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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Eliptic Curve Cryptography Question

What happens if the the next point generated in and ECC system is not an integer by integer coordinate? I'm new to ECC, so this is probably a dumb question, but any explanation would be appreciated.
William Grannis
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8 bit linear feedback shift register Non-zero coefficients

An 8-bit linear feedback shift register with connection polynomial C(X) = 1+aX +bX^2 +cX^3 +dX^4 +eX^5 + fX^6 +gX^7 +hX^8 is used to generate a pseudo-random binary sequence. This pseudo-random sequence is used as the enciphering key of a stream…
Pkr96
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RSA- why does it work

Recently studied some of the mathematics behind the RSA encryption scheme. From what I have seen, the proof that finding the prime factorization of a number is super-polynomial time is yet to be found. I'm trying to sharp my common sense about…
Yaron Scherf
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Maths behind RSA -- where do I turn?

I am a reasonably seasoned software developer (20 years) and am at more or less have year 12 maths. Well, actually, I barely remember limits, derivatives, integrals, etc. I have a good "intuitive" understanding of math-related problems. I want to…
Merc
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How to perform modulo operation on a fraction?

Please help me out in performing modulo operation on a fraction. I saw a reference to Gauss algorithm but was not able to find anything there. example : (1/4) mod 23. What is the answer to this? And detailed step by step explanation is highly…
sbp
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Caesar cipher in number theory

Why is the caesar cipher given by: $C\equiv P+k\,(mod\,26) \,$with$ \,0 \leq \,$C$\,\leq25$? For me is this more logic: $C\equiv P+k\,(mod\,26) \,$with$ \,0 \leq \,$P$\,\leq25$ Because of the modulo 26 it's alwas true that $ \,0 \leq…
WinstonCherf
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Encryption algorithm that can be used without a computer

SIM cards have a PIN and a PUK numbers. Since PINs are used frequently, I know it by heart. I want to write down the PUK to a paper, but I don't want to do it in plaintext, but in a way only I can read it. With a computer, there are several…
Tamás Sallai
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Time complexity to calculate the prime factorization of a large number

I was wondering what is the best(least) approximate time that even the fastest computers take to find prime factors of a very large integer, eg. $2000$ bit-integer, since it has various implications in cryptography for example the RSA algorithm.
john doe
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What is the notion behind proxy re-signatures?

Concept of Proxy Signatures serving the main purpose of delegation is clear. But what exactly is proxy re-signatures? How and why is it performed? Does it use the same warrant generating and proxy signing mechanisms? Thanks!
bala maverick
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Finding involutory keys in Affine Cipher

Let $n=pq$ , and let $p$ and $q$ be distinct odd primes. Deduce that the number of involutory keys in the Affine Cipher over $\mathbb{Z}_n$ is $n+p+q+1$. I honestly have no idea how to go about this problem. I know that $n|(a^2 -1)$ and …
Temirzhan
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Randomized Encryption is Deterministic WLOG

This problem is from Katz/Lindell: 2.2 Prove that, by redefining the key space, we may assume that $\text{Enc}$ is deterministic without changing $\text{Pr}[\text{Enc}_k(m)=c]$ for any $m, c$. After banging my head against this problem for a few…
CRYPTONEWBIE
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question about RSA encryption

A number $x$ has been encrypted with the RSA encryption to $x^5 = 16 \mod 35$ What is $x$? I know that the answer must be 11, but has anyone an idea how to find out x in a systematic way? I could not find such a way to solve it (with public key and…
user52047
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Find the reduction $ - 23 \pmod {67} $

I do not understand what the question is asking me to do? Because if I do $-23 \pmod {67} = 44$? I am not sure if it is correct?
Angjelin Malaj
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Diffie-Hellman key exchange, choosing the secret key

I very well understand the Diffie-Hellman key exchange method, at least I think I do. And I was trying to implement it to try it out. I went and calculated a very large prime number $p$ about $400$ digits long. And I set $g$ to $5$. I generated a…
Ali Shriem
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How does eve find the message m that Bob encrypted?

The following is given: $p=13$, $g=7$, $A=5$, $(c1,c2)=(10,8)$ I know $A=g^a \to a=3$ the message $m$ should be $c2*c1^{-a}$, which is $8\times 10^{-3} \mod 13$ but I don't know how to calculate the inverse part.
Alicia
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