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cryptography

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by

zora shaikh

on 9 January 2013

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Transcript of cryptography

CRYPTOGRAPHY what is cryptography????? Study of design of techniques for ensuring secrecy and authenticity of information. Presented by:
Saiful Shaikh
GCQ “Hidden writing”

Increasingly used to protect information

Can ensure confidentiality

Integrity and Authenticity too Introduction History Scytale – Spartan method involved wrapping a belt around a rod of a given diameter and length

Atbash – Hebrew cipher which mirrored the normal alphabet (shown in The Da Vinci Code)

Caesar – Shift all letters by a given number of letters in the alphabet

Vignère – Use of a key and multiple alphabets to hide repeated characters in an encrypted message -->Dates back to at least 2000 B.C.

-->Pen and Paper Cryptography

-->Examples

Scytale

Atbash

Caesar

Vigenère Invention of cipher machines
Examples
Confederate Army’s Cipher Disk
Japanese Red and Purple Machines
German Enigma The Mechanical Era Computers!


Examples
Lucifer

Rijndael

RSA

ElGamal Terminology Plaintext – A message in its natural format readable by an attacker

Ciphertext – Message altered to be unreadable by anyone except the intended recipients

Key – Sequence that controls the operation and behavior of the cryptographic algorithm

Keyspace – Total number of possible values of keys in a crypto algorithm

Cryptosystem – The combination of algorithm, key, and key management functions used to perform cryptographic operations

Encryption-The process of converting information into a form which is not readily intelligible

Decryption-The reverse process of encryption Cryptosystem Services Confidentiality
Integrity
Authenticity
Nonrepudiation
Access Control Types of Cryptography -->Stream-based Ciphers

One at a time, please
Mixes plaintext with key stream
Good for real-time services

-->Block Ciphers

Amusement Park Ride
Substitution and transposition Encryption Systems -->Substitution Cipher

Convert one letter to another
Cryptoquip

-->Transposition Cipher

Change position of letter in text

Word Jumble

-->Monoalphabetic Cipher

Caesar -->Polyalphabetic Cipher

Vigenère

-->Modular Mathematics

Running Key Cipher

-->One-time Pads

Randomly generated keys Steganography -->Hiding a message within another medium, such as an image
-->No key is required
-->Example
Modify color map of JPEG image Cryptographic Methods -->Symmetric

Same key for encryption and decryption
Key distribution problem

-->Asymmetric

Mathematically related key pairs for encryption and decryption
Public and private keys -->Hybrid

Combines strengths of both methods Asymmetric distributes symmetric key
Also known as a session key
Symmetric provides bulk encryption

-->Example:
SSL negotiates a hybrid method Attributes of Strong Encryption -->Confusion

Change key values each round
Performed through substitution
Complicates plaintext/key relationship

-->Diffusion

Change location of plaintext in ciphertext

Done through transposition Symmetric Algorithms DES
Modes: ECB, CBC, CFB, OFB, CM
3DES
AES
IDEA
Blowfish RC4
RC5
CAST
SAFER
Twofish Asymmetric Algorithms Diffie-Hellman

RSA

El Gamal

Elliptic Curve Cryptography (ECC) Hashing Algorithms -->MD5

Computes 128-bit hash value
Widely used for file integrity checking

-->SHA-1

Computes 160-bit hash value
NIST approved message digest algorithm Questions? The Modern Era Thankyou....:)
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