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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Use large key size for RC4 to avoid RC4 bias

I saw a question on StackOverflow where RC4 was initialized by a 1024 bit key (with 2048 the maximum key size, if I'm not mistaken). Will such a large key size possibly solve any of the bias of the ...
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can deep learning simulate an algorithm? [closed]

I will begin with a simple example to illustrate my point. Consider a known data set consisting of two columns ...
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1answer
69 views

Insecure MAC built on pseudorandom function

this is a question about Katz-Lindell book, introduction to modern cryptography, 2nd edition, exercise 4.7, part c. For (a) and (b) it is clear that the Macs are insecure, but for (c) I am struggling ...
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Help on Algebraic Side Channel Attacks

I am a master student in computer security, I am preparing a dissertation thesis in the theme is: Algebraic cryptanalys by auxiliary channels, I need reference on this theme (book, thesis, ...), and ...
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1answer
55 views

Is there any practical use of reduced rounds of AES

There are lots of attacks which are on reduced block ciphers. There are practical attack on five rounds of AES-128five rounds aes broken in six minutes. I was just wondering if there is any practical ...
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Can zkSNARK or other zero-knowledge proofs be used to proof message authenticity without revealing private key?

The situation: Alice and Bob are exchanging messages encrypted by some known asymmetric encryption protocol. All their encrypted messages, as well as public keys are intercepted by Charlie. Can ...
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Factorization problem

Say, $X= a\cdot b$, where $(a, b) \in Z_q^*$ and $q$ is a large prime. If $X$ is given, then what is the complexity (or hardness) of finding $a$ and $b$? Note that, either $a$ or $b$ can be reused to ...
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Correlation power analysis attack on Camellia

I'm investigating a correlation power analysis on a black-box ASIC I have. I want to learn about correlation analysis and it seems this ASIC implements Camellia. I searched for researches that did ...
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1answer
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18 rounds encryption in embedded?

I have a power trace of a decryption. It seems like I'm watching a 18 rounds decryption algorithm. I cannot think about any other algorithm implemented in ASIC except Cammelia who has 18 rounds. ...
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1answer
50 views

How to find a small generator with small inverse? Does it have negative impact to security? (for Schnorr subgroup of $\mathbb{Z}/P\mathbb{Z}$)

Given a prime $P$ with $$P= r \cdot q+1$$ with $q$ prime as well. I'm looking for a generator $g$ of the Schnorr subgroup with order $q$ which is small by value and has a inverse (to $\bmod P$) which ...
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What are the security implications of knowing the private polynomial $\mathcal{F}$

First, affine transformations $S,T$ are defined by $S=A_1+v_s, T=A_2+v_t$. Let the private polynomial function $\mathcal{F}$ be known. The short description of the public key map is $P(X) = T \circ \...
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Is there a feasible way to reconstruct the key from the (Triple-)DES round key?

Assume there is a closed source application which uses Triple-DES with a fixed/hardcoded key to decrypt large amounts of data. Someone managed to extract the round keys from a process memory dump and ...
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Which is the smallest safe elliptic curve (bit-length)?

At https://safecurves.cr.yp.to/ some elliptic curves are listed which passed certain security test. The smallest bit-length of a safe curve listed there is 221 bits. At wiki page discrete logarithm ...
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How do I calculate the conditional probability of a Caesar cipher?

I have a frequency distribution of letters for the plaintext and the ciphertext. I'm trying to determine the conditional probabilities to identify the plaintext/ciphertext pairings. If I encrypt ...
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Differential cryptanalysis of FEAL-4 recovering last subkeys

I am familiar with the differential cryptanalysis of small SPN-based ciphers like here: Tutorial of Amazing King with SPN (or mentioned in the book "The Block Cipher Companion" or the Tutorial of ...
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Breaking RC5 without rotations

I'm trying to follow Schneier's self-study course in cryptanalysis and am ashamed to say I am stuck on the very first problem of breaking 8-round RC5 without any rotations (i.e. just XOR and modular ...
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Help with cryptanalysis of branching in schemes based on Multivariate Public Key Cryptography

I'm familiarized with the structure of branching found in Multivariate Cryptography, as it allows us to partition a $n$-tuple over $F_{q}$ into a $k$-tuple where the $i$-th element is in $F_{q^{\...
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1answer
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Understanding Fourier Coefficient

In Bogdanov's and others, PRESENT: An Ultra-Lightweight Block Cipher, they mention that the S-box in PRESENT fulfill four primary conditions. They denote the Fourier coefficient as $$S_b^W (a) = \sum_{...
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Reverse Java random seed using 81 calls to nextInt with a bound of 4?

I'm trying to reverse the Java random seed using 81 calls to nextInt(bound) with a bound of 4. I am wondering if it is at all ...
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Differential cryptanalysis for DES reduced to Four Rounds and about S/N

I'm reading the paper "Differential Cryptanalysis of the Data Encryption Standard(2009)" and I was stuck in a certain part while reading it. In chapter 4, they explained about differential ...
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1answer
127 views

How safe is my method

I'm building a website. I have an API which takes 2 parameters: delete_user(user_id, hash). And there is method to evaluate hash using SHA512: ...
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Scrypt cipher - known vulnerabilities and cryptanalysis? [duplicate]

there is a Scrypt cipher which is used for exmaple by some cryptos like LItecoin for their mining algorithm. I never heared of scrypt. I know eg SHA256 which is well analyzed and considered as secure ...
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what if the S-boxes in DES were “optimal”

if we assume that the s-boxes in DES were optimal. that is for each s-box, every cell in the DDT equals to 4. is there a differential characteristic in a good probability?
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Symbolic computation in finite fields [closed]

What I want to know is how to perform symbolic finite field computations in SAGE math? Such computations are required in building algebraic models for cryptanalysis. To explain this mathematically ...
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1answer
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A5/2 session key derivation

Let talk about Implementation and performance analysis of Barkan, Biham and Keller’s attack on A5/2. In this paper, mentioned that we need to brute force attack on register 4 ($R_4$) to get keystream ...
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Why is p-value 0 although proportion is higher than threshold?

In the finalAnalysisReport.txt (the result file of NIST tests), there are several columns including P-VALUE and PROPORTION. ...
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59 views

At what modulus size does the logjam reduction stage become impractical?

Attacking a Diffie-Hellman exchange with logjam involves a massive precomputation effort once for the group, and then a comparatively simple reduction stage that is necessary to break each individual ...
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How to break transposition cipher? [closed]

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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1answer
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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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1answer
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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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1answer
158 views

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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1answer
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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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203 views

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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1answer
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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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380 views

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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1answer
78 views

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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143 views

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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1answer
64 views

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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