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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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Cryptanalysis for a monoalphabetic substitution cipher

As part of capture the flag game, I'm trying to figure out what is the cipher two messages have been encrypted with, so I can actually start looking for the keyword, which in turn is going to be the ...
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2answers
174 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 ...
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33 views

Is this the correct way to crack a AES-256-CBC Encrypted file? [on hold]

I am currently engaging in a capture the flag competition. I have been tasked to crack a encrypted file. Things I know. It is most likely a openssl encrypted file. The password is English words. ...
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0answers
28 views

What am I doing wrong with this Diffie - Hellman Key generation?

I am currently trying to diffie hellman Problem. I cant figure out what I am doing wrong as the md5 hash is not being accepted into any online aes decrypter. You recieved an important message from ...
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0answers
40 views

How to proof that this cipher is perfectly secure?

I am new to Computer Security and I am trying to solve the following exercise: Consider the following encryption function which transmits one letter. Let n be a fixed positive integer. The ...
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2answers
42 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.
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0answers
32 views

Leveraging patterns in ciphertext

I've got a cipher I believe to be polyalphabetic, which may or may not have a key in which I've discovered some patterns, and I'd like to know how I can use these patterns to try to understand how the ...
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0answers
34 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
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0answers
43 views

I invented 5 encryption codes, how can I sell these? [closed]

I don't know how I could sell it, please can someone help me? it's must be Unbreakable Encryption Code.
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3answers
210 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 ...
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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 ...
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0answers
25 views

polynomial degree in Interpolation attack

I don't quite understand, why do they know that degrees of XR and XL are at most 3^r and 3^r - 1. Can anyone explain it? Thanks in advance. ]1]1
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2answers
46 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 ...
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0answers
34 views

Algebraic Span on non-commutative groups

I'm interested on non-commutative cryptography. Some time ago here Adi Ben-Zvi, Arkadius Kalka, and Boaz Tsaban demonstrated how to find a solution to some of the well known PKE protocols based on ...
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1answer
75 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 \...
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1answer
77 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 ...
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0answers
26 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 ...
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0answers
29 views

Affine Cipher plus

How to attack this affine cipher; $m+n (a_0,a_1,a_2,a_3,\ldots, a_4,\ldots,k_0,k_1,k_2, k_3, k_4,\ldots)$,with $\gcd(a_i,26)=1,i = 0,1,\ldots,m − 1.$ here are the keyspace $(a_0,a_1,a_2,a_3, a_4,\...
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0answers
59 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 ...
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2answers
171 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 ?
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1answer
203 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 ...
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1answer
46 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 ...
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1answer
87 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 ...
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0answers
76 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 $\phi(n)$...
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1answer
46 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 ...
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1answer
61 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 ...
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1answer
55 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 ...
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1answer
66 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 ...
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0answers
39 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 ...
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2answers
131 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, ...
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4answers
997 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 ...
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1answer
316 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 ...
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1answer
119 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+...
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0answers
38 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
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1answer
76 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 ...
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1answer
55 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 ...
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1answer
37 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 ...
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2answers
100 views

How sensitive to change are elliptic curve formulae In layman's terms?

Take for example a curve from a recent question such as #25519:- $$y^2 = x^3 + 486662x^2 + x$$ It's considered "safe". What are are the implications of amending it very slightly to:- $$y^2 = x^3 + ...
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0answers
40 views

Preserving location privacy

What are cryptographic techniques that could be used so that if I wanna to enable a server to send message to certain nodes in a network with preserving the privacy location for them ??
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1answer
70 views

How does future secrecy fail for Signal group messaging?

In the paper More is Less: On the End-to-End Security of Group Chats in Signal, WhatsApp, and Threema, the abstract claims that We additionally show that strong security properties, such as ...
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0answers
56 views

What was the BassOmatic cipher, and what made it so weak?

According to Wikipedia, this homebrew cipher was originally used in PGP, before Phil Zimmermann replaced it with IDEA. Supposedly, insecurities in the algorithm were pointed out to him, leading to ...
3
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1answer
104 views

autokey script gone wrong!

I tried to make a script to encode a txt with the autokey cipher. From my poor understanding of the cipher I created another cipher which has nothing to do with autokey: first I encoded a txt with a ...
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7answers
3k views

Possibility of Chosen Plaintext Attack (CPA) in real-world scenario?

In CPA, it is said that the adversaries get ciphertext for the choice of plaintext of adversaries through an encryption oracle. Is this a realistic assumption in real-world, in which the adversaries ...
2
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1answer
44 views

Minimum number of active s box to be resistance to differential cryptanalysis

I am calculating the minimum number of active s_boxes for block cipher using mixed integer programming, when can we say that block cipher is resistance to differential cryptanalysis after which round? ...
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2answers
54 views

rotor machines: secrecy of wiring

During the heydays 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 ...
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1answer
51 views

How can two keys have the same KCV?

I have two keys and they have the same KCV. How is this possible? I have encrypted data with both keys and I have the same result. Both keys are the result of the derivation of the same IMK, one was ...
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2answers
112 views

How to beat a substitution cipher when adding a pseudo-random number stream?

From view-source:https://web.archive.org/web/19990224060310if_/http://www.cl.cam.ac.uk:80/PGP/pgpdoc1/pgpdoc1_29.html: When I was in college in the early ...
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1answer
87 views

Cryptanalysis on affine like matrix based strange cryptographic scheme [closed]

This is a garage made encryption scheme provided as cryptanalysis practice during 34C3 CTF. The challenge is done under the following assumptions All Mersenne twister instances are MT19937 64bit ...
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1answer
47 views

Is this problem same as discrete logarithm?

Given $g,h\in\mathbb Z_p$ where $g$ generates $\mathbb Z_p^\star$ Discrete logarithm problem is to find $z$ such that $g^z\equiv h\bmod p$ holds. Take the problem given $g,g',h$ where $g^z\equiv h\...
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4answers
170 views

Practical perfect security in bitwise XOR vs integer addition/subtraction cipher

XOR already provides perfect security in theory but it's hard to apply it in practice due to strict requirements. I was thinking about whether simple addition/subtraction in integer format would not ...