Discovery · Systems Project 9
Sending Messages
Take it apart. Push it through a tube. Put it back together at the other end.
Student PIN:
Try It — It Will Not Fit Through the Tube
Take a picture. Try to pass it to your partner through a kitchen-roll tube.
It does not fit. So cut it into small pieces and send them one at a time.
Your partner cannot see the pieces coming and must put the picture back together at the other end.
| Question | My answer |
|---|---|
| How many pieces did you send? | |
| How long did it take to rebuild? | |
| Did any piece end up in the wrong place? |
Now make it easier
Mix the pieces up and do it again. But first, agree on one rule that will make rebuilding faster.
| Round | Time to rebuild | Pieces in the wrong place |
|---|---|---|
| First try, no rule | ||
| Second try, with our rule |
You Just Invented a Protocol
Most groups end up numbering the pieces. That is a rule both ends agreed on before sending anything, and it is the only reason the picture came back together.
Computers do exactly this, millions of times a second.
Learn It — Packets, Rules, and Secrets
Big things do not travel well. So computers chop information into small pieces called , send them separately, and rebuild them at the far end.
A is the set of rules both ends agreed on beforehand — how to number the packets, what to do if one goes missing, how to know when the message is complete.
Packets Do Not Travel Together
Pieces of the same picture can take different routes and arrive out of order. They can even arrive after pieces of somebody else’s picture.
The protocol is what sorts that out. Without it, everything is just a pile.
HTTP and HTTPS
When you load a web page, your computer uses a protocol called HTTP — Hypertext Transfer Protocol. It is the agreement that lets any browser talk to any web server.
You will more often see HTTPS. The extra S stands for secure. It means the browser is using a protected connection to the website — the packets are scrambled so people along the way cannot easily read them.
⚠ How to Check Before You Type Anything Private
Look at the start of the address. Prefer addresses that begin with https://.
A browser might also show a connection or site-controls icon near the address. It may look like a padlock — or it may not. Different browsers show this differently, so do not hunt for one special picture.
If the browser says Not secure or shows a warning, stop. Ask a trusted adult before you enter a password, address, or other private information.
HTTPS protects the connection. It does not mean everything on the page is true or safe.
Encryption
scrambles a message so that only the intended reader can unscramble it.
The scrambling follows a rule, and that rule is the . Whoever has the key can read the message. Whoever does not, cannot.
Here is a simple key. Every letter shifts three places along the alphabet.
| plain | A | B | C | D | E | F | G | H | I | J | K | L | M |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| coded | D | E | F | G | H | I | J | K | L | M | N | O | P |
| plain | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
| coded | Q | R | S | T | U | V | W | X | Y | Z | A | B | C |
Notice the end wraps round: X becomes A, Y becomes B, Z becomes C.
Do It — Send It, Sort It, Hide It
1. Three groups, three jobs
Your class splits into senders, distributors, and receivers. Each sender has a different colour of paper, cut into twelve numbered pieces.
Senders
Push your pieces through the tube, one at a time, into the middle.
Do not hand them to anybody.
Distributors
Take each piece from the pile and work out who it belongs to.
Send it down that receiver’s tube.
Receivers
Collect what comes out of your tube.
Rebuild your sheet in number order.
How did the distributors know where each piece belonged?
2. Break it on purpose
Run it again, but this time the senders use paper that is all the same colour.
| Question | My answer |
|---|---|
| Could the distributors still sort the pieces? | |
| What information was missing? | |
| What would you add to each piece to fix it? |
Every Real Packet Carries an Address
The colour was doing the job an address does. A real packet says who it is for, who it came from, and where it belongs in the message.
3. Lose one on purpose
Run it once more. This time a distributor quietly drops one piece on the floor.
Did the receiver notice? How?
Real protocols do exactly what you just suggested. The receiver asks for that packet again.
4. Go and look at real protocols
Open a browser. Look at the address bar on several sites, including the KIPR site.
| Site | HTTP or HTTPS? | Looks protected? (icon / warning) |
|---|---|---|
5. Decode this
Somebody sent you a message. Use the key from Learn It to read it. NHHS BRXU SDVVZRUG VHFUHW
| Question | My answer |
|---|---|
| Who was the sender and encrypter? | |
| Who was the receiver and decoder? | |
| Why does the key matter? |
6. Make your own key
Invent your own way of scrambling letters. It does not have to be a shift — swap pairs, reverse the alphabet, use symbols.
My key works like this:
7. Trade and decode
Swap encrypted messages with a partner — and swap keys. Decode theirs.
8. Now try it without the key
Get a message from a different pair, but do not take their key. Try to crack it.
| Question | My answer |
|---|---|
| Did you crack it? | |
| What did you try first? | |
| Which letters gave the most away? |
⚠ Simple Keys Are Easy to Break
A letter shift can be cracked by trying all twenty-five of them. Real encryption uses keys so large that guessing them all would take longer than anyone has.
The idea is the same. The size is not.
Score It — Checkpoint
Say what it means
| Word | In my own words |
|---|---|
| Packet | |
| Protocol | |
| Encryption | |
| Key | |
| The S in HTTPS |
Quick decode
Same key as before. Shift each letter back three places.
| Coded | Says |
|---|---|
| URERW | |
| VHQVRU | |
| SDFNHW |
Can you do it again?
Think about it
In the tube activity, the pieces arrived out of order and it still worked. Why is that better than insisting everything arrives in the right order?
You had to share your key with your partner before they could read anything. If someone were listening, how would you get a key to them safely?
Your robot’s program is a message from you to the Wombat. What would go wrong if part of it arrived and part of it did not?
Next
You have seen how easily a message can be read by somebody it was not meant for. Most of what you send every day is about you.
In Systems Project 10 — Guarding Your Information, you find out what you are giving away and how to stop.
When you are finished, press the button to turn in your work and save a copy.
KIPR · Botball Explorer · Discovery