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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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Breaking the Geheimschreiber using known-plaintext attack

I'm taking an intro course to cryptology, and we have an assignment challenging us to break the Geheimschreiber, or G-Schreiber, using a known plaintext attack. The plaintext is the Latin alphabet ...
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39 views

Cryptoanalysis using Frequency Analysis

Hy community, I have read some documents to decrypt ciphertext without key using Frequency analysis. here are my questions : If the most occurring Char is not 'E' then how do we start? Let's say I ...
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Can neural cryptanalysis be applied to AES?

In this Wikipedia article about Neural cryptography (section applications) it states: In 1995, Sebastien Dourlens applied neural networks to cryptanalyze DES by allowing the networks to learn how ...
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What is the common way to find the distance dual of linear block code?

I know the distance of dual of reed solomon codes is n-k+1 beacuase it is MDS code. Now us consider the following linear block code \begin{equation} C:\mathbb{F}^{k}\rightarrow \mathbb{F}^{n}\\ (c_0,...
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Factoring RSA weak modulus

Given a public key for RSA, I have extracted the modulus which looks like this : ...
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1answer
92 views

$\boxplus$- key addition vs $\oplus$- key addition

GOST cipher , Hight cipher and SEA cipher use key addition based on modular arithmetic addition (module key size $\boxplus$) compared to many ciphers which use arithmetic addition modulo 2 ( $\oplus$)....
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36 views

A key-generator outputs an encrypted string that only changes the second half - what weaknesses could that expose?

The company I work for provides a software solution. The software is licensed and I have access to the license generator (which, BTW rules me out as a cracker - I don't need to crack the license, I ...
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How can I determine the Hill cipher key in this case?

I have been struggling with a Hill cipher problem for many days, without any luck. I have the following ciphertext, which I know is an encrypted excerpt from an Edgar Allan Poe story: ...
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1answer
57 views

$m^b = z^b \pmod{n}$ - single solution $m = z$?

If i have the following equation: $$m^b = z^b \pmod{n}$$ Where all numbers are taken from the multiplicative group $\mathbb{Z}_n^*$. Suppose I know the values $z$ and $b$. Can I state that $z = m$, ...
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Finding generator element for multiplicative group of order $n$ - feasible?

Given a multiplicative group of order $n$, how hard is it to find a generator element (such that all other elements can be expressed as powers of that generator)? What would be the complexity?
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63 views

One-time pad encryption - how does the receiving side decrypt the message?

If a message is sent using one-time pad scheme, which generates random bits in order to, for example, XOR them with the message's bits - how does the receiving side generate the exact series of bits ? ...
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37 views

Using the same RSA key for verifying a website and digital signature

We have the (same) RSA key for verifying a website and for digital signature. A user would send a nonce encrypted using the public key, the websites returns the nonce by decrypting it using the ...
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How to change the following commitment scheme to pederson commitment?

In my question here Zero knowledge set membership protocol The suggested solution allows a prover to choose a commitment $C$. Then, A trusted third party ($T$) can validate if $C$ is valid or not. ...
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Problem while decrypting Hill cipher

I have a plaintext "monday" and ciphertext "IKTIWM" and $m=2$. I want to find the key of the Hill cipher. I made a matrix $$ \begin{bmatrix} a_1 & a_2 \\ a_3 & a_4 \end{bmatrix}\begin{...
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1answer
63 views

Zero knowledge set membership protocol

I read that paper Efficient Protocols for Set Membership and Range Proofs of Camenisch et. al that describes the zero knowledge range proof. The paper applications looks interesting like if you want ...
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Could any one suggest alternative Zero knowledge proof protocol to Schnorr protocol ZKP?

I read that Schnorr protocol cannot be proved zero knowledge on that link: Perfect zero knowledge for the Schnorr protocol? Could any one suggest alternative Zero knowledge proof protocol so a prover ...
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92 views

Unbreakable Hill cipher

Why don't we use hill cipher of 100 × 100? or even bigger. That would be closely unbreakable. The number of keys possible 2 × 2 hill cipher is 157248. for 100 × 100 number is beyond limits.
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Zero Knowledge range proof

I like the idea of a Zero Knowledge range proof. But I read that, to prove my age in a range, a commitment is required by a trusted party (TP) stating my age. How does that work? is the commitment a ...
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66 views

How complex must round constants be to resist slide attacks?

A key schedule that generates round keys by XORing a round constant with the key is linear and can be vulnerable to related key attacks, but let's ignore that for now. Constants are necessary to avoid ...
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50 views

flaw in perfect secrecy of shift cipher?

Why do we say shift cipher is perfectly secure when it is easy to break it (source)? Let's say I have a plaintext. "Australia is a big country"; I encrypt it using a shift of 2; That ciphertext can be ...
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Hamming Weight of Solutions to the Frobenius Equation

My area of research is algorithms for calculating optimal addition chains. I have a new high performance algorithm that at its core benefits from estimating the number of set bits ($v(n)$ Hamming ...
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Why commutativity gives an invariant subspace?

In A Generic Approach to Invariant Subspace Attacks the authors defined an invariant subspace as: $$F(u + A) = v + A$$ Where $F:\mathbb{F}_2^n \to \mathbb{F}_2^n$,$u, v \in \mathbb{F}_2^n$, and $A$ ...
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Given Seed, keyfragment and cipher text, how to get actual text using LFSR? [duplicate]

$\text{seed = 1100010001101001}$ $\text{key fragment = 110001010000101011001011111101100}$ $\text{cipher text = 0xa50b839547f7fe7cf882}$ What is the actual text and how to evaluate it? I would ...
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62 views

McEliece cryptosystem

There is something intriguing me about this cryptosystem. That is : Let $(S, G, P)$ be the secret key: $S$ : invertible matrix $G$ : generator matrix for some linear code $C$ $P$ : permutation ...
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1answer
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Mixing Autokey with Regular Vignere

It seems to me that cryptanalysis of the autokey cipher relies on patterns being found in key attempts, easy when it's English you're looking for, but how can you do this if you're just getting ...
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Finding maximal $n$-affine subset

We obtained $l$ vectors $B_i$ of $c$ bits $b_{i,j}$. These are an altered form of vectors $A_i$ where the last $n$ bits of each $A_i$ are an affine function of the other bits of that $A_i$. We want ...
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How to get unknown constants from linear congruential generator

I need to crack this linear congruential generator. I have $$X_{n+1}=a⋅X_n +b \pmod m$$ I know: $m=31,X_3=30,X_4=19,X_5=26$ How can I find $a,b$ and $X_0$? I have got already the following ...
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71 views

Computing a probability

Let $(w_1,\cdots,w_l) \in (\{0,1\}^\lambda)^l$, and $r_1,\cdots,r_l $ are chosed as uniformly random from $Z^*_q$ such that $r_1+\cdots+r_l=0$ and $q$ is a large prime number. Also, Let $F$is a ...
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2answers
500 views

Can AES be used with a static key?

I am making an embedded system for a project that uses AES. As I cannot accommodate key generation (hardware constraints) I am using a static key. I can use another small algorithm to create dynamism ...
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1answer
609 views

Decrypting Ciphertext with partial Key Fragment using LFSR and Berlekamp-Massey

Edit Does the state register (the LFSR) always have to remain with 16 bits (I'm assuming yes). If so, are we shifting the register right by one (lfsr>>1) ...
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1answer
60 views

For two LUKS volumes made with the same password, can stealing the encryption key from one volume allow access to the other?

A running computer has two LUKS volumes that were made with the same password. One volume is open (key is in RAM), the other is closed. If the running computer is stolen, is the closed volume safe? ...
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Old French Cipher w/ Text Hidden In Drawing

I'm trying to find a cipher challenge I saw a few years back, it was an old drawing (I think 1800's or earlier) with clouds and stars on it and French text was hidden in the image. Does anyone happen ...
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1answer
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RSA - are we able to encrypt into any possible ciphertext in $Z_n$ given a specific key?

Given a public key $(e,n)$, if we are free to choose the plaintext does that mean we are able to generate any possible ciphertext in $Z_n$ ? Because if we were given $e$ we can say that the ...
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1answer
64 views

RSA - source and image - all are possible?

Given a key $e = 3$ (the public exponent for RSA) and a group of numbers, say $Z_n^*$ (the multiplicative group of $n = pq$, where $p$ and $q$ are primes as requested by RSA). I can find the ...
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119 views

Explaining Chaotic Cryptography

I will venture myself into studying chaotic cryptography. However, I find it hard to explain what chaotic cryptography entails to those that have some knowledge of cryptography. Neither can I explain ...
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Decrypting ciphertext that is missing a block

In the AES encryption, suppose that the key is known. The ciphertext is also known except for a block of the same size as the key. For example, the adversary knows $k, c_0, c_1, \dots, c_{n - 1}$; ...
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1answer
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S-AES RC[i] Generation. Can someone explain how to generate the RC[i]s for these two problems I have?

I don't know exactly how to find the RC[ 1 ] of 80, or the RC[2] of 30. Can someone explain how to find them? Here is a picture of the problem I am having with two questions.
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1answer
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Patterns flaw to sign a counter with public key encryption protocol

In modern asymmetric encryption protocol, like secp256k1, are there any flaws if you want to sign a counter? i.e: use a private key to sign from 1-n is that any chance make n+1 easier to guess?
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Is it a cryptographic risk to share the same encrypted data over and over again?

Regular scenario Let's say I have secret files which I will encrypt. The resulting container will be shared and might be intercepted. Not good, but that's okay - that's why I encrypted the data in ...
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1answer
71 views

Checking if a sentence is English after decryption

I wrote a program that will loop through the anagrams of a word and run each one through the decryption of a columnar transposition cipher on a document. However, for a certain word, the number of ...
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1answer
78 views

Is the hash function $h(x\|y) = AES_x( y)$ collision resistant?

If $x$ and $y$ are both 128-bit strings would the function $h(x||y) = AES_x(y)$, where $x\|y$ means concatenation, be considered collision resistant ? Is there an easy way to find $(x_1, y_1)$ and $(...
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If you wrote a reversible SHA-256 algorithm, how many “metadata” bits would be required for reversability?

I was reading about reversible computing while thinking about FPGA circuits. I realized that it would be possible to write a reversible SHA-256 algorithm if you stored some additional information as "...
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1answer
78 views

Countermeasures to prevent integral cryptanalysis against 4-rounds AES

Integral cryptanalysis against 4-rounds AES is practical (Security of the AES with a Secret S-box). I did two experiments in order to find the impact and remove the integral distinguisher of 4 rounds:...
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1answer
58 views

Encrypt twice with DES using same key ? $\operatorname{DES}(\operatorname{DES}(x,k), k)$

Does encrypting with $\operatorname{DES}$ in the following way $$\operatorname{DES}(\operatorname{DES}(x,k), k)$$ make $\operatorname{DES}$ as strong as $\operatorname{2DES}$ with 2 keys? Because we ...
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DES - encrypt 3 times - DES(DES(DES, k), k'), k) - stronger than 2DES with 2 different keys?

What if were to use DES in the following way: For a given plaintext x and key k we will perform: ...
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How could I test my own Cipher? [closed]

I recently developed a new cryptographic algorithm. I just initiated with just nothing in mind. But being near to completion (though my algorithm is constantly developing. Now it is version 11.02), I ...
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1answer
83 views

Show that if a fixed key MAC is not collision resistant then the MAC function is not computation resistant for every key K

I'm really having some trouble with this one. Let $H$ be a MAC function. For every key $K$ we can create an unkeyed hash function (i.e.an MDC) by using $H$ to hash messages with the fixed key $K$. ...
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Do trinomials weaken the Alternating Step Generator?

The Alternating Step Generator was proposed by Christoph G. Günther: Alternating step generators controlled by de Bruijn sequences, in proceedings of Eurocrypt 1987. It's perhaps the conceptually ...
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Cryptanalyze strategy for cipher text [closed]

I have the following ciphertext that I want to decipher: bnmkogt vgyhni uioopkm xswercvdf yuiogvbnm ghjy cftyhng tgeyjn xdrtygvc zsefx xdrgbhu tgbnmko tgbnmhyui yhnmko vbnmgyuiok So far, what I ...
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1answer
145 views

AES Mix columns bit example

I have been given a 4x4 matrix and each entry is an 8-bit long byte. I have been given the 4x4 matrix that I need to multiply each column by of the first matrix by. $$\begin{pmatrix}2 & 3 & 1 ...