7. voice and video calls and chat over the Internet

8. uses a proprietary Internet telephony (VoIP) network called the Skype protocol

9. the main difference between Skype and standard VoIP clients is that Skype operates on a peer-to- peer model, rather than the more usual client– server model

13. most critical part to the Skype operation

14. IP address and port number of an online Skype node

16. 1.1 x 10^77 possible keys

17. 1536 to 2048 bit RSA to negotiate symmetric AES keys

19. Normally, a string of characters represented using a fixed number of bits per character, as in the ASCII code

20. separating the input into component symbols and replacing each with a code, arithmetic coding encodes the entire message into a single number, a fraction n where (0.0 ≤ n < 1.0)

22. subsequent startups, a SC only sent a HTTP 1.1 GET request to the server to determine if a new version is available

28. media traffic flow to and from the UDP port configured in dialog box

30. OSCAR used in ICQ is named v7

32. is used on the TCP connection between all clients and servers

33. flap sequence numbers are used for errors detection Offset Field Type/Size (in bytes) Remarks 00 FLAP ID Byte/1 Always contains 2A. It is mark of packet start. 01 Channel Byte/1 1 = login, 2 = SNAC layer, 3 = error, 4 = disconnect 02 Number in sequence Int 16/2 Incremented by 1 each time a packet sent. Wraps to 0 after FFFF 03 Data size Int 16/2 Size does not include FLAP header FLAP Header OSCAR I.

35. length depends on FLAP

36. the SNAC communication layers sits on top of the FLAP layer

38. 16-bit value for the length of the Value field, and then the actual data in the Value field (variable length)

39. TLVs make sending a variable length string like &quot;nickname@gmail&quot; as simple as defining a TLV with values {0x0011, 0x000c, &quot;nickname@gmail.com&quot;}. OSCAR II.

40. Authorization based on MD5

41. Protocol negotiation

42. Retrieving offline messages

43. Any Questions? U mad? Problem?

44. So... Thank you for your attention