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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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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What would the cryptographic impact be of knowing the output of /dev/urandom?

Another noob question, I know, but something I'm unsure about. If I somehow magically knew the output of /dev/urandom at any given time, how much would that weaken a given encryption system? Or, ...
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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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342 views

Computing entropy for a passphrase ( minimal word length … )

Edit: 2013-05-17 . 2013-05-27 After reading first answer from Tom Leek and some docs around the web, I've begin to write some options to my tool genpassphrase.pl: $ ./genpassphrase.pl -h Usage: ...
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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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820 views

How to generate cryptographically strong pseudorandom data very rapidly?

What's the best way to go about generating a fast stream of cryptographically strong pseudorandom data without installing uncommon packages? Drawing from /dev/urandom is far too slow. I had an idea ...
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How much time / “entropy collected” should generating a RSA 2048bit keypair take?

The purpose of my question is get an better idea about reasonable amout of time the generation of the RSA public/private keypair should take? To be less vague let me specify the question and define I ...
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422 views

How genuine are password entropy calculations?

I apologise for perhaps the confusing title, I'll try and elaborate a little better. Many discussions I see surrounding password entropy focus on the specific context of the range of choices ...
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/dev/random security holes

I'm doing some reading into the security issues surrounding /dev/random but it's proving to be hard to find good sources of information. Can anybody help? I've asked Google and got a bunch of articles ...
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158 views

Reliable random seed for RNG

I want to create my computer passwords with a RNG, but I am thinking about one thing: I would use python to write that script and the RNG is controlled by one seed, most likely the time. If I would ...
3
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1answer
165 views

PHP - Serializing user inputs

My entropy gathering system works by serializing user inputs: $entropy=sha1(microtime().$pepper.$_SERVER['REMOTE_ADDR'].$_SERVER['REMOTE_PORT']. ...
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When changing a password, does it have to be completely different?

When changing a password how important is it to have a significantly different one? For example is it bad to reverse the sequencing of the old password to make a new one or change a few numbers?
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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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2answers
387 views

How can you securely generate keys on AWS?

Our application needs to generate secure keys for long term storage on AWS using openssl. But I've seen some instance where entropy falls dangerously low on AWS machines and this doesn't appear to be ...
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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 ...
2
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3answers
1k views

Recompute Rainbow table with salt?

So, as I understand it, you prepend a password with salt before you hash it so that the resulting hash can't be used with a rainbow table to find the original password, as you could if the password ...
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4answers
438 views

If the attacker knows part of the password but not the length, does that help him in any way?

The idea behind this is that if knowing part of the password and not the length is useless, "passwords" can be easily stored in cleartext or paper since you would just add your own n characters ...
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4answers
402 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 ...
2
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3answers
184 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, ...
2
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1answer
71 views

Usefulness of bcrypt(UUIDv4())

One of my colleagues is working on securing OAuth 2 client IDs and secrets for our OAuth server and he has come up with this scheme where he would not only use UUID v4 to generate random values, but ...
2
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1answer
502 views

Does client certificate authentication demand more server-side entropy?

We have a secure web service running Apache that requires client certificates for access. This service has a problem with running out of entropy. We have several other sites that use TLS that get ...
2
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2answers
115 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 ...
2
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3answers
414 views

How secure is to seed PRNGs with the sequences from CSPRNG?

Background: Implementing online casino, I would like to use a number of PRNGs with high throughput, like MersenneTwisterFast. I know it is not cryptographically strong, but quite unpredictable when ...
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1answer
53 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 ...
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1answer
215 views

How to estimate the number of entropy bits & search space of a signature system like passtouch?

Apologies if I'm using the wrong lexicon, I'm just reading up about password systems out of interest. After seeing the xkcd strip on passphrases and coming across the passtouch system (youtube demo) ...
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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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Passphrase generator and strength & recovery time estimator. Right strength and randomness?

Questions about the strength of pass phrases frequently popup, as does: how to generate a strong passphrase? I tried to combine both in a tool. The free tool also includes recovery time estimations ...
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How many bits of entropy should I aim at for my password? [closed]

I mainly use 2 passwords: 1 is a 4 word full lowercase passphrase of 18 letters long which I use wherever possible. The other is basically 3 words and a digit with the first word in full uppercase and ...
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2answers
652 views

Password entropy match for alphanumeric but there are special characters in password

I have a problem cracking some of the fundamentals on passwords' entropies. Namely: I have read this article about a guy cracking DKIM of Google (maybe more noticing that the keys are only 512 bits) ...
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1answer
189 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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1answer
180 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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1answer
92 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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1answer
110 views

Minimum SHA256'd UTF8 encoded passphrase length not stored anywhere

For a passphrase that is UTF8 encoded and then SHA256'd, what is the minimum length to achieve a practically collision free result? The implementation is for a 32 byte cryptocurrency ed25519 seed ...
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605 views

Using passwords made of words

People say don't use passwords in the dictionary but if you use two words isn't it alright? Dictionaries have at least 10,000 entries so just two words will be 100,000,000 possibilities (and that's ...
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1answer
205 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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1answer
2k views

Why is /dev/random so slow on Linux? [duplicate]

If it's true you only need about 128 bits of entropy to fuel enough data forever, why is it that /dev/random is so slow? My system has uptime of 214 days! Is it really only gathering .000000001 bits ...
0
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1answer
89 views

How strong is this encryption? [closed]

Given Dictionary containing 1000 three-letter words: dictionary=abc,def,ghi,jkl,mno,pqr... Randomly chosen words from the dictionary: 10-bits-passwords=abc,def,ghi Randomly chosen three words from ...
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1answer
96 views

Does adding an extra, non-entropic keyfile lower security? [duplicate]

Suppose I create two TrueCrypt volumes using keyfiles. The first volume uses a keyfile generated by TrueCrypt, whereas the second one uses the same keyfile in addition to a second, non-entropic ...
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1answer
136 views

physical access proof smart card for disk encryption [closed]

Current full disk encryption on mobile devices rely on low entropy passwords like PIN numbers or pattern locks. Being able to use a smartcard with such mobile devices is a tempting idea. I know that ...
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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" ...