This document discusses cryptography and its history. Cryptography began as early as 2000 BC in Egypt and has evolved over three eras: the manual era involving pen and paper ciphers, the mechanical era with the invention of cipher machines, and the modern era utilizing computers. Modern cryptography combines computer science and mathematics to encrypt data for security. Key aspects include encryption, decryption, symmetric and asymmetric keys, and different cipher algorithms. The document also covers categories of cryptography, notable cryptographers, applications, and some limitations of early cryptography techniques.

1. SOURASHTRA COLLEGE
CRYPTOGRAPHY
BY
L.S.KARNAN
II YEAR
B.Sc., Mathematics

2.  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:

3. KEYWORDS:
• Cryptography
• Cryptanalysis
• Encryption
• Decryption
• Symmetric key
• Asymmetric key
• Algorithm

5. 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

7. 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.

8. MODELS:
Ancient Cryptex Modern Cryptex
Sumerians
- Cuneiform writings Skytale

11. 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:

12. MATHS
Encryption
NZGSH
Decryption
MATHS
Example:
Plain text
Cipher textPlain text
NZGSH
Cipher text

13. {
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

14. CATEGORIES OF CRYPTOGRAPHY:

17. CRYPTOGRAPHERS:
Caesar Leon Battista
Alberti
Blaise de Vigenere

18. CRYPTANALYSERS:

19. 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.

20. - 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: