In computing, entropy is the randomness collected by an operating system or application for use in cryptography or other uses that require random data. This randomness is often collected from hardware sources, either pre-existing ones such as mouse movements or specially provided randomness ...

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Random padding in hash functions

In this answer, it was recommended that you add random padding when hashing messages for a trusted timestamp, such as for predictions, in order to avoid dictionary and brute force attacks (at least ...
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How much stronger does a paragraph/sentence based password becomes with random characters added?

I was reading some questions on here regarding the correct horse battery staple method, and the conclusion was that, assuming any words in the list of most common English words, every word adds about ...
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What is the difference between Shannon entropy and saying that tossing a 6-sided die 100 times has more than 256-bit entropy? [migrated]

I'm confused. I thought that tossing a 6-sided die 100 times had a greater than 256-bit entropy because 6^99 < 2^256 < 6^100. (A similar concept appeared in this XKCD comic, where choosing four ...
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Does manipulating a random password significantly reduce its entropy?

Suppose I generate a password using a secure random number generator and all the available character classes. For example, c.hK=~}~$Nc!]vFp9CgE. Consider that this password may need to be used in an ...
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Add a file as entropy source for /dev/random

What I have: A large file containing lots of secret, true-random bytes (yes, I'm sure they're not merely pseudo-random). I'll call it F. What I want to do: Tell Linux that it can use this file as an ...
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Password: ham,ham,ham,bacon,bacon,ham

Why do we bother with dice ware? Is rolling dice and looking up in a printed book (or using a digital analogue) a string of N random words any more secure than simply repeating a word or two N times? ...
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A simple question about entropy and random data

Let's say I roll a 6-sided die 100 times and record the results into a 100 character string, for example: //this is obviously an example (and very unlikely) outcome ...
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3answers
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Calculating how secure my password is

I generally use GnuPG for encrypting my files and as far as I know its strength ultimately depends on the passphrase I use. So, I would like to know: how can I mathematically calculate how secure my ...
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22answers
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XKCD #936: Short complex password, or long dictionary passphrase?

How accurate is this XKCD comic from August 10, 2011? I've always been an advocate of long rather than complex passwords, but most security people (at least the ones that I've talked to) are ...
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11answers
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Password rules: Should I disallow “leetspeak” dictionary passwords like XKCD's Tr0ub4dor&3

TLDR: We already require two-factor authentication for some users. I'm hashing, salting, and doing things to encourage long passphrases. I'm not interested in the merits of password complexity rules ...
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Which format of secret would be the most efficient for human memory? [closed]

I am talking about something-you-know identification factor. Examples of those formats are passwords, passphrases, pin-s, picture passwords ( ...
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2answers
287 views

How much entropy is good enough for seeding a CSPRNG?

I have some fundamental questions on using Cryptographically Secure Pseudorandom Number Generators (CSPRNGs). What should be the size of the seed that I initialize a CSPRNG with? How often should I ...
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Does adding a non-entropic part to a password makes it less secure?

Suppose I'm encrypting a file via AES using a password of my choice, or creating a TrueCrypt volume using a password and no keyfiles. Which of the following two passwords would be more secure: ...
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How secure is Snowden's MargaretThatcheris110%SEXY password?

In an extra from Edward Snowden's interview with John Oliver, Snowdon advises that a good password to use is one such as MargaretThatcheris110%SEXY.. Also, on the Errata Security blog, Robert Graham ...
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5answers
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How much is the entropy of a randomly generated password reduced if I regenerate until I get a password I like? [duplicate]

In many of the answers and comments on the well-known XKCD #936: Short complex password, or long dictionary passphrase? question, the importance was stressed of generating the password randomly, and ...
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output from CryptGenRandom [closed]

Can we capture the output of Windows CryptGenRandom function. Suppose an application is utilizing CryptGenRandom, as a user can we know what is the Random Number generated and given to the ...
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Evaluating a noise source for a RNG - defining a one-paramter family for RNG [closed]

I am trying to evaluate a noise-source as a means of providing entropy to a random number generator. I am running into trouble when it comes to determining the probability distribution that has the ...
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3answers
173 views

How secure are “pattern” passwords?

I was watching a TED Talk about password security recently which covers quite a few different types of passwords and compares how secure they are and how easy they can be remembered. One type of ...
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1answer
51 views

How to check randomness of a hash?

I have a REST api in which the server allots a unique token each time a user is logged in. Its a hash containing numbers,letters and a one or two special chars. I want to check the entropy of these ...
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1answer
162 views

/dev/random in EC2 cloud

is /dev/random any good in AWS EC2 for use in making a shared key that will be passed over a secure channel? i am concerned that a launched instance would have not much entropy to begin with. what ...
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0answers
28 views

General Entropy as opposed to Password Entropy [duplicate]

I know that the formula for the entropy of a message is: (I believe b can be set to 2) but when calculating the entropy of a password websites usually only compute log2(p-1), ignoring the first ...
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2answers
663 views

Credit card number entropy?

I want to confirm that this understanding is correct: A card has 16 digits plus a CV2 The first 6 digits are an issuer identification number The last digit of the 16 is a Luhn mod 10 check digit. ...
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9answers
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How long should the password be?

The minimum password length recommended is about 8 characters, so is there any standard/recommended maximum length of the password?
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1answer
91 views

VM production server and low entropy

I'm monitoring a VM functioning as our production server. I noticed it has at many times, quite low entropy (/proc/sys/kernel/random/entropy_avail). On average our server(which among other stuff does ...
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2answers
564 views

Linux kernel entropy - does it matter to /dev/urandom and what is a minimum?

This question had been asked several times, but still something's not clearly understood from other answers I have a few servers running with a custom built linux kernel (minimal driver modules etc), ...
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10answers
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Why does the user pick the password?

Almost every web service I can imagine has the user pick the password. Why is this? Couldn't the system choose a better password? It doesn't have to be some complicated mess; see ...
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1answer
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Evaluating the Entropy of the PRNG in OpenSSL

I've have a question on the PRNG in OpenSSL. I would like to understand how do you evaluate the diversity/entropy of the PRNG used in the OpenSSL (Cryptographic Library). If this is the wrong ...
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Password strength metrics

In the question Source code as password I suggested using a combination of entropy and as @Lawtonfogle put it 'meatspace difficulty'. As suggested in the xkcd comic correct staple horse battery is a ...
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0answers
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What is the most efficient password scheme in terms of entropy per convenience [closed]

Although the main points are right, but now six words are needed, which is both inconvenient to remember, and inconvenient to type. My question is, has then been any case studies on the most ...
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1answer
124 views

How to keep a reasonable level of entropy in an encrypted file?

Encrypted (or random) data, by nature exhibit a high entropy value and non unencrypted data will exhibit a low entropy value. From an attacker point of view the precense of this high entropy value in ...
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3answers
250 views

is it feasible to improve the entropy of XKCD #936 by using a larger dictionary?

XKCD #936 uses a limited subset of the English language, only 2000 words. I just looked it up, and the English language has over a million words, a sizeable subset of those having special characters, ...
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4answers
2k views

password complexity policy for non “English” passwords

In an internationalized application, what is the best practice for a policy on complexity of passwords? I am not having luck searching for the answer. Wikipedia lists these items for password ...
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4answers
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Why OpenSSL can't use /dev/random directly?

I couldn't find the answer for the reason anywhere, even the wiki page doesn't explain it. This seems like using a PRNG for seeding an another PRNG. The first one (/dev/random) may itself be seeded by ...
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4answers
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Is there a length beyond which increasing password length provides no additional security?

Assuming that the password is stored hashed and salted, and that it is a string of random characters, is there a point where adding to password length doesn't add security? Since the hash will have a ...
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1answer
251 views

Soundness of GRC.com Haystack padding concept [duplicate]

I was wondering how sound is the concept presented by the Gibson Research Corporation (see below if you do not want to follow the link) about simple passwords (= very easy to remember) with the ...
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2answers
141 views

How secure is a MD5 hash of an 128bit key

Apparently, for the Android KeyChain an encrypted master key is stored along the MD5 hash of the unencrypted Key. How secure is that? MD5 is known to have collisions, but I guess we can assume with an ...
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3answers
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Java SecureRandom doesn't block? How?

I know from experience that reading from /dev/random blocks when the Linux kernel entropy pool runs out of entropy. Also, I've seen many articles and blog entries stating that when running on Linux, ...
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12answers
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How reliable is a password strength checker?

I've tested the tool from Microsoft available here which tests password strength and rates them. For a password such as "i am going to have lunch tonight", the tool rates it's strength as "BEST" and ...
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1answer
206 views

Where does /dev/random get its entropy?

I read over and over about how /dev/random gets its entropy from "hardware events." What exactly are these hardware events and how can we be sure that it is random enough?
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11answers
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One liner to create passwords in linux?

How do you create a readable password using bash with one line? What if i'm looking for 128 bits of entropy? EDIT By readable I mean the 94 printable ascii characters (without space). It can use ...
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1answer
261 views

How negative are virtual machines (vms) to /dev/urandom?

I looked at the questions here and here. This then piqued my interest as I've recently been involved with looking into FIPS compliance, and in my vm environment /dev/urandom compliance testing ...
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4answers
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Is an 80 bit password good enough for all practical purposes?

I know that asking how many bits of entropy comprise a strong password is rather like asking the length of a piece of string. But assuming the NSA is not on to you, and that it is hardly worthwhile ...
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1answer
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Can a dictionary attack crack a Diceware passphrase?

Everyone knows the words used in Diceware passwords (all 6^5 = 7776 words are published) -- they're all common words. Everyone seems to know that we're not supposed to use dictionary words for ...
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Are passwords made up from concatenating a few foreign words better than shorter random characters? [duplicate]

Does it make sense to insert a foreign word into a paraphrase to mitigate against brute force? For example: "pussiMeansCatInEskimo" "caballoMeansHorse" "CatIsGatto" "SalopeMeansBitch" ...
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2answers
442 views

Can the human brain generate cryptographically secure random numbers?

A security conscious friend of mine was attempting to generate entropy using random dice rolls to generate a random password, and I became curious about the security of random number generators and ...
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1answer
242 views

What multiplier to use when calculating the average time to crack passwords with a given entropy?

Suppose that we have a process that generates passwords with entropy E. I'd like to compute the average time it would take for a brute-force attack to crack an MD5-hashed instance of such a password. ...
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4answers
8k views

Google Account: implications of using application-specific passwords

In the wake of the recent Mat Honan story I decided to try out two-factor authentication on my Google account. But in order to keep using it with Exchange, the Android OS, Google Talk and Google ...
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38answers
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What is your way to create good passwords that can actually be remembered?

What are the methodologies which can be used to generate "human" good quality password? They have to ensure a good strength and also easy to remember for a human being.
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2answers
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Is it really “Time to add a word” if there are no tools to crack passphrases of 3 words and up?

It's "time to add a word" says Arnold Reinhold, the creator of Diceware, in his blog (3/2014). He advices to use 6 word sentences (or 5 words with one extra character chosen and placed at random) from ...
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Why do password strength requirements exist?

Password strength is now everything, and they force you to come up with passwords with digits, special characters, upper-case letters and whatnot. Apart from being a usability nightmare (even I as a ...