![]() The password "wUm09n#i4" will not be on any of these lists and as such, will be guessed later in the order, making it inherently stronger.Ĭreating a memorable and secure password for every account is impractical and can be skipped altogether by using a password manager. It doesn't matter how many bits of entropy a password contains if it's on a dictionary of common passwords, as these are usually tried first. From the example above, "Summer2017" is an extremely common password, found on almost every list you can find for brute forcing passwords. ![]() Lists of millions of leaked passwords can be found online and these are usually the starting point for an attacker attempting to gain access. But why is "Summer2017" a terrible password and "wUm09n#i4", with 59.1 bits of entropy, a good password when they both have roughly the same bits of entropy? Enter the dictionary attack.Ī dictionary attack involves creating a list of common passwords and generating permutations on them instead of brute forcing every combination. For those interested in maths, finding the bits of entropy is calculated by e = L * log(C)/log(2) where L is the length of the password and C is the size of the character set.Ĭlearly having a higher number of bits of entropy indicates a stronger password. ![]() This number is about equal to 2^59.5 and so "Summer2017" has 59.5 bits of entropy. This means the number of guesses to guarantee we find the password is 62^10. The size of the character set for this password is 26 (upper case) + 26 (lower case) + 10 (numbers) = 62 characters. The password "Summer2017" is 10 characters long, and uses upper and lowercase alphanumeric characters. Web based brute forcing would be much slower.) (Note: these numbers are based on GPU hash breaking and require a data dump of password hashes. Someone with a data mining system might be able to get 2^55 passwords or possibly more, depending on their hardware. For some context, it's realistic that a normal person with a single graphics card on their computer can guess about 2^49 passwords per day. A password with n bits of entropy would require 2^n guesses to guarantee that password will be found. A password that requires at most 2 guesses to find has 1 bit of entropy. This measurement is known as bits of entropy.Ī password that is already known has zero bits of entropy. We can now measure the strength of a password as the number of guesses it would take to guarantee we guess the password, assuming we know the character set the password uses. Eventually, this script would find all passwords that are strictly lower case alphabetical characters. An example of this might be to start with "a", then "b", then "c" and continue until "z", at which point the program would try "aa", then "ab" and so on. ![]() This involves setting up an automated script to literally attempt all possible combinations of characters for that password. These requirements are in place to raise the entropy of a password and make it much harder for an attacker to guess your password.Ī common way to break passwords on a user account is to use a "brute force" method. It's common to see "Your password must contain characters from three of the following categories" to be able to set your password. Passwords are obviously required to keep your online accounts and data safe, but how strong is your password? The idea of a strong password can be hard to quantify and most places require your passwords to meet some requirements.
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