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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8
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2answers
99 views

Is there a threshold of bits of entropy below which hashing becomes meaningless?

I just read a help page by a mail provider in which they state that all mobile phone numbers will be stored as a salted hash. This strikes me as interesting, since phone numbers don't contain a lot ...
16
votes
5answers
4k views

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, ...
6
votes
1answer
105 views

Does eliminating the possibility of repeat words make Diceware passwords significantly less secure?

I read about Diceware passphrases and whipped up a little program to generate passwords in that style. I do this by taking the list of dictionary words to create passwords and "ordering them" by a ...
3
votes
2answers
48 views

With openssl des3, what are the passphrase parameters?

I'm using OpenSSL's des3 tool to encrypt a file, e.g. openssl des3 -salt -k SUPER_SECURE_PASSPHRASE < inputFile > outputFile Everything's working, but now I have to choose a final, fixed ...
3
votes
2answers
42 views

Is there any practical weakness to using MT19937 to generate passphrases?

Suppose I use MT19937 to choose random words out of (say) the Diceware word list. I know MT19937 is not considered a cryptographically secure PRNG, but Wikipedia suggests the weakness is rather ...
22
votes
3answers
1k views

How can we accurately measure a password entropy range?

I've given myself the task of writing code that determines the strength of a password, and really want to break out of a lot of already established ways we do that, as they're often lacking, not ...
20
votes
2answers
1k views

How do I ensure there is sufficient entropy on an embedded system at first boot?

I'm working on an embedded system that will generate an SSL key the first time the system boots. I would like to avoid the problems discovered by Heninger et al. and Lenstra et al. where embedded ...
5
votes
1answer
140 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 ...
2
votes
1answer
60 views

Strength of variable-length generated password

I am contributing to the Word Sequencer plugin for KeePass password manager, which can generate diceware-style passwords using a high-quality PRNG. Something in particular I'm working on is estimating ...
5
votes
1answer
106 views

Resetting the Windows RNG

According to this research, Windows seems to produce the same sequence of random numbers indefinitely when a process is kicked off before a VM snapshot is taken. This is a huge issue obviously when ...
0
votes
2answers
62 views

How much entropy should passphrases for encrypting ssh keys have?

When one generates keys using ssh-keygen one gets prompted for a passphrase to encrypt the generated key with. How strong should such a passphrase be, entropywise, to withstand a full-blown ...
2
votes
2answers
43 views

Securing a Secure Entropy Service

Many moons ago, I answered a question about Java blocking due to a lack of entropy in /dev/random. (http://security.stackexchange.com/a/53025/41709) My main suggestion was to use /dev/urandom, but I ...
11
votes
2answers
1k views

How should I make diceware passphrases more memorable?

I find that truly random diceware passphrase, more often than not, either contain a word that is easily misspelled or has an order that is illogical. I think there are three ways to make a diceware ...
1
vote
2answers
120 views

Does using NATO's phonetic alphabet increase password strength?

Given an alphanumeric password intended to be strong yet easy to remember, we change each alphabetic character by its NATO alphabet counterpart (e.g. 'cat' becomes 'charliealphatango'). I understand ...
83
votes
11answers
15k views

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 ...
4
votes
1answer
84 views

Password security and entropy - degeneracy question

I have written a short password generator which uses a mixture of words from a dictionary and randomly generated passwords, and I'm wondering if I did the entropy calculations correctly. Usually I use ...
764
votes
23answers
153k views

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 ...
1
vote
2answers
85 views

What would typically be considered an acceptable string entropy for passwords?

I have gained interest in creating a way to check password strength (think password strength meters - yes - another one). I've found many ways to award a score on a policy driven approach (one ...
0
votes
2answers
137 views

Do you need more then 128bit entropy

UUID use 128 bit numbers. Currently it is not feasible to randomly produce two UUIDs that are the same. Does that means 128 bits of entropy is suitable for all cryptographic operations? I would ...
2
votes
1answer
124 views

What is the entropy of a password made with pwgen?

pwgen is a unix utility that generates "memorable" passwords randomly. The man page says the entropy is lower than truly random passwords with the same specification. What is the actual entropy of a ...
0
votes
1answer
34 views

Entropy on payload

How can I guess if a payload is obfuscated or encrypted? in other words can I apply Shannon Entropy algorithm to a binary payload? any advice will be appreciated, thanks in advance
5
votes
1answer
151 views

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 ...
0
votes
2answers
96 views

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 ...
4
votes
4answers
174 views

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 ...
3
votes
4answers
1k views

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 ...
5
votes
2answers
290 views

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? ...
0
votes
1answer
51 views

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 ...
11
votes
3answers
964 views

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 ...
6
votes
0answers
109 views

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 ( ...
7
votes
2answers
330 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 ...
5
votes
2answers
241 views

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: ...
20
votes
4answers
4k views

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 ...
5
votes
5answers
644 views

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 ...
3
votes
1answer
80 views

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 ...
1
vote
0answers
20 views

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 ...
2
votes
3answers
215 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 ...
1
vote
1answer
61 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 ...
5
votes
1answer
347 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 ...
2
votes
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 ...
5
votes
2answers
910 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. ...
45
votes
9answers
16k views

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?
7
votes
2answers
736 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), ...
50
votes
10answers
11k views

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 ...
2
votes
1answer
126 views

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 ...
4
votes
2answers
447 views

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 ...
3
votes
0answers
144 views

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 ...
1
vote
1answer
193 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 ...
2
votes
3answers
302 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, ...
8
votes
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 ...
15
votes
4answers
9k views

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 ...