Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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”).

2
votes
1answer
107 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 ...
1
vote
2answers
46 views

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. In the worst case scenario for the attacker, how hard is it for ...
0
votes
0answers
44 views

Can you tell how many times data has been encrypted?

I'm using multiple RSA keys to encrypt a piece of data. The data length is constant but the data itself is not. Each time I encrypt I prepend a 64 bit string to the newly encrypted ciphertext. This ...
-1
votes
0answers
34 views

Extending hash functions from fixed length to variable length Messages [duplicate]

We know that if we have hash function $h:\{0,1\}^{2n}\to \{0,1\}^n$, we can construct hash function $H:\{0,1\}^{*}\to \{0,1\}^n$ with the following construction: Formally, for $s \geq 1$ and a ...
3
votes
1answer
50 views

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.
2
votes
1answer
23 views

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?
0
votes
1answer
57 views

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 ...
0
votes
1answer
68 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 ...
0
votes
1answer
70 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 $(...
4
votes
2answers
194 views

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 "...
0
votes
0answers
22 views

Client puzzle protocol implementation or how we can implement puzzle with HMAC functionality?

I'm learning about client puzzles for DoS (Denial of Services) Protection, and I came across this question. Client puzzle protocol implementation, how we can implement puzzle with HMAC functionality? ...
3
votes
1answer
70 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:...
0
votes
0answers
30 views

DES twice - with k and then with complementary key?

What if we were to use DES in the following way: for a given text x and key k we would perform ...
0
votes
1answer
41 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 ...
1
vote
2answers
73 views

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: ...
-2
votes
1answer
62 views

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 ...
0
votes
1answer
65 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 $K$. ...
8
votes
0answers
170 views

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 ...
0
votes
0answers
48 views

N-time pad reused key attack

I`ve read a lot about many-time pad attacks on this site but neither of them helped me with my problem. I have an assignment for my computer security course: *You intercepted some cryptograms. They ...
1
vote
0answers
72 views

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 ...
0
votes
1answer
78 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 ...
3
votes
2answers
92 views

What is the key space of a 2-key Triple DES

I am assuming the 2-key triple DES is equivalent to double des. I know the key size is 2x56 = 112 bits. Is this the key size the same as the keyspace? e.g. would the keyspace be 112 bits (2^112)
2
votes
2answers
247 views

What is the name of an attack where the compromise of one key compromises the whole system?

Consider the following: A whole system depends on the security of one private key and if this key is, for any reason, compromised, the whole system will be compromised. What's a suitable name for ...
3
votes
2answers
74 views

McEliece post quantum cryptography

Can someone explain me in basic simplistic english if possible how does McEliece asymmetric encryption works and why its quantum safe ? Thanks in advance.
2
votes
0answers
41 views

Differential analysis tools for cryptographic hash function

Is there any software tools available for conducting differential analysis test on cryptographic hash functions? If so, suggest few of them
3
votes
3answers
235 views

Is it possible to exactly reverse engineer an unknown cipher inside a black box?

Consider the following arrangement:- There is an unknown cipher algorithm operating inside the black box. You can enter infinite key /plain text pairs, and observe all of the outputs. The box might ...
1
vote
0answers
37 views

Statistical test strange behaviour [closed]

Hi I'm running the dieharder test suite (this) to test an algorithm, but I've found somethings that I don't understand. This is the command that I run to test my binary file ...
2
votes
2answers
48 views

How may passwords are available to use in this scenario?

Password string consisting of one or more of the 26 characters A..Z and can be of any length from $1$ to $8$ characters. How may password available to use this scenario? As my calculation, it should ...
3
votes
1answer
82 views

Can modular multiplicative inverse be used to create a secure cipher?

Let $N$ be a large number; and $(e, d, N)$ be a secret-key; where $e$ is a one-time random factor, and large enough (say the more or less the same number of bits as $N$), where $e < N$ and $e * d \...
4
votes
1answer
84 views

Random Masking of Padded RSA Ciphertext through homomorphism

I had asked a question related to this before: Oblivious Decryption: Decrypting with a private key, without knowing the message @rikhavshah has an answer, which I would like to discuss the security ...
1
vote
0answers
28 views

Question on nCPA Security and Uniform Permutations

I feel I am misunderstanding the idea of nCPA security and its relation to uniform permutations. In particular I've been reading the paper "Hoang, Morris Rogaway; An Enciphering Scheme Based on a Card ...
1
vote
0answers
72 views

Prove the advantage of a ROR-CPA is less than or equal to the advantage of a IND-CPA

Note that this is a homework problem assigned in Comp 655, UNC-CH. Please do not give an explicit answer as the instructor prohibited consulting outside resources. The problem is as follow: Prove ...
1
vote
2answers
260 views

How secure is ChaCha20? [closed]

I want to implement a stream cipher to encrypt very sensitive data in my Python code. I heard about the ChaCha20 algorithm and the PyCryptodome library , but how secure is it ?
3
votes
1answer
228 views

Attack of the Middle Square Weyl Sequence PRNG

The Middle Square Weyl Sequence PRNG was proposed as illustration of properties of CSPRNGs in this answer (now deleted). This PRNG was introduced (without claim of cryptographic security) by Bernard ...
-3
votes
1answer
51 views

One Time Pad small key multiple times

i'm ask what is the wrong if i used small key multiple times in OTP .? for example : key .. . 10 10 10 10 10 10 plain .. 11 01 01 11 01 00 cipher 01 11 11 01 11 10 what can hacker know about ...
4
votes
1answer
93 views

Cryptanalysis in the middle ages — publications

Are there any publications, articles or literature discussing cryptanalysis and crypt breaking techniques in the middle-ages? I have seen various manuals from the middle ages describing various types ...
2
votes
0answers
96 views

Efficient way of knowing large factors of $\phi(n)$ given small prime factors and $n$

Knowing large prime factor$(r > n^{1/4})$ of $\phi(n)$ can easily factorize n and hence learn $\phi(n)$. If we have knowledge on all small prime factors $(2< r_i << n^{1/4})$ of $\phi(n)$...
-1
votes
1answer
55 views

3DES Feasibility and Security [closed]

Questions are as following: Is 3DES still feasible (in terms of security and performance) to use? Is 3DES safe to use in ECB mode? Every time on giving the same input (plain text) to encrypt via 3DES ...
1
vote
1answer
63 views

Fast evaluation of polynomials

Let $x_1,\dots,x_n$ and $y_1,\dots,y_N$ be some known integers modulo $2^k$, where $n\ll N$. For each $x_i$, I have the following polynomial: $$P_i(z)= \prod_{j=0}^{k-1}(z+2^jx_i) \mod 2^k.$$ Note ...
2
votes
1answer
57 views

Does DROWN attack break 2048-bit key itself or just the plaintext encrypted with the RSA key

Does the DROWN attack enable breaking strong RSA keys (e.g. the 2048-bit key itself) or enable breaking the plaintext (i.e. pre-master key) that is encrypted with a 2048-bit (or any strong) RSA, if ...
-2
votes
1answer
119 views

RSA Time Complexity on Best Case, Average Case and Worst Case

I am currently learning the work arounds about RSA algorithm. I wanted to know the time complexity of the encryption part and decryption part on Best Case, Average Case and Worst Case. Im new in ...
1
vote
0answers
42 views

Mersenne Twister's vulnerabilty with small-size distributions

C++ rookie here, trying to wrap his head around (CS)PRNGs. I (assume that I) already understand the concept of the Mersenne Twister being "broken" (i.e. not cryptographically secure) due to its ...
2
votes
2answers
198 views

Tiny Encryption Algorithm (TEA) weakness

The Wikipedia states that different multiples of a magic constant are used to prevent simple attacks based on the symmetry of the rounds. The magic constant, ...
0
votes
4answers
1k views

Can the same One-Time-Pad be re-used with some tricks

Let’s say I have a message $m$ of $n$ bits. And a predetermined pad of $k*n$ bits. And for every bit $b$ of this message $m$, I’m creating random sequence $s$ of $k$ bits. I also have a predetermined ...
5
votes
1answer
453 views

Deep Learning application in decryption?

If the output of an algorithm when interacting with the [encryption] protocol matches that of a simulator given some inputs, it ‘need not know’ anything more than those inputs. Can a machine learn to ...
1
vote
1answer
147 views

how to compute the correlation between two binary vectors?

We find different equations to compute the correlation or correlation coefficient: $\begin{align*} corr &= \frac{a+d}{a+b+c+d}\\ &= \frac{(a+d) - (b+d)}{a+b+c+d}\\ &= \frac{(a+...
2
votes
0answers
53 views

Strict Avalanche Criteria in Sage

Is there any inbuilt functionality in sage to check if any S-Box satisfies Strict Avalanche Criterion or not?
4
votes
1answer
80 views

Sequence test for an image cipher

I am reading a paper on security analysis of a cipher image using the paper at the following URL: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8306512&tag=1 It indicates some ...
-1
votes
1answer
65 views

Is this problem still as hard as discrete logarithm (modified ElGamal)?

I am trying to find a vulnerability or proof for the following problem: ElGamal part. Given $g\in\mathbb Z_p$ where $g$ generates $\mathbb Z_p^\star$, select randomly $k\in\mathbb Z_p$ and calculate ...
1
vote
1answer
39 views

How can process algebra help to design security protocols?

Would you please tell me how process algebra could help me to design security protocols? More specifically, can I use it for proving the security of protocols? Is process algebra used for any ...