Cryptography

Experiment Title:

Coding Breaking and Secret Messages

Objective:

Learn about how messages can be coded and decoded

Background on Cryptography

Cryptography is the practice (meaning coding and decoding) and study of techniques for secure communication in the presence of third parties (can be anyone outside of the basic conversation). Think about when you are little and you have your own language and your parents figure out what you are trying to say in order to understand what you would like, this is the basic idea of decryption, taking something that might appear to be gobbledy-gook and turning it into something that can be understood by more people than just yourself. Now think of when you have a diary at home and a sibling who really wants to be like you and insists on reading your diary, to keep your thoughts and feelings to yourself you may come up with your own language that your sibling does not know, this is the basic idea of encryption, taking something that most people can follow and understand and turning it into something that very few people can figure out.

Now we know what encryption and decryption is but how do we get from a to b and back again? The answer is that we use ciphers. Ciphers are algorithms (series of commands that change things from on thing to another based on key information provided to it). Let’s use a simple encryption method to demonstrate this:

I have the alphabet: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z and I want to encrypt it with an alphabet shift cipher (meaning that one letter becomes a different letter in the alphabet). This would be done using a cipher that looks at the letter you start with an changes it to another letter that is a set number of letters away. In the cipher think about the alphabet as moving and just circling back on itself, let’s look at an alphabet shift cipher that shifts by six letters:

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In this shift A becomes G, B becomes H, C becomes I and so forth. The cipher will change the letters from their first source to their changed letter. Let’s go through and encrypt a simple message using this cipher.

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Now looking at what the phrase has become unless you knew the cipher or were very good and figuring out what the cipher could be this phrase would no longer make any sense, hence the phrase has now been encrypted. But now we need to decrypt our message. Since we know our first cipher all we have to do is reverse it and go from the encrypted message back to the original decrypted message. Let’s look at what our reverse cipher would look like:

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From here we can simply apply the decryption cipher to our encrypted message and get our original message out:

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We have just done a very basic cryptographic experiment and rocked it. Now we let’s work with some more intense cryptographic methods.

Now we will go through and see if we can encrypt and decrypt message using several other encryption and decryption methods. Please refer to the cryptography packet for more information.

Materials

• Lab notebook
•  Pen
• Cryptography packet

Method

Prepare Experiment

• Get your lab notebook
• Get the cryptography packet

Run Experiment

• Using the cryptography packet work through 5 different ciphers to both encrypt and decrypt messages
• Note: The ciphers will increase in difficulty, if you do not understand how to complete one ask for help as the next ones will be more difficult

Analyze Data

• Work with your teacher to review the answers and see how to do each of the problems

Conclusions

Cryptography has been around for centuries if not millennia and has been found to be very helpful in keeping messages secret or between two parties rather than everyone. Today you have learned how to both encrypt and decrypt messages. Doing this will help you to learn some of the basic principles behind coding (like for computer games) by creating algorithms (a series of events used to take you from the beginning of something to the end of something, i.e. from a non-encrypted message to an encrypted message or from an encrypted message to a decrypted message).

Make It Your Own

Now see if you can create your own cipher based on what you learned today. Is it easy to create a difficult cipher? Is it difficult? Think about the steps involved in creating a cipher and implementing it, can you write out these steps?

Extension Activities to do at home

You now know how to encrypt and decrypt a message if you have the proper knowledge of the cipher being used. Now see if you can extend this idea to writing out a program or algorithm for implementing the cipher. Start with something simple like the alphabet shift cipher. See if you can write down all of the steps that a computer would need to know in order to encrypt a letter. If you get through this look at the Google free coding tutorials online and see if you can start programming some of the stuff you have learned, make sure you get your parents permission.