Computer and Network Security

1. Computer and Network Security Rabie A. Ramadan

2. CIA Triad • Security Goals • Confidentiality, • Integrity , and • Availability

3. Confidentiality To ensure confidentiality To ensure confidentiality • The property of preventing disclosure of information to unauthorized individuals or systems. • Real Scenario • a credit card transaction on the Internet requires the credit card number to be transmitted from the buyer to the merchant and from the merchant to a transaction processing network. • The system attempts to enforce confidentiality by encrypting the card number during transmission, by limiting the places where it might appear (in databases, log files, backups, printed receipts, and so on), and by restricting access to the places where it is stored. • If an unauthorized party obtains the card number in any way, a breach of confidentiality has occurred.

4. Integrity • Data cannot be modified without authorization. • Real scenarios: • Integrity is violated when an employee (accidentally or with malicious intent) deletes important data files, • When a computer virus infects a computer, • When an employee is able to modify his own salary in a payroll database, • When an unauthorized user vandalizes a web site, • When someone is able to cast a very large number of votes in an online poll, and so on. • Preventing by Access Control and Encryption

5. Availability • The information must be available when it is needed. • Highly available systems aim to remain available at all times. • Real Scenarios • Power outages, • Hardware failures, • DoS attacks (denial-of-service attacks). • Preventions by fault tolerance , access control, and attack prevention mechanisms.

6. Confidentiality Ensures that computer-related assets are accessed only by authorized parties. Sometimes called secrecy or privacy. Integrity Assets can be modified only by authorized parties or only in authorized ways. Availability Assets are accessible to authorized parties at appropriate times. The opposite is denial of service. Security Goals (Summary)

7. Strong protection is based on Goals relations Security Goals

8. Computer Security- generic name for the collection of tools designed to protect data and to thwart hackers Network Security - measures to protect data during their transmission Internet Security - measures to protect data during their transmission over a collection of interconnected networks Goals are Applied to

9. Crossing the water to the right is a Threat to the man. Ex. (Computer) software failures Crossing the water through the wall crack is a Vulnerability. Ex. (Computer) Open ports Somebody or another system destroyed the wall is an Attack Ex. (Computer) sending an overwhelming set of messages to another system to block it. Threats , vulnerability, and Attacks

10. Passive Attacks Attempts to learn or make use of information from the system but does not affect system resources. Eavesdropping or monitoring of transmissions Active Attacks Attempts to alter system resources or affect their operation. Attacks

11. Release of message contents / snooping PassiveAttacks

12. TrafficAnalysis/ spoofing Passive Attacks are hard to be detected PassiveAttacks (Cont.)

13. Active Attacks

14. Masquerade One entity pretends to be a different entity Active Attacks

15. ReplayAttack Passive capture of a data unit and its subsequent retransmission to produce an unauthorized effect. Active Attacks (Cont.)

16. ModificationAttack Some portion of a legitimate message is altered, or that messages are reordered, to produce an unauthorized effect Active Attacks (Cont.)

17. DenialofService Prevents or inhibits the normal use or management of communications facilities Active Attacks (Cont.)

18. Which of the following attacks is a threat to which of the security goals? Group Activities

19. Answer Security Attacks Confidentiality Integrity Availability Snooping Denial of Service Modification Traffic Analysis Masquerading Replaying

20. Authentication - assurance that the communicating entity is the one claimed Access Control - prevention of the unauthorized use of a resource Data Confidentiality –protection of data from unauthorized disclosure Data Integrity - assurance that data received is as sent by an authorized entity Non-Repudiation - protection against denial by one of the parties in a communication Security Services

21. Specific security mechanisms: Implemented on specific layer (OSI model) Encipherment, digital signatures, access controls, data integrity, authentication exchange, routing control, notarization Pervasive security mechanisms: Not related to a specific layer Trusted functionality, security labels, event detection Security Mechanisms

22. Model for Network Security

23. Using this model requires us to: Design a suitable algorithm for the security transformation. Generate the secret information (keys) used by the algorithm. Develop methods to distribute and share the secret information. Specify a protocol enabling the principals to use the transformation and secret information for a security service. Model for Network Security

24. Symmetric Cipher Model

25. Known as: Conventional Encryption Single-Key Encryption Plaintext Original text/msg Ciphertext Coded msg Enciphering/Encryption The process of converting the plaintext to ciphertext Deciphering/Decryption The process of converting the ciphertext to plaintext Symmetric Cipher Model

26. Cryptography The developed encryption schemes Cryptanalysis Techniques used to get the plaintext out of the ciphertext without prior knowledge to the encryption scheme (breaking the code) Cryptology Both the cryptography and cryptanalysis Symmetric Cipher Model (Cont.)

27. Unconditional Security The ciphertext provides insufficient information to uniquely determine the corresponding plaintext. Computational Security The time needed for calculations is greater than age of universe More Definitions

28. Symmetric Cipher Model (Cont.)

29. Requirements Strong Key  the opponent can not figure it out even if he/she has a number of ciphertexts The key must be exchanged through a secure channel Y = E(K,X) ~ Y = EK(X) X =D(K,Y) ~ X = DK(Y) Symmetric Cipher Model

30. Always possible to simply try every key Most basic attack, proportional to key size Brute Force Search

31. Substitution Ciphers

32. You are spying on your friend Ahmed while he is chatting with John, you received the following message: “Ygjcxgvqmnnvjgrgumfgpv” Can you decrypt this message? Lets have Fun

33. Ahmed is telling John: “Ygjcxgvqmnnvjgrgumfgpv” “We have to kill the president” Encryption Key: Replacement Table Plaintext ABCDEFGHIJKLMNOPQRSTUVWXYZ Ciphertext CDEFGHIJKLMNOPQRSTUVWXYZAB Encryption Technique Each letter is replaced by the second one after it Remove blanks Answer

34. Earliest known substitution cipher by Julius Caesar first attested use in military affairs replaces each letter by 3rd one after it E.g. meet me after the party PHHW PH DIWHU WKH SDUWB Caesar Cipher

35. Transformation : Mathematically give each letter a number a b c d e f g h i j k l m 0 1 2 3 4 5 6 7 8 9 10 11 12 n o p q r s t u v w x y Z 13 14 15 16 17 18 19 20 21 22 23 24 25 Then have Caesar cipher as: C = E(p) = (p + k) mod (26) p = D(C) = (C – k) mod (26) Caesar Cipher (Cont.)

36. Cryptanalysis Only have 26 possible ciphers A maps to A,B,..Z Could simply try each in turn Caesar Cipher (Cont.)

37. Rather than just shifting the alphabet Could shuffle (jumble) the letters arbitrarily Each plaintext letter maps to a different random ciphertext letter The key is 26 letters long Plain: abcdefghijklmnopqrstuvwxyz Cipher: DKVQFIBJWPESCXHTMYAUOLRGZN Plaintext: ifwewishtoreplaceletters Ciphertext: WIRFRWAJUHYFTSDVFSFUUFYA Monoalphabetic Cipher

38. now have a total of 26! = 4 x 1026 keys with so many keys, might think is secure but would be !!!WRONG!!! Language Characteristics Problem Using the occurrence frequency of each letter , we can deduce the letters in the ciphertext Monoalphabetic Cipher Security

39. English Letter Frequencies

40. Invented by Charles Wheatstone in 1854, but named after his friend Baron Playfair. Encrypts multiple letters Uses Playfair Matrix Uses some of the rules to interpret the matrix Playfair Cipher

41. A 5X5 matrix of letters based on a keyword Fill in letters of keyword (Avoid repetition) Fill rest of matrix with other letters E.g. using the keyword MONARCHY Playfair Key Matrix

42. Plaintext encrypted two letters at a time: if a pair is a repeated letter, insert a filler like 'X', eg. "balloon" encrypts as "ba lx lo on" If both letters fall in the same row, replace each with letter to right (wrapping back to start from end), eg. “ar" encrypts as "RM" If both letters fall in the same column, replace each with the letter below it(again wrapping to top from bottom), eg. “mu" encrypts to "CM" Otherwiseeach letter is replaced by the one in its row in the column of the other letter of the pair, eg. “hs" encrypts to "BP", and “ea" to "IM" or "JM" (as desired) Playfair Rules

43. Based on Playfair encryption, encrypt the word “Hello” Key : Note: The key is an arrangement of all of the alphabetic letters Group Activity

44. Step 1: Group the letters He ll o 1st rule  repeated letters ll He lx lo Step 2: find the corresponding text in the key He  EC - rule 2 H and e on the same row (replace each with letter to right)  EC Lx  QZ -- rule 3 L and x at the same column (replace each with the letter below it)  QZ loBX -- rule 4 l and o at different rows and columns (replaced by the one in its row in the column of the other letter of the pair) E (Hello) “ECQZBX” Answer

45. Security much improved over monoalphabetic Since have 26 x 26 = 676 diagrams Was widely used for many years (eg. US & British military in WW1) It can be broken, given a few hundred letters since still has much of plaintext structure Security of the Playfair Cipher

46. Another approach to improving security is to use multiple cipher alphabets Makes cryptanalysis harder with more alphabets to guess and flatter frequency distribution Use a key to select which alphabet is used for each letter of the message Use each alphabet in turn Repeat from start after end of key is reached Polyalphabetic Ciphers

47. Simplest polyalphabetic substitution cipher effectively multiple Caesar ciphers key is multiple letters long K = k1 k2 ... kd ith letter specifies ith alphabet to use use each alphabet in turn repeat from start after d letters in message decryption simply works in reverse Vigenère Cipher

49. eg using repeated keyword deceptive key: deceptivedeceptivedeceptive plaintext: wearediscoveredsaveyourself ciphertext:ZICVTWQNGRZGVTWAVZHCQYGLMGJ From the previous table lookup the key letter then the plain text letter. The cipher letter is the intersection letter Example

50. have multiple ciphertext letters for each plaintext letter Letter frequencies are obscured But not totally lost Security of Vigenère Ciphers