13, w12 and w14 are used as input to the next round
(in that order) along with the next 6 subkeys, z7 to z12.
 This procedure is followed for eight rounds in total giving four
output blocks which we’ll call w81, w82, w83 and w84.
 Four more steps using the last four subkeys complete the
encryption:
e1 x z49 -- >y1
e2 + z50 -- >y2
e3 + z51 -- >y3
e4 x z52 -- >y4
Note:
For the purpose of the algorithm, a key of all zeros is defined
as being equal to 2^16 for modular multiplication steps .

37. Conclusion Of IDEA Algorithm
 As electronic communications grow in
importance, there is also an increasing need for data
protection
 When PGP was designed, the developers were looking
for maximum security. IDEA was their first choice for
data encryption
 The fundamental criteria for the development of IDEA
were military strength for all security requirements
and easy hardware and software implementation .

39. Message Sending using Secret key
Exchange
1. KEY EXCHANGE:-
(a) At Sender:-
 Take 128 bit key(binary bits) from keyboard.
 Divide them into 16 rows and 8 columns.
 Each row convert into decimal value, we will get 16
elements.
 Apply RSA Encryption Algorithm(C=Me mod n) on
each element we will get 16 cipher values which is
known as KEY.
 Send this KEY to receiver.

40. (b) At Receiver:-
 Receiver receives that 16 cipher values i.e KEY , then
apply RSA Decryption Algorithm(M=Cd mod n) on
each value.
 The result will be 16 decimal values.
 Convert each decimal value into binary bit.
 Place them in each row of matrix we will get 16 rows
and 8 columns matrix.
 Combine row after row then we will get 128 bit key.

41.  Secret Key Exchange can be done by RSA Algorithm
and Message Passed between Sender and Receiver by
IDEA Algorithm.
 Like Key Exchange Message will also Exchange but
procedure is different.

42. CONCLUSION
 IDEA is a well-known cipher that has been analyzed by
many researchers for the past decade, and, yet, no attack
against five or more of its 8.5 rounds has been found.
 Due to its strength against cryptanalytic attacks and due to
its inclusion in several popular cryptographic
packages, IDEA is widely used.
 The system was developed to offer the industry a set of
well-proven and tested crypto tools for faster and
optimized implementation of IDEA into security products.
It supports standard programming languages and allows
the implementation of the IDEA algorithm without
extensive knowledge in cryptography.
 The system provides fast and well – known algorithm
covering all aspects of cryptography with optimized
modules for encryption/decryption.

43. CONCLUSION
 The system comes with key generator.
 The system is specified with respect to secret key
cryptography standards.
 The system is suitable for use in a wide range of
application.
 The system allows for faster implementations of
encryption into security products.

44.  The project can be extended to provide encryption to
videos, photos and audio to enable security exchange
of information through them.
 In this way providing security to various means of
communication can be possible and helps in effective
communication through a network.