Cryptography

SOURASHTRA COLLEGE

CRYPTOGRAPHY

BY

L.S.KARNAN

II YEAR

B.Sc., Mathematics

Cryptography is the Study of art and science of keeping messages secure.

Some other authors defined the cryptography as “Cryptography

is the process of writing using various methods (“ciphers”) to keep messages secret”.

Modern Cryptography combines the studies of Computer Science and Mathematics for the purpose of Encoding information to ensure that data is secure.

CRYPTOGRAPHY:

KEYWORDS:

• Cryptography

• Cryptanalysis

• Encryption

• Decryption

• Symmetric key

• Asymmetric key

• Algorithm

HISTORY OF CRYPTOGRAPHY:

Cryptography probably began in or around

2000 B.C. in Egypt.

There are three eras in the history of Cryptography:

▪ The Manual era

▪ The Mechanical era

▪ The Modern era

Manual era:Manual era refers to pen and paper Cryptography and

dates back to 2000 B.C.

E.G. - Scytale, Caesar, Vigenere.

Mechanical era:

Mechanical era refers to the invention of cipher machines.

E.G. - Japanese Red and Purple Machines, German Enigma.

Modern era:The Modern era of cryptography refers to computers.

There are infinite permutations of cryptography available

using computers.

E.G. - Lucifer, RSA, ElGamal.

MODELS:

Ancient Cryptex Modern Cryptex

Sumerians

- Cuneiform writings Skytale

Encryption: c = Ee(p)

Decryption: p = Dd(c)

Here p is a block of plaintext,

c is a block of ciphertext,

E is the encryption function,

e is the encryption key,

D is the decryption function and

d is the decryption key.

FORMULA:

MATHSEncryption

NZGSHDecryption

MATHS

Example:

Plain text

Cipher textPlain text

NZGSH

Cipher text

{

A B C D E……………Y Z

26 25 24 23 22…………... 2 1

1 2 3 4 5……………25 26 FORWARD NUMBER

FORWARD LETTER

BACKWARD NUMBER

M - 14 - N vice - versa

A - 26 - Z

T - 07 - G

H - 19 - S

S - 08 - H

For DecryptionFor Encryption

CODING METHOD :

F.LB.N

CATEGORIES OF CRYPTOGRAPHY:

CRYPTOGRAPHERS:

Caesar Leon Battista

Alberti

Blaise de Vigenere

CRYPTANALYSERS:

APPLICATIONS:

Privacy/confidentiality

Integrity

This method is followed in Military

This method is used in ATM centers

Now-a-days, internet is very insecure therefore

Cryptography method is followed to safeguard to

transmit data.

- Takes a long time to figure out the code

- It takes long to create the code

- If you were to send a code to another person in

the past, it will take long to get to that person

- OVERALL CRYPTOGRAPHY IT'S A

LONG PROCESS.

LIMITATIONS: