cryptographyvsstegnography

What is meant by cryptography ? • Its Greek word

• Crypto means “ Secret”

• Graphie means “ Writing “

Why Cryptography ? • To convert the plain text to unreadable text

What is need of Cryptography ?

To secure the Sensitive Information

• Username – Password

• Credit Card Number etc..

CRYPTOGRAPHY COMPONENT

Cryptanalysisbasic component of cryptography is a cryptosystem

Cryptanalyst • Person working for unauthorized interceptor

Cryptographer

• Person working for legitimate sender or receiver

Cryptology

• encryption and decryption

Cryptosystem A cryptosystem is a 5-tuple ( , D , M , K , C)

• M is the collection of plaintexts

• K is the set of keys

• C is the set of cipher texts

o = K → C is the set of encipher (encryption)o D = C K → M is the set of deciphering (decryption)

How it works ?

Note • Plaintext M : collection of original messages

• Cipher text C : set of messages in encrypted form

Cryptosystem

Encryption Decryption

• Process of encoding (enciphering / encryption ) a message

• Process of decoding (deciphering or decryption) an encrypted message to its original form.

securesender

securereceiver

channel data, control messages

data data

Alisa Kishan

Trudy

CRYPTOGRAPHY

CRYPTOGRAPHY

SYMMETRIC-KEY

CRYPTOGRAPHY

ASYMMETRIC-KEY

CRYPTOGRAPHY

Types of Cryptosystems Symmetric Key Cryptosystems

• Also called single-key cryptosystems

• M = D ( K , E ( K , M ) )

• The encryption key and decryption key are the same

Symmetric Cryptosystems Basic techniques for classical ciphers (Encryption)

Substitution

Transposition

Mono-alphabetic

Poly-alphabetic

Stream

• One letter is exchanged for another

• The order of the letters is rearranged Classical ciphers

• Letters of the plaintext alphabet are mapped into other unique letters

• Letters of the plaintext alphabet are mapped into letters of the cipher text space depending on their positions in the text

• Key stream is generated and used to encrypt the plaintext (Symmetric Key Algorithms)

Transposition

Example :-

T 5 T RH 3 H C E EE 1 I E T GK 4 S S M AE 2 I A E SY 6 S S

TRHCEEIETGSSMAIAEASSCipher-Text :-

Refer (by key): IETGIAESHCEESSMATRSS

Columnar

• IEEIRSHSMESCSTATGSEA

T H E K E Y5 3 1 4 2 6

T H I S I SA S E C R ET M E S S AG E

Types of Cryptosystems Asymmetric cryptosystem

• M = D (Kd , E (Ke , M ) )

• The encryption key and decryption key are not the same• Kd ≠ Ke

Asymmetric Key Cryptosystem (Public Key Cryptosystem)

Uses public and private keys

• Public key for encryption• Private key for decryption

Examples

• RSA

• Trapdoor one-way function

• Elliptical curve cryptography

RSA Principle Developed by Ron Rivets , Adi Shamir, and Leonard Adleman. (MIT, 1977)

C = me mod (pq)

• P , q : any two large prime numbers (more than 512 bits)

• e: public key

• d: private key

• Knowing C and e, it is “infeasible” to calculate m without knowing d , p and q

• Knowing d, p and q, it is easy to find the original plaintext message m = Cd mod (pq)

RSA Principle

{m, e, p, q; C= me mod(pq)}

{C, e, p, q; m=Cd mod(pq)}

Sender

Intruder

Receiver

{C, e}

What is Steganography?What is Steganography?

• STEGANOS – “Covered”• GRAPHIE – “Writing”

Its Greek Words:

Steganography is about Hiding messages Digital Applications of Steganography

• Can be hidden in digital data - MS Word (doc)

- Web pages (html) - Sound files (mp3, wav, cda)- Video files (mpeg, avi)

- Digital images (bmp, gif, jpg) Today, steganography is used primarily

to protect digital rights

• “watermarking” copyright notices

• “fingerprinting” a serial ID

History of History of SteganographySteganography Chinese silk balls

Invisible ink-jet technology

Microdots Easter eggs

Hiding a message within a text Shift some words by one point/pixel

- Shifted words (or their first letters) make the sentence Use different fonts

- Letter by letter or word by word

A Real ExampleA Real Example During WW2 the following cipher

message was actually sent by a German spy “Apparently, neutral’s protest is

thoroughly discounted and ignored. Isman hard hit. Blockade issue affect pretext for embargo on by products, ejecting suets and vegetable oils.”

Hidden Message

• “ Pershing sails from NY June 1”

ModernModern Steganography Steganography

Hiding one message within another (“container”)

Most containers are rich media

• Images , audio, video ,mp3 etc.

Copyright notices embedded in digital art

• Prove ownership

Digital cameras EXIF tags

• Not secretive, but hidden from the eyez• Embed info such as camera type, date, shutter

speed , focal length,..

Similarly , possible to embed messages in invisible parts of html pages

Steganography Steganography SystemSystem

ComparisonComparisonCryptography

C = Ek (P) Plain text

P = Dk (C)

Key

Steganography

secret message

cover image

f Stego message

f Ciphertext

Hiding a Message in an ImageHiding a Message in an ImageOriginal Picture Embedded picture