# 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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### How can we know how good a TRNG is?

Imagine that a perfect TRNG generates 100 bits, which are then fed into a high quality PRNG such as ChaCha20, which generates 1000 bits. How many bits of entropy is in the 1000 bits? Depends on who is ...
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### Reversing XOR operation

Consider the XOR operation, $$A = B \oplus C$$ I know $A$ but I don't know $B$ or $C$. Question: Can I get $B$ or $C$ from $A$ ?
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### 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.
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 <...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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. ...
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### 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 ...
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### 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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### Password entropy requirements for online dictionary attacks on OPAQUE?

My understanding is that for PAKE protocols such as OPAQUE (https://eprint.iacr.org/2018/163.pdf), the the adversary has no choice but to just do online attacks on the password. If this is true, I ...
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### How to calculate entropy of a specific cryptosystem?

I want to calculate the entropy of a specific cryptosystem such as the Caesar cipher or Vernam cryptosystem etc but I don't quite understand how to do so. Any help?
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### What are the key difference between Shannon entropy and Guessing Entropy?

Any body can explain, what are the key differences between Shannon entropy and Guessing Entropy? In some research I got entropy uses binary search or balanced Huffman tree. Guesswork uses linear and ...
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Previously I thought about a pair of 8-bit uniformly distributed random numbers $(a,b) \in \{0,1\}^8$, and $X$ to be bitwise XOR, $Y$ to be 8-bit addition. But it turned out that revealing $a \text{ ... • 573 2 votes 3 answers 242 views ### What does$(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 ... • 573 2 votes 1 answer 122 views ### 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) ... • 183 0 votes 1 answer 74 views ### 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 ... • 1,241 3 votes 1 answer 199 views ### 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 ... 2 votes 1 answer 2k views ### 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 ... 8 votes 1 answer 211 views ### 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 ... • 15.7k 1 vote 0 answers 56 views ### Could anybody help by applying a secure multiparty secret sharing scheme? Suppose that we have a multi-secret sharing scheme as it is described in the literature Let there be$I$agents and say that$S$is the space of the (uniform) random variables$s=(s_1,s_2,\cdots,s_I)\...
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Is the $t$ out of $n$, namely $(t,n)$, threshold in the secret sharing scheme related to the entropy of the random variable that is shared according to the scheme? What changes in the secret sharing ...