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# Questions tagged [cryptanalysis]

Analysis of individual security aspects of a cipher or algorithm, not the security of a cipher or algorithm in general (which would lean towards “algorithm-design”).

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### Can linear congruential generator be used in public-key cryptography?

The question is not about generating pseudo-random numbers with linear congruential generator. I'm exploring the possibility of using a Linear Congruential Generator (LCG) in the context of public-key ...
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### Can Index of Coincidence be used for ciphertext containing letters, numbers, and symbols? (All characters in cipher are from ASCII table)

I have been trying to figure out how to approach performing cryptanalysis on the following ciphertext, but am stumped on whether I can use classical techniques such as IoC to derive useful information ...
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### Cryptanalysis of xorshift + multiplication mixer

Suppose we have a $2w$-bit integer $s$, a $2w$-bit odd round key $k$, and some constant $c$ then we can define the following permutation: ...
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1 vote
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### Could this method allow two people using weak cryptography to bootstrap their way to unbreakable cryptography (e.g. otp)

Encryption schemes are usually explained to the general public in terms of "time required to break" where strong encryption like AES-256 should in theory take millions of years. Given that ...
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### How to find openSSL's AES T-table location for cache side channel attack

Let us assume I have a physically-indexed last-level cache, which is shared between the victim and adversary. Both the victim and attacker have their own copy of openSSL library in the caches. Victim ...
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### How to prove the conclusion " linear operation $\mathsf{XOR}$ does not affect the division property"?

Division property is proposed as a generalized integral property at Eurocrypt 2015 by Yosuke Todo in his paper Structural evaluation by generalized integral property, And in paper Integral ...
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1 vote
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### Is generating random blake256 hashes until packed points is on the curve, a safe algorithm to avoid the discrete log between the generated points?

I know there’re many questions that ask how to safely HashToCurve, but I want to know if the method I found in an actual implementation is secured against the ...
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1 vote
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### Choice of algorithm for ECDLP when you have information regarding private key

Okay, I have a ECDSA public key $P$. The curve is arbitrary and not necessarily secure. The finite field of curve, $q$, is a $315$ bit prime. I know the following information regarding key: The ...
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### Is using the polynomials ring $\mathbb{Z}_{2}[x]/(x^8+1)$ in RLWE secure against brute force attack?

Given the ring $R_2=\mathbb{Z}_{2}[x]/(x^8+1)$, initiate a public key encryption based on RLWE $(A,b=As+e)$ where all the parameters are selected as polynomials over the given ring. Under the ...
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### Can I prove AES-GCM nonce reuse just from the bytes?

I have AES-GCM output with GMAC tag. The plaintext consists of some bitfields I know the structure of. When I generate input which should only affect timestamps and counters in very specific bytes, I ...
1 vote
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### Does encrypting a billion short and similar jsons with known structure make encryption less secure?

Let's say we have a billion short individual json files with same regular structure: {"name": "<name>", "id": <id>}. Each ...
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### How would I go about reverse engineering a hash function given input string and generated hash

I have a wireless capture of data and it's 12 bit hash. I am trying to identify the actual function that would have generated the hash data. I tried all the generic 12 bit CRC polynomials but none of ...
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### 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 ...
1 vote
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### Is a Shift Cipher with Random Insertions Unbreakable?

Imagine an Encryption Algorithm which applies a classic Shift Cipher (also called Caesar or ROT-X) to a text (with only lowercase [a-z] and the space ...
197 views

### How to identify if a legacy encryption algorithm used in my programming language is secure?

I used an open-source programming language called Lucee / Cfscript that is closely related to Adobe Coldfusion. The default function that developers use to encrypt and decrypt data (usually for ...
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### Impact of Ryan and Heninger's CRYPTO 2023 paper on post quantum cryptosystems

From Schneier's blog, which seems to have been written in response to a somewhat recent Quanta magazine article: The winner of the Best Paper Award at CRYPTO this year (2023) was a significant ...
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### Can I change the radio frequency according to my encryption algorithm?

I know that information can be changed by changing the frequency of electromagnetic vibrations.My question is, can I change the frequency according to my encryption algorithm? That way I can get a ...
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### Can HKDF be safely used as a round function in a Feistel Cipher

Hello my question is it practical to use HKD as a round function in a Feistel Cipher I know you should not roll your own crypto, this is for learning purpose's only. Take a look at my code and let me ...
129 views

### Not understanding elliptic curve scalar multiplication to produce Ethereum address

This is the equation Public key = Private key * G Here, ...
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### Given and encrypted message, is it theoretically possible to decrypt a message without the key or guessing it? If so, what methods could be used?

Decrypting an AES-Encrypted Message Without the Key: A Cryptographic Challenge Summary: I am investigating the possibility of decrypting an AES-encrypted message when the encryption key is unknown ...
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1 vote
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### Is it faster to decrypt than to encrypt in all cryptography systems? [closed]

I am using a cryptography system in which the Feistel structure and permutation cipher are combined. I am amazed by the result; decryption is so much faster than encryption. My system is working ...
63 views

### How to estimate the bias of linear cryptanalysis given the input and output masks

Assume the input linear mask is $a$, and output mask is $b$，for a block cipher $F$ with $r$ round,How to accurately and quickly estimate the bias of linear cryptanalysis? which is \begin{equation*} ...
1 vote
112 views

### Hard decisional problem on bilinear groups

Problem: Given $g, g^a, g^b, g^c \in G$ and an efficient bilinear map $e:G \times G \longrightarrow G_T$, distinguish $g^{abc}$ from a random element of $G$. Is it a hard problem?
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196 views

### Speed comparison of encryption algorithms

I am trying to compare various encryption algorithms in terms of encryption duration, decryption duration, information entropy, NPCR, UACI, and correlation coefficients. I used a Lena 256x256 ...
160 views

### Judgment of Results from NIST Randomness Testing

I am using the NIST suite to test the randomness of binary numbers and I have a 64KB dataset. I am confused with the results in finalAnalysisReport.txt. I have the ...
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1 vote
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### Cryptanalysis of S-box [closed]

Because of implementation constrains, I merge some 4-bit S-boxes to find a 8-bit S-box with good properties such as nonlinearity, resistance against differential and linear cryptanalysis. Does the ...
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