Lecture 1 Math 173A SSI20 PDF

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Lecture 1 for 173A Summer...

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1.1 Simple Substitution Ciphers Sunday, June 21, 2020

11:53 PM

Ciphertext: JSJRDKFQQNSLGFHPGWJFPYMWTZLMNRRNSJSYQZHNZX Encrypted using a Ca :s Inventwithpython.com/cipherwheel

tter in the alphabet

This Cipher lends itself well to modular arithmetic!

Plaintext: enemyfallingbackbreakthroughimminentlucius

Enemy Falling Back. Breakthrough imminent. Lucius.

.

Small example Monday, June 22, 2020

12:49 AM

Encrypt the plaintext "Once upon a time." using a Shift Cipher with key n = 15.

Decrypt the Ciphertext "PCSIW TNP A AXKGS WPEEX ANTKT GPUIT G" assuming key n = 15 was used to encrypt the message.

Cryptanalysis: Breaking a code Monday, June 22, 2020

12:55 AM

sends an encrypted message to

. Alice and Bob both know the key for encrypting/decrypting.

intercepts this message, and she does not know the key. Any information she can gather or infer about the key will be to her advantage.

Best known strategy Monday, June 22, 2020

1:20 AM

Letter Frequency Analysis Monday, June 22, 2020

1:28 AM

Near the bottom of our Canvas course page, you'll find some lab files. Download these, and then visit Cocalc.com

1.2 Divisibility and Greatest Common Divisors Monday, June 22, 2020

1:46 AM

https://www.math.uci.edu/~ndonalds/math13/notes.pdf

Recall Definitions and Results Monday, June 22, 2020

1:53 AM

Finding the gcd using the Euclidean Algorithm Monday, June 22, 2020

10:21 AM

Extended Euclidean Algorithm example Monday, June 22, 2020

10:29 AM

General Result Monday, June 22, 2020

10:30 AM...