# 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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### 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 ...
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### 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: ...
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### 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 ...
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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 ...
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### What does $(a+b) \bmod{256}$ and $a$ XOR $b$ reveal about $a, b$?

Say $a$ and $b$ are some uniform random $8$ bits so that the entropy of $a$ and $b$ is 8 bits each. If I show you $(a+b) \bmod{256}$ and $a$ XOR $b$, then what can you tell about $a$ and $b$? Or how ...
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### What is the methodology for selecting symbol bit length and window size when performing Shannon Entropy Analysis?

When performing Shannon Entropy analysis on something like an RNG or a file, you must: Select a symbol bit length and number of samples would will perform analysis on at a time (IE: windows size) ...
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### Mapping number into number with big algorithmic entropy - how to do it?

I need to parameterize some PRNG, let's assume I need 32-bit numbers. But when numbers doesn't look very random it gives bad results. The creators of SplitMix had similar problem (note that from what ...
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### Extractor and Min-Entropy proof

I'm following a course that speaks about cryptography. In this course we talked about Min-Entropy ($H_{\infty}$) and Extractor. To show that an extractor $Ext:\{0,1\}^n \rightarrow \{0,1\}^l$ that ...
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### Which hashing function is good enough for session IDs?

Background I'm building a URL shortener, and the URL to shorten may contain a SessionId. For the URL shortener to not compromise the security of the SessionId, I must use a shortening strategy that ...
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### Where did Whitfield Diffie say "If you can make random numbers, you can have a private conversation"?

I've seen the following (alleged) quotation on this site and other places:- If you can make random numbers, you can have a private conversation. -Whitfield Diffie. Yet we (Google & me) can't ...
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### Difference between Non-uniformly random and Uniformly random

I am reading up on Key Deriving Functions (KDF) and in a section of the Real-World Cryptographic book by David Wong, a comparison is being made with Pseudorandom number generator (PRNG). And one of ...
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### Signature of low-entropy data: can they be faked?

I am working on an application where I have a physical product identification label containing a block of public, low-entropy data (~50 bytes) such as serial number and other info, all readily ...
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### To what degree does a high PKBDF-HMAC-SHA1 iteration count compensate for a weak passphrase entropy?

Lost a LUKS-encrypted laptop at the end of 2019 and now trying to figure out the odds of a very sophisticated attacker being able to break in. The LUKS container was created mid-2017 with LUKS1 ...
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### What can chaos provide to cryptography?

Chaos-based cryptography is facing a lot of criticism, however, some people argue that it can provide many cryptographic primitives, such as stream ciphers, block ciphers, hash functions, public-key ...
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### Estimation of the entropy of keys derived from truly random numbers

NOTE: This question is based on my assumption that $X$ is a "truly random number" if and only if it's length measured in bits is equal to its entropy measured in bits. In other words, when ...
1 vote
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### l-Diversity logarithm

I wanted to make a little example for anonymization evaluation using l-Diversity. For that I'm using the following formula for Entropy l-Diversity ($E$ is the equivalence class, $S$ are all possible ...
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### Don't human generated passwords used with key derivation functions reduce the security of symmetric encryption?

The key size for AES is chosen as 256 because that's considered the minimum keysize which can protect against a brute force attack - i.e. $2^{256}$ tries. However, in practice, for a lot of ...
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For example, for a randomly generated password of 28 lowercase letters, which is about 128 bits of entropy, how would adding a space after every four characters affect it? ...
1 vote
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### Randomness extraction on correlated data in TRNG

True random number generator (TRNG) designs I read about mostly consist of two digital stages: Low-frequency sampling (of a physical noise source) Randomness extractor The noise signal is sampled at ...