Symmetric crypto

Question 1

What is symmetric encryption and what does it provide from the security requirments?

Answer 1

Symmetric encryption uses a shared key. It only provides Confidentiality

Question 2

what is one time pad and what is its requirements?

Answer 2

OTP is stream cipher it uses XOR and key stream.
Key otp must have same size as message.
Key must be used only once.
Key must be perfectly random.

Question 3

What is Kerchkoffs principle?

Answer 3

It states that the cipher method must not be required to be secret. the security should depends on the key which must be kept secret.

Question 4

What are the modes of encryption for block cipher?

Answer 4

ECB - electronic cipher book
CBC - cipher block chaining
OFB -output feedback mode
CTR - Counter mode

Question 5

Why do we need the initializing vector?

Answer 5

to prevent having the same plaintext result in the same (guessable) ciphertext