Submitted by :Ashish Harkare Chetan Bhardwaj Gaurav Wadhwa Kartikya Pande

8/14/2019 Submitted by :Ashish Harkare Chetan Bhardwaj Gaurav Wadhwa Kartikya Pande

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Submitted by :-

Ashish Harkare (08020541124)

Chetan Bhardwaj (08020541129)

Gaurav Wadhwa (08020541127)

Kartikya Pande (08020541128)

Samridhi Singla (08020541126)

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Introduction

Originated from the greek words,Kryptos and Graphos

The first known use of this technique by

Julius caesar

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What is Cryptography?

Cryptography is the science of using mathematics toencrypt and decrypt data.It enables you to store

sensitive information or transmit it across insecure

networks (like the Internet) so that it cannot be read by

anyone except the intended receiver.

It is used in applications present in technological

advanced societies eg. Security of ATM cards,

computer passwords and e-commerce.

Cryptanalysis is the source of analyzing and breaking

secure communication.

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Encryption and Decryption

Plaintext or clear text.

Cipher

Key

Encryption

Ciphertext

Decryption

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How does Cryptographywork?

Netprog: Cryptgraphy 5


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Why Cryptography?

The main use of cryptography is to provide

the following :

(1) Privacy or confidentiality

(2) Data integrity

(3) Authentication

(4) Non-repudiation.

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Secret Key Cryptography( Symmetric cryptography)

Single key used to encrypt and decrypt.

Key must be known by both parties.

Assuming we live in a hostileenvironment , it may be hard to share asecret key.

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Secret Key Cryptography( Symmetric cryptography)

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Advantage of SymmetricCryptography

The encryption process is simple

Each trading partner can use the same publiclyknown encryption algorithm - no need to develop

and exchange secret algorithms

Security is dependent on the length of the key


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Disadvantage

If a user has n trading partners, then n secret keys

must be maintained, one for each trading partner

Authenticity of origin or receipt cannot be provedbecause the secret key is shared

Management of the symmetric keys becomes

problematic


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Problems with Managementof Symmetric Keys

Partners must always use the exactsame key to decrypt the encryptedmessage

key exchange is difficult because theexchange itself must be secure with nointervening compromise of the key

management of keys is difficult as

numbers of trading partners increases,especially when multiple keys exist foreach trading partner


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Public Key Cryptography -Solution for Managing Symmetric

Keys public key cryptography simplifies themanagement of symmetric keys to the point

whereby a symmetric key can be used not

only for each trading partner, but for eachexchange between trading partners

additionally, public key cryptography can be

used to unambiguously establish non-

repudiation of origin and receipt


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Public Key Cryptography( Asymmetric cryptography)

Relatively new field - 1975

Each entity has 2 keys:private key (a secret)

public key (well known).

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Private keys are used for decrypting.

Public keys are used for encrypting.

encryptionplaintext ciphertext

public key

decryptionciphertext plaintext

private key

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Using Keys


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Asymmetric Key Uses

confidentiality

digital signatures

both uses depend on the association of

a key pair with one, and only one owner

of the keys

both uses depend on one of the keys in

the key pair being secret from everyonebut the owner of the key


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Real World Usage ofAsymmetric Encryption

public key encryption algorithms areconsiderably slower than symmetric keyalgorithms

rarely used as encryption methodology forbulk messages or parts of messages

normally used in conjunction with aMessage Integrity Check (MIC) or to encrypt

a symmetric key, where the MIC orsymmetric key is what is encrypted usingpublic key encryption algorithms


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disadvantage

software encryption using DES (symmetric keyalgorithm) is 100 times faster than software

encryption using RSA (asymmetric key

algorithm) - estimate provided by RSA Data

Securities

hardware encryption using DES (symmetric

key algorithm) is anywhere from 1,000 to

10,000 times faster than hardware encryptionusing RSA (asymmetric key algorithm)


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Digital Signature Public key cryptography is also used to

provide digital signatures.

signingplaintext signed message

private key

verificationsigned message plaintext

public key

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Transmitting over an insecurechannel.

Alice wants to send Bob a private message.

Apublic

is Alices public key.

Aprivate is Alices private key.

Bpublic is Bobs public key.

Bprivate is Bobs private key.

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Hello Bob,

Wanna get together?

AliceAlice BobBob

encrypt using Bpublic decrypt using Bprivate


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OK Alice,

Your place or mine?

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AliceAlice BobBob

decrypt using Aprivate encrypt using Apublic


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Bobs Dilemma

Nobody can read the message fromAlice, but anyone could produce it.

How does Bob know that the messagewas really sent from Alice?

Bob may be comforted to know that onlyAlice can read his reply.

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Alice can sign hermessage! Alice can create a digital signature and

prove she sent the message (or

someone with knowledge of her private

key). The signature can be a message digest

encrypted with Aprivate.

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Message Digest

Also known as hash function or one-way transformation.

Transforms a message of any lengthand computes a fixed length string.

We want it to be hard to guess.

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Message Digest

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Alices Signature

Alice feeds her original message through ahash function and encrypts the messagedigest with Aprivate.

Bob can decrypt the message digest usingApublic.

Bob can compute the message digesthimself.

If the 2 message digests are identical, Bobknows Alice sent the message.

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AliceAlice BobBob

Sign with Aprivate check signature using Apublic

encrypt using Bpublic decrypt using Bprivate

Revised Scheme


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Why the digest?

Alice could just encrypt her name, andthen Bob could decrypt it with Apublic.

Why wouldnt this be sufficient?

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Implications

Suppose Alice denies she sent themessage?

Bob can prove that only someone withAlices key could have produced the

message.

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Another possible problem

Suppose Bill receives a message from Aliceincludinga digital signature.meet me at the library tonight

Bill sends the same message to Joe so that itlooks like the message came from Alice.

Bill includes the digital signature from themessage Alice sent to him.

Joe is convinced Alice sent the message!

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Solution?

Always start your messages with:Dear Bill,

Create a digest from the encryptedmessage and sign that digest.

There are many other schemes as well.

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Speed

Secret key encryption/decryptionalgorithms are much faster than public

key algorithms.

Many times a combination is used:use public key cryptography to share a

secret key.

use the secret key to encrypt the bulk of thecommunication.

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Secure Protocols

There are a growing number ofapplications for secure protocols:email

electronic commerceelectronic voting

homework submission

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Secure Protocols

Many application protocols include theuse of cryptography as part of the

application level protocol.

The cryptographic scheme employed is partof the protocol.

If stronger cryptographic tools become

available we need to change the protocol.

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SSL and TLS

Secure Sockets Layer (SSL) is adifferent approach - a new layer is

added that provides a secure channel

over a TCP only link.

TLS is Transport Layer Security (IETF

standard based on SSL).

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SSL and TLS

Transport Layer Security (TLS)Protocol and its predecessor, Secure

Sockets Layer(SSL), are cryptographic

protocols that provide security and dataintegrity for communications over

TCP/IP networks such as the Internet

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SSL layer

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Application

SSL

TCP

IP

Application

SSL

TCP

IP


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Advantages of SSL/TLS

Independent of application layer

Includes support for negotiatedencryption techniques.easy to add new techniques.

applications like web browsing,electronic mail, Internet faxing, instantmessaging and voice-over-IP (VoIP

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Common Symmetric KeyAlgorithms

Data Encryption Standard - DES Triple DES

RC2 and RC5

IDEA


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Data Encryption Standard -DES

most widely used commercial encryptionalgorithm

in the public domain, available to all

a U. S. government encryption standard

security is known and is dependent solely

on the key length

data sequenced into 64 bit blocks prior toencryption, each block encrypted


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Triple DES

variant on DES which encrypts message

3 times with 2 independent 56 bit keys

effective key length is 112 bits

brute force attack on Triple DES is not

feasible

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Submitted by :Ashish Harkare Chetan Bhardwaj Gaurav Wadhwa Kartikya Pande