Question

Q3. Answer with yes or no and give a reason.

1-Is DES vulnerable to a brute-force attack?

2-Is 3DES vulnerable to a brute-force attack?

3- Is AES vulnerable to a brute-force attack?

Answer 1

3.1) Brute Force attack consists of an attacker submitting many keys with the hope of eventually guessing correctly.

DES is the most widely used method of symmetric data encryption ever created. Its 56-bit key size means that there are 2⁵⁶ possible encryption keys for any given message. It is vulnerable to brute-force search of the whole keyspace, either by large collections of general-purpose machines or even more quickly by specialized hardware.

3.2) In triple DES the cipher algorithm is applied three times to each data block. A brute force attack consists of trying each key until the right one is found. Also in 3DES, we are equally likely to find the key on the first, second, & third try. On average we expect to find the key after trying half of the keys which is 2⁵⁵ of the keys. This is not impossible considering the current processing speed. For a brute-force attack, however, the outlook is far less optimistic. In the worst case, the correct key combination will be the last one we try, meaning we will have tried 2¹⁶⁸ operations, which is a large keyspace to be searched. So 3DES is not vulnerable to brute force attacks.

3.3) AES-256 is secure to brute force attacks.

If you assume:
Every person on the planet owns 10 computers.
There are 7 billion people on the planet.
Each of these computers can test 1 billion key combinations per second.
On average, you can crack the key after testing 50% of the possibilities.

Then the earth’s population can crack one encryption key in 77,000,000,000,000,000,000,000,000 years!

In brief terms the difference between cracking the AES-128 algo & AES-256 algo. is considered minimal. Whatever will break 128-bit will probably also crack 256-bit.

Hope this helps. If you have any queries or suggestions regarding the answers please leave them in the comments section so I can update and improve the answer. Thank you.