Cracking Codes with Python · An Introduction to Building and Breaking Ciphers by Sweigart, Al -- Read -- Imperial Library of Trantor

Index

Title Page Copyright Page Dedication About the Author About the Technical Reviewers Brief Contents Contents in Detail Acknowledgments Introduction

Who Should Read This Book? What’s in This Book? How to Use This Book Downloading and Installing Python Downloading pyperclip.py Starting IDLE Summary

Chapter 1: Making Paper Cryptography Tools

What Is Cryptography? Codes vs. Ciphers The Caesar Cipher Why Double Encryption Doesn’t Work Summary Practice Questions

Chapter 2: Programming in the Interactive Shell

Some Simple Math Expressions Storing Values with Variables Summary Practice Questions

Chapter 3: Strings and Writing Programs

Working with Text Using String Values Printing Values with the print() Function Printing Escape Characters Quotes and Double Quotes Writing Programs in IDLE’s File Editor Source Code for the “Hello, World!” Program Checking Your Source Code with the Online Diff Tool Using IDLE to Access Your Program Later How the “Hello, World!” Program Works Summary Practice Questions

Chapter 4: The Reverse Cipher

Source Code for the Reverse Cipher Program Sample Run of the Reverse Cipher Program Setting Up Comments and Variables Finding the Length of a String Introducing the while Loop Improving the Program with an input() Prompt Summary Practice Questions

Chapter 5: The Caesar Cipher

Source Code for the Caesar Cipher Program Sample Run of the Caesar Cipher Program Importing Modules and Setting Up Variables Constants and Variables The for Loop Statement The if Statement The in and not in Operators The find() String Method Encrypting and Decrypting Symbols Displaying and Copying the Translated String Encrypting Other Symbols Summary Practice Questions

Chapter 6: Hacking the Caesar Cipher with Brute-Force

Source Code for the Caesar Cipher Hacker Program Sample Run of the Caesar Cipher Hacker Program Setting Up Variables Looping with the range() Function Decrypting the Message Using String Formatting to Display the Key and Decrypted Messages Summary Practice Question

Chapter 7: Encrypting with the Transposition Cipher

How the Transposition Cipher Works Source Code for the Transposition Cipher Encryption Program Sample Run of the Transposition Cipher Encryption Program Creating Your Own Functions with def Statements Passing the Key and Message As Arguments The List Data Type The Transposition Encryption Algorithm Augmented Assignment Operators Moving currentIndex Through the Message The join() String Method Return Values and return Statements The __name__ Variable Summary Practice Questions

Chapter 8: Decrypting with the Transposition Cipher

How to Decrypt with the Transposition Cipher on Paper Source Code for the Transposition Cipher Decryption Program Sample Run of the Transposition Cipher Decryption Program Importing Modules and Setting Up the main() Function Decrypting the Message with the Key Calling the main() Function Summary Practice Questions

Chapter 9: Programming a Program to Test Your Program

Source Code for the Transposition Cipher Tester Program Sample Run of the Transposition Cipher Tester Program Importing the Modules Creating Pseudorandom Numbers Creating a Random String Testing Each Message Checking Whether the Cipher Worked and Ending the Program Calling the main() Function Testing the Test Program Summary Practice Questions

Chapter 10: Encrypting and Decrypting Files

Plain Text Files Source Code for the Transposition File Cipher Program Sample Run of the Transposition File Cipher Program Working with Files Setting Up the main() Function Checking Whether a File Exists Using String Methods to Make User Input More Flexible Reading the Input File Measuring the Time It Took to Encrypt or Decrypt Writing the Output File Calling the main() Function Summary Practice Questions

Chapter 11: Detecting English Programmatically

How Can a Computer Understand English? Source Code for the Detect English Module Sample Run of the Detect English Module Instructions and Setting Up Constants The Dictionary Data Type Implementing the Dictionary File Counting the Number of English Words in message Removing Non-Letter Characters Detecting English Words Summary Practice Questions

Chapter 12: Hacking the Transposition Cipher

Source Code of the Transposition Cipher Hacker Program Sample Run of the Transposition Cipher Hacker Program Importing the Modules Multiline Strings with Triple Quotes Displaying the Results of Hacking the Message Getting the Hacked Message Calling the main() Function Summary Practice Questions

Chapter 13: A Modular Arithmetic Module for the Affine Cipher

Modular Arithmetic The Modulo Operator Finding Factors to Calculate the Greatest Common Divisor Multiple Assignment Euclid’s Algorithm for Finding the GCD Understanding How the Multiplicative and Affine Ciphers Work Source Code for the Cryptomath Module Summary Practice Questions

Chapter 14: Programming the Affine Cipher

Source Code for the Affine Cipher Program Sample Run of the Affine Cipher Program Setting Up Modules, Constants, and the main() Function Calculating and Validating the Keys Writing the Encryption Function Writing the Decryption Function Generating Random Keys Calling the main() Function Summary Practice Questions

Chapter 15: Hacking the Affine Cipher

Source Code for the Affine Cipher Hacker Program Sample Run of the Affine Cipher Hacker Program Setting Up Modules, Constants, and the main() Function The Affine Cipher Hacking Function Calling the main() Function Summary Practice Questions

Chapter 16: Programming the Simple Substitution Cipher

How the Simple Substitution Cipher Works Source Code for the Simple Substitution Cipher Program Sample Run of the Simple Substitution Cipher Program Setting Up Modules, Constants, and the main() Function The sort() List Method Wrapper Functions The translateMessage() Function Generating a Random Key Calling the main() Function Summary Practice Questions

Chapter 17: Hacking the Simple Substitution Cipher

Using Word Patterns to Decrypt Overview of the Hacking Process The Word Pattern Modules Source Code for the Simple Substitution Hacking Program Sample Run of the Simple Substitution Hacking Program Setting Up Modules and Constants Finding Characters with Regular Expressions Setting Up the main() Function Displaying Hacking Results to the User Creating a Cipherletter Mapping The hackSimpleSub() Function Calling the main() Function Summary Practice Questions

Chapter 18: Programming the Vigenère Cipher

Using Multiple Letter Keys in the Vigenère Cipher Source Code for the Vigenère Cipher Program Sample Run of the Vigenère Cipher Program Setting Up Modules, Constants, and the main() Function Building Strings with the List-Append-Join Process Encrypting and Decrypting the Message Calling the main() Function Summary Practice Questions

Chapter 19: Frequency Analysis

Analyzing the Frequency of Letters in Text Matching Letter Frequencies Source Code for Matching Letter Frequencies Storing the Letters in ETAOIN Order Counting the Letters in a Message Getting the First Member of a Tuple Ordering the Letters in the Message by Frequency Calculating the Frequency Match Score of the Message Summary Practice Questions

Chapter 20: Hacking the Vigenère Cipher

Using a Dictionary Attack to Brute-Force the Vigenère Cipher Source Code for the Vigenère Dictionary Hacker Program Sample Run of the Vigenère Dictionary Hacker Program About the Vigenère Dictionary Hacker Program Using Kasiski Examination to Find the Key’s Length Source Code for the Vigenère Hacking Program Sample Run of the Vigenère Hacking Program Importing Modules and Setting Up the main() Function Finding Repeated Sequences Calculating the Factors of the Spacings Finding the Most Likely Key Lengths Getting Letters Encrypted with the Same Subkey Attempting Decryption with a Likely Key Length Returning the Hacked Message Calling the main() Function Modifying the Constants of the Hacking Program Summary Practice Questions

Chapter 21: The One-Time Pad Cipher

The Unbreakable One-Time Pad Cipher Summary Practice Questions

Chapter 22: Finding and Generating Prime Numbers

What Is a Prime Number? Source Code for the Prime Numbers Module Sample Run of the Prime Numbers Module How the Trial Division Algorithm Works Implementing the Trial Division Algorithm Test The Sieve of Eratosthenes Generating Prime Numbers with the Sieve of Eratosthenes The Rabin-Miller Primality Algorithm Finding Large Prime Numbers Generating Large Prime Numbers Summary Practice Questions

Chapter 23: Generating Keys for the Public Key Cipher

Public Key Cryptography The Problem with Authentication Steps for Generating Public and Private Keys Source Code for the Public Key Generation Program Sample Run of the Public Key Generation Program Creating the main() Function Generating Keys with the generateKey() Function Creating Key Files with the makeKeyFiles() Function Calling the main() Function Hybrid Cryptosystems Summary Practice Questions

Chapter 24: Programming the Public Key Cipher

How the Public Key Cipher Works Source Code for the Public Key Cipher Program Sample Run of the Public Key Cipher Program Setting Up the Program How the Program Determines Whether to Encrypt or Decrypt Converting Strings to Blocks with getBlocksFromText() Using getTextFromBlocks() to Decrypt Writing the encryptMessage() Function Writing the decryptMessage() Function Reading in the Public and Private Keys from Their Key Files Writing the Encryption to a File Decrypting from a File Calling the main() Function Summary

Appendix Debugging Python Code

How the Debugger Works Debugging the Reverse Cipher Program Setting Breakpoints Summary

Index Resources

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