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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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 ...
10
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3answers
2k 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, ...
57
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12answers
9k views

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
143 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
4k views

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 ...
0
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1answer
68 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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4answers
86 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 ...
12
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4answers
3k views

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 ...
564
votes
21answers
112k 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 ...
15
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1answer
4k views

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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7answers
822 views

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" ...
3
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2answers
232 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 ...
0
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1answer
74 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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votes
4answers
7k 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 ...
42
votes
38answers
8k views

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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votes
2answers
268 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 ...
35
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9answers
3k views

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 ...
2
votes
1answer
52 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 ...
8
votes
1answer
356 views

General purpose slow/unique hash routine for dup checking of private data, without storing the data itself?

I am wondering if there is a percentage of uniqueness known to be lost with every repeat of various hash routines, like MD5, SHA1, and how that might compare with other algorithms. If theoretically I ...
8
votes
2answers
1k views

How can a passphrase with 256 bits of entropy practically be constructed & memorized?

Quoting Wikipedia: A password with, say, 42 bits of strength calculated in this way would be as strong as a string of 42 bits chosen randomly[.] Assuming that interpretation is correct, combined ...
2
votes
3answers
251 views

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 ...
1
vote
1answer
84 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 ...
2
votes
1answer
83 views

How many bits of entropy does an identifier contain?

According to https://www.owasp.org/index.php/Insufficient_Session-ID_Length: Assuming that the session identifiers are being generated using a good source of random numbers, we will estimate the ...
3
votes
2answers
113 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 ...
12
votes
4answers
4k 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 ...
0
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2answers
987 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 ...
3
votes
2answers
234 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 ...
10
votes
1answer
206 views

Where does a Hyper-V guest get its entropy when generating a certificate authority key pair?

According to findings by the EFF's SSL observatory, there are "tens of thousands of keys that offer effectively no security due to weak random number generation algorithm." My understanding of that ...
2
votes
3answers
295 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 ...
3
votes
2answers
269 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. ...
14
votes
4answers
7k views

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 ...
34
votes
9answers
9k 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?
22
votes
3answers
5k views

Is it appropriate to use haveged as a source of entropy on virtual machines?

While looking for solutions to entropy pool depletion on virtual machines, I came across an interesting project called haveged, which is based on the HAVEGE algorithm (HArdware Volatile Entropy ...
0
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1answer
80 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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2answers
563 views

Can I use hardware random number generation on my computer? Am I already using it?

A lot of computer security depends on encryption: SSL connections, TCP packet sequencing, encrypted files, etc. These depend on random number generation to ensure that attackers can't guess the ...
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votes
1answer
108 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 ...
2
votes
2answers
559 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 ...
2
votes
0answers
123 views

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 ...
2
votes
1answer
450 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? ...
0
votes
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 ...
2
votes
2answers
1k 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 ...
21
votes
2answers
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 ...
10
votes
4answers
2k views

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 ...
29
votes
5answers
2k views

Are there any guidelines for passwords that need to be read out loud?

I recently saw the movie Olympus Has Fallen. Like in many action movies, at the end a missile is launched, and the hero (Mike Banning, played by Gerard Butler) has 60 seconds to recall the launch in ...
4
votes
2answers
171 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: ...
0
votes
1answer
91 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 ...
17
votes
2answers
579 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 ...
4
votes
2answers
277 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 ...
12
votes
3answers
2k views

Why are passwords limited to 16 characters?

What is the reason that most websites limit to 16 characters? I would have thought the longer the password the more difficult it makes it for someone to crack it? Is it something to do with hash ...
3
votes
2answers
298 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: ...