School of Computer Science & Information Technology

Presentation On

Elementary Cryptography

Presented by:

Anshul Jain (NM)

Sumit Lole (CS)

M.Tech. II sem

Guided by:

Dr. D.S. Bhilare

Agenda Introduction

Basic Terminologies Techniques of Cryptography Need of Cryptography Encryption Algorithm

Symmetric Asymmetric

Uses of Encryption Digital Signature

What is Elementary Cryptography? “Hidden Writing” Increasingly used to protect Information.

Goal of Cryptography Ensure security of communication over insecure

medium Privacy (secrecy, confidentiality) Integrity

Communicate even with possibility of adversaries

Introduction

Basic Terminologies

Encryption Encryption is the process of encoding a message

so that its meaning is not obvious Decryption

Decryption is the reverse process, transforming an encrypted message back into its normal, original form

Cryptosystem A system for encryption and decryption is called a

cryptosystem.

Cont… Plaintext Ciphertext Key –

key refers to a sequence of symbols or a numerical value used by an algorithm to alter information & making that information secure

Encryption algorithm The cryptosystem involves a set of rules for how to

encrypt the plaintext and how to decrypt the ciphertext. Cryptanalysis

Cryptanalysis is an attempt to break the ciphertext.

Substitution Technique Caesar Cipher Monoalphabetic Cipher Homophonic Cipher Polygram substitution cipher Polyalphabetic Cipher

Vigenère

Transposition Technique Rail Fence Technique. Vernam Cipher(One -time Pads)

Randomly generated Pad Running Key Cipher. Playfair Cipher. Hill Cipher.

Techniques of Cryptography

Cont… 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

Confusion Ciphertext has no clue about Plaintext

Diffusion Spreading plain text across rows and columns

http://www.simonsingh.net/The_Black_Chamber

Need of Encryption

Confidentiality Integrity Authenticity Nonrepudiation Access Control

Encryption Algorithm

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

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 CiphertextOriginalPlaintext

Symmetric Cryptosystem

Asymmetric Algorithm

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

encryptionplaintext ciphertext

public key

decryptionciphertext plaintext

private key

Cont… It is also called as public key cryptography

Encryption DecryptionPlaintext Ciphertext

OriginalPlaintext

Asymmetric Cryptosystem

Decryption Key Kd

Encryption Key Ke

Comparison

Secret Key (Symmetric) Public Key (Asymmetric)

Number of Key 1 2

Protection of Key Must be kept secret One key must be kept secret 7 other can be freely exposed

Best Uses Cryptographic workhorse; secrecy and integrity of data, single characters to blocks of data, messages, files

Key exchange, authentication

Key Distribution Must be out-of-band Public key can be used to distribute other keys

Speed Fast Slow; typically, 10,000 times slower than secret key

Symmetric Algorithm Data Encryption Standard (DES)

Double DES Triple DES

Advance Encryption Standard (AES) Blowfish IDEA

Data Encryption Standard The data encryption algorithm

developed by IBM was based on Lucifer, and it is known as the Data Encryption Standard

It is also known as Data Encryption Algorithm

The DES algorithm is a careful and complex combination of two fundamental building blocks of encryption: Substitution and Transposition

DES uses only standard arithmetic and logical operations on numbers up to 64 bits long

Cont… 1st 64 bit plain text is handed over to initial

permutation function. IP is performed over the plain text. IP produces two halves of the permuted blocks

left plain text (LPT) & right plain text (RPT). Now LPT & RPT goes 16 rounds of encryption

process, each with its own key. Now LPT & RPT are rejoined and FINAL

PERMUTATION (FP) is performed on the combined block.

The result is 64 bit cipher text.

Advance Encryption Standard Developed by NIST in January1997 Algorithm had several restriction:

unclassified publicly disclosed available royalty-free for use worldwide symmetric block cipher algorithms, for blocks of

128 bits usable with key sizes of 128, 192, and 256 bits

It was adopted by US government in December 2001

Cont…

AES primarily uses: Substitution Transposition Shift Exclusive OR Addition Each cycle consist of

four step Byte substitution Shift row Mix column Add sub key

Comparison between DES & AES

DES AES

Date 1976 1997

Block Size 64 bits 128 bits

Key Length 56 bits(effective length)128, 192, 256 ( possibly more) bits

Encryption Primitive

Substitution, permutation

Substitution, shift, bit mixing

Cryptographic Primitive

Open Open

Design Close Open

Selection Process

SecretSecret, but accepted open public comment

Asymmetric Algorithm

Rivest Shamir Adleman (RSA) Encryption Diffie-Hellman Elliptic Curve Cryptography (ECC)

RSA It is named after its three inventors Rivest

Shamir and Adleman This algorithm was introduced in 1978 and

to date remains secure. RSA has been the subject of extensive

cryptanalysis, and no serious flaws have yet been found.

The encryption algorithm is based on the underlying problem of factoring large numbers.

Cont…

The two keys used in RSA, d and e, are used for decryption and encryption

Keys are actually interchangeable: Either can be chosen as the public

Let encryption key e and the decryption key d. P = E(D(P)) = D(E(P)) Any plaintext block P is encrypted as Pe mod n. The decrypting key d is carefully chosen so that (Pe)d

mod n = P

Cont… Choose any two prime numbers p=17 & q=11 Calculate n = p x q n = 187 Calculate n’ = (p-1) x (q-1 ) n’ = 160 Select e as relative prime to n’ and less than

n’ e=7 Calculate d such that d x e = 1 mod n’ d =

23 Public {7,187} Private {23,187}

Diffie- Hellman It is a cryptographic protocol that allows

two parties that have no prior knowledge of each other to jointly establish a shared secret key over an insecure communications channel. This key can then be used to encrypt subsequent communications using a symmetric key cipher.

Cont…

Uses of Encryption Cryptographic Hash Function Key Exchange Digital Signature Public Key Protocol Certificate

Cryptographic Hash Function Cryptography can be used to seal a file,

encasing it so that any change becomes apparent. One technique for providing the seal is to compute a cryptographic function, sometimes called a hash or checksum or message digest of the file.

Digital Signature

A digital signature is a protocol that produces the same effect as a real signature: It is a mark that only the sender can make, but other people can easily recognize as belonging to the sender. Just like a real signature, a digital signature is used to confirm agreement to a message.

Properties of Digital Signature

A digital signature must meet two primary conditions: It must be unforgeable. If person P signs message M

with signature S(P,M), it is impossible for anyone else to produce the pair [M, S(P,M)].

It must be authentic. If a person R receives the pair [M, S(P,M)] purportedly from P, R can check that the signature is really from P. Only P could have created this signature, and the signature is firmly attached to M.

It is not alterable. After being transmitted, M cannot be changed by S, R, or an interceptor.

It is not reusable. A previous message presented again will be instantly detected by R.

Thank You