RSA

The idea

RSA is an asymmetric cipher: anyone can encrypt with your public key, but only you (holding the private key) can decrypt. Its security rests on the difficulty of factoring large numbers.

The cast

• p, q — two primes (your secret)
• n = p·q — modulus (public)
• φ(n) = (p-1)(q-1) — Euler's totient
• e — public exponent (coprime to φ)
• d — private exponent (e⁻¹ mod φ)