RSA problem - how to find $d$

Question

For example, let $p = 3$ and $q= 11$, choose $e = 3$. What computation I have to apply in order to find the corresponding $d$? I know it's 7, but I want to know the exact process to be applied to find it.

Answer 1

Ok, RSA is a asymmetric crypto system. Which means you have a separate key for encryption and decryption.

Remember RSA is based on cyclic groups. So don't forget the modulo.

Here are the basic equations. $n$ is the product of $p$ and $q$. $\varphi(n) = (p-1)*(q-1)$

$gcd (e, \varphi(n)) = 1$ - for calculating the e. e is random but must fit this equation.

$d = e^{-1} \bmod{\varphi(N)}$ And now you can calculate d.

Hope I could help you. But this would only take 2 minutes to google