Computer Network Security

Consider a “one-way” function h. Then, given the value y = h(x), it is computationally infeasible to find x directly from y.

a. Suppose that Alice computes y = h(x), where x is Alice’s salary, in dollars. If Trudy obtains y, how can she determine Alice’s salary xl

Don't use plagiarized sources. Get Your Custom Essay on
Computer Network Security
Just from $13/Page
Order Essay

Hint: Adapt the forward search attack to this problem.

b. Why does your attack not violate the one-way property of h?

c. How could Alice prevent this attack ? We assume that Trudy has access to the output of the function h, Trudy knows that the input includes Alice’s salary, and Trudy knows the format of the input. Also, no keys are available, so Alice cannot encrypt the output value.

Suppose that Alice uses a stream cipher to encrypt plaintext P, obtaining ciphertext C, and Alice then sends C to Bob. Suppose that Trudy happens to know the plaintext P, but Trudy does not know the key K that was used in the stream cipher.

a. Show that Trudy can easily determine the keystream that was used to encrypt P.

b. Show that Trudy can, in effect, replace P with plaintext of her choosing, say, P’. That is, show that Trudy can create a ciphertext message C” so that when Bob decrypts C’ he will obtain P’.

Suppose that a particular cipher uses a 40-bit key, and the cipher is secure (i.e., there is no known shortcut attack).

a. How much work, on average, is an exhaustive search attack?

b. Outline an attack, assuming that known plaintext is available.

c. How would you attack this cipher in the ciphertext-only case?

Place Order
Grab A 14% Discount on This Paper
Pages (550 words)
Approximate price: -
Paper format
  • 275 words per page
  • 12 pt Arial/Times New Roman
  • Double line spacing
  • Any citation style (APA, MLA, Chicago/Turabian, Harvard)

Try it now!

Grab A 14% Discount on This Paper

Total price:

How it works?

Follow these simple steps to get your paper done

Place your order

Fill in the order form and provide all details of your assignment.

Proceed with the payment

Choose the payment system that suits you most.

Receive the final file

Once your paper is ready, we will email it to you.