Building a Codebook

Semaphore

With just two flags, how can we send a message?

Semaphore A B Cs

If this is A, B and C… what is D?

The Sensible Patterns in Semaphore

The first half of the alphabet is reasonably logical:

• 
  A to G
  One arm straight down, the other ticking clockwise by 45 degrees for each letter.

• 
  H to N
  One arm to the bottom right, the other ticking clockwise by 45 degrees. Trick: Skip J!

• 
  J
  J is one arm straight up, one arm straight left. Weird, I know.

The Less-Sensible Patterns in Semaphore

The second half of the alphabet, not so logical:

• 
  O to S
  One arm right, the other ticking clockwise.
• 
  T to Z
  Running out of combinations now, but same pattern.
• 
  Ignore Message
  Arms at top-right and bottom left, forming a slash symbol.

Add Semaphore to your Codebook

Complete the Semaphore section of your codebook,
so you can use it for the upcoming challenges.

Semaphore Challenge

Decode the secret message.

Who actually uses Semaphore?

Seamen
Widely adopted semaphore in the 1900s,
and it is still used for emergency communications.

Semaphore is great and all but…

What about long distance?

Semaphore is great for short-range visual communication, but quite often we want to send messages to people we can’t actually see.

Morse Code

Dah-dah dah-dah-dah di-dah-dit di-di-dit dit.

Srsly tho.

Dots and Dashes

All of morse code is made up of dots and dashes,
which are communicated as long and short beeps.

How do we know which dot and dash combination
stands for each letter?

Assigning Letters their Code

We want to communicate as fast as possible,
so the letters we use most should have the shortest codes.

Letters in Morse Code

Dots and Dashes

• 
  A dash is three times
  as long as a dot
• 
  Each dot or dash is separated
  by a gap the same length as a dot

Letter Frequencies

This is a chart of the letter frequencies in the English language.

Letter Frequencies from Morse’s Era

Back when Mr Morse was around,
he calculated the letter frequencies as follows:

Build the Morse Code Chart

Let’s fill in the Morse Code chart using the letter frequencies.

Add Morse Code to your Codebook

Complete the Morse Code section of your codebook,
so you can use it for the upcoming challenges.

Communicating with Morse Code

Letters and Words

• 
  Letters are separated by a gap
  the same length as three dots
• 
  Words are separated by a gap
  the size of seven dots

Morse Code Challenge

Decode the secret message: Bunnies Love Chocolate

Morse Code Game

Listen to the Morse Code
and type the letter you hear.

Play Now

Morse Code is pretty cool too, but…

What about storing more complex data?

Morse Code is great for communicating quickly using words and numbers, but what about if you want to send sound or an image?

Binary Code

Hiding messages in bits of data.

How big is a bit?

At the most basic level, electronic things have two states:

• 
  Off
• 
  On

That’s a bit.

Representing Bits

• 
  0 and 1
• 
  White and Black
• 
  Off and On
• 
  Low and High

We can represent bits in lots of different ways,
but they all mean the same thing.

Coding Letters in Binary

A=1, B=2, C=3, D=4…

How many bits would we need to code
all of the letters from A to Z?

Binary Combinations

• 
  One Bit
  Two combinations
• 
  Two Bits
  Four combinations
• 
  Three Bits
  Eight combinations

Now can you figure out how many
bits we need for 26 letters?

Counting in Binary

Can you see the pattern?

Alphabet in Binary

We can make 1=A, 2=B, 3=C

Add Binary to your Codebook

Complete the Binary Alphabet section of your codebook,
so you can use it for the upcoming challenges.

Binary Challenge

01000

01111

01010

Decode the secret message

Codebook: Complete!

Okay, now let’s put our knowledge to the test…
Take me to the next chapter!