Book Image

Hands-On Cryptography with Python

By : Samuel Bowne
Book Image

Hands-On Cryptography with Python

By: Samuel Bowne

Overview of this book

Cryptography is essential for protecting sensitive information, but it is often performed inadequately or incorrectly. Hands-On Cryptography with Python starts by showing you how to encrypt and evaluate your data. The book will then walk you through various data encryption methods,such as obfuscation, hashing, and strong encryption, and will show how you can attack cryptographic systems. You will learn how to create hashes, crack them, and will understand why they are so different from each other. In the concluding chapters, you will use three NIST-recommended systems: the Advanced Encryption Standard (AES), the Secure Hash Algorithm (SHA), and the Rivest-Shamir-Adleman (RSA). By the end of this book, you will be able to deal with common errors in encryption.
Table of Contents (9 chapters)

Challenge 1 – the Caesar cipher

After a Caesar cipher review, we'll have an example of how to solve it and then your challenge. Remember how the Caesar cipher works. You have an alphabet of available characters, you take in the message and a shift value, and then you just shift the characters forward that many steps in the alphabet, wrapping around if you go around the end. The script we end up with works for any shift value, including normal numbers, such as 3, or even numbers that are larger than 26; they just wrap around and can scramble any data you put it.

Here's an example:

  1. For ciphertext, you can decipher it by just trying all the shift values from 0 to 25, and one of them will just be readable. This is a simple brute-force attack. Let's take a look at it.

Here, in Python, go to the caesar4 script, that we had before. It takes in a string and shifts it by any value you specify. If we use that script, we can run it as follows:

  1. Then, if we put in HELLO and shift it by 3, it turns into KHOOR.
  2. If we want to crack it, we can use the solution script as follows:

  1. So, if we use that script, we can run it:
  1. If we put it in KHOOR, it'll shift it by a variety of values, and you can see the one that's readable at 23, which is HELLO. So, the example we discussed before of longer ciphertexts and so on will become readable down at 3, where you see its DEMONSTRATION:
  1. Your challenge is to decipher this string: MYXQBKDEVKDSYXC.

In the next section, we'll have a challenge on base64.