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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Does having a minimum number of digits improve password security?

Some password systems will enforce at least X of a type of character - a common one I see is 'minimum 3 numeric characters'. As far as I understand, simply allowing certain character classes, like ...
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2answers
3k views

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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2answers
366 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 ...
6
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2answers
792 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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4answers
181 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 ...
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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 ...
5
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1answer
490 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 ...
5
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2answers
1k 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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2answers
251 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: ...
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1answer
165 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 ...
5
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1answer
113 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 ...
5
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1answer
153 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 ...
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3answers
1k views

Pseudo Random Generator is not initialized from the (entropy pool)?

The RHEL5 manuals state that /dev/urandom will use the entropy pool until it's exhausted, and then it will resort to a fall-back pseudo-random algorithm, so that it will never block. But when ...
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2answers
405 views

How can I create a secure password?

I know the standard tricks, create a long password, numbers, symbols, capital letters, etc. My questions is how do I judge password security. I heard different tricks to make secure passwords. For ...
4
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1answer
949 views

Open-source alternative for CryptGenRandom?

Let's say that for some reason I don't trust CryptGenRandom. Are there any open source software Windows entropy collectors to get cryptographically secure random numbers from for seeding purposes? ...
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2answers
265 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 ...
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2answers
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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 ...
4
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3answers
605 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 ...
4
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1answer
495 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 ...
4
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1answer
645 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
200 views

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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3answers
364 views

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, ...
3
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2answers
5k views

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
449 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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4answers
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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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3answers
2k 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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3answers
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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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2answers
2k 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 ...
3
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3answers
342 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, ...
3
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1answer
76 views

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) ...
3
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2answers
166 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
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3answers
294 views

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?
3
votes
1answer
197 views

PHP - Serializing user inputs

My entropy gathering system works by serializing user inputs: $entropy=sha1(microtime().$pepper.$_SERVER['REMOTE_ADDR'].$_SERVER['REMOTE_PORT']. ...
3
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1answer
104 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 ...
3
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1answer
101 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 ...
3
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0answers
157 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 ...
3
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2answers
65 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 ...
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2answers
453 views

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 ...
2
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4answers
538 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 ...
2
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1answer
449 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 ...
2
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1answer
104 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
votes
1answer
561 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
125 views

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 ...
2
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2answers
51 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 ...
2
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2answers
195 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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1answer
74 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 ...
2
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1answer
164 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 ...
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3answers
244 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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3answers
594 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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2answers
53 views

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 ...