Plaintext, Ciphertext e Cifrario di Cesare: le basi della crittografia

Plaintext, Ciphertext and Caesar Cipher

Before diving into the deep world of modern cryptography, let’s understand some basic terms: plaintext, ciphertext, key and algorithm, with a simple example: the Caesar cipher.

🧠 Basic Terms

• Plaintext: The readable message (e.g. HELLO).
• Ciphertext: The scrambled output after encryption.
• Algorithm: The rule used to encrypt and decrypt.
• Key: A number or string that controls the algorithm.
• Certificate: A digital ID that links a public key to a person or server.

🔁 Example: Caesar Cipher

1. Write the alphabet normally.
2. Below it, rotate the alphabet by n letters (e.g. 5).
3. Replace each letter using the new alphabet.

Example with rotation 5:

HELLO becomes MJQQT

🔓 Decryption?

Reverse the substitution.

🔁 What is ROT13?

A Caesar cipher with 13-letter rotation. Apply it twice and you’re back to the original.

🔐 What matters most?

• The algorithm used
• The key applied

Without both, the ciphertext is just gibberish!

🎯 Quiz time