🎯 Lab Overview

This lab walks you through the history of encryption — from a 2,000-year-old cipher to the same math that secures your bank's website today. There are three hands-on activities, each unlocking the next:

1. Caesar Cipher — encode/decode messages, then try to crack one
2. Key Exchange (Diffie-Hellman) — simulate two people agreeing on a secret key in full view of an eavesdropper
3. Public/Private Keys (RSA-lite) — encrypt and decrypt using two different keys

Once all three are complete, a 20-question randomized assessment unlocks. That part runs in fullscreen — leaving it is detected and logged on your certificate.

🔤 Activity 1: The Caesar Cipher

The Caesar cipher shifts every letter in a message forward by a fixed number of positions in the alphabet. A shift of 3 turns A into D, B into E, and so on. It's one of the oldest known ciphers — Julius Caesar reportedly used it to send military orders.

Try It Yourself

🕵️ Crack This Code

Below is a message encrypted with a Caesar cipher using a secret shift you don't know. Since there are only 26 possible shifts, you can simply try all of them — this is called a brute-force attack.

🤝 Activity 2: The Handshake (Diffie-Hellman Key Exchange)

Symmetric encryption (like the Caesar cipher) uses one key to both encrypt and decrypt. The problem: how do two people agree on that key over a connection someone else might be listening to?

Diffie-Hellman solves this. Two publicly known numbers — a prime p and a base g — are shared openly. Each person picks a secret number they never share, does some math to create a public value, and exchanges that public value. Both sides can then calculate the exact same shared secret — but an eavesdropper watching everything public still can't feasibly figure it out.

🔑 Activity 3: Public & Private Keys

Diffie-Hellman solves key agreement. But there's another approach entirely: asymmetric encryption, where two different keys are used — a public key anyone can see, and a private key only you have. Anyone can encrypt a message with your public key, but only your private key can decrypt it.

This tool uses tiny numbers so the math is visible — real systems like RSA use numbers hundreds of digits long, which is what actually makes them secure.

📝 Final Assessment

You've unlocked the assessment. It pulls 20 randomly selected questions from a larger bank, in random order, with answer choices shuffled — covering everything from the three activities.

Each question requires a correct answer before you move on — wrong answers just give you a hint and let you try again, no penalty.

✅ Lab Complete!

Nice work — you've finished the Encryption & Key Exchange lab.

Your verification code:

This code is generated from your name, date, and results. It changes if any of those change.