Bits, bytes and secret-looking messages

The idea

The same number can be written in different bases: decimal 15 and hexadecimal F name the same quantity. A byte contains eight bits, and two hexadecimal digits can describe one byte. To turn text into bytes, you also need a character encoding such as UTF-8. Decoding works when both sides agree on the representation. A hash has a different job: it produces a fingerprint for comparison, not a message you can decode back.

A tiny experiment

message = "Hi"
payload = message.encode("utf-8")
print(payload.hex())
print(bytes.fromhex("4869").decode("utf-8"))

4869
Hi

Read it one step at a time

1. encode changes the Python string into bytes using UTF-8.
2. hex displays those bytes as hexadecimal digits. Here H corresponds to 48 and i to 69 in hex.
3. fromhex reconstructs the bytes; decode turns them into text again. These steps need no secret key.

Make one change

Change the first message to "Hi!". What extra hexadecimal pair appears?

Keep following the trail

• Activity 03: Read Tony's message
• Activity 05: Which note matches?
• Activity 07: Read the radio-station note
• Activity 10: Repair the Genesis copy

Sources & further reading

• Python binary sequences and hexadecimal
• Base64 encodings

Companion notes for Coding Adventure by James Colby. Historical claims link to their sources; the examples are written for this learning trail.