Entropy is a measure of information content, which can be viewed as the uncertainty in a random selection.

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How feasible would it be to generate 300 million public key pairs in 8 hours?

Assume there is a hypothetical situation where one would need to generate hundreds of millions of public key pairs of reasonable strength in a limited time. What would be required in terms of ...
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What is the difference between Shannon entropy and saying that tossing a 6-sided die 100 times has more than 256-bit entropy?

I'm confused. I thought that tossing a 6-sided die 100 times had a greater than 256-bit entropy because $6^{99} < 2^{256} < 6^{100}$. (A similar concept appeared in this XKCD comic, where ...
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Testing PRNG quality from ECC public keys?

Having a large set of ECC public keys $P_i = n_iB$ on a fixed curve $E$ over a prime field, is there a way to determine if coefficients $n_i$ were generated using a bad PRNG? In other words, can a ...
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179 views

Chopping off SHA256 entropy?

I have a NoSQL key-value database. I want to insert couple million of records to it. For the key generation, I'm, using a prefix (something like data-one-) and ...
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374 views

How to crack SHA256 only letters

I recently created a program that hashes a password using SHA256 and potentially using salt. How can I crack that if I know that the password only contains lowercase letters?
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761 views

TRNG vs PRNG - Entropy?

How much more entropy gives a Hardware Random Number Generator or True Random Number Generator compared to a Pseudo Random Number Generator? I know it depends on which TRNG is used, but I'm thinking ...
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1answer
571 views

Can hash functions improve a lousy PRNG?

If I have a poor PRNG, could a cryptographically secure hash function make a better output? Say the PRNG can produce as much numbers as you wish, reasonably random, but not good enough to be used in ...
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85 views

Better lower bound on min-entropy

In “Randomness Condensers for Efficiently Samplable, Seed-Dependent Sources” by Dodis, Ristenpart, and Vadhan (PDF), I have seen the statement that: any tuple of distributions $(X,Z)$ is $ε$-close ...
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213 views

How many bits of entropy does an elliptic curve key of length n provide?

A FAQ for an open source project makes the claim: Indeed, an elliptic curve key of length n provides $n/2$ bits of security. I have two questions: What is the practical difference between "...
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1answer
247 views

Will hashing over and over eventually give the same hash?

There are many cases in maths where doing the same thing over and over again will bring you closer to a value. Derivation of polynomials is the striking example: no matter what you start with, you end ...
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190 views

Meaning of entropy of a bitstring in NIST SP 800 - 90A

From NIST SP 800 - 90A from January 2012 (see http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf), page 6: For the purposes of this Recommendation, an n-bit string is said to have ...
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1answer
127 views

Is randomsound for increasing entropy pool not doing what it is supposed to do?

I am using randomsound because I thought it would be a good idea to inject some additional entropy into the entropy pools of my linux machines (clearly those machines have a corresponding sound card). ...
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100 views

HKDF entropy extraction

I collect entropy from the following sources: system_entropy = System provided crypto entropy stream (CryptGenRandom on Windows) user_entropy = User-provided entropy - in a form of a byte stream of ...
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1answer
68 views

Why perfect secrecy can be ensured when a plain message and a cipher-text based on one-time pad are correlated?

First, some well-known results are as follows. For random variables $X$ and $Y$, we have $$H(X,Y) \leq H(X) + H(Y).$$ The equality is achieved when $X$ and $Y$ are independent. Second, in one-time ...
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2k views

If you hashed a hash an infinite number of times would you end up with a unique hash?

If you took a hashing algorithm for example MD5 and repeatedly passed the output hash back into the algorithm an arbitrarily large number of times would you eventually end up with one unique hash? My ...
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223 views

Has human-generated entropy ever been a real problem?

I know the topic of human brains generating random numbers has been discussed here and in Cognitive Sciences before, but I am interested in a particular part of it: In an introductory book to ...
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677 views

Is this a good entropy collector and whitening technique?

I'm just reviewing a program someone wrote to provide high quality random data using an entropy collector and a hash based whitening technique. I'll try summarize the process: Collect entropy from ...
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1answer
52 views

Errata for NIST SP 800-63

I'm looking through the latest version of NIST SP 800-63, and there is a table (Table A.1) in the Appendix that supposed give the "entropy" of a password for a 94 character alphabet for various ...
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1answer
104 views

Randomness in generation of Virtual Machines from pre-built Image [closed]

I am studying Multi-Tenancy vs. Virtualization, and I got thinking about randomness, true randomness, virtualization etc, and I couldn't find anything on it. From what I gather, ...
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1answer
167 views

Should I remove these use cases of MD5/SHA1 from my program?

I have a web app (a register and login system) written already but i am now improving it. One of its design goals was high security. I have some use cases of md5 and sha1 in it and now i am in doubt ...
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3answers
1k views

Estimating random number entropy for input into 256 bit hash

Assuming a random number generation process outputs lots of numbers between 0-9. First I gathered up a bunch of the numbers, converted them to binary and created a bitmap. Not so random as you can ...
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11answers
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Algorithm: How to use x and y mouse movement co-ordinates to generate random data?

Background: I'm making a program for fun as a learning exercise. I want to generate some actual random key material (not pseudorandom) from a JavaScript program. For my program is just for encrypting/...
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1answer
105 views

Is this JS library using openssl genrsa -rand improperly?

pem, a JS wrapper around openssl, has the following code in it: var params = ['genrsa', '-rand', '/var/log/mail:/var/log/messages', keyBitsize ]; Am ...
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1answer
700 views

How to accurately calculate Unicity Distance for English?

The Unicity Distance for the DES cipher is around $8.6$ characters, and can be calculated using the $U=H(k)/D$ formula, where $D = R - r$, and where $R = 8$ is the number of bits in a byte (ASCII is 7 ...
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1answer
170 views

Noisiest RF band for random number generation

I've been looking into the difference between PRNGs and proper RNG techniques. One that I particularly like is the idea of tuning a radio to a certain frequency and bandwidth and just listening to the ...
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711 views

Is there a kind of OS entropy pool on Windows systems? [closed]

I am wondering if Windows provides an equivalent of /dev/urandom from linux ? Or any kind of system entropy pool ?
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159 views

Entropy in relation to computer security [closed]

I am going over some lecture notes and my lecturer is off sick, so not sure where to turn. There is this equation that I cannot understand as it's given with a couple of examples. I was hoping ...
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CSPRNG's (ELI5) What's the purpose of multiple seeds/ regenerating sources of entropy (i.e. /dev/random)?

Why is there a need to generate more than one high entropy seed? It would seem like if the original source of entropy is high quality, than some 512 bits should be more than enough to seed a CSPRNG ...
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318 views

How do you test randomness?

Suppose I receive a list of 1 million coinflips, and I want to know how likely it is that the list was randomly generated. My first thought would be to count the number of heads and tails, which ...
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1answer
422 views

How to calculate the entropy of passwords? [duplicate]

Here is a cartoon about password entropy. http://xkcd.com/936/ I dont quite understand how the entropy is calculated in the cartoon assuming they are calculate correctly. But in general, I dont have ...
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Could RDRAND (Intel) compromise entropy?

I was recently discussing the issue of RDRAND in Intel chips and the whole issue about how NSA could potentially be influencing Intel to weaken or create backdoors in their design. This petition was ...
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Entropy of two concatenated random values

In this Intel blog posting, the author claims: The amount of work required to brute-force predict a random value that has n bits of entropy is $O(2^n)$. If you concatenate two values together, the ...
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96 views

Entropy Loss of KDFs

Am I losing any entropy when using KDFs, such as the ones in NIST Special Publication 800-108? For example, can I derive 128-bit session keys from a (uniformly random) 128-bit master key?
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1answer
110 views

run length testing [closed]

Looking for guidance/references with/about calculations: I am designing a widget that creates N-bit binary sequences. My customers target spec for the sequence's minimum entropy is X bits/bit. I plan ...
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1answer
283 views

PAK Diffie-Hellman vs. sharing high-entropy key

In order to setup an authenticated shared secret key between two clients, I am faced with the choice between two possibilities: Let users set a (low-entropy) shared password and then perform some ...
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160 views

CSPRNG that cannot be used as random extractor

Are there any specific CSPRNG's that cannot be used as randomness extractor within a TRNG? In other words, can you simply provide enough entropy gathered from a good entropy source as seed in any ...
8
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1answer
304 views

Is there a cryptographic function or system in which it becomes HARDER to break as time passes?

Is there a function or system which is time depending in which the effort required to brute force the decryption increases with time? It is easy to break encryption from many years ago because ...
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211 views

Collecting entropy: can I use timing of reading as a separate source from the reading itself?

I'm implementing an entropy gathering program. For that I collect 2 bits from two gpio-pins connected to a random source. I whiten this stream of bits using the von Neumann decorrelation algorithm. ...
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104 views

Protocol: Coin Flipping over phone

Protocol: Coin Flipping over telephone Hypothesis: Alice and Bob have agreed: a one to one function $f$ which is easy to compute $f(x)$ from $x$ and while given any value $f(x)$ it is nearly ...
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259 views

What is the entropy per Diceware word if a random symbol is inserted into a random position in the word?

On the Diceware page is this little gem: For extra security without adding another word, insert one special character or digit chosen at random into your passphrase... Inserting a letter at ...
2
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1answer
183 views

Is it possible to get better randomness by using multiple PRNGs?

I don't know if this question even makes sense, but: Is there be any benefit or impact to some sort of hierarchical (e.g. a PRNG drives the decision for which PRN to pull from a set of PRNGs) or ...
3
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2answers
136 views

Could scrypt salts contribute to entropy if passwords & salts are only stored in human memory?

I'm unsure of how exactly the salt is manipulated by scrypt and its potential contribution if any to overall password entropy if passwords & salts are stored only in human memory for a ...
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1answer
740 views

Mixing Entropy Sources by XOR?

Assume that I have two sources of entropy (say, a hardware RNG and a CSPRNG) and that the two sources are independent (do not know anything about the internal state of the other RNG). Can I mix them ...
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1answer
6k views

Calculation of time to crack SHA-256 hash

A problem is given: 1 million users are authenticated with 9-digit PIN codes (e.g. 343534643). The PIN values are stored as hash values in a database. The hash is SHA-256, and is computed as: ...
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229 views

Padding to increase entropy and size of (otherwise) small JSON objects

Maybe this better fits, the security stackexchange... I'm building a web API. We want to enable some relatively simple encryption, instead of going full-blown OAuth2 (which frankly, IMO, sucks). So I ...
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Tactics available to help prove security of a new system?

I believe that the accepted tactic to "prove" a system as secure is to allow the crypto-community to review it and if no vulnerabilities are found over a long period of time (5 or 6 years), then a new ...
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Generating Encryption Keys from Biometric Fingerprint Templates

How would one go about generating Encryption Keys from Biometric Fingerprint Templates extracted from a fingerprint using either Griaule SDK or DigitalPersona SDK or any other SDK that will return the ...
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676 views

Seed / reseed DRBG too often?

There are limits to how much you can use a the DRBG before you have to reseed it, but are there any limits to how much you must use it before reseeding? Take the following scenarios as an example… ...
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1answer
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Is AES key length a size of the key or entropy?

While educating my self I'm having hard time to understand what an 128 bit AES key actually means? Is it a key length or entropy? Please explain to me trough following example (assuming AES): ...