# crypto

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A

PRESENTATION ON

CRYPTOGRA

PHY AND

ENCRYPTION

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CRYPTO

GRAPHY

CRYPTOGRAPHY

The word CRYPTOGRAPHY is derived from Greek word,

kryptos,

which means "hidden, secret"; and , grph,meaning "I

write.It may be defined as the practice and study of hiding

information.

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Terminology

Cryptology:All-inclusive term used for the study of securecommunication over non-secure channels and relatedproblems.

Cryptography: The process of designing systems to realize

secure communications over non-secure channels.

Cryptoanalysis: The discipline of breaking the cryptographicsystems.

Coding Theory: Deals with representing the informationusing codes. It covers: compression, secrecy, and error-correction.

Recently, it is predominantly associated with error-correcting

codes which ensures the correct transmissions over noisy-channels.

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The Aspects of Cryptography

Modern cryptography heavily depends on mathematicsand

the usage of digital systems.

It is a inter-disciplinary study of basically three fields:MathematicsComputer ScienceElectrical Engineering

Without having a complete understanding of

cryptoanalysis(or cryptoanalytic techniques) it isimpossible to design good(secure, unbreakable)cryptographic systems.

It makes use of other disciplines such as error-

correcting codes compression.

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Overview of Cryptography

People want and need privacy and security whilecommunicating

In the past, cryptography was heavily used formilitary applications to keep sensitive information

secret from enemies (adversaries).Eg: Julius Caesar used a simple shift cipher to

communicate with his generals in the battlefield.

Nowadays, with the technological progress, our

dependency on electronic systems has increasedso we need more sophisticated techniques.

Cryptography provides most of the methods andtechniques for a secure communication.

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Cryptographic process

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Cryptographic Methods

7

Symmetr ic

Same key for encryption and decryption

Key distribution problem

Asymmetr ic Mathematically related key pairs for encryption and

decryption

Public and private keys

Hybr id Combines strengths of both methods

Asymmetric distributes symmetric key

Symmetric provides bulk encryption

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Encryption

Encryption is a process in which the senderencrypts/scrambles the message in such a waythat only the recipient will be able to decrypt/

descramble the message. Encryption is the conversion of data into a

form, called a cipher text, that cannot be easilyunderstood by unauthorized people.

Decryption is the process of convertingencrypted data back into its original form, so itcan be understood.

Encryption/decryption is especially important in

wireless communications.

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Private-Key Cryptography

traditional private/secret/single keycryptographyuses onekey

shared by both sender and receiver

if this key is disclosed communications are

compromised also is symmetric, parties are equal

hence does not protect sender from receiverforging a message & claiming is sent by sender

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How it works????

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Problems

Key distribution is an awkward process.

Key distribution for multiple keys can be an

hassle.

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Types

Stream ciphers

Stream ciphers operate on a single bit (byte orcomputer word) at a time and implement some form offeedback mechanism so that the key is constantly

changing. Block cipher

It encrypts one block of data at a time using the samekey on each block.

In general, the same plaintext block will alwaysencrypt to the same ciphertext when using the samekey in a block cipher whereas the same plaintext willencrypt to different ciphertext in a stream cipher.

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Secret key cryptography algorithms

Data Encryptio n Standard (DES)

DES was designed by IBM in the 1970s and adoptedby the National Bureau of Standards (NBS) [now theNational Institute for Standards and Technology

(NIST)] in 1977 for commercial and unclassifiedgovernment applications. DES is a block-cipheremploying a 56-bit key that operates on 64-bit blocks.DES has a complex set of rules and transformations.

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Secret key cryptography

algorithms

Variants of DES Trip le-DES (3DES):A variant of DES that employs up to

three 56-bit keys and makes three encryption/decryption

passes over the block. DESX:A variant devised by Ron Rivest. By combining

64 additional key bits to the plaintext prior to encryption,

effectively increases the keylength to 120 bits. Here, the

input plaintext is bitwise XORed with 64 bits of additionalkey material before encryption with DES and the output

is also bitwise XORed with another 64 bits of key

material.

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Secret key cryptography

algorithms

Advanced Encrypt ion Standard (AES)

NIST develop a new secure cryptosystem for U.S.

government applications i.e. the Advanced Encryption

Standard. It became the official successor to DES inDecember 2001. AES uses an SKC scheme

called Rijndael, a block cipher designed by Belgian

cryptographers Joan Daemen and Vincent Rijmen.

The algorithm can use a variable block length and keylength; the latest specification allowed any

combination of keys lengths of 128, 192, or 256 bits

and blocks of length 128, 192, or 256 bits.

http://www.esat.kuleuven.ac.be/~rijmen/rijndael/index.htmlhttp://www.esat.kuleuven.ac.be/~rijmen/rijndael/index.html8/10/2019 crypto finaale.ppt

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Secret key cryptography

algorithms

Rivest Ciphers (akaRon's Code)Named for Ron Rivest, a series of SKC algorithms.

RC1:Designed on paper but never implemented.

RC2:A 64-bit block cipher using variable-sized keys designed to replace

DES. It's code has not been made public although many companies havelicensed RC2 for use in their products.

RC3:Found to be breakable during development.

RC4:A stream cipher using variable-sized keys; it is widely used incommercial cryptography products, although it can only be exported usingkeys that are 40 bits or less in length, but keys this small can be broken

easily by criminals, amateurs and govts. RC5:A block-cipher supporting a variety of block sizes, key sizes, and

number of encryption passes over the data.

RC6:An improvement over RC5, RC6 was one of the AES Round 2algorithms.

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Secret key cryptography

algorithms

Internat ional Data Encrypt ion A lgo ri thm

(IDEA)

Secret-key cryptosystem written by Xuejia Lai

and James Massey, in 1992 and patented byAscom. It offers strong encryption using a 128-

bit key to encrypt 64-bit blocks, which makes it

resistant to brute-force attacks.

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Public-Key Cryptography

PKC depends upon the existence of so-called one-way functions, ormathematical functions that are easy to computer whereas theirinverse function is relatively difficult to compute. Here are two simpleexamples:

Multiplication vs. factorization:Suppose that I have two numbers, 9 and16, and that I want to calculate the product; it should take almost no

time to calculate the product, 144. Suppose instead that I have anumber, 144, and I need to find which pair of integers I multipliedtogether to obtain that number. I will eventually come up with thesolution but whereas calculating the product took milliseconds,factoring will take longer because it first need to find the 8 pair ofinteger factors and then determine which one is the correct pair.

Exponentiation vs. logarithms:Suppose I tell you that I want to take thenumber 3 to the 6th power; again, it is easy to calculate 36=729. But if Itell you that I have the number 729 and want you to tell me the twointegers that I used,xand yso that logx 729 = y, it will take you longerto find all possible solutions and select the pair that I used.

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Public-Key Cryptography

probably most significant advance in the 3000

year history of cryptography

employs twokeys that are mathematically

relateda public & a private key

asymmetricsince parties are notequal

complements rather thanreplaces private key

crypto

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How it works????

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Public-Key Characteristics

Public-Key algorithms rely on two keys where:

it is computationally infeasible to find decryption key

knowing only algorithm & encryption key

it is computationally easy to en/decrypt messageswhen the rel