1. Cryptography Made by:- Shray Jali

3. Formed from the Greek words kryptós, "hidden", and logos, "word".

7. We need to define a way by which we can exchange these private keys in a secure manner between distant entities

10. Early Cryptography 500- 600 BC 486 BC: Greece 60 –50 BC: JuliusCaesar Substitution cipher Used by Hebrew Shift letters by X positions E.g. X = 3: A -> D, B -> E, C ->F, ..

13. modern Cryptography 1976: Diffie-Hellman Key Exchange Private key: This key must be know only by its owner. Public key: This key is known to everyone

15. Variable Key Size (512, 1024, or 2048 bits)

17. Uses a block cipher called IDEA

18. Uses Digital Signatures

19. Uses Web Trust

22. Suitable for online encryption of data, e.g. Encrypting Voice Comms

24. Encryption operates on plaintext using the encryption key and the modulus to produce cipher text

27. Hashing is an irreversible process with no keys, the clear message is the only input for the hashing process

29. MD4 is a long-used hash function which is now broken; MD5, a strengthened variant of MD4, is also widely used but broken in practice

31. Document to be signed is sent through a complex mathematical computation that generates a hash.

32. Hash is encoded with the owner’s private key then stored.

33. To prove future ownership, stored hash is decoded using the owner’s public key and that hash is compared with a current hash of the document.

34. If the two hashes agree, the document belongs to the owner.Digital Signature

35. Digital signature Symmetric key signature Shray Sir Sumit A, KA ( B, RA, t, P) KB ( a, RA, t, P, Ksir( A,t, P)) Public key signature SHRAY’s COMPUTER SUMIT’s COMPUTER Shray’spvt key DA Sumit’s public key EB Sumit’spvt key DB Shray’s public key EA P P DA(P) DA(P) EB(DA(P))

37. Applications of digital certificates

38. World Wide Web transactions

39. Virtual private networks

40. Electronic mail

41. Client-server applications

43. Authentication

44. Data integrity

45. Availability

46. Non-repudiation

47. Access control

49. Protecting confidential company information, telephone calls

50. e-business

51. e-lottery

52. e-transactions