# Questions tagged [cryptography]

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

1,340 questions
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### Extended Euclidean Algorithm yielding incorrect modular inverse

In order to solve an ElGamal cryptographic problem, I need to solve 8x≡1 (mod 17) Or simply, find the inverse of 8 in the context of modular 17. By the Extended ...
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### Elliptic curve addition: why does it work in any field?

Supposing I have an elliptic curve E(K): y^2 = x^3 + Ax + B with char(K) != 2,3, why do the formulas for EC addition work in any field. The formulas make sense in ℝ, for example we calculate the slope ...
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### Understanding an excerpt of notes on RSA using the Chinese Remainder theorem

I have a description in my cryptography notes of a way to make RSA more efficient using the Chinese Remainder Theorem. Let $p,q$ be large primes, $N=pq$ , $e$ be the public encryption exponent, $d$ ...
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### Can anyone decipher this RSA encryption? [closed]

The given public key is (1602467, 829) and the message is: 618010.854516.292790.447129
How can i create a generator matrix for $(5,3)$ Linear block-code over $GF(2^2)$. Most of the books mention the operations on this matrix and also that the choice of the basis vector is not unique ...
I've been working for a while on these 2 sequences, which arose in cryptography : $$\forall b\geq2,$$ \delta_b = \lim\limits_{p\in\mathbb{N}\to\infty}\left[\sum_{n=0}^{\infty}\left(1-b^{-p}\right)^{...