Alices computer stores files using the following steps:

1. For each file F, the computer creates an encrypted version of the file S = EK(F) using the

encryption method E(), where K is the encryption key.

2. Then, it replaces the original file F with the encrypted version S.

3. Later, when she tries to access the encrypted file S, she is asked to input the key K. If she

inputs the key correctly, the computer allows her to access the file F.

4. After accessing the file, when she tries to update the contents of the file F, she is asked

again to input the key K.

5. If she inputs the key correctly, the updated version is saved and encrypted again using the

method E(). Otherwise, she is locked out after three incorrect attempts.

Given the above scenario, answer the following questions from your intuition.

Q1: If the key K is stored in an unencrypted text file in the same directory where F is located, and

an attacker can login into her computer, how much security does the employed encryption method

offer to her?

Q2: If we assume that the text file contains the hash value of K instead of the key itself, does it

increase the security of the file F? How? What happens if Alice decides to hash the text file itself

instead of just hashing the key K?

Q3: As an attacker, how can you compromise the file F if the computer adopts hashing as the

security mechanism instead of encryption and stores h(F) in place of EK(F)? Hence, h() is the hash

function. Ignore the key K since the computer does not use encryption anymore.