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1. NETWORK SECURITY
CRYPTOGRAPHY
BY:
R.Thushara Bharathi (CSE)
S. Jahnavi (CSE)

2. WHAT IS NETWORK
∗ A network Is an interconnection or a
media between two or more systems
to share information among them.
∗ The various threats caused to
network are :
 Remote Login
 Application Backdoors
 SMTP Session Hijackings
 Operating System Bugs
 Spams
 Viruses etc.

3. NETWORK SECURITY
∗ The security provided to the network is
called network security which at present
is looming on horizon as a massive
problem.
∗ There are two kinds of Network Security
mainly as :
 Transit Security
:
it just encrypts the packets to be
transferred.
 Traffic Security
:
it acts just as a screen between hosts
& remote sites.

4. PROBLEMS & ATTACKS
∗ There are few intertwined areas in network security as:
 Secrecy
 Authentication
 Non-Repudiation
 Integrity Control etc.
∗ The threats are classified into two categories :
Passive Attacks :
A passive attack is one in which the attacker eavesdrops and
listens to the message but can’t modify the message.
Active Attacks :
An active attack is one in which the attacker modifies, deletes,
replay or introduce new messages into the stream of message.

5. CRYPTOGRAPHY
∗ It is derived from the Greek word that
meant for secret writing.
∗ Cryptography is the ability to send
information between particulars in a
way that it prevents others from
reading the data.
∗ The data is transferred by applying
two techniques by changing the plain
text & Cipher texts as Encryption (P
to C) & Decryption (C to P).

6. PRINCIPLES & SERVICES OF
CRYPTOGRAPHY
∗ The two fundamental principles of cryptography are:
 Messages must contain some Redundancy (information
not needed to understand the message).
 Some method is needed to foil replay attacks (validation
of messages by timestamp) i.e. freshness.
∗ The services provided by the cryptography are as follows:




Integrity Checking
Authentication
Protection to the data
Confidentiality of information etc.

7. ENCRYPTION & DECRYPTION
∗ The way of converting the
plain text to the cipher text
by the means of few keys
is called as “encryption”.
∗ The way of converting the
cipher text to the plain text
by the use of keys that are
suitable to it is called as
“decryption”.

8. SUBSTITUTION CIPHER
∗ Replacing of each letter or
group of letters of plain text
into cipher text by another
letters is called as “substitution
cipher”.
∗ The substitution may be :
 Monoalphabetic Substitution
 Digrams
 Trigrams

9. TRANSPOSITION CIPHER
∗ The change offered in the
position of the text i.e. By
jumbling the words is called
as “transposition cipher”.
∗ And the technique used
here is termed as “mass
technique”.

10. SECRET-KEY ALGORITHMS
∗ The implementation of a simple cryptography using
single key is done by the secret-key algorithms.
∗ This can be done by p-box, s-box and product
cipher.

11. ELEMENTS OF PRODUCT CIPHERS
∗ Transpositions & substitutions can be done through
p-box (a).
∗ Substitutions can be done through s-box (b).
∗ Mapping of the p-box with s-boxes form product
cipher (c).

12. PUBLIC-KEY ALGORITHMS
∗ Public key algorithms
are formed when it
satisfies the following
requirements:
 D(E(P))=P.
 Difficulty to deduce D
from E.
 E cannot be broken
by a chosen plain
text attack.

13. RSA ALGORITHM
∗ RSA is derived from the names of
the 3 discoverers named Rivest,
Shamir, Adleman.
∗ The RSA algorithm is one of the
widely used in the key algorithms.
∗ But takes much time for the large
volumes of data encryption. This is
done by few mathematical
principles as:
 Choose 2 large primes.
 Compute n=pxq & z=(p-1)x(q-1).
 Find e, exd=1 mod z.

14. ADVANTAGES & DISADVANTAGES
∗ Advantages :
 Used to protect the data from the others.
 Used to send the data / packet in a secured way
from the source to destination.
 Avoids in knowing the data in the way of
sending.
∗ Disadvantages:
 Hacking is done now-a-days easily even for the data
encrypted with 48 bits though the bits are extended
by 52-bits.

15. PROPOSED CONCEPT
∗ As known the data has been easily hacked even for
the 52- bit encryption too. So, the encryption bits of
52-bits should be given with the combination of both
numerals and alphabets ( for example one alphabet is
placed for 13-bits each).
∗ The placement of alphabet is known only to the
particular sender & receiver such that it secures the
data to be sent.