Week 9

Question 1

Classification of hacker

Answer 1

1. Intersection ( eavesdrop information)
2. Interruption (denial of service)
3. Modification (modify content)
4. Fabrication ( insert counterfeit information)
5. Invasion ( steal information of node)

Question 2

Process of network attack

Answer 2

1. Hacker gathers information (footprinting, scanning, enumeration)
2. Gains access to become network member
3. Launches attack

Question 3

Methods of hacker become network

Answer 3

1. Brute force attack
2. Address spoofing
3. Replay packet
4. Session hijacking (watch on-going connection, send disassociation to client, use same parameter as client to act as client)

Question 4

Type of attack

Answer 4

1. Denial of service attack
2. Man in the middle attack
3. Data modification attack

Question 5

Security goals

Answer 5

Confidentiality
Integrity
Authentication
Non- repudiation
Certification
Access control
Availability

Question 6

Explain cryptosystem

Answer 6

System where sender conceal data into cipher text using encryption
Receiver transforms cipher text back to plain text using decryption

Question 7

Explain caesar cipher
venegere cipher
Transposition cipher

Answer 7

Caesar cipher: shift by 3 letter
Venegere: use a repeating key
Transposition: convert plaintext into matrix, then read based on key order and column

Question 8

Explain multiple letter cipher and playfair cipher

Answer 8

Playfair works by, getting key, place into matrix, order it first by key, then remaining alphabet. Then break words into pair, then draw rectangle, picking value of opposite sides.
If same row, move most left to right, then pick right value.
if same column, pick value below it.

Question 9

Hardest cipher to crack

Answer 9

Block cipher
Stream cipher

Question 10

Difference between block cipher and stream cipher

Answer 10

Block cipher: process as a block at a time
Stream cipher: Process messages as bit/byte when en/decrypt. Real time

Question 11

Explain fiestel cipher

Answer 11

Word, key, round function
1. Input block split into two half
2. For L1, get from R0. For R1, get R0 value, undergo permutation using round function, XOR combine w L0

To decrypt, get result then do same process, but reverse key

Question 12

Explain DES

Answer 12

Data Encryption Standard
Its built upon fiestel cipher, with caviat is that it include a function which expand the bit, exclusive OR operation, then subsitute it into original bit amount

Proceed with fiestel cipher process

Question 13

Explain AES

Answer 13

Advanced Encryption Standard
Used to replace DES
Consist of 128,192,256 bits keys

Question 14

How does the AES algorithm work

Answer 14

1. Convert the 128-bit plaintext into 4 by 4 matrix
2. Add round key into matrix using XOR
3. Loop, subbytes, shift row, random column, add round key
4. Final loop, subbytes, shift row, add round key

Question 15

How does decryption in AES algorithm work

Answer 15

1. Add round key into matrx using XOR
2. Loop, inverse shift row, inverse sub types, add round key, inverse random column.
3. Inverse shift row, inverse sub types, add round key