![]() ![]() The on-line version of the UK government doesn't, no bank I'm aware of does, and doesn't. True.Īnother take away is that very few sites will allow the stronger and easier to remember technique of choice from a word list, such as "correcthorsebatterystaple". Depending on which special characters you allow and a few other factors, the random 10-character password would have something like 65 bits of entropy, a measure of its strength. Interpreting the following rules as anything more than a very rough rule of thumb method". This is an extreme example, but if I repeatedly generate passwords like this, I get entropy values greater than 48 most of the time. NIST says of the above, "Readers are cautioned against For example, it displays an entropy value of 79.73 bits for ÍéÐ¥õÂ, even though a six-character extended ASCII password has a maximum possible entropy of an entropy of at most 6 8 48 bits. If we compare NIST's estimate to Blafasel's original query on 50 bits, the entropy diverges 131,072 times. The two current answers diverge in strength by a factor of 32. In this shot, we are going to learn how to build a password estimator that will help you to determine if your password is secure. The difficulty of assessing the entropy of short sequences, particularly human produced ones is the take away from this question. NIST therefor estimates that the entropy is 33 bits if we interpolate for 11 characters and use dictionary and composition rules. The reasoning behind this table is within the document at $\S$ A.2.1 Guessing Entropy Estimate. Table A.1 (reproduced below in case of link rot):. Btw, this whole discussion has strong parallels with password-based-authentication vs 2FA. Granted that this is now deprecated, but the relevant publication was NIST Special Publication 800-63 Version 1.0.2, Electronic Authentication Guideline. The reason is that these entropy calculators assume a sequence of random characters from an RNG that follows a uniform distribution, which isn’t the case when people choose their own passwords. One official way to estimate the strength of a user selected password such as "Tr0ub4dor&3" is to look at NIST recommendations. If you want an even more thorough explanation of this comic, I can only recommend you read the bear's answer on this over on InfoSec.SE. In both cases it can be assumed that the attacker knows the possible choices influencing the entropy estimation and that it's actually a uniformly random decision which word / pick is done. It's estimatated that the word itself "Troubador" comes up in dictionaries which contain about $2^$ which means $4\times 11=44$ bits of entropy. ![]() Interestingly enough the reasoning for the entropy rating are actually justified in the comic by the little boxes which each represent 1 bit of uncertainty. Also, XKCD is always applicable when it comes to these sorts of things. I don't get nearly the amount of entropy stated in the comic. Entropy calculators make assumptions about how the passwords were generated, and therefore they can both disagree with each other and also be wildly wrong. ![]()
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