Encoding, encryption, and hashing

This lesson adapts the learning objective in the University of Oviedo Cryptography Applications lab: understand what encoding is for and distinguish it from encryption and hashing.

Learning objectives

By the end, you should be able to:

• Explain why Base64 is not encryption
• Predict whether a transformation is reversible
• Identify when a secret key is required
• Use a hash for comparison without claiming it hides the input
• Save a reproducible Serialize workflow

Part 1: encoding preserves data

Install Decode Base64 and run the included sample. Anyone who knows the alphabet can reverse the representation; no secret is involved.

Try the same idea with:

• Hexadecimal to text
• Base64url
• URL parameters

Check yourself: If two people have the same Base64 text, do they need a shared secret to recover the bytes? Why not?

Part 2: a classical cipher uses a key

Install Decode a Vigenère cipher. The operation needs the key LEMON; changing that key changes the recovered text.

Vigenère is useful for teaching key-dependent transformation, but it is not suitable for modern confidentiality. A real encryption workflow must also specify mode, nonce or IV handling, authentication, key encoding, and key management.

Part 3: hashing is one way

Install Calculate a SHA-256 digest. Change one character in the input and observe the completely different digest.

Then install Calculate HMAC-SHA256. HMAC adds a secret key so a receiver can authenticate a message. It still does not encrypt the message.

Comparison

Assignment

Create three tabs with the same input sentence:

1. Encode it as Base64 and decode it again.
2. Calculate its SHA-256 digest.
3. Calculate HMAC-SHA256 with a clearly labeled demonstration key.

Write one sentence explaining what assurance each output does—and does not—provide.