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Hands-On Cryptography with Python
Hands-On Cryptography with Python

Hands-On Cryptography with Python: Leverage the power of Python to encrypt and decrypt data

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Hands-On Cryptography with Python

Hashing

Hashing has two main purposes: the first is to put a fingerprint on a file so you can tell whether it has been altered, and the second is to conceal passwords so you can still recognize the correct password and enable login but a person who steals the hash cannot easily recover the password from it.

In this chapter, we will cover the following topics:

  • MD5 and SHA hashes
  • Windows password hashes
  • Linux password hashes
  • Challenge 1 – cracking Windows hashes
  • Challenge 2 – cracking many-round hashes
  • Challenge 3  cracking Linux hashes

MD5 and SHA hashes

After explaining what a hash function is, we will deal with MD5 and then the SHA family: SHA-1, SHA-2, and SHA-3. We will also acquire a bit of information about cracking hashes.

What are hashes?

As mentioned earlier, one point of using hashes is to put a fingerprint on a file. You can take all the bytes in the file and combine them together with a hash algorithm, and this creates a fixed-links hash value. If you change any part of the file and recalculate the hash, you get a completely different value. So, the idea is that if you have two files that are supposed to be identical, you can calculate the hash of each file, and if the hash of both files match, then the files are identical.

A very common...

Windows password hashes

In this section, we will see how to get hashes with Cain and then how MD4 and Unicode work. Then, we'll discuss cracking hashes with Google and cracking hashes with wordlists.

Getting hashes with Cain

Cain is a free hacking tool that can harvest Windows hashes from a running operating system. In order to test it, we'll make three accounts on Windows Server, the very latest version of the Windows operating system. You can use the user command at the Command Prompt to do this. You can add a user named John with a password P@sw0rd, a user named Paul with a password, and a user named Ringo with password P@sw0rd999:

If you run Cain, it can harvest the hashes. The following...

Linux password hashes

In this section, we will first discuss how to get the hashes from an operating system, and then look at the salting and stretching procedures that make Linux hashes much stronger. We will then discuss the specific hashing algorithm used by modern versions of Linux, and finally look at cracking hashes with wordlists and Python.

Here, we have created three users to test the software in much the same way as we did earlier on Windows. John and Paul have the same password and Ringo has a different password:

You get the hashes from the /etc/shadow file, from which we will print out the last three records. So, you will see John, Paul, and Ringo, and after each username comes $6, which indicates that it is a type 6 of password, which is the most modern and secure form. Then there is a long, random string of characters that goes up to the...

Challenge 1 – cracking Windows hashes

After a review of Windows hashing and an example of 1-digit hashing, we will give you two challenges—one with a 2-digit password and one with a 7-digit password. Here's how Windows hashes look in Python:

The algorithm uses hashlib to do an MD4 for the hash of the password, but before you do that, encode in Unicode which is utf-16le, and then calculate the hexdigest of the results to get the long number, The number starts with 464, in this case, which is a Windows password hash.

Thus, you can write a program that will try all the characters in this string, which will consist of 10 digits, and then calculate the hash for each one of them. You will be left with a simple dictionary with 10 values:

You can crack this 1-digit hash using a 1-digit password as follows:

So, here's a challenge. The password is a 2-digit...

Challenge 2 – cracking many-round hashes

After a review of how MD5 and SHA work in Python, we will see what a many round hash is, and then you will get two challenges to solve.

MD5 and SHA are both easy to calculate:

From the hashlib library, you just need to use the hashlib.new method and put the name of the algorithm in the first parameter, the password in the second parameter, and then add the hex-digest to it to see the actual result in hexadecimal instead of just an address to the object. To do many rounds, you just repeat that process.

You need to put the password in h and then use the current h, to calculate the next h and repeat this over and over and over. Here's a little script that prints out the first 10 rounds of a multi-round MD5 hash:

This technique is called stretching, and it's used by stronger password hashing routines, such as the Linux password...

Challenge 3 – cracking Linux hashes

After a review of Linux hashes, we'll show you your challenge.

Linux hashes are salted and stretched, and there are various versions of them. We are covering the current version, which is version 6, that is, the most secure form:

The hash is a long string starting with the dollar sign; the 6 indicates the version, then you have a dollar sign followed by salt, and another dollar sign followed by the hash. To calculate them in Python, you need to import a special SHA-512 crypt library, as you use the format shown earlier.

Here's your third challenge: a 3-digit password in this format. The salt value is penguins and the hash is this long mess starting with a P instance.

MD5 and SHA hashes


After explaining what a hash function is, we will deal with MD5 and then the SHA family: SHA-1, SHA-2, and SHA-3. We will also acquire a bit of information about cracking hashes.

What are hashes?

As mentioned earlier, one point of using hashes is to put a fingerprint on a file. You can take all the bytes in the file and combine them together with a hash algorithm, and this creates a fixed-links hash value. If you change any part of the file and recalculate the hash, you get a completely different value. So, the idea is that if you have two files that are supposed to be identical, you can calculate the hash of each file, and if the hash of both files match, then the files are identical.

A very common hash is MD5; it's been around for a couple of decades. It's 128 bits long, which is rather short for a hash function, and it's reliable enough for most purposes. People use it to put a fingerprint on downloads, and malware samples, and all sorts of things, and they are also sometimes...

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Key benefits

  • Explore popular and important cryptographic methods
  • Compare cryptographic modes and understand their limitations
  • Learn to perform attacks on cryptographic systems

Description

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.

Who is this book for?

Hands-On Cryptography with Python is for security professionals who want to learn to encrypt and evaluate data, and compare different encryption methods.

What you will learn

  • • Protect data with encryption and hashing
  • • Explore and compare various encryption methods
  • • Encrypt data using the Caesar Cipher technique
  • • Make hashes and crack them
  • • Learn how to use three NIST-recommended systems: AES, SHA, and RSA
  • • Understand common errors in encryption and exploit them
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Table of Contents

4 Chapters
Obfuscation Chevron down icon Chevron up icon
Hashing Chevron down icon Chevron up icon
Strong Encryption Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Half star icon Empty star icon 3.8
(4 Ratings)
5 star 50%
4 star 0%
3 star 25%
2 star 25%
1 star 0%
Stephen Hale Aug 13, 2019
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Good reference book
Amazon Verified review Amazon
Blk Jul 04, 2019
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As described
Amazon Verified review Amazon
Kenhou Sep 30, 2018
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
出版日がJune 2018にもかかわらず使ってるのはPython 2.7.12。p.10に記載はされているが、購入前にわかると良心的だと思う。
Amazon Verified review Amazon
Bryan D. Jul 04, 2020
Full star icon Full star icon Empty star icon Empty star icon Empty star icon 2
Some good information, but poor editing and bad code examples really made this book hard to follow. As well the scripting infromation provided was quite bad, I can convert from python2 with little trouble, but found the code to be clunky and unreadble. I did like the technical information, but I think ill check out the documention for the modules covered in the book.
Amazon Verified review Amazon
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