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# CryptographyVsStegnoGraphy

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### CryptographyVsStegnoGraphy

1. 1.  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..
2. 2.  CRYPTOGRAPHY COMPONENT
3. 3.  Cryptanalysis basic component of cryptography is a cryptosystem  Cryptanalyst • Person working for unauthorized interceptor  Cryptographer • Person working for legitimate sender or receiver  Cryptology • encryption and decryption
4. 4.  Cryptosystem  A cryptosystem is a 5-tuple (Ε , D , M , K , C) • M is the collection of plaintexts • K is the set of keys • C is the set of cipher texts  How it works ? o Ε = Μ × K → C is the set of encipher (encryption) o D = C × K → M is the set of deciphering (decryption) Note • Plaintext M : collection of original messages • Cipher text C : set of messages in encrypted form
5. 5.  Cryptosystem  Encryption • Process of encoding (enciphering / encryption ) a message  Decryption • Process of decoding (deciphering or decryption) an encrypted message to its original form. Alisa Kishan data, control channel messagesdata secure secure data sender receiver Trudy
6. 6.  CRYPTOGRAPHY CRYPTOGRAP HYSYMMETRIC-KEY ASYMMETRIC-CRYPTOGRAPHY KEY CRYPTOGRAPHY
7. 7.  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
8. 8.  Symmetric Cryptosystems  Basic techniques for classical ciphers (Encryption)  Substitution • One letter is exchanged for another  Transposition • The order of the letters is rearranged Classical ciphers  Mono-alphabetic • Letters of the plaintext alphabet are mapped into other unique letters  Poly-alphabetic • Letters of the plaintext alphabet are mapped into letters of the cipher text space depending on their positions in the text  Stream • Key stream is generated and used to encrypt the plaintext (Symmetric Key Algorithms)
9. 9.  Transposition Example :- Cipher-Text :- TRHCEEIETGSSMAIAEASS T 5 T R H 3 H C E E E 1 I E T G K 4 S S M A E 2 I A E S Y 6 S SRefer (by key): IETGIAESHCEESSMATRSS T H E K E Y 5 3 1 4 2 6 Columnar T H I S I S A S E C R E • IEEIRSHSMESCSTATGSEA T M E S S A G E
10. 10.  Types of Cryptosystems  Asymmetric cryptosystem • M = D (Kd , E (Ke , M ) ) • The encryption key and decryption key are not the same • Kd ≠ Ke
11. 11.  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
12. 12.  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)
13. 13.  RSA Principle{m, e, p, q; {C, e, p, q;C= me mod(pq)} m=Cd mod(pq)} Sender Receiver Intruder {C, e}
14. 14.  What is Steganography?  Its Greek Words: • STEGANOS – “Covered” • GRAPHIE – “Writing”  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
15. 15.  History of Steganography  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
16. 16.  A 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”
17. 17.  Modern 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
18. 18.  Steganography System
19. 19.  ComparisonCryptography C = Ek (P) Plain text P = Dk (C) f Ciphertext KeySteganography secret message f Stego message cover image
20. 20.  Hiding a Message in an Image Original Picture Embedded picture