Passwords should be truly random and should contain enough entropy to mitigate bruce-force attacks to the extent of one’s threat model. The command line utility bc is very useful when calculating entropy. (number of possibilities per value) ^(number of values)įor two six-sided dices, number of combinations equals 6 ^2 or 36.Ĭalculating password entropy is done using the following formula.įor two six-sided dices, entropy equals log 2(36) or ~5.17 bits. Say we have two six-sided dices, how many combinations are there?Ĭalculating number of combinations is done using the following formula. This may sound a bit counter intuitive, but is great information to be passing on to users in your security awareness training program.Password entropy is a measure of password strength. Take this into a format that is really easy for your users to remember, and ace the special characters and upper lower case thing and try:Īll of a sudden you no longer need to write them down and they have doubled in strength, more than double in fact, than a shorter password with special characters and upper/lower case changes. HorseChickenFloat – more than 13 characters, but easy to remember Now we run some analysis on this password… If we take a fairly common approach to users choosing passwords, like taking a word or a name and adding special characters, sounds great right? Say your name is Andrew, and you choose a password to remember, check, 128+ bits = Very Strong often overkill.60 – 127 bits = Strong can be good for guarding financial information.36 – 59 bits = Reasonable fairly secure passwords for network and company passwords.28 – 35 bits = Weak should keep out most people, often good for desktop login passwords.Let’s look at some examples using the table below as a guide: The no complexity requirement is of interest, and here’s why, Entropy is your best defence. A minimum length of 10 characters, consisting of at least three of the following character sets:.A minimum length of 13 alphabetic characters with no complexity requirement or.In the 2016 Australian Information Security Manual (Controls), the Australian Signals Directorate recommends: A password’s entropy can be calculated by finding the entropy per character, which is a log base 2 of the number of characters in the character set used, multiplied by the number of characters Password entropy is usually expressed in terms of bits: A password that is already known has zero bits of entropy one that would be guessed on the first attempt half the time would have 1 bit of entropy. Password entropy is based on the character set used (which is expansible by using lowercase, uppercase, numbers as well as symbols) as well as password length. This measure of strength is called Entropy. The strength of a password is a function of length, complexity, and unpredictability. Usually strength can be measured by how many trials an attacker who does not have direct access to the password would need, on average, to guess it correctly. Password strength is a measure of the effectiveness of a password in resisting guessing, brute force cracking, dictionary attacks or other common methods.
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