The following calendar will be populated with links to worksheets, videos, activities and daily posts, so you can catch up on anything you’ve missed and revisit important material.

**Monday, August 24th:**- What we did in class: We explored discord a little, and learned Caesar cipher. Under “Resources” you’ll find the cryptosystem organizer sheet. You’ll also find a useful Cryptography Tools Sheet. Here’s the partially-filled caesar cipher sheet (we will complete this) and the Caesar example.

- After-class daily post link: Due Wed Aug 26
- Other useful resources: Caesar Cipher Demo and Boxentrique

**Wednesday, August 26th:**- What we did in class: We took up the Modular Arithmetic User’s Manual Concept Check Sheet and talked about some subtleties of modular arithmetic. We finished talking about Caesar cipher and its cryptanalysis (frequency analysis), using the concepts on the Cryptosystem Organizer sheet. We introduced Vigenere cipher, did an example, and began to talk about cryptanalysis of Vigenere.
- Slides from today.
- Filled Caesar cryptosystem sheet.
- Filled Vigenere cryptosystem sheet.
- Note: Relevant parts of the text are in Chapter 2.
- Cryptography Tools Sheet (frequencies, Vigenere square and multiplication table mod 26) — also available under “Resources”.

- After-class daily post link: Due Friday August 28th

**Friday, August 28th:**- What we did in class: We began with cryptanalysis of Vigenere cipher. Then we discussed one-time pads. Slides from class.
- Here’s a video I made that hopefully clarifies the cryptanalysis.
- Here’s some more detail about variations on the method to solve Vigenere ciphertexts. It’s also in Chapter 2 of your text.
- After-class daily post link: Due Mon Aug 31st

**Monday, August 31st:**- What we did in class: We discussed affine cipher and Hill cipher. Here are class notes, and an affine cipher cryptosystem sheet.
- After-class daily post link: Due Wed Sept 2nd

**Wednesday, September 2nd:**- What we did in class: We discussed wartime ciphers (ADFGXV and Enigma), as well as DES/AES and some terminology for classical cryptography. Here are notes from class.
- After-class daily post link: Due Fri Sept 4th

**Friday, September 4th:**- What we did in class: We worked through the Sage worksheet on sage.colorado.edu (identikey login, then click “Published”) titled MATH 4440/5440 IntroductionToSageForCrypto. Click “edit a copy” to work through it yourself.
- After-class daily post link: Due Wed Sept 9th

**Wednesday, September 9th:**- What we did in class today: We took up the worksheet from the Modular Arithmetic in Motion video (here are solutions). Then we did an in-class follow-up activity.
- After-class daily post link: Due Fri Sept 11th

**Friday, September 11th:**- What we did in class today: We introduced the notions of multiplicative order, primitive root, multiplicative generator, and discrete logarithm, and the discrete logarithm problem. Here are class notes.
- After-class daily post link: Due Mon Sept 14th

**Monday, September 14th:**- What we did in class today: We introduced public-key cryptography (as compared to symmetric key cryptography), and the Diffie-Hellman Key Exchange. We characterized the unit group as those elements coprime to the modulus. Here’s the first page of notes (I sadly lost the rest of them but you can see them on the canvas video). Then we worked on a worksheet. Here’s a Jamboard version.
- After-class daily post link: Due Wed Sept 16th

**Wednesday, September 16th:**- What we did in class today: We proved that the unit group is made up of those residues which are coprime to the modulus. We defined Euler’s phi function. We discussed Gauss’ method of finding multiplicative inverses. We gave a little teaser for the next method of solving the discrete logarithm problem. Here are notes.
- After-class daily post link: Due Fri Sept 18

**Friday, September 18th:**- What we did in class today: We did an activity to discover how to most efficiently compute modular exponents. We covered successive squaring and the double-and-add (AKA square-and-multiply) algorithm. Here are notes.
- After-class daily post link: Due Mon Sept 21