The document provides an overview of cryptography techniques including: 1) Symmetric key cryptography uses the same key for encryption and decryption while asymmetric key cryptography uses a public key for encryption and a private key for decryption. 2) Traditional ciphers include monoalphabetic and polyalphabetic substitution ciphers as well as transposition ciphers while modern ciphers include XOR, rotation, DES, and AES ciphers. 3) DES uses a 64-bit key to encrypt 64-bit blocks via complex rounds while AES was designed as an improvement over DES with key sizes of 128, 192, and 256 bits.

1. A
Seminar
on
Presented By:
Peeyush Sahu
8th Sem
Department of Computer Science & Engineering
Dr. C.V. Raman University Kota Bilaspur (C.G.)
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4. Cryptography
Asymmetric Symmetric
Key Key
Public Key Private Key Secret Key
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5. Sender Receiver
Shared secret
Key
Plain Text Plain Text
Encryption Decryption
Cipher
Text
In Symmetric Key Cryptography, the same key is used by the sender (for
encryption) and the receiver (for decryption). The key is shared.
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6. To the Public
Receiver’s Public Key
Receiver’s Private Key
Sender Receiver
Plain Text Plain Text
Encryption Decryption
Cipher
Text
In Asymmetric Key Cryptography, there are two keys: a private key and a
public key. The private key is kept by the receiver. The public is announced to
the public.
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7. Ciphers
Modern
Traditional Modern
Round
Ciphers Ciphers
Ciphers
Substitution Transposition Rotation
XOR Ciphers DES AES
Ciphers Ciphers Ciphers
Mono Poly
Alphabetic Alphabetic
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8. Mono Alphabetic Substitution Cipher :
Plain Text : HELLO
Cipher Text : KHOOR
Poly Alphabetic Substitution Cipher :
Plain Text : HELLO
Cipher Text : ABNZF
Transposition Cipher :
A transposition cipher reorders (permutes) symbols in a block of Symbols. For example :
Plain Text : 2 4 1 3
Cipher Text : 1 2 3 4
Example :
Simple Message : HELLO MY DEAR
Encrypted Message : ELHLMDOYAZER
XOR Cipher :
It uses the Exclusive-OR operation as defined. It needs two data inputs plaintext one is
key and another is message. The size of all are same.
Rotation Cipher :
In this cipher the I/P bits are rotated to the left or right. It can be keyed or keyless.
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9. DES (Data Encryption Standard) :
The algorithm encrypts a 64-bits plaintext block using a 64-bit key .
 It has two transposition blocks (P-boxes) and 16 complex round ciphers.
 The heart of DES is DES Function. It applies a 48-bit key to the rightmost 32
bits Ri to produce a 32-bit O/P.
 It is made up of four operations: an XOR, an Expansion permutation, a group of
S-boxes and a straight permutation.
AES (Advanced Encryption Standard) :
 It was designed because DES’s key was too small.
 It is designed with three key sizes:
a. 128
b. 192
c. 256
 It is very complex round cipher.
 It has three different configurations with respect to the number of rounds and key
size.
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