Exercise: Try the Caesar Cipher

Module 3 · Section 3 of 4

Exercise: Try the Caesar Cipher

Try the oldest known cipher yourself. The Caesar cipher works by shifting each letter a fixed number of positions along the alphabet — shift by 3, and A becomes D, B becomes E, C becomes F. To decrypt, you shift back by the same number.

This is how Julius Caesar sent military orders across the Roman empire 2,000 years ago. It sounds simple because it is. But it established the core principle behind every encryption system that followed: transform the message using a shared secret (the shift number), and only someone who knows the secret can reverse it. That relationship — plaintext, transformation, ciphertext, key — is the same relationship at the heart of the encryption protecting your bank account today.

Use the interactive tool below to encrypt and decrypt messages, experiment with different shift values, and get a feel for what it means to work with a cipher rather than just read about one.

Try the Caesar Cipher interactive exercise