Week 10

Question 1

What is the seven Security Goals

Answer 1

1. Confidentiality
2. Integrity
3. Authentication
4. Non-repudiation
5. Certification
6. Access control
7. Availability

Question 2

What is Stream Cipher

Answer 2

Real-time symmetric encryption algorithm

Question 3

Explain RC4

Answer 3

RC4 is funamental Stream Cipher

Works by:

1. Get both Stream and Key value

Key scheduling algorithm
2. Undergo iteration of whole of stream, where S[i], stream value is based on i=( value of previous step +S[iteration] +K[iteration]) mod (length of Stream). Then swap places based on computed value

Keystream generation
3. Formula should be given. Amount of time run based on length of data

Then XOR both result

Question 4

Explain public key cryptosystem

Answer 4

Contains two keys, one for encryption, the other for decryption
Idea is, anyone can lock it, but only secret key owner can decrypt it

Question 5

Explain RSA algorithm

Answer 5

1. Pick 2 large prime number
2. calculate n= pxq and n1=(p-1)x (q-1)
3. Encryption key 1 <e <n1, GCD(e, n1)=1
4. Decryption key= e^(-1)mod (n1)

It becomes,
- Public key (e, n)
-private key (d, n)

To send encrypt:
-message ^(e) mod n

Decrypt:
- message ^(d) mod n

Question 6

How to ensure message is not tampered?

Answer 6

Use hash function
-Ensure one way
- Low correlation
- Strong collision resistance