# Questions tagged [modular-arithmetic]

Modular arithmetic is a system of arithmetic for integers, where numbers "wrap around" upon reaching a certain value… the modulus.

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### Alphabet Substitution Cipher

The cipher is AFGYogkyjuroxronglojkxo Hints: Alice said Adobe was attacked this year, find the sum of digits of that year. (Alice - a++) Bob said i would want to know the month as well, i'm ...
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### Trying to understand the basic principle of RSA from Wikipedia

Quote from https://en.wikipedia.org/wiki/RSA_(cryptosystem)#Operation A basic principle behind RSA is the observation that it is practical to find three very large positive integers $e$, $d$, and $n$,...
1 vote
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### RSA: in $E(x) \equiv x^e \pmod N$, do we apply the mod function to $x^e$?

When one is computing $E(x) \equiv x^e \pmod N$ (where $N = pq$) in RSA, what is the precedent for which number in the residue class of $x^e$ to have as the result of this computation? Does this mean ...
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### How secure is this modified RSA (SRA / Mental Poker) algorithm?

I'm making a peer-to-peer game client using an already existing protocol where messages are broadcasted to all people on the network, and messages are already proven to be from a given user. One of ...
1 vote
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### RSA: does it matter that we recover something congruent to x rather than equal to it?

In the proof that RSA successfully decrypts the message $x$, we show that $x^{e^{d}}\equiv x \pmod N$. However, I am wondering whether it is a problem that we don't recover $x$ exactly, but merely a ...
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### Question on Number Theoretic Transformation (NTT) Condition

For the NTT I know the following preconditions, which must be fulfilled for the primitive $N$-th root of unity: $$\omega^N \equiv 1$$ $$\sum_{i=0}^{N-1} \omega^{ik} \equiv 0 \quad k=1,\ldots,N-1$$ ...