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Questions tagged [entropy]

Entropy is a measure of how predictable the outcome of a random process is, or how much uncertainty one has about an unknown quantity in one's state of knowledge, defined in terms of the probability distribution on possible outcomes or quantities.

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Password entropy, or at least establishing reasonable upper and lower bounds on it

I use, and have always used, cryptographically secure randomness as a source for my passwords. However, the final coding of that random stream into something a website will accept as a password has ...
2 votes
1 answer
99 views

Does the actual length of a password or salt provide any additional entropy to that contained within them?

I refer to the following wiki description of the Argon2 key derivation function:- ...
7 votes
4 answers
969 views

Can a deck of cards be used as a practical source of cryptographic randomness?

This is not a duplicate of Entropy measurement from shuffled cards, as this concerns use of cards as a cryptographic entropy source, rather than calculating entropy from some number of cards. The ...
3 votes
1 answer
564 views

Enumerating the bias of NIST and Pearson randomness extractors

The following is an extract from a paper about using your mobile phone as a true random number generator (TRNG). The mobile phone bit is incidental to this question though. I'm interested in the ...
5 votes
1 answer
181 views

Are USB TRNGs still useful given the recent /dev/(u)random merger?

I'm referencing Jason A. Donenfeld's Random number generator enhancements for Linux 5.17 and 5.18 available here. In summary:- significant outward-facing change is that /dev/random and /dev/urandom ...
0 votes
3 answers
375 views

How to calculate the entropy for a fixed length random passwords which has restrictions on the type of characters used

If we have a set amount of usable characters, but no other restrictions on the potential characters in a completely random fixed length password, we can easily calculate the entropy by doing: $\log_2(...
3 votes
1 answer
184 views

equivalence between entropic perfect secrecy and single probability

i'm new to information theory. I know the standard perfect secrecy definition: $$ P(M=m|C=c) = P(M=m) , $$ for all $m$ and $c$, respectively the message and the cypher. Now, i can use the entropic ...
3 votes
1 answer
697 views

Cracking a key using a combination of partial keys

As part of a cryptanalytic attack I've carried out, I used a divide-and-conquer strategy to divide the secret key $k$ into several equal-sized partial keys $k = {k_1, k_2, ...}$. The attack works ...
5 votes
3 answers
933 views

Is this probability negligible?

Let $X \in \{0,1\}^{2n}$ be a uniformly distributed random string and $Y \in \{0,1\}^{2n}$ such that $H(Y) = n$. Does this imply that $Pr(X=Y) = 2^{-n}$? If it's not, is this probability necessarily ...
1 vote
2 answers
114 views

Relation between seed entropy of a CSPRNG and the output entropy

Since Linux 5.18, the internal state of the ChaCha-based CSPRNG is a 256 bits (32 bytes) BLAKE2s hash. There is also a fast key erasure mechanism which reseeds the CSPRNG every minute (source). I know ...
3 votes
2 answers
786 views

How much entropy is lost due to collision?

If entropy is hashed with SHA-256 for example, and the input has exactly 256 entropy bits, how much entropy is reduced after hashing due to collision? Is there any reference that explains how to ...
15 votes
2 answers
3k views

The effect of truncated hash on entropy

Suppose I have a 128-bit random binary string (128 bits of entropy), then I hash it using SHA-256, then I take the first 128 bits of the output hash. Does the taken bit string still have (almost) 128 ...
12 votes
1 answer
7k views

Relation between entropy and min-entropy

I understand that the entropy is the number of bits that can encode a set of messages. However, I don't understand what the min-entropy is and how it is related to entropy. Let's describe a simple ...
3 votes
1 answer
267 views

Entropy extraction from a Zener diode TRNG

My project is to build a true random number generator that relies on the avalanche effect in a Zener diode. This for a messaging device that uses one-time-pad encryption. Reading about similar ...
0 votes
0 answers
46 views

Entropy output from 256-bit Argon2 input [duplicate]

I would like to deterministically derive two different 256-bit keys from a single passphrase -- one used as an ECDSA private key, the other as a symmetric key for AES-GCM. Would a KDF output ...
1 vote
2 answers
88 views

Should I Test A PRNG Using A Fixed Entropy Source For Its Seed?

I want to test a C implementation of Hash_DRBG—which test_demo.c file I will modify to produce random binaries indefinitely to STDOUT as to be used by piping its output—using DIEHARDER for a research. ...
2 votes
1 answer
116 views

Alternative definition of secret sharing using entropy

I ame reading the paper "Secret-Sharing schemes: A survey" by Amos Beimel. Here there are two definitions of secret sharing. The first one states:\ A distribution scheme $\langle \Pi,\mu \...
3 votes
1 answer
440 views

Is there any way to measure entropy of encryption algorithms in python?

I am new to cryptography and I am trying to find a way to measure ciphertext entropy of encryption algorithms such as AES, Chacha20, etc for a school project. Is there any way to do it on Python? I ...
5 votes
4 answers
1k views

How to compute the dataset size required by dieharder tests?

I am trying to use the dieharder random number test suite. However, this suite requires massive amount of data (this paper claims 228GB for no rewinding for every test) for most of the tests. I'd like ...
1 vote
1 answer
270 views

How strong should my password manager's master password be?

I use an offline password manager, I want to use a future proof very strong master password and I'm going to choose one of these options from the EFF's large wordlist, a randomly chosen 8 word ...
1 vote
1 answer
116 views

Manual entropy collection from sources with an arbitrary base

I'm writing a tool for manually collecting entropy from sources like coins and dice, and I'm wondering how to best deal with the case where the desired number of bits of entropy is not representable ...
0 votes
1 answer
56 views

How large should a seed possibility space be to generate a secure ECDSA key pair?

I have a function that generates a random 16 character length (upper + lower case letters plus numbers) seed password: ...
0 votes
2 answers
146 views

From Entropy's perspective how Encryption affects a Message?

How Ciphers, specifically, Substitution Ciphers and Transposition Ciphers manipulate the Entropy of Plaintext w/wo the aid of Entropy Source? Reversely, how Decryption manipulates the entropy of ...
5 votes
2 answers
32k views

Calculation of time to crack a 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: ...
1 vote
0 answers
185 views

Can someone give a comprehensive guide on how to run NIST SP 800 90B entropy assessment c code in windows? [closed]

I am trying to run the github code in windows 11. I don't know what all I need to install in my laptop to run the C++ code. It would be a great help if someone can point out the steps to run the code.
3 votes
1 answer
234 views

Does PBKDF2 HMAC 512 really only produce a maximum of ~128 bits of entropy? Regardless of input?

Andreas Antonopoulos effectively states: an input of 256bits of entropy into PBKDF2-HMAC-SHA512 will ONLY output a 64 byte hash containing ~128 bits of entropy. He states the algorithm essentially ...
3 votes
2 answers
144 views

A HRNG that is NIST 800-90 compliant is not suitable for use for OTP generation right?

A HRNG that is NIST 800-90 compliant must use a DRBG in some way regardless of whether it adheres to a RBG1, RBG2 RBG3(XOR), or RBG3(RS) construction. This violates the requirement that the OTP is ...
3 votes
2 answers
702 views

Why does NIST SP 800-90C RBG3 construction require XOR or reseeding a DRBG with a physical entropy source to produce full entropy?

NIST 800-90C defines 3 classes of random bit generation (RBG) constructions: RBG1, RBG2 and RBG3. All constructions must include a DRBG from NIST SP 800-90A. The particular construction in question is ...
3 votes
6 answers
4k views

Would sending audio fragments over a phone call be considered a form of cryptology?

I have been wondering if sending audio fragments over a phone call would be considered a form of cryptology. Let's say that you own two mobile phones and say that one of your phones is on the Verizon ...
5 votes
3 answers
513 views

Maximum entropy of a hash function?

Let $H(h,k)$ be the expected entropy of some random oracle $X:\left\{0,1\right\}^h \to \left\{0,1\right\}^k$, where $h$ does not necessarily equal $k$. Then, is it true that $\lim\limits_{h\to\infty}...
1 vote
0 answers
106 views

Predicting compromised OpenSSL 3.0 DRBG

The OpenSSL 3.0 rand function's DRBG uses the getrandom() system call to get 48 bytes of secure entropy from the kernel. It also ...
8 votes
3 answers
9k views

Using 32 hexadecimal digits vs equivalent 16-character string password

Assume I'm using a cryptographic algorithm to pseudo-randomly generate a string that is specified to be 16 characters long. The string will be used as a passphrase when encrypting a file. So, for ...
2 votes
0 answers
40 views

Proving the minimal entropy of Dilithium-QROM?

I am working with the securit yof CRYSTAL's Dilithium signature in the QROM. I am working with Kiltz et al.'s approach through lossy ID-schemes and looking at the proof of minimal entropy for the $DFS[...
4 votes
0 answers
401 views

Use of scrambler LFSR for randomness extraction of semi-random source

I am using a linear feedback shift register (LFSR) in a scrambler configuration as a randomness extractor for a weakly random source. This source is semi-random (aka. Santha-Vazirani source): the bits ...
0 votes
0 answers
73 views

Hashing a seed full of entropy with a cryptographic hash function and emiting a key with the same size as input: can a collision attack occurs?

I read this in the documentation of HighwayHash: By contrast, 'strong' hashes such as SipHash or HighwayHash require infeasible attacker effort to find a hash collision (an expected 2^32 guesses of m ...
5 votes
2 answers
592 views

Conditional entropy between ciphertext, plaintext and the key

If we have a (possibly imperfect) cryptosystem that generates ciphertext $C$ from plaintext $P$ and key $K$, we have: $H(C, P, K) = H(C | P, K) + H(P, K)$ where $H$ is entropy. My question is why ...
43 votes
2 answers
33k views

What is entropy?

We discuss a lot of topics and use measures of entropy to determine how difficult it is for an attacker to be successful. What does entropy mean in the context of cryptography? How is entropy ...
3 votes
2 answers
374 views

How to calculate probability of cracking a password from entropy?

I am working on a project for my maths assessment where I research the effect of complexity and length on a given password. Currently, I am working on calculating the probability of guessing a ...
1 vote
2 answers
234 views

Entropy for TLS 1.2: how much is needed for linux servers?

I am trying to fix issues with a server where the server keeps freezing up and needs to be restarted. I recently started hearing about entropy and it importance to secure tls keys in linux. The one ...
2 votes
2 answers
1k views

Why is AES ciphertext entropy always close to 8?

I have three binary files: 31744 byte length, 5712980 byte length and 10806008 byte length. The alphabet is all 256 symbols from 00 to ff. I compute the Shannon entropy, replacing probability with ...
17 votes
5 answers
4k views

Examples of frauds discovered because someone tried to mimic a random sequence [closed]

[Moderator note: this question now lives there] So, I'm preparing a talk about the well known fact that humans are bad at the task of generating uniformly random sequences of numbers when asked to do ...
3 votes
2 answers
950 views

Entropy of a counter

I wondered whether my understanding of entropy is correct, that a 256-bit counter that starts at 0 and counts to 2^256 - 1 by a <...
1 vote
1 answer
292 views

Can I use a cryptographic hash function such as sha256 for Randomness Extraction [duplicate]

I want to transform a semi random input to a shorter, uniformly random bit string. Assuming there is enough entropy in the semi random input, can I use a collision resistant hash function to extract ...
4 votes
2 answers
297 views

Are the GPS coordinates a good source of entropy?

Are the GPS coordinates (latitude and longitude) a good source of entropy? If yes, why? If no, why? The question would investigate on the fact if the GPS location data can be used as source of entropy ...
1 vote
1 answer
119 views

Hashing a seed together with a block counter and using as a encipherment scheme: Will this have the same security in bits as the seed used?

A user of this forum said that the whole entropy of a seed goes to the hashed result if using a counter and also that is suitable for key generation even if the internal state or digest size of the ...
6 votes
4 answers
2k views

Bits of entropy needed to choose a random element from a list?

Suppose I want to choose a random element from a list of size $2^n$, for any integer $n$. (Here, random is to mean an equal probability of selecting every item.) My intuition says I'd need $n$ bits of ...
1 vote
0 answers
371 views

Configuring entropy source for OpenSSL [closed]

I'm using OpenSSL 1.0.2 and FOM 2.16 and am trying to figure out a way to draw entropy from Intel (RDRAND/RDSEED) if it's available, and from the Linux OS (/dev/random or /dev/urandom) if it's not. ...
13 votes
3 answers
8k views

What happens to entropy after hashing?

What happens to entropy after hashing? Suppose you have a key with entropy $k$. Can entropy $k$ be increased by hashing the key?
2 votes
2 answers
110 views

How does combining data affect the resulting file entropy?

If i add a password which has (X) bits of entropy as a tag to a picture which has (Y) bits of entropy, will the resulting image have an entropy equal to (X + Y) ? How many bits of entropy i get if i ...
0 votes
1 answer
356 views

Does hashing a secret/seed make it effectively 2X less secure?

In many cryptocurrency projects I noticed that 32-byte seeds/secrets are hashed to arrive at new 32-byte keys. The reason why is because you can then, with the addition to an index, use the same seed ...

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