Cryptography.ppt

Cryptography

BY-NISHANT BANSAL

11112030

Overview

Basic Definitions History of Cryptography Cipher Types Cryptography Methods Common Types of Attacks

Definitions -

Cryptology

Cryptography

Cryptanalysis

Steganography

Cryptosystem

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

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.

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.

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.

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.

CiphersIn 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.

Answer: WELCOME

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 .

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

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.

CRYPTOGRAPHY METHODS

Symmetric Same key for encryption and decryption

Key distribution problem

Asymmetric Key pairs for encryption and decryption

Public and private keys

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

OriginalPlaintext

Symmetric Cryptosystem

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

Asymmetric Algorithm

Private keys are used for decrypting. Public keys are used for encrypting

encryptionplaintext ciphertext

public key

decryptionciphertext plaintext

private key

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.

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.

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

One must acknowledge with cryptography noamount of violence will ever solve a math problem

― Jacob Appelbaum, Cypherpunks: Freedom and the Future of the Internet