Learn to deploy proven cryptographic tools in your applications and services
Cryptography is, quite simply, what makes security and privacy in the digital world possible. Tech professionals, including programmers, IT admins, and security analysts, need to understand how cryptography works to protect users, data, and assets. Implementing Cryptography Using Python will teach you the essentials, so you can apply proven cryptographic tools to secure your applications and systems. Because this book uses Python, an easily accessible language that has become one of the standards for cryptography implementation, you’ll be able to quickly learn how to secure applications and data of all kinds.
In this easy-to-read guide, well-known cybersecurity expert Shannon Bray walks you through creating secure communications in public channels using public-key cryptography. You’ll also explore methods of authenticating messages to ensure that they haven’t been tampered with in transit. Finally, you’ll learn how to use digital signatures to let others verify the messages sent through your services.
- Learn how to implement proven cryptographic tools, using easy-to-understand examples written in Python
- Discover the history of cryptography and understand its critical importance in today’s digital communication systems
- Work through real-world examples to understand the pros and cons of various authentication methods
- Protect your end-users and ensure that your applications and systems are using up-to-date cryptography
Table of Contents
Introduction xvii
Chapter 1 Introduction to Cryptography and Python 1
Exploring Algorithms 2
Why Use Python? 2
Downloading and Installing Python 3
Installing on Ubuntu 4
Installing on macOS 4
Installing on Windows 4
Installing on a Chromebook 4
Installing Additional Packages 5
Installing Pip, NumPy, and Matplotlib 6
Installing the Cryptography Package 7
Installing Additional Packages 8
Testing Your Install 9
Diving into Python Basics 9
Using Variables 10
Using Strings 11
Introducing Operators 11
Understanding Arithmetic Operators 11
Understanding Comparison Operators 13
Understanding Logical Operators 13
Understanding Assignment Operators 14
Understanding Bitwise Operators 15
Understanding Membership Operators 15
Understanding Identity Operators 16
Using Conditionals 16
Using Loops 17
for 17
while 18
continue 18
break 18
else 18
Using Files 19
Understanding Python Semantics 20
Sequence Types 20
Introducing Custom Functions 26
Downloading Files Using Python 27
Introducing Python Modules 28
Creating a Reverse Cipher 29
Summary 30
Chapter 2 Cryptographic Protocols and Perfect Secrecy 31
The Study of Cryptology 32
Understanding Cryptography 32
Cryptography’s Famous Family: Alice and Bob 33
Diffie-Hellman 34
Data Origin Authentication 34
Entity Authentication 35
Symmetric Algorithms 36
Asymmetric Algorithms 36
The Needham-Schroeder Protocols 36
The Otway-Rees Protocol 38
Kerberos 39
Multiple-Domain Kerberos 40
X.509 41
Formal Validation of Cryptographic Protocols 46
Configuring Your First Cryptographic Library 47
Understanding Cryptanalysis 47
Brute-Force Attacks 47
Side-Channel Attacks 48
Social Engineering 48
Analytical Attacks 48
Frequency Analysis 48
Attack Models 49
Shannon’s Theorem 50
One-Time Pad 51
XOR, AND, and OR 51
One-Time Pad Function 56
One-Way Hashes 58
Cryptographic One-Way Hashes 59
Message Authentication Codes 60
Perfect Forward Secrecy 60
Published and Proprietary Encryption Algorithms 61
Summary 62
References 62
Chapter 3 Classical Cryptography 65
Password Best Practices 66
Password Storage 66
Hashing Passwords 67
Salting Passwords 67
Stretching Passwords 68
Password Tools 68
Obfuscating Data 69
ASCII Encoding 70
Base64 Encoding Text 70
Binary Data 72
Decoding 72
Historical Ciphers 72
Scytale of Sparta 73
Substitution Ciphers 73
Caesar Cipher 74
ROT-13 76
Atbash Cipher 77
Vigenère Cipher 77
Playfair 79
Hill 2x2 83
Column Transposition 87
Affine Cipher 90
Summary 93
Chapter 4 Cryptographic Math and Frequency Analysis 95
Modular Arithmetic and the Greatest Common Devisor 96
Prime Numbers 97
Prime Number Theorem 98
School Primality Test 98
Fermat’s Little Theorem 100
Miller-Rabin Primality Test 100
Generate Large Prime Numbers 104
Basic Group Theory 106
Orders of Elements 107
Modular Inverses 109
Fermat’s Little Theorem to Find the Inverse 110
Extending the GCD 111
Euler’s Theorem 111
Pseudorandomness 115
Breaking C’s rand() Function 116
Solving Systems of Linear Equations 117
Frequency Analysis 120
Cryptanalysis with Python 123
Using an Online Word List 125
Determining the Frequency 126
Breaking the Vigenère Cipher 129
Summary 138
Chapter 5 Stream Ciphers and Block Ciphers 139
Convert between Hexdigest and Plaintext 140
Use Stream Ciphers 141
ARC4 147
Vernam Cipher 148
Salsa20 Cipher 149
ChaCha Cipher 151
Use Block Ciphers 156
Block Modes of Operations 158
ECB Mode 158
CBC Mode 159
CFB Mode 160
OFB Mode 162
CTR Mode 163
Tricks with Stream Modes 164
DIY Block Cipher Using Feistel Networks 165
Advanced Encryption Standard (AES) 167
Using AES with Python 167
File Encryption Using AES 169
File Decryption Using AES 169
Summary 169
Chapter 6 Using Cryptography with Images 171
Simple Image Cryptography 171
Images and Cryptography Libraries 174
Understanding the Cryptography Library 174
Understanding the Cryptosteganography Library 175
Image Cryptography 175
File Cryptography Using Fernet 176
Image Cryptography Using Fernet 179
AES and Block Modes of Operations 180
Exploring a Simple ECB Mode Example 181
Exploring a Simple CBC Mode Example 185
Applying the Examples 186
Steganography 187
Storing a Message Inside an Image 188
Storing a Binary File Inside an Image 192
Working with large images 195
Summary 197
Chapter 7 Message Integrity 199
Message Authentication Codes 200
Hash-based Message Authentication Code 201
Using HMAC to Sign Message 202
Message Digest with SHA 203
Binary Digests 204
NIST Compliance 205
CBC-MAC 206
Birthday Attacks 207
Crafting Forgeries 209
The Length Extension Attack 209
Setting Up a Secure Channel 210
Communication Channels 211
Sending Secure Messages over IP Networks 212
Create a Server Socket 212
Create a Client Socket 213
Create a Threaded Server with TCP 214
Adding Symmetric Encryption 215
Concatenate Message and MAC 218
Summary 221
References 222
Chapter 8 Cryptographic Applications and PKI 223
The Public-Key Transformation 224
Exploring the Basics of RSA 226
Generating RSA Certificates 229
Constructing Simple Text Encryption and Decryption with RSA Certificates 231
Constructing BLOB Encryption and
Decryption with RSA Certificates 232
The El-Gamal Cryptosystem 235
Elliptic Curve Cryptography 238
Generating ECC Keys 240
Key Lengths and Curves 241
Diffie-Hellman Key Exchange 242
Summary 245
Chapter 9 Mastering Cryptography Using Python 247
Constructing a Plaintext Communications Application 248
Creating a Server 248
Creating the Client 250
Creating the Helper File 251
Execution 252
Installing and Testing Wireshark 253
Implementing PKI in the Application Using RSA Certificates 255
Modifying the Server 256
Modifying the Client 257
Modifying the Helper File 258
Execution 259
Implementing Diffie-Hellman Key Exchange 261
Modifying the Server File 262
Modifying the Client File 264
Modifying the Helper File 266
Creating the Diffie-Hellman Class File 270
Execution 275
Wrapping Up 276
Index 277
