This document provides an overview of cryptography. It begins with basic definitions related to cryptography and a brief history of its use from ancient times to modern ciphers. It then describes different types of ciphers like stream ciphers, block ciphers, and public key cryptosystems. It also covers cryptography methods like symmetric and asymmetric algorithms. Common types of attacks on cryptosystems like brute force, chosen ciphertext, and frequency analysis are also discussed.

1. Cryptography
BY-NISHANT BANSAL
11112030

3. Overview
 Basic Definitions
 History of Cryptography
 Cipher Types
 Cryptography Methods
 Common Types of Attacks

4. Definitions -
 Cryptology
 Cryptography
 Cryptanalysis
 Steganography
 Cryptosystem

5. Cryptography is everywhere
 Secure communication:
–web traffic: HTTPS
–wireless traffic: 802.11i WPA2 (and WEP), GSM, Bluetooth
 Encrypting files on disk: EFS, TrueCrypt
 Content protection (e.g. DVD, Blu-ray): CSS, AACS
 User authentication
… and much much more

6. History of Cryptography
 The first known evidence of the use of cryptography (in some form)
was found in an inscription carved around 1900 BC, in the main
chamber of the tomb of the nobleman Khnumhotep II, in Egypt.
 Around 400 B.C., the Spartans used a system of encrypting
information by writing a message on a sheet of papyrus.
 Around 100 B.C., Julius Caesar was known to use a form
of encryption to convey secret messages to his army generals
posted in the war front.

7.  During the 16th century, Vigenere designed a cipher that was
supposedly the first cipher which used an encryption key.
 At the start of the 19th century when everything became
electric, Hebern designed an electro-mechanical contraption
which was called the Hebern rotor machine.

8.  The Engima machine was invented by German engineer Arthur
Scherbius at the end of World War I, and was heavily used by the
German forces during the Second World War.

9.  IBM in early 1970s designed a cipher called Lucifer. Lucifer was
eventually accepted by NIST and was called DES or the Data
Encryption Standard.
 In 2000, NIST accepted Rijndael, and named it as AES or the
Advanced Encryption Standard.

10. Ciphers
In cryptography, a cipher is an algorithm for performing encryption or
decryption—a series of well-defined steps that can be followed as a
procedure. An alternative, less common term is encipherment.

11. Answer: WELCOME

12. Stream cipher
 A Stream Cipher is a secret-key encryption algorithm that encrypts a
single bit at a time. With a Stream Cipher, the same plaintext bit or byte
will encrypt to a different bit or byte every time it is encrypted.
 e.g. :
Plain text: Pay 100
Binary of plain text: 010111101 (hypothetical)
Key: 100101011 ----- Perform XOR
____________________
Cipher text 110010110 ----- ZTU9^%D
 To decrypt make the XOR operation of the cipher text with the key .

13. Block cipher
 Block cipher technique involves encryption of one block of text at a
time .Decryption also takes one block of encrypted text at a time.
Length of the block is usually 64 or 128 bits.
e.g. :
Plain text: four and five
Four and five
Key Key Key
wvfa ast wvfa --- cipher text

14. Public Key Cryptosystem
 Public key cryptography is a scheme that uses a Pair of keys for
encryption: a Public key, which encrypts data, and a corresponding
Private key (secret key) for decryption.

15. CRYPTOGRAPHY METHODS
 Symmetric
 Same key for encryption and decryption
 Key distribution problem
 Asymmetric
 Key pairs for encryption and decryption
 Public and private keys

16. Symmetric Algorithm
 It is also called as Secret Key Cryptography
 Single key used for both encrypt & decrypt
 Key must be known to both the parties
Encryption Decryption
Key
Plaintext Ciphertext
Original
Plaintext
Symmetric
Cryptosystem

17. Symmetric Algorithm
 Data Encryption Standard (DES):
56 bits key
 Advance Encryption Standard (AES):
128, 192 or 256 bits key
 International Data Encryption Algorithm(IDEA):
128 bits key

18. Asymmetric Algorithm
 Private keys are used for decrypting.
 Public keys are used for encrypting
encryption
plaintext ciphertext
public key
decryption
ciphertext plaintext
private key

19. Hybrid cryptosystem
 A hybrid cryptosystem can be constructed using any two separate cryptosystems:
 a key encapsulation scheme, which is a public-key cryptosystem,
 a data encapsulation scheme, which is a symmetric-key cryptosystem.

20. COMMON TYPES OF ATTACKS
Brute force
 Trying all key values in the keyspace.
Chosen Ciphertext
 Decrypt known ciphertext to discover key.
Dictionary Attack
 Find plaintext based on common words.
Frequency Analysis
 Guess values based on frequency of occurrence.

21. References
 An introduction to cryptography and cryptanalysis
-Edward Schaefer,Santa Clara University
 http://en.wikipedia.org/wiki/History_of_cryptography
 https://securityblog.redhat.com/2013/08/14/a-brief-history-of-
cryptography/
 Contemporary Cryptography - Rolf Oppliger
 Cryptography Theory And Practice - Douglas Stinson
 Modern Cryptography Theory and Practice - Wenbo Mao

22. One must acknowledge with cryptography no
amount of violence will ever solve a math problem
― Jacob Appelbaum, Cypherpunks: Freedom and the Future of the Internet