# Tag Archives: cryptography

## Symmetric+RSA vs. RSA and Davida’s Attack

Alice wants her friends to send her stuff only she can read. RSA public-key encryption allows her to do that: she chooses huge primes $p$ and $q$ and releases $N = pq$ along with an encryption exponent $e$ such that ${\rm gcd}(e,(p-1)(q-1)) = 1$. If Bob wants to send Alice a message $m$, he sends […]

## The Discrete Logarithm, Part 1

Given a group $G$, and an element $g\in G$ (the "base"), the discrete logarithm $\log_g(h)$ of an $h\in G$ is an element $x\in G$ such that $g^x = h$ if it exists. Its name "discrete logarithm" essentially means that we are only allowed to use integer powers in the group, rather than extending the definition […]

## Book Review: Levy's 'Crypto'

Today, public-key cryptography is everywhere, offering some measure of security for virtually all internet commerce transactions and secure shell connections. It's hard to imagine life without it, even though most people aren't aware of it. Steven Levy's Crypto is a great book to explain it and how it all came about. In fact, I first […]