Introduction

RSA (Rivest–Shamir–Adleman) was  introduced  in 1978 by Ronald Rivest, Adi Shamir and Leonard Adleman. RSA was the first practical public key  cryptosystem. You can take a look at the original paper from its creators here.

The Problem RSA Solved

Before RSA, cryptography relied on symmetric encryption: the same key was used for both encryption and decryption. This created a major challenge: how do you securely share the secret key with someone you've never met? This is known as the key distribution problem.

Design Goals

The creators' goal was to ensure that two essential properties of the traditional postal mail system are preserved:

• Messages are private: Only the intended recipient can read them
• Messages can be signed: You can prove who sent a message

RSA elegantly solves both problems using a pair of keys: one public (anyone can know it) and one private (kept secret).

Mailbox Analogy: Think of RSA keys like a mailbox:

• The mailbox location is public: anyone can find it and drop letters inside
• The key to open it is private: only you can unlock it and read the mail

Similarly, anyone can use your public key to encrypt messages for you, but only you can decrypt them with your private key.

Why RSA Matters Today

RSA is everywhere in modern computing:

• HTTPS: Securing your web browsing
• SSH: Secure remote server access
• Digital certificates: Verifying website identities
• Email encryption: PGP/GPG protocols

During this journey, you'll learn the fundamentals of RSA and how it works under the hood. Let's start by understanding the mathematics that make this magic possible.