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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.
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If decryption key is hacked then is it safe to change encryption and decryption key?

Suppose the decryption key $d$ of a RSA cryptosystem is hacked and instead of choosing a new $n$ if encryption and decryption keys are changed with same $n$,then is this safe ? My attempt: Previous encryption key $e$ and decryption key $d$ are…
ビキ マンダル
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What about the case when $\mbox{gcd} (m, p q) \neq 1$ in RSA's key generation step?

in key generation, gcd(m, p*q) = 1, so how to solve if it is not equal 1? gcd(e, φ(n)) = 1 The key generation steps in RSA are as follows: Randomly choose two different, large prime numbers p and q ○ Calculate the so-called RSA modulus (RSA…
zain
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Crack RSA by using user signatures

Lets say I have a secret $s$ that is encrypted with a public key $(N,e)$. We know $e=35567$. However we don't know $N$. We can ask the user to sign any message $m$ with his private key $(N,d)$ _ of course $d=e^{-1}\mod{\phi(N)}$ _ However the user…
rudeus123
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Can you derive the public key from a PGP encrypted message without knowing the content of the message?

I am working on a system to transfer short messages while obfuscating the intended recipient. In essence, it combines many messages encrypted using PGP, and periodically publishes a file containing those messages. The recipients would then download…
Electron-Capture
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How to calculate x^3 mod n = 427

I got a message: 427, this message will be signed with RSA key, but only the public part of the RSA key is available so KeyPub:(N=3901, e = 3). To my knowledge 427 would get signed with d, so the multiplicative inverse of 3 modulo 3901 = 2601. My…
sorfog
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Explain RSA in a math language that I can understand

Having not a super high-level background in math, I can't understand several parts of RSA. I know that you select a number n, and two numbers e and d. Then you have ed= mod(φ(n)), which looking it up means that ed is equal to the number you get when…
Throwaway34
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Why is the complexity of N=pq for RSA considered as exponential time?

I'm studying about RSA algorithm for 16-bits and noticed that the complexity of N=pq is considered as exponential time. In the algorithm, p and q are two random and distinct strong primes. All the prime numbers, except 2, are odd numbers. So, when p…
AmI Alive
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Is this key encryption secure over many devices?

I need to generate a 16-byte key (outKey) among many devices that is unique to each, can be calculated by some but cannot be calculated by anyone. Each device has a unique 16-byte ID that can be seen publicly. My implementation adds 2 more 16-byte…
Jack0220
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Is RSA encryption a good way to create a certificate that is easy to verify, but hard to forge?

I had this fun idea to create a certificate that you can earn by solving a puzzle game that I created a couple of months back. So the player solves a puzzle, enters their name, and a pdf rolls out with their name stating that they solved it. This…
user3635700
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How do we know that LCM works the same as Phi for the RSA cryptosystem?

In the case of Euler's phi function, we know from the Euler generalization of Fermat's little theorem that $M^{\phi(n)} \equiv 1$ mod n. However a lot of modern RSA implementations use LCM ($\lambda(p-1,q-1)$), where $pq = n$, instead of $\phi(n)$.…
wasianpower
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Mathematics for cryptography.

Besides number theory, what other areas should I study for crypto. I did my undergrad in Comp Sci so the crypto course didnt have much mathematical topics. But for a grad specilisation in crypto I need to get acquainted with the required…
TheNoob
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Formalizing the use of frequency analysis to break substitution ciphers

Frequency analysis is a very effective way to break substitution ciphers. However, with the methods I've seen, a lot of the work requires guesswork and intuition of a human, so it would be interesting to design a method without this. In general, if…
Christian Doucette
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If sent the same message m to Alice and Bob, how someone who follow the channel can find m ?

Alice has public key (n,ea) and Bob has public key (n,eb) with gcd(ea,eb)=1. If sent the same message m to Alice and Bob, how someone who follow the channel can find m ?
SSMath
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cryptography - coin flipping protocol

Description of the coin-flipping protocol: Alice chooses primes p and q and computes $n = pq$. She sends $n$ to Bob while keeping $p$ and $q$ secret. Bob receives $n$, and chooses $x$ to computer $x^2 = y \bmod n$. Bob sends $y$ to Alice. Alice…
docnet
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What is the name of this cryptographic protocol?

I once heard Terence Tao explain basically the following protocol for how Alice can send a secret to Bob over an unsecure channel without either of them meeting up beforehand to exchange keys. Alice puts her padlock on a box and sends Bob the box.…
Jack M
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