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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14 views

How to break transposition cipher?

how to break a transposition cipher, especially a turning-grille-cipher? For example: $\begin{array}{rrrrrr} T & E &R& E & W& E \\ ...
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Is there practical Attack on A5/1 Cryptosystem?

There are several and several attacks on A5/1 Cryptosystem, but most of them are impractical. In 2008, Elad Barkan , Eli Biham and Nathan Keller release a practical attack on GSM. Is there any ...
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What is degree of state bits and how do i count it?

in the this paper,section 3,autors attack hamsi-256.Also they explain the weakness that are exploited.Im not so good at math,and also not native english speacker, so i dont understand term "degree of ...
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Why is this attack complexity equal that exact number of bit operations?

in the this paper,section 3,autors attack hamsi-256. Im trying to make a parametrized version, so i need to understand how do they estimate the complexity of attack in bit operations,that reads as ...
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How to extract encryption and MAC keys using KDF (X9.63) defined by javacardx.security.derivation [migrated]

As per Java Card v3.1 new package is defined javacardx.security.derivation https://docs.oracle.com/en/java/javacard/3.1/jc_api_srvc/api_classic/javacardx/security/derivation/package-summary.html KDF ...
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Why isn't there a final permutation on SPN-based ciphers?

I am doing some research on differential cryptanalysis. Most people who are familiar with that cryptanalysis technique do know the tutorial from Heys (Heys Tutorial). I came currently to the question, ...
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How to extract the keyword from a mono-alphabetic substitution cipher

I am a beginner to cryptography and I have the following question. I know that to extract plaintext from a mono-alphabetic substitution cipher I can perform shifting the characters by $n$ times until ...
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AES-CTR key reuse attack with same IV and known plain text [duplicate]

this is from an IT Security exercise which my friend and me cannot solve. Given 2 AES-CTR stream-cipher encrypted files Same known initalizing vector Same (unkown) key Same 128bit Counter ...
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Can we retrieve his private key using his public key in ECC?

A paper wallet is the name given to an obsolete and unsafe method of storing bitcoin which was popular between 2011 and 2016. It works by having a single private key and bitcoin address, being printed ...
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What is the difference between PKCS1 v1.5 and PKCS7? Is PKCS7 a superset of specifications in PKCS1 1.5?

I have a requirement wherein we have to verify the PE binaries generated for an aarch64 platform. These binaries are then signed using the opensource sbsign tool ...
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2DES and 3DES against a DES build with complimentary

I saw this complicated question and I am not really sure about it, would appreciate your view on it. Is the following build stronger than 2DES or 3DES with 2 different keys (or even normal DES)? $...
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Is this the right way to implement ElGamal scheme over Elliptic Curves over prime field? [duplicate]

I'm fairly new to Cryptography, especially elliptic curves in general. I learned to do Point Multiplication, Scalar Multiplication and also programmatically implemented them. But I was trying to do ...
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Any speed up methods for finding the index of a random value produced by the Inversive congruential generator?

The Inversive congruential generator produces random values with: $$x_{n+1} = a\cdot x_{n}^{-1} + b \mod P$$ (special case if $x_n=0$ -> $x_{n+1}=b$) starting with an initial value $x_0$ With well ...
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How would you decrypt an affine cipher with only the ciphertext? [duplicate]

If I have only the ciphertext but the alphabet and the value of a and b are all unknown ... how would I go about this? I understand decryption with the key and alphabet, that is fairly easy but if we ...
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Why is it bad to encrypt the same message M with the same key K in both CTR and CBC modes of operation?

It is apparently not good - more precisely it is not secure - to encrypt the same data message M using the same cryptographic K with a block cipher (e.g. AES, but this is not relevant) in both CTR and ...
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Question about RSA timing attack and a Chosen Ciphertext Attack on RSA

I am quite new to the RSA and I have a couple of questions that confuse me. Q1: A Timing attack on RSA can be prevented _____________________________ A. By performing the “square and multiply” ...
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Using Viterbi algorithm to decrypt Vernam cipher

I'm reading a book on cryptography and it mentions the Viterbi algorithm being used to decrypt Vernam cipher if the same key is used multiple times. According to the book the Viterbi algorithm takes ...
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Hashing using asymmetric cryptography

Every now and then, we read that some hashing function has been weakened or broken, but we almost never hear this for asymmetric cryptosystems like RSA or ECC. That's because while asymmetric ...
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What is linearization attack

I know that In cryptography, the linearization attack is a method of cryptanalysis for block ciphers I am looking for an example of linearization attack couldn't find it online Could anyone ...
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Any shortcut to compute the cipher text for AES applied $n$ times to initial message $m_0$? Or compute $n$ for given $m_0, m_n$?

Knowing all AES parameters (including the key k) with $AES(m_0,k)\rightarrow c_0$ $c_0\rightarrow m_1$ $AES(m_1,k)\rightarrow c_1$ $c_1\rightarrow m_2$ ... $AES(m_{n-1},k)\rightarrow c_{n-1}$ $c_{n-1}...
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Any theory about period length for AES applied to itself?

For example AES-128 starting with a 128-bit message $m_0$ and static 128 key $k$ $AES128(m_0,k)\rightarrow c_0$ $c_0\rightarrow m_1$ $AES128(m_1,k)\rightarrow c_1$ $c_1\rightarrow m_2$ ... continue ...
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Security defined with space complexity

My question is about security defined through space complexity. Suppose I have an encryption function $C=E(K,P)$ for which it can be proved (algebraically) that given $P,C,$ the possible keys which ...
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Is it possible to crack the trifid cipher without the keyword?

I was learning about the classical ciphers and was looking up the methods to break them without the keywords and when I searched up "cryptanalysis of the trifid cipher" I couldn't find anything. I ...
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What is the best way to attack enigma without any a priori knowledge about the plaintext?

I know in great (great great great) detail about how they cracked enigma during the second world war. Looking into it, I decided to have a crack at breaking it. I've come apon a single problem with my ...
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Weakness in double encryption [duplicate]

In the "Introduction to Cryptography: With Coding Theory" by Trappe and Washington, in the chapter about DES algorithm the authors say that: "If double encryption is equivalent to single encryption,...
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Why is double encryption that's equivalent to single encryption no better than single encryption?

In the "Introduction to Cryptography: With Coding Theory" by Trappe and Washington, in the chapter about DES algorithm the authors say that: "if a cryptosystem is such that double encryption is ...
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Lineary of Sbox in DES

I'm not a mathematician, and i would like to understand in the most concise way (if possible) why choosing linear S-Box functions makes the DES algorithm attackable. Thanks
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Property of a good cipher system

In the "Introduction to Cryptography: With Coding Theory" by Trappe and Washington, in the chapter about DES algorithm the authors say that: "In a good cipher system, each bit of the ciphertext ...
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Algorithms for solving systems of quadratic multivariate polynomials

What are the best algorithms for solving systems of $k$ polynomials equations where these are quadratic multivariate polynomials on $k$ variables? I've encountered such systems on my research and I'm ...
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Are there ready-to-use software that can try many decryption techniques on a ciphertext, with no information?

Let's say I receive a 1 MB encrypted file, but I get no information about the encryption method, and no password. The only thing I can guess is that the person probably used a weak encryption method ...
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Enhancing Differential-Linear Cryptanalysis

I'm studying Differential-Linear Cryptanalysis, and I'm trying to understand the context from the article Enhancing Differential-Linear Cryptanalysis by Eli Biham et al. There are some difficult ...
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One way secure DES key transfer to defend against attacker [closed]

I have a question about cryptanalysis. A transmit message to B with radio waves, A use modulator to transmit bytes with radio, B obviously use demodulator. A encrypts and B decrypts the messages ...
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How to break an unknown ciphertext - transposition of some kind [closed]

I've been challenged to crack a code. All I know about it is that is was hand-enciphered, and that it is a transposition cipher of some kind. When I was given it, I started plugging it into my ...
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Most efficient way to crack a monoalphabetic substitution cipher with spacing intact

I've got a cipher I've been challenged to crack by hand. It's a monoalphabetic substitution cipher, and the English spacing is intact, so all of the words are the right size. Is there a more ...
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Building Key Streams from PRNGs

I am reading an intro book about cryptography and the author tries to explain why using pseudo random number generators is vulnerable. Given PRNG equation; \begin{align} S_0 &= \text{seed}\\ S_{...
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In DES : Matsui's notation(LC) vs Biham's notation(DC)

I'm doing linear attack for 8 rounds DES. And I just wondering about the difference between matsui's notation and Biham's notation. In Matsui's paper, numbers bits from 0 to 63 from right to left. In ...
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Understanding LFSR stream ciphers and the content scrambling system

I'm a little confused over how exactly Linear Feedback Shift Registers (LFSR) work, I kind of get it, but not really, can someone help me understand it? I know it XORs bits in a loop against some mask,...
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Finding repeated groups of letters in the Kasiski examination

While doing the Kasiski examination I came to a problem. If there is the following group of letters in the cipher: AA and later on a group AAA is found. Does it count as two repeats or just one? And ...
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Attacks against RC4 when index $i$ is unknown

RC4 uses two 8-bit indices. One, $j$, is key-dependent and secret, and the other, $i$, increments by one for each byte output. The $i$ index is typically considered to be public, but what if the RC4 ...
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Parameters for high density SIS

I am considering the SIS problem of finding $x\in \mathbb{Z}^m$ such that for random $A\in\mathbb{Z}_q^{n\times m}$, $Ax=0$ and $\lVert x\rVert < \beta$ for some $p$-norm and bound $\beta < q$. ...
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Are slide attacks effective if the primitive is sandwiched? And key schedule vs. Even-Mansour

Suppose you have a cryptographic permutation consisting of identical rounds, that makes it vulnerable to a slide attack. But if you sandwich it between two XORs of key material. Is it still vulnerable?...
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Differential cryptanalysis filtering process

This question is a little more implementation based. I am writing my masters thesis on differential cryptanalysis and I wrote a program to evaluate some things about differential cryptanalysis. I ...
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Help, Feedback and Solutions to a problem on a PoC CSPRNG

Background I do not recommend trying to roll your own crypto. This is just a for-fun PoC, which won't be used in any public or private scenario. I am creating a PoC nearly-true random number ...
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How can I guess that a combination of Atbasch and Caesar / Vigenère has been used?

If I'm given a ciphertext, what kind of patterns, index of coincidence, frequency analysis would lead me to guess that it had been encrypted by a combination of Atbasch plus Caesar / Vigenère?
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Applications of machine learning in classical ciphers?

Machine learning is definitely applicable in analyzing simple shift ciphers like Caesar and affine ciphers, as well as substitution ciphers like Vigenère, but is it possible for machine learning to ...
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How are data science and cryptography related?

Are there any interesting connections between the fields of data science and cryptography? Data science involves the use of statistical analysis to analyze data while cryptography also involves ...
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How do discrete logarithm with modulo a prime and a non-prime compare?

Let $c_N = g^i \mod N$ and $N=p \cdot q$ and $c_P = f^j \mod P$ and $P$ a prime We assume $N,P$ has the same bit-length. $P$ is the best type of prime you can choose (e.g. safe prime). $N$ is a ...
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Constructing Differential Characteristics for Feistel Cipher

I have to construct for every i-round of Feistel cipher, for $i \in \{3,4,5,6,7,8\}$, a differential characteristic with there properties: $Pr[\Delta x = a \overset{f_i}{\rightarrow} \Delta y = b] = ...
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Guess the number of characteristics in differential cryptanalysis

I am doing some research on differential cryptanalysis for my master thesis. I analyzed some toy ciphers like the one in the popular tutorial about differential and linear cryptanalysis from heys Link....
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How to check a file was encrypted (really & correctly)

I would like to audit how an implementation of an encryption algorithm is really performed with the following given data of the problem: the encryption mechanism is reversible (this isn’t a signature)...