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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Some misunderstanding on the Security Proof with Oracle

I have a question about the security proof. Suppose that I proved the following relations. That is, I proved that $Adv_A \le Adv_A^{O} \le Adv_B$, where A,B are some cryptographic schemes and O is an ...
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237 views

What is the current security level of an algorithm?

I was reading a paper of some years ago about a cryptography and a phrase got my attention. We want to ensure a security level of at least $2^{80}$ I know that $2^{80}$ was used as rule of thumb ...
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Probability of choosing a base successfully in Pollard p-1 factorization method

In a problem about pollard p-1 factorization method, where $n=pq$. We choose some random base $a$ , and an exponent $B$, where hopefully $p-1$ has small prime factors, and if so we hope to estimate $p ...
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How to decode Playfair when only a small part of key is available?

How to decode Playfair when only a small part of key is available? What is the plain text for this message? Can someone explain how to recover the plain text for this message? Is there a program that ...
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How would having multiple independently encrypted versions of the same plaintext impact confidentiality?

Suppose I have some unknown plaintext P which I encrypt N times, each time with a completely new and random key and IV. Would knowing that all the encrypted output came from the same identical ...
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Katz/Lindell 2.4 - Generalizing from 2 messages to any message space?

I'm trying to solve problem 2.4 in "Introduction to Modern Cryptography" (2nd edition) for self-study. The problem asks to prove that perfect secrecy $$ Pr[M = m | C = c] = Pr[M = m] $$ ...
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Prove that the affine cipher over Z26 has perfect secrecy if every key is used with equal probability of 1/312

Prove that the affine cipher over Z26 has perfect secrecy if every key is used with equal probability of 1/312. Just some guidance/help with this problem would be greatly appreciated not sure how to ...
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Calculating statistical distance for simple addition cipher?

I'm looking at the solutions to this problem set for self study. One of the questions is to calculate the statistical distance for the following scheme: The message space is equal to the key space, ...
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Why is WalnutDSA specified for COSE?

WalnutDSA was a 1st-round entrant in the NIST Post-Quantum Cryptography project. It had a significant cryptanalytic break close to almost breaking the security of the cryptosystem, only survived due ...
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Why don't we use Blowfish if it hasn't been cracked?

Since Blowfish is old, well-audited, and has no published attacks, why are we using AES instead? I know that Bruce Schneier said that Blowfish is insecure and told people to transition to Twofish, but ...
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How to Prove matrix $m \times m$ is invertible is equivalent to be $LI$ over $\mathbb{Z_{2}}$?

I came up with one problem that says that a $m \times m$ matrix is invertible is the same as to say that its rows are LI (linearly independent) over $\mathbb{Z_{2}}$. First of all, I'd like to know ...
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How to solve cipher encrypted with Vigenère + Columnar Transposition?

Vigenère's weakness is Kasiski's test and index of coincidence. However, if you put columnar transposition on top of Vigenère, that weakness is gone. The text is now shuffled and you can't search for ...
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Security in a pipeline

I am new to cryptography, I am trying to design a secure pipeline environment for the fast transfer of messages. To reduce the Key size I am planning to encrypt the messages with AES session keys (for ...
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Trapdoor recovery from lattice-based preimage sampling

[GPV] and [MP] (references below) give constructions of the trapdoor function defined by $$ f_{\mathbf A} (\mathbf x) = \mathbf A \mathbf x, $$ where $\mathbf A \in \mathbb Z_q^{n \times m}$ is ...
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In the reduction proof below, where OWF exists only if is a PRG. I am not able to understand the highlighted part

I am able to understand how G(x) id generated. But then what is the use of variable z. Also if the probability is >1/2 + e then the distinguisher wins! Then how is this still a OWF
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Is it possible to crack a Linear Congruential Generator if I only know the modulus of the output?

Edit suggested by fgrieu: I have one hundred integers in $\{0,1,2,3,4,5\}$ which I suspect are consecutive values of $\lfloor x_n/2^{16}\rfloor\bmod6$ computed as $x_{n+1}:=a\cdot x_n+b\bmod m$, with $...
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Verify that a point belongs to secp256r1

I need to verify that the point in this public key ...
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Shamir Secret Sharing - P not prime

I was wondering what will happen if I use the Shamir Secret Sharing scheme with $P$ not being a prime, let's say it is $255$. An adversary which holds $k'$ shares ($k'<$ threshold $k$ ) can attack ...
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Breaking vigenere cypher using the one-time pad flaw when used for a second time

I got an idea which may be wrong because I may have missed some important factor but for the moment I don't know if I really did. Let BM be the method used to break a reused one-time pad cipher (which ...
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how high is the possibility of getting a hash collision in text files?

Just for an example, let's say I downloaded "the adventures of tom sawyer" from gutenberg in .txt file format and saved it to my usb thumb drive. And as you can see, usb drive is not an ...
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How to find iteration exponent in a cycling attack?

In Simmons and Norris paper they demonstrate the cycling attack with the following example: p = 383 q = 563 s = 49 and t = 56957 ( a prime) The attacker knows the publicly available r = pq = 215,629 ,...
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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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Cracking a key using a combination of partial keys

As part of a cryptanalytic attack I've carried out, I used a divide-and-conquer strategy to divide the secret key $k$ into several equal-sized partial keys $k = {k_1, k_2, ...}$. The attack works ...
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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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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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recover plain text from cipher text in AES-128 ECB mode [duplicate]

I have a scenario where I do not have the key but I have plaintext 1, ciphertext 1, and ciphertext 2. Ciphertext 2 is built using the same key that was used to build ciphertext 1. Is there somehow a ...
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How do we find differentials in differential cryptanalysis when we don't the details about the S-boxes

I m new to cryptanalysis and trying to understand differential cryptanalysis. I have read the paper by Howard M. Heys. I understood the concept of differentials but I m not able to understand how to ...
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cracking a one time pad using key reuse

There is a one time pad which works as follows: given message "hello" and key "asdfg", it produces "hwoqu". It only works with the 26 english letters. The output is (h(7) ...
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Chaos-based AES, is it secure?

In the link below, the author uses the aes as a basis for his cipher. In his words: The thesis investigates and explores the behavior of the AES algorithm by replacing two of its original modules, ...
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Understanding non-linearity in Salsa20 over various rings

In his design of Salsa20, Bernstein writes to ensure non-linearity he chose 32-bit addition (breaking linearity over $Z/2$), 32-bit xor (breaking linearity over $Z/2^32), and constant-distance 32-bit ...
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How to decide if an element is a public key in NTRU encryption scheme?

First, I'm using the settings of https://en.wikipedia.org/wiki/NTRUEncrypt, with $L_f$ set of polynomials with $d_f+1$ coefficients equal to 1, $d_f$ equal to $-1$ and the remaining $N-2d_f-1$ equal ...
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Structure of composition of permutations

If $P_1, P_2$ are finite permutations, what can we say about $P_3 = P_1 \cdot P_2$? That is, what properties of the composition of permutations can be inferred from the properties of the permutations ...
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Crypt-analysis for finding information hidden in images?

I was wondering if anyone is familiar with any historical aspects (as to whether someone was able to) for discovering code using images on the web as a transport method ? As in hiding byte values in ...
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A query regarding SHA256 output hash structure vs input entropy?

Given an Input string of N bytes where some bytes positions in the string are fixed/immutable (F Bytes) and rest of the bytes positions can contain any value as we want or are configurable/variable (V ...
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Introduce a reference for cryptanalysis of WhatsApp software

I am studying on cryptanalysis of WhatsApp software. I know this is secure software but I want to present a documentary on this topic as a seminar at the university for applied mathematics students. ...
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Poly1305 reuse of r

Poly1305 uses $r, r^2, r^3$ and $r^4$. I understand this if $r$ is a generator of the finite field. But since $r$ can be any random non-zero number, won't its exponents be non-uniform distributed? ...
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How to understand security analysis of encryption algorithm based on identity based and certificateless cryptosystem?

I am trying to understand the security analysis of cryptographic algorithms mainly identity based and certificateless public key encryption algorithm. I am finding it hard to understand the ...
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RSA algorithm implementation

$$m^{ed} \equiv m \bmod n$$ $n =pq$, so by Chinese Remainder Theorem it is equivalent to $$m^{ed} \equiv m \bmod 𝑝, m^{ed} \equiv m \bmod q$$ where $n=p\cdot q$ So how did 2 come from 1 by the ...
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How effective is quantum computing against elliptic curve cryptography?

I've been reading the Wikipedia page on Elliptic-Curve Cryptography and I came across the following. in August 2015, the NSA announced that it plans to replace Suite B with a new cipher suite due ...
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Will using large keys with Classic cryptographic algorithms beat quantum computers?

This is a purely theoretical question. Everyone is talking about quantum cryptography being the next big thing as quantum computers will be much faster than the computers we have today. So, from my ...
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What are some statisitcal characteristics of a hill cipher?

Given a ciphertext, after performing a frequency analysis on it, how would you identify it as a hill cipher? What should i expect to see in the statistics?
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Algebraic differential cryptanalysis

I have been studying on algebraic methods on cryptanalysis of block ciphers. This is where I am reading from currently I need some help to understand Attack C. Excluding equations from the first r ...
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Is Paillier secure from known plaintext attack for single character message?

Assuming I have three messages m1,m2,m3 where m1=m2=m3=1 and I compute c1,c2 and c3. Does that mean that c1=c2=c3 in cipher-text from ? If not, how many times can I encrypt a message m=1 and still ...
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What is the easiest encryption/cipher to brute force?

This is just a casual exploration of what could be effectively the worst possible block cipher, but I think it has some educational value on how ciphers work. I've been reading about unicity distance ...
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Differential analysis of SPN

Reference : Tutorial by HM Heys If we find a differential trail that holds with some non negligible probability for n-1 rounds for a n rounds SPN structure, then we can recover some of the bits of the ...
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(Non)security of algebraically derived EC keys

I recently had a situation where I needed to derive a secondary Curve25519 private key from an existing one programmatically. The obvious solution was to use a KDF, but I wondered at the time about ...
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An unbreakable Hill cipher?

Why don't we use a Hill cipher of 100 × 100? Or even bigger? That would be close to unbreakable. The number of possible keys in a 2 × 2 Hill cipher is 157248. For 100 × 100 the number is beyond limits....
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Rotor machines: secrecy of the wiring

During the heyday of rotor machines, the internal rotor wiring was always a closely guarded secret. Even fully cleared repair staff was not allowed to do anything that could reveal it. As the wiring ...
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Playfair Cipher + Vigenère Cipher?

I'm researching cryptography for a school project, came across the above two ciphers, and something occurred to me. Would combining these two schemes give a considerably stronger encryption than ...
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Differential and Linear Cryptanalysis

I have been reading about differential and linear cryptanalysis. They were mainly introduced by Adi Shamir and Biham to show the weakness of DES. However, many articles state that differential and ...

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