Objectives

Students will be able to:

  • Explain the relationship between cryptographic keys and passwords.
  • Explain in broad terms what makes a key difficult to "crack."
  • Reason about strong vs. weak passwords using a tool that shows password strength.
  • Understand that exponential growth is related to an encryption algorithm’s strength.
  • Explain how and why the Vigenère cipher is a stronger form of encryption than plain substitution.
  • Explain properties that make for a good key when using the Vigenère Cipher.

Exemplar

Introduction to keys

 

is an open and public system. We all send and receive data over shared wires and other connections eg public wifi.

Even though the Internet is public, we use it to exchange a lot of private information eg:

  • credit card information
  • bank account numbers
  • passwords
  • emails

How is my private stuff kept secret when I transmit it from my computer to the server storing my Facebook account? Or my bank account? Or my Amazon account?

encryption - the sending system (eg your computer's browser) scrambles the information to hide the original message. A key is used to do this.

decryption - the receiving system (eg the server storing your Facebook account) unscrambles the information to reveal the original message. It will need that key!

Remember - a hacker can try to crack the encrypted message without the key eg by doing a brute force attack on the message.

So, what's the problem with this system? Think about it. Is it as safe as it seems?

Homework

Reading - Blown To Bits Chapter 5 p12-14

Visual Thinking Exemplars

Tags

Caesar Cipher algorithm computationally hard secret symmetric key crack decryptasymmetric public key private key encrypt

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