Introduction Block ciphers The feistel for block ciphers Data encryption standards(DES) Public key cryptography RSA encryption

1. NETWORK SECURITY
NAME OF THE STAFF : Mrs. M. FLORANCE DYANA
NAME OF THE STUDENT : S.MAREESWARI,
J.GAYATHRI DEVI,
R.KAVITHA.
REGISTER NUMBER : CB17S 250393
CB17S 250370
CB17S 250383
SUBJECT CODE : P8MCA27
CLASS : III BCA-A
BATCH : 2017-2020
YEAR : 2019-2020

3.  Introduction
 Block ciphers
 The feistel for block ciphers
 Data encryption standards(DES)
 Public key cryptography
 RSA encryption

4. Introduction
 Symmetric ciphers use symmetric algorithms to encrypt
and decrypt data.
 These ciphers are used in symmetric key cryptography.
A symmetric algorithm uses the same key to encrypt
data as it does to decrypt data.

5.  Symmetric ciphers are the opposite of symmetric
ciphers, like those used in public-key
cryptography.
 These ciphers use asymmetric algorithm which
use one key to encrypt data and a different key to
decrypt ciphers.
 For example,
 A symmetric algorithm will use key K to encrypt
some plain text information like a ciphertext.

6. Block ciphers
 Block ciphers is one in which the plaintext is
divided in blocks and one block is encrypted at
one time producing a ciphertext of equal length
 Similar to substitution ciphers on very big
characters: 64 bits or 128 bits are typical block
lengths.
 Many modern ciphers are block ciphers.

7. The feistel structure for block ciphers
 The DES algorithm for encryption and
decryption , which is the main theme of this
lecture, is based on what is known as the Feistel
structure.
 Named after the IBM cryptographer Horst Feistel
structure and first implemented in the Lucifer by
Horst Feistel and Don Coppersmith.

8. Data encryption standards(DES)
 DES is a symmetric system
that was once a predominant
standards in the 1970s but
has since fallen our of favour
due to its low security.
 Its introduction sparked
heated debate about the role
of standards in cryptography
and led to much research and
innovation in the field.

9.  DES use block ciphers. The block ciphers in
DES consists of 56 random bits, and 8 more bits
are used for error detection.
 These error detecting bits makes DES
unmalleable-attacks can’t change the ciphers on
its way to its destination because they might
accidentally delete a bit used for error detection,
and then receivers would known the data had
been attacked.

10. public-key cryptography
Public –key cryptography refers to a
class of cryptographic system in
which each actor uses two keys:
public key , private key
The guiding principle is that messages
Intended for a specific person should
be encrypted using their public key in
such a wat that the message can be
only be decrypted through the use of
the corresponding private key.

11.  Public-key cryptography is important for
securely transmitting messages across a
potentially insecure channel, meaning that it is
assumed all communications can be read by a
malicious attacker.
 As such, public-key cryptography is especially
important for ensuring the security of the
internet.

12. RSA Encryption
RSA encryption
algorithm, used to
securely transmit
message over the
internet.
It is based on the
principle that it is easy to
multiply large numbers,
but factoring large
number is very difficult.