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Questions tagged [cryptography]

Questions on the mathematics behind cryptography, cryptanalysis, encryption and decryption, and the making and breaking of codes and ciphers.

Please only post questions about the mathematics of cryptography here.

  • Coding and implementation specific questions should go to Stackoverflow with encryption or cryptography tags.
  • You may also consider asking at Cryptography Stack Exchange which is for asking questions about the mathematics and properties of cryptographic systems, their analysis ("cryptanalysis") and subsidiary topics that generally make up cryptology.
1915 questions
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Solvability of matrix filling

Matrix $A$ has dimension $n \times n(n-1)$. We want to fill $A$ using integers between $1$ and $n$, inclusive. Requirements: Each column of $A$ is a permutation of $1, \dots, n$. Any submatrix formed by two rows of $A$ cannot have identical…
Cyker
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Assume p and q are approximately of the same size, argue for or against if its easy to solve RSA-problem using Pollard's p-1 factorization method

Assignment: Assume $p$ and $q$ are approximately of the same size (p 1000 digits and q 1001 digits), argue for or against if its easy to solve RSA-problem using Pollard's $p-1$ factorization method Against: First we note that if $p$ and $q$ is of…
Linelina
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Decrypt the code in Croatian.

Decrypt the code in Croatian and specify the key K = (s, b) if you know that Cesar's key code with the key K was used to encrypt (use the instruction that the keyword is a name of a European country). Write also the intermediate steps. ASMYJ HMMCV…
user560461
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If $f$ is a one-way permutation, is $f \circ f$ also a one way permutation?

A one-way permutation is a bijective one-way function. If $f$ is a one-way permutation, does this imply that $f \circ f$ also a one-way permutation? What about $f \circ g$, where both $f$ and $g$ are one-way permutations?
greedIsGoodAha
  • 145
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Cryptography - RSA algorithm - basic question

I have just read a very basic introduction to the RSA algorithm. Let's suppose my two prime numbers are $p=29$ and $q=37$. Then $n=pq=1073$ and $e=5$. $n$ and $e$ are public. If I want to send the letter U, which is n°21 in the alphabet, I would…
Tom
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Show that the map $f_e : Z/NZ\longrightarrow Z/NZ ; f_e(x) = x^e$ is bijective.

Let $p_1,...,p_s$ be distinct prime number, and put $N = p_1 \cdots p_s$. Let $e$ a positive integer such that $gcd(e,\phi(N)) = 1$. Show that the map $f_e : \mathbb{Z}/N\mathbb{Z} \rightarrow \mathbb{Z}/N\mathbb{Z} , f_e(x) = x^e$ is bijective. I…
Haley
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RSA probabilistic decryption problem

I encountered this problem in an algorithms book and could not see how multiplicative could be used as a probabilistic algorithm. Using the fact that RSA is multplicative: $$P_A(M_1) P_A(M_2)\equiv P_A(M_1M_2)\pmod n$$ if someone could efficiently…
user782220
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What are some good resources to study Cryptography?

What are some good resources to study Cryptography? I have knowledge of abstract algebra .Is it enough to take up Cryptography as a special paper or I will have to undergo courses in some other topics. Also I want to know some books other than…
Learnmore
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How much mathematics is there in graphic(al?) cryptography?

I've recently looked at my passport and it has several graphics that are used to avoid counterfeits. I've identified some simple sine waves, but there are complex backgrounds that seem to zoom in and out, along with text, and different shades of…
Pedro
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RSA Encryption (Block division)

I have a fair idea of what RSA encryption is and how to do it, but I don't quite understand the following bit given in my textbook: I have an exam tomorrow and I'm expected to encrypt a string of text (e.g., "meet me tomorrow.") using RSA…
Rafay
  • 135
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block cipher algorithm

Consider a block cipher algorithm with the properties: - Input, output block length is 64 bits and key size is 56 bits. - Given a key K, the key scheduling requires 2 microseconds. - After the key scheduling produces all subkeys, the encryption or…
alaamub
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Drawing a 5-stage binary LFSR with feedback Sm+5= Sm + Sm+1

Any guidance on how to draw this would be greatly appreciated I know this is more of a visual thing but I also want to go on to determine all the possible (different) cycles that are generated by this LFSR. What is its characteristic polynomial and…
AnalysisisKey
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Find $D$ in RSA cryptosystem

For the following encryption key $(n, E)$ in the RSA cryptosystem, compute $D$. $(n, E)= (451, 231)$ So I know $n=11*41$, so $m=400$. Now $D=$ inverse of $231 \ (mod \ 400)$. However I am not sure how to find the inverse of $231$ in $mod\ 400$. Help…
Ryan
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coding and decoding message with RSA.

First of all, I know how to solve the following exercise; the problem is that there is no solution. "In RSA, Alice chooses $p=53$, $q=63$, public key ($n=3339, e=13$). When Bob sends the message $m=5$, what is the message that Alice will…
nicolasmanic
  • 129
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DLP in a Cyclic group

Let $q$ be a prime. $G$ is a cyclic group of order $q^2$. Show that for solving the DLP in $G$ it's enough to solve two distinct DLPs in two groups of order $q$. --- We are looking for an $x$ such that $\alpha^x=\beta$ in this group $G$. By the CRT…
unterbrause
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