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May 20, 2015




  • 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. CRYPTOGRAPHY COMPONENT 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. 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 How it works ? o = 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. Cryptosystem Encryption Process of encoding (enciphering / encryption ) a message Decryption Process of decoding (deciphering or decryption) anencrypted message to its original form. AlisaKishan data, controlchannelmessagesdatasecuresecuredatasender receiver Trudy 6. CRYPTOGRAPHYCRYPTOGRAPHYSYMMETRIC-KEY ASYMMETRIC-CRYPTOGRAPHYKEY CRYPTOGRAPHY 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. 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. Transposition Example :-Cipher-Text :-TRHCEEIETGSSMAIAEASST 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 SRefer (by key): IETGIAESHCEESSMATRSST H E K E Y5 3 1 4 2 6 ColumnarT H I S I SA S E C R E IEEIRSHSMESCSTATGSEA T M E S S AG E 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. 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. RSA Principle Developed by Ron Rivets , Adi Shamir, and LeonardAdleman.(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 withoutknowing d , p and q Knowing d, p and q, it is easy to find the original plaintext message m = Cd mod (pq) 13. RSA Principle{m, e, p, q; {C, e, p, q;C= me mod(pq)} m=Cd mod(pq)} SenderReceiver Intruder{C, e} 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 protectdigital rights watermarking copyright notices fingerprinting a serial ID 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. A Real Example During WW2 the following cipher messagewas actually sent by a German spyApparently, neutrals protest is thoroughlydiscounted and ignored. Isman hard hit.Blockade issue affect pretext for embargo onby products, ejecting suets and vegetableoils. Hidden Message Pershing sails from NY June 1 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. Steganography System 19. ComparisonCryptography C = Ek (P) Plain textP = Dk (C) f CiphertextKeySteganography secret message f Stego message cover image 20. Hiding a Message in an Image Original PictureEmbedded picture