Mathematics Stack Exchange
Mathematics Stack Exchange

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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binary montgomery multiplication

In the paper paper-montgomery-multiplication there are a lot of algorithm explained how to make a montgomery multiplication on bit level. But I have problems to understand that correctly. I have written Algorithm 1 (page 2 in paper) in Verilog (just…
rennreh
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Vigenere cipher strength of multiple keys?

If when using a Vignere cipher I replace the key word often with a word earlier in the ciphered plain text would this be stronger due to not being able to do analysis with a repeated key or would it be fundamentally weaker due to sending the key for…
shai horowitz
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How to solve RSA without calculator?

I'm trying to create a ciphertext, and I need to solve this congruence: $$ C = 20^{23} \bmod 377. $$ How would I be able to simplify this so that I can do it without a calculator? Since there won't be any calculators allowed in the exam. Thanks!
user610121
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Mathematical Basis of OAuth Encryption

There are numerous explanations of the common public-private key system available online, explaining how large primes are used to encrypt messages. Is there any similar guide to the mathematics of OAuth 1.0a? Searching for mathematical basis of…
NoBugs
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CipherText only attack, historical cipher

I have the following…
Gabriele Picco
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Decrypting RSA when given N and E but not d

The cipher text is O1v3nFbVCbuZLUeJDZO9L9 using the base-64 alphabet N=15241604814814604814814604814814609737853 e=47 I know to work out d you factorize n which equals p and q then you get (p-1)(q-1) and finally e^-1 mod (p-1)(q-1) and then c^d mod…
Pkr96
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Deciphering Hill Cipher with only cipher text

A Hill Cipher over the above $27$-symbol alphabet: $A=0$, $B=1,\ldots,Z=25,$ Space$=26$, was used to produce the ciphertext: KVBDA RYFIBDOAATBDJCZRBDGFGDASSUDEGFSJNOCPXQ…
Pkr96
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Property of a cryptographic function

What property of a cryptographic function is described below? B = F(A) A = F(B)
user7939
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Affine Cipher Question

I have an encrypted message (26 letter English) that was encrypted by an affine cipher. I know the first two letters of the plaintext are "th" which map to "AE" in the ciphertext. When I try to create a system of equations to try and get an…
Temirzhan
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Hill cipher chosen plaintext attack

i am working modulo 26 in the alphabet $A,B,C,\cdots,Z$ where $0=A,1=B$ etc. I may see the encryptions (using the Hill cipher) of $[3,0,6]; [7,14,8]$ and $[13,14,20]$. Is it now possible for me to find de encryption matrix in $GL_3(\mathbb Z /26 …
user42761
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Cryptographic System

The Mad Hatter sets up what he believes is a zero-knowledge protocol. The integer n is the product of two large primes p and q and he wants to prove to the March Hare that he knows the factorization of n without revealing to anyone the actual…
kaitlyn314
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Let $ E: y^{2}=x^{3}+x+1 \pmod{193)} $ be an elliptic curve and $ P=(x,y) $ be a point on the curve of order $3$

Let $ E: y^{2}=x^{3}+x+1 \pmod{193} $ be an elliptic curve and $ P=(x,y) $ be a point on the curve of order $3$. How do I find $x$ and $y$ if $P=(x,y)$ is of order $3$. I know how to find the set $ E_{193}(1,1)$, but i have no idea how to find $x$…
MAS
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How to solve such system of boolean equations effectively?

I am trying to solve such system of boolean equations: $b_{i}^{0}=\oplus_{j=0}^{i}a_{j}^{0} \land a_{i-j}^{1}, i\in[0..31] $ $b_{i}^{1}=\oplus_{j=0}^{30-i}a_{1 + i + j}^{0} \land a_{31 - j}^{1}, i\in[0..30]$ Note: $a_i^j$ - is unknown bit, $b_i^j$ …
Alex Aparin
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Converting Integer to ASCII string

I was reading up on how to convert strings to integer representations for RSA encryption. See this link. Basically, the string-to-integer conversion goes as follows: a(char_1)*256^n + a(char_2)*256^(n-1) + ... + a(char_n)*256^0 where n = string…
Azmisov
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Finding the encryption key for a cipher given the plaintext and the ciphertext

The given cipher text is this: CWT VIFTDBOTBC NDINIAMRA GTDT DTYTQCTS PK CWT RMPIED ANIZTAOMB MA XDDTRTFMBC CI CWT NDIPRTOA CWMC CWT RXPDMDK ATDFXQT XA UMQXBV Using frequency analysis and some trial and error I have the plaintext: THE GOVERNMENT…
DavinaGoodman
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