Lesson video

Hello, my name is Mrs. Jones and I'm really pleased you decided to join this lesson today.

In this lesson, we will look at encryption and the work of Alan Turing during the war to break the Enigma code, and use this knowledge to help decode binary messages and crack the code.

So let's get started.

Welcome to today's lesson.

Today's lesson is called Turing's Mug Cryptography Challenge from the unit, Data Representation, Text and Numbers.

And by the end of this lesson, you'll be able to decode binary messages to crack a hidden code.

There are two key words to today's lesson.

Encryption.

Encryption is the process of converting information or data into an unreadable format called cypher text.

Decrypting.

Decrypting is the process of converting encrypted data, cypher text, back into its original readable format called plain text.

There are two sections to today's lesson.

The first is Decode Binary Messages and the second, Crack the Code.

So let's start with decode binary messages.

Encryption is the process of converting a message from plain text into cypher text.

Encryption is used to protect data.

For example, it may be used to encrypt your messages or photos you send to friends or the contents of your mobile phone.

It is also used by organisations and governments to protect sensitive data and plans.

Alan Turing is widely considered to be the father of computing.

You can see a picture of him here.

During World War II, his secret work at Bletchley Park was central to decrypting German communications.

Let's have a quick check, fill in the gaps to complete the sentence.

Blank is the process of converting a message from blank to blank so that the message cannot be understood unless it is decrypted again.

Pause the video to consider your answer and then we'll check it.

Let's check your answer.

Encryption is the process of converting a message from plain text to cypher text so that the message cannot be understood unless it is decrypted again.

Well done if you got that correct.

Turing was an eccentric man.

In his wartime office, he would lock his mug to the radiator with a combination lock so that no one would use it.

You can see a picture of it there with the mug attached to the radiator.

You have been asked to crack the code of the three-digit combination lock.

There is a pattern of white and black circles in one of Turing's notebooks.

You suspect that these are binary numbers.

Sam says, how can I convert these dots to binary numbers? You can see on the right the dots, some of them white, some of them are black.

Lucas says, remember Sam, binary is a base-two number system, so perhaps the dots represent the place values.

So let's look at the first one.

I can see that now.

So the first row uses black dots to represent place values one and four.

So the first row represents 00101 in binary.

So you can see there that where it's white, it represented a zero and where it was black, it represents a one underneath the correct numbers across the top.

Let's have a quick check.

Decode the remaining binary messages.

So the first one was 00101.

Remember that the white is zero and the blacks are one.

Pause the video to complete the rest and then we'll check them.

Let's check your answers.

So we have the second one, it's 01110.

The next one is 01001.

The next one, 00111.

The next one, 01101.

And the last one, 00001.

Well done if you've got those correct.

Sam says, these binary codes still don't mean anything though.

Really good point.

So Lucas says, maybe we need to do another step, Sam.

We could try converting the binary numbers to decimal.

In a sense, binary digits act like switches.

Flip one to on and the corresponding multiplier is included in the sum.

Here we have eight and one that have been switched on, and we add those two together to get nine in decimal.

Instructions to convert binary to decimal.

Write the multipliers over the bits.

Start with one on the right and double each time you move from right to left.

You can see, there we go, one doubled is two, then four, eight, 16.

For each bit set to one, select its corresponding multiplier.

So we have 16, eight, and two that all have a one underneath it.

Add up the selected multipliers.

The sum is the decimal number.

So we add up 16 plus eight plus two, gives us 26 in decimal.

Sam says, 00101 in binary is five in decimal.

But what could five mean? So you can see here that the binary with multipliers across the top, we have four and one added together is five.

Lucas says, it could relate to the letter in the alphabet, Sam.

So five would be the letter E.

Let's do an activity.

Convert the remaining binary numbers to decimal.

Once you have the decimal values, convert them to letters of the alphabet and see if you can crack the code.

Pause the video, back through the slides, use your worksheet and then we'll go through the answers.

Let's check your answers.

So the next one was 01110, which is decimal number 14.

The 14th letter of the alphabet is N.

The next one, 01001, decimal is nine, which is the I is the letter of the alphabet.

Next one was 00111, which in decimal is seven.

And the seventh letter of the alphabet was G.

01101 in decimal is 13, and the 13th letter of the alphabet is M.

And the last one, 00001, in decimal is one.

And the letter of the alphabet, the first one is A.

We have the letters down there and we can spell out the word enigma.

Well done if you got that correct.

Let's move to the second part of today's lesson, Crack the Code.

During World War II, German officers used a special device called an Enigma machine to encrypt all of their communications.

You can see an image there of what the Enigma machine looked like.

This meant that the Allied forces could not find out crucial information about their battle plans or locations.

Sam says, we have discovered the word enigma, Lucas, but this doesn't reveal the combination of the padlock.

Lucas says, maybe we're missing something, Sam.

You decide to flip through Turing's notebook, trying to find the word enigma.

Hidden in the middle of the notebook, you find a list and the word is on it.

You are on the right track, but what are the three numbers next to the word? You see there the word enigma and we have six, 79, and 111.

Sam, I found this strange display on Turing's desk.

How does this display work? Pause the video, look at that diagram, try and work out, how does that work? Then we'll go through it.

Let's check your answer.

If the binary digit is set to one, then it will turn that LED on.

The LEDs can be turned on in different combinations to display each digit.

If you follow the line from the first one, you can see that it goes all the way to the middle light in that sequence.

And if you follow each one, anyone that's got a one next to it has a red lit light that's showing that number four on that display.

Well done if you got that correct.

Let's have a check.

What binary value would you need to display the number three? Think about the number three and which of those lights need to be switched on.

Is it A.

1001111? B.

0001111? C.

1111000? Pause the video to consider your answer and then we'll check it.

Let's check your answer.

The answer was A.

1001111.

Well done if you got that correct.

Sam says, I think I know what to do, Lucas.

If we convert the three numbers in the notebook to binary, we can use these binary codes on the display.

Lucas says, great idea, Sam.

Sam says, oh no, I've forgotten how to convert decimal to binary.

Let's recap how to convert a decimal number to a binary number.

Which multipliers do I select to assemble a number, a sum of 13? Which binary digits do I set to one? Start with the leftmost bit.

Go through the bits from left to right.

So we start with 16.

Do I need to select multiplier 16 to assemble a sum of 13? Do I set this binary digit to one? Does 16 go into 13? No, it should be set to zero.

Setting it to one would include 16 in the sum, which would mean the sum would exceed 13.

Now move to the next one.

Do I need to select multiplier eight to assemble a sum of 13? Do I set this binary digit to one? Does eight go into 13? Yes, it should be set to one.

Setting it to zero would exclude eight from the sum.

So the sum would never reach 13 because the rest of the multipliers only add up to seven.

So we've used eight, so now we need to work out what we have left.

13 minus eight leaves us with five and five is what we carry over.

Move to the next one.

Do I need to select multiplier four to assemble a sum of five? Do I set this binary digit to one? Does four go into five? Yes, it should be set to one.

Setting it to zero would exclude four from the sum, so the sum would never reach five because the rest of the multipliers only add up to three.

And because we've used four, we need to work out what we have left.

Five minus four equals one.

One is what we carry over.

And we move to the next one.

Do I need to select multiplier two to assemble a sum of one? Do I set this binary digit to one? Does two go into one? No, it should be set to zero.

Setting it to one would include two in the sum, which would mean the sum would exceed one.

We move to the last one.

Do I need to select multiplier one to assemble a sum of one? Do I set this binary digit to one? Yes.

We now have 01101, which is 13 in decimal.

You can check it by adding eight, four, and one together to make sure it's 13.

Let's do a quick check.

This display uses a seven bit binary number.

What place values will be needed for conversion? Pause the video, consider your answer and then we'll check it.

Let's check your answer.

The answer would be one, two, four, eight, 16, 32, and 64.

There are seven place values so that we can use seven bit binary number.

Well done if you got that correct.

Let's have another check.

What happens if the decimal number doesn't need seven bits? Pause the video, consider your answer, then we'll check it.

Let's check your answer.

We will just need to fill the leading binary digits with zeros.

For example, for 13, the seven bit binary value is 0001101.

Well done if you got that correct.

Let's do the activity.

Use the three numbers next to the word enigma and convert them to binary.

Use these binary values on the display to generate the three digits for the combination lock.

Note, blank digit machine displays are provided as an additional resource for the lesson.

Pause the video, use the additional resource, go back through the slides, and then we'll go through the answers.

Let's check your answers.

For the first part, we have the numbers six, 79, and 111.

In binary, those are six is 0000110.

79 is 1001111.

And 111 is 1101111.

And if we use these binary values on the display to generate the three digits for the combination lock, we have one, three, nine.

Well done if you got that correct.

Sam says, yes, we cracked the code.

Lucas says, we did it, Sam.

The combination code was 139, one, three, nine.

In summary, encryption is the process of converting a message from plain text into cypher text.

Encryption is used to protect data.

During World War II, German officers used a special device called an Enigma machine to encrypt all of their communications.

During World War II, Alan Turing's secret work at Bletchley Park was central to decrypting German communications.

Well done for completing this lesson, Turing's Mug Cryptography Challenge.