Question

AES and RSA are not secure (with respect to chosen-plaintext attack) however, AES and RSA can be secure version using a technique called randomized encryption. Applying this technique to AES, we need to have an initialization vector (IV). We have a message m with 128 bits, show how to encrypt m with secured AES. Explain why IEEE 802.11 (i.e., WEP) is not secure due to the inappropriate usage of an IV.

Answer 1

AES and RSA can be made secure using randomized encryption( or random padding).In this technique we have to reserve very last byte to tell how many bytes of padding were added. Suppose we have a message of 128 bits or 16 bytes. For a 4 byte blocksize cipher. we will have one byte for our message part and remaining three bytes.In these 3 bytes two bytes are used for random padding.Last byte will contain a hex number.

IEEE 802.11(I.E. WEP) is not secure due to following reasons:

1) In this key length is quite short, therefore it is more prone to attack
2) Reusing keys is a major weakness in any security system. And WEP reuse keys.
3) Weak keys are susceptible to attack
4) WEP does have a message integrity check but hackers can change
messages and recompute a new value to match