1. Problem A system password policy is set at maximum of 7 characters. Each char
ID: 3688837 • Letter: 1
Question
1. Problem
A system password policy is set at maximum of 7 characters. Each character can only be English alphabet with case-insensitive characters.
Suppose Mallory tries to break a 7 character password by trying all possible combinations. Suppose the system allows her unlimited attempts.
How many attempts would she have to do?
If she has only 2 hours to launch this attack, how much time she has for trying one attempt (use worst case)?
What is this type of attack called? (where all possible combinations allowed by password space are attempted?)
Explanation / Answer
1. The number of attempts needed to be calculated with the following formula:
Different combinations = number of possible characters password length
7 characters
(26 upper case letter,
26 lower case letters)
527= 1,028,071,702,528
2. The time limit given is 2 hour and hence
time taken per attempt = total time / total number of combination
let us convert 2 hour into nanoseconds =2 x 60 x 60 x 10^9 = 7200000000000
time taken per attempt = 7200000000000 / 1,028,071,702,528 = 7.0034 nanoseconds
3. The type of attack is called Brute-force attacks. The Brute-force attack is carried out by hackers which intend to crack your passwords with the help of software which simply tries different character combinations in quick succession. The algorithm is quite easy and limited to the trial and error of as many character combinations as possible. For this reason it is also called “exhaustive search”. The attacker normally uses a high-performance computer, which can perform a large number of calculations per seconds and thus can check a large number of combinations in a short time.
In practice, this method is often used successfully, because many users use short passwords, which in addition only consist of characters of the alphabet, which drastically reduces the number of possible combinations and makes it easier to guess the password.
7 characters
(26 upper case letter,
26 lower case letters)
527= 1,028,071,702,528
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