An archive of lecture notes and topics for Fall 2026 will accumulate here as the semester progresses.

Daily Post Solutions

• Daily post due Monday, August 24th — classical ciphers (problems 9–12)
• Daily post due Wednesday, August 26th — modular arithmetic practice sheet, XOR, Sage worksheet, cancellation, and exponents (problems 3–8)
• Daily post due Friday, August 28th — affine known-plaintext attack, modular inverses, and the $3^{519}$ competition (problems 3–5)
• Daily post due Monday, August 31st (AI generated) — unit groups and $\varphi(n)$, a badly chosen affine key, powers of $a$ repeating, Hill cipher key recovery, and double-and-add (problems 2–7)
• Daily post due Wednesday, September 2nd (AI generated) — the $\varphi$ formula, successive squaring, Euler’s theorem and tower exponents (problems 1, 3–7)
• Daily post due Friday, September 4th (AI generated) — a complete worked example of the Diffie-Hellman key exchange exercise, message to ciphertext and back (problems 3–4)
• Daily post due Wednesday, September 9th (AI generated) — big-oh comparisons, and baby-step giant-step for $34 = 3^x \pmod{113}$ (problems 3–4)

Lectures

Friday, August 21st, 2026:

• First day slides: A Whirlwind Tour of Cryptography

Monday, August 24th, 2026:

• Introduction to modular arithmetic, including addition and multiplication and reducing as you go, NOT reducing exponents, and writing caesar cipher in terms of modular arithmetic.

Wednesday, August 26th, 2026:

• Multiplicative inverses and Hill cipher.

Friday, August 28th, 2026:

• Formal mathematics of inverses and gcd.