1) Computer security involves network security, host security, physical security, and encryption techniques like hashing and public/private key encryption. 2) Passwords should be complex, containing a mix of characters, and different for each account. Strong passwords are at least 16 characters. 3) Hackers can be categorized by their motives - white hats help security, black hats harm systems, and grey hats can be either. Black hats are also called crackers.

3. Host Security.

4. Physical Security.

5. … etc

7. Public / Private key encryption.

8. Hashing: a true one way function?

9. Md5? Md6 is in the kitchen now.

10. Sha1, sha256, sha512, sha1024

11. Tunneling.

12. Ssl (ssh, https, … etc)

13. Data Hiding ?!

15. Never Underestimate your potential opponent.

16. Never underestimate how your data/computer is important to others (may be more than how it's important to you).

17. Password is like a toothbrush, never share it.

19. Password containing only lower case characters is lamer.

20. Passwords containing your birth date/phone number is more lamer.

21. Passwords containing a sequense of digits like 123456 is the lamest.

22. Single password used among everything is a DISASTER.

24. Good password is 16 digit, the more the better.

25. 32 character password equals 256 bit key, I call this secure.

26. Use transliterated Arabic.

27. Typing hacker style.

29. The word 'hacker' originally mean the one who makes furniture only by an axe.

30. Hackers means sharp minded, skilled persons.

31. Great inventions are hacks.

32. Gnu/Linux: an OS made by hackers.

34. Black Hat hacker: A bad guy.

35. Grey Hat hacker: sometimes good, sometimes bad.

36. Normally white hats tend to help others (free or for a fee) and make the world a better place. Black hats tend to make the world much worse for their own benefits only.

37. Both use the same knowledge, have the same skills.

38. Black Hats are also called Crackers.

40. Level 2: moderate: can cause sever damage, you must be skilled to deal with them.

41. Level 1: Elite. If one of them is after you, run (unless you do know that you can handle him).

43. STFW.

45. Network mapping.

46. Port scanners.

47. Vulnerability scanners.

49. Network attacks: sniffing, IP spoofing, session hijacking.

50. Denial of Service: Stopping service, exhausting resources, remotely exhausting resources (SYN flood, DDoS, .. etc)

53. Software firewall in GNU/Linux is IPTABLES.

54. Let's do some Packet filtering using iptables.

56. Netfilter is a kernel patch (now it's basic in all modern kernels, unless you compiled your own without it)

57. Iptables is just a configuration tool for netfilter.

58. You can uninstall iptables, but not netfilter.

59. Netfilter cannot be stopped. Anyway you can remove all rules so it doesn't do anything.

60. Iptables rules are volatile, you have to put them in a startup script to start with booting.

63. Nat table

65. FORWARD chain

66. OUTPUT chain

69. iptables -t (table) -D (chain) (rule number)

71. iptables -X

76. iptables -A INPUT -p icmp –-icmp-type echo-reply -j ACCEPT

78. iptables (-t filter) -A OUTPUT -p tcp –-sport 80 -m state –-state ESTABLISHED -j ACCEPT

80. FTP has 3 types of connections:

81. Control Port: Port 21, normal 3 way connection initiated by client.

82. Active connection: Port 20, normal 3 way connection RELATED to the previous connection, initiated by client

83. Passive connection: 3 way connection RELATED to the control connection, initiated by the server from a random port on the server to a random port at the client

87. iptables -A INPUT -p tcp --sport 1024: --dport 1024: -m state --state RELATED,ESTABLISHED -j ACCEPT

88. Thank You,,,