what’s the Substitution rule?

7^25 mode 23
21

what’s Euclid’s rule
gcd(x, y) = gcd(x mod y, y)
what’s the extension of Euclid’s algorithm

What’s Fermat’s little theorem?

What’s Euler’s theorem?

How to calculate Euler’s function for a composite of two primer numbers?

When does the inverse of x mode y exist?
gcd(x, y) =1
What’s Euler function?

RSA protocol, what sender and receiver should do?
