MEGA CHALLENGE:

Use the automatic "Super EnDec Simulator" ENCODER to encrypt a secret message to a friend.

Then use the automatic "Super EnDec Simulator" DECODER to encrypt a secret message for your friend.

ACTIVITY

We wrote a program for NetAdventure called "Super EnDec Simulation," which encodes and decodes messages using the simple replacement code scheme we've been talking about. There are two parts to the EnDec Simulation: an Encoder mode and a Decoder mode. When the simulation starts the EnDec will be in the Encoder mode, which allows you to either load a sample message into the Encoder or type in a message of your own. By swapping letters around you can create your own replacement code - the resulting encoded message will appear in the lower window.

If you want, you can export this coded message to your computer's clipboard to paste into an email message to a friend, or if you have access to a printer you could paste it into a word-processing program and print it out. You can also try switching to the EnDec's Decoder mode to see how well the Decoder does at decoding your message. Remember, the longer your coded message is, the more likely the Decoder will come up with a good initial translation based on the English Language letter frequency.

1) Encryption

Use the EnDec simulator's "ENCODER" mode to encrypt your secret message to a friend.

When you have encoded a secret message give your message to a friend to decode, then answer the following questions:

a) Enter the translation key for your secret message.

b) Explain any strategies you used.

c) Explain any problems you had with encryption.

2) Decryption

Use the EnDec simulator's "DECODER" mode to decrypt an secret message from a friend.

When you have decoded your friend's secret message answer the following questions:

a) Enter the translation key needed to crack your friends code.

b) Explain any strategies you used.

c) How helpful was it that the decoder does an initial translation for you using the English frequency of letters? Explain your answer.

3) Coded Varieties

Remember, the NetAdventure Super decoder operates on this principle. It assumes that text has been encoded with a simple random replacement scheme (in other words, each letter is replaced with another randomly selected letter, everywhere it appears in the text). The NetAdventure Super decoder finds the number of times each letter appears in the encoded text and ranks the letters according to their relative frequencies. Then it replaces the most common letter in the text with E, the most frequently occurring letter in English, the second most common letter in the text with T, and so on.

There are many different ways to encrypt a message. Using the letter to letter method demonstrated in the simulator is not the only way. As discussed in the Get Ready section, you can use a DNA method of encryption. Explore the links in the Get Ready section to discover other forms of encryption.

Use the EnDec simulator's "DECODER" mode to decrypt a message coded in DNA. Visit this link to code a message in DNA: http://www.dna2z.com/DNA-o-gram/. Then paste your message in the simulator and try to decode it.

How to import your DNA-o-gram into the EnDec simulator:

1) Click this link: http://www.dna2z.com/DNA-o-gram/

2) Click the "Send a DNA-o-gram" link in the new window.

3) Type a message you wish to encode into the blank field, then click the "Encode" button.

4) The new page will show your DNA-o-gram. With the mouse, hold the button down and select the text of you DNA-o-gram.

5) With your text selected: go to the "Edit" menu at the top of the browser window and select "copy"

6) Close the DNA-o-gram window, and return to the EnDec simulator.

7) Make sure you are in the "Decoder" mode.

8) Click the "Add Text" button.

9) Click the "Paste" button.

10) You may be asked "Do you want to provide the contents of your clipboard to this movie?" Click "OK".

11) Your DNA-o-gram should be displayed in window. Click the "Done" button.

12) Now try to decode your message.

QUESTION:

Were you able to decode the message using the simulator?

Give an explanation why you could or couldn't decode the message.

Clue 1

Technical tip: to run this game you need the ShockWave plug-in.
If you already have it installed then the application will load at
the bottom of this page.
If you don't have it installed click below and follow the directions.

http://sdc.shockwave.com/shockwave/download/
Get the ShockWave plug-in.

Clue 2

When the EnDec starts running, you will be in Encoder mode. You can switch to the Decoder mode by pressing the Switch To Decoder button on the lower right side of the EnDec.

Load a sample coded message into the Decoder by pressing the "Load Code" button at the upper left. Press the "1", "2", or "3" button, followed by the "Done" button to load in a sample message.

Be patient - the Decoder needs to count how many times each letter appears in the coded message, so it might take a little while to load the code into the Decoder.

The coded message should appear in the top window. Above the two rows of letters you will see green "frequency" bars. The number of green bars show how often the corresponding letter in the top row appears in the coded text. You'll notice that the order of the top row of letters represents the frequency of each letter. The most frequent letter in the code will be the first letter in the top row. The least frequent letter will be the last letter.

Sometimes some of the letters will have the same frequency. The EnDec will rank the letters sharing the same frequency in alphabetic order. The bottom row of letters is the substitution code the Decoder will use. It is initally set to the general English language letter frequency we mentioned above. The bottom window displays the decoded message.

Clue 3:

Click the help button on the Super EnDec Simulator for more specific instructions on how to use the Simulator.