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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Why doesn't the number of bytes required by GnuPG generating the key decrease?

I ran a gpg --gen-key on a remote machine connected with SSH and left it to do its job. It finished successfully, however during the execution time it asked to perform random actions to collect more ...
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Convert SHA-256 to SHA-1 and MD5 - Increase bit length/entropy?

I know this is a real dumb question and I am certainly talking complete rubbish, but let me explain: We have a long SHA-256 hash, e.g.: ...
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HPET effects on CSPRNG for Linux OS

HPET or High Precision Event Timer is a hardware built-in clock source available in most processors. I would use the computer to generate CSPRNG and do cryptographic operations. My question is: Is ...
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Would a Password Using All Possible Unicode Code Points Cause Problems in Traditional Hashing Algorithms, such as Bcrypt?

I've been toying around with this idea, but hypothetically, if you had a password manager that would use any possible renderable (e.g. not control characters such as BEL, NUL, DEL, etc., or surrogate ...
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Is it better to choose less-vulnerable random password?

I have created a random password generator function (which can be found here if anyone wants a look), which will churn out passwords with a random mix of letters, numbers, and other characters. This ...
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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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What's eating my entropy? Or what does entropy_avail really show?

Below are graphs with the value of /proc/sys/kernel/random/entropy_avail on a Raspberry Pi. This answer which might not be correct describes it as: The pattern always comes to the same "stable" saw ...
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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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What are possible methods for calculating password entropy?

I noticed there are tons of questions and answers about password entropy on this forum, some even suggesting formulas for calculating it. None did answer my exact question. What are possible or ...
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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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Confused about (password) entropy

There seem to be many different 'kinds' of entropy. I've come across two different concepts: A) The XKCD example of correcthorsebatterystaple. It has 44 bits of entropy because four words randomly ...
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How is the available entropy in /dev/random calculated (or estimated)?

It seems (to a non-expert) that /dev/random is acclaimed to be useable as a source of pure random data. However, I am curious as to the analysis of the file /dev/random. /dev/random is a collection ...
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How can I measure (and increase) entropy on Mac OS X?

I'd like to generate a bunch of keys for long term storage on my MacBook. What's a good way to: measure the amount of entropy and ensure it is sufficient before each key is generated, and ...
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Why are low-entropy passwords considered OK in many cases?

When talking symmetric encryption, a 56 bit key is known to be so weak. If you use it for your encryption, you are considered a goner as you wont survive brute-force. When talking passwords however, ...
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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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How secure are these password schemes?

On One liner to create passwords in linux?, I see advice generally of the form head -c16 /dev/urandom | md5sum. They're all random combinations of text manipulation commands, sha1, base64 and md5sum ...
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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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philosophical: restricting the password space increases security

This is more of a philosophical question. Suppose that you are trying to choose a good password for a particular online service, say your bank's e-banking service. Now the bank has some restrictions ...
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How fast is it to bruteforce a 48-bit key with current technology?

Say you have a truly random hexadecimal key formatted as 1234.5678.ABCD, with 48-bit entropy. Assuming the key is stored with no hashing/salting, how fast/easy would it be to brute force it with ...
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Entropy in Address Randomization

I am trying to understand the concept behind address randomization (ASLR). I'm reading the related wikipedia article which states: Security is increased by increasing the search space. Thus, ...
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Can I generate a random 32 bit key by using the Java hashCode and random English words?

I want to generate and communicate a 32 bit key to Bob over a phone conversation. I know he happens to have the same Java and OS installed as I have. Suppose I have a dictionary of 100,000 (English) ...
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Why do Google 2-factor authentication SMS codes never start with a 0? [closed]

When you use 2-step authentication to log to your Google Account, you can get an SMS on your mobile-phone with a G-123456 style code. I think that I never got a code with a leading zero. Is there a ...
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Would a multilingual Diceware password be more secure than a monolingual one? [duplicate]

I've been reading up on Diceware recently, and I'm wondering if using a mix of languages would make it even more secure. On the face of it, it would force a potential attacker to consider an even ...
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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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Calculating password entropy?

Whenever I look at password entropy, the only equation I ever see is E = log2(RL) = log2(R) * L, where E is password entropy, R is the range of available characters, and L is the password length. I ...
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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 ...
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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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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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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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 ...
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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 ...
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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 brute-...
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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 ...
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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 ...
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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 ...
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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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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 ...
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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 capital,...
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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 ...
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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 ...
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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
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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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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? ...