Simple Encryption - Caesar Cipher & Random Substitution Cipher
Purpose: Students will understand the early forms of encryption and how they work.
Vocabulary:
- Encryption: a process of encoding messages to keep them secret, so only "authorized" parties can read it.
- Decryption: a process that reverses encryption, taking a secret message and reproducing the original plain text.
- Cipher: the generic term for a technique (or algorithm) that performs encryption.
- Caesar Cipher: a technique for encryption that shifts the alphabet by some number of characters
- Random Substitution Cipher: map every letter of the alphabet to a random different letter of the alphabet.
Activity 1: Caesar Cipher.
In Roman times Julius Caesar is reported to have encrypted messages to his soldiers and generals by using a simple alphabetic shift - every character was encrypted by substituting it with a character that was some fixed number of letters away in the alphabet.
With pencil and paper, how long does it take you to Decrypt the following message:
serr cvmmn va gur pnsrgrevn
- How long does it take you?
- How difficult was it to crack?
- How many letter shift was it?
Hint:
- Write out the alphabet on a piece of paper.
- Start with the shortest word and crack it first. That letter shift will apply to all the other words.
- Each time you decrypt a letter, now apply it to all matching letters in the other words.
- Next, decrypt the letters that are near the ones you have already cracked.
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Activity 2: Caesar Cipher.
Lets try another one.
With pencil and paper, how long does it take you to Decrypt the following message:
sqivvc glvmwxqew
- How long does it take you?
- How difficult was it to crack?
- How many letter shift was it?
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Visit: Code Studio.org_U4Ch1L7_ Simple Encryption:
This lesson will allow you to decript messages encrypted in the Caesar Cipher method. Level #1 explains how the Tool works.
Go to Level #2 -
Decrypt the messages from the pulldown menu. Time yourself. Enter your own message!
Click Here!
Journal: Approximately, how much faster was the computer than when you decrypted the message with paper and pen?
Activity 3: Random Substitution Cipher
What if instead of shifting the whole alphabet, we mapped every letter of the alphabet to a random different letter of the alphabet? This is called a Random Substitution Cipher. Now, instead of the secret message being encoded with a simple alphabetic shift, you'll face messages encoded with random substitution. This is much harder to crack and requires a more sophisticated tool.
Log on: Code Studio.org_U4Ch1L7_ Simple Encryption (You will be working with a see a far more sophisticated version of the encryption tool.). The only way you will figure it out is to just poke around!
- Instructions: Click Here!
- ( Puzzle 5)
- Read the instructions and click "Ok" to move onto the actual Random Substitution Cipher tool.
- Then, for 5 Minutes, Just Play!!!!
- Then continue onto Level 6 and view the animation at the bottom of the screen - this will show you how to use "Frequency" to crack an encryption. Click Here!
- Then return to the Random Substitution Cipher tool and see if you can crack the code by applying what you have learned about Frequency (level 5). Click Here!
Once the students understand the concept of Random Substitution Cipher...Move On to "Encryption with Keys & Passwords."
Harrington Hints (games that will allow you to learn how to successfully decrypt a Random Substitution Cipher): Click Here!
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