Cryptography

I carry my unwritten poems in cipher on my face!

—George Eliot

This chapter introduces you to algorithms related to cryptography. We will start by presenting the background, then we will discuss symmetric encryption algorithms. We will then explain the Message-Digest 5 (MD5) algorithm and the Secure Hash Algorithm (SHA) and present the limitations and weaknesses of symmetric algorithms. Next, we will discuss asymmetric encryption algorithms and how they are used to create digital certificates. Finally, we will present a practical example that summarizes all of these techniques.

By the end of this chapter, you will have a basic understanding of various issues related to cryptography.

The following topics are discussed in this chapter:

• Introduction to cryptography
• Understanding the types of cryptography techniques
• Example – security concerns when deploying a machine learning model

Let’s start...

Introduction to cryptography

Techniques to protect secrets have been around for centuries. The earliest attempts to secure and hide data from adversaries date back to ancient inscriptions discovered on monuments in Egypt, where a special alphabet that was known by only a few trusted people was used. This early form of security is called obscurity and is still used in different forms today. In order for this method to work, it is critical to protect the secret, which would be the secret meaning of the alphabet in the above example. Later in time, finding foolproof ways of protecting important messages was important in both World War One and World War Two. In the late 20^th century, with the introduction of electronics and computers, sophisticated algorithms were developed to secure data, giving rise to a whole new field called cryptography. This chapter discusses the algorithmic aspects of cryptography. One of the uses of these algorithms is to allow secure data exchange between two...

Understanding the types of cryptographic techniques

Different types of cryptographic techniques use different types of algorithms and are used under different sets of circumstances. As different situations and use-cases have different requirements of security based on the business requirements and the data classification, the selection of the right technique is important for a well-designed architecture.

Broadly, cryptographic techniques can be divided into the following three types:

• Hashing
• Symmetric
• Asymmetric

Let’s look at them one by one.

Using the cryptographic hash function

The cryptographic hash function is a mathematical algorithm that can be used to create a unique fingerprint of a message. It creates an output, called a hash, from plain text. The size of the output is usually fixed but can vary for some specialized algorithms.

Mathematically, this looks as follows:

C₁ = hashFunction(P₁)

This is explained as follows...

Example: security concerns when deploying a machine learning model

In Chapter 6, Unsupervised Machine Learning Algorithms, we looked at the Cross-Industry Standard Process for Data Mining (CRISP-DM) life cycle, which specifies the different phases of training and deploying a machine learning model. Once a model is trained and evaluated, the final phase is deployment. If it is a critical machine learning model, then we want to make sure that all of its security goals are met.

Let’s analyze the common challenges faced in deploying a model such as this and how we can address those challenges using the concepts discussed in this chapter. We will discuss strategies to protect our trained model against the following three challenges:

• Man-in-the-Middle (MITM) attacks
• Masquerading
• Data tempering

Let’s look at them one by one.

MITM attacks

One of the possible attacks that we would want to protect our model against is MITM attacks. A...

Summary

In this chapter, we learned about cryptographic algorithms. We started by identifying the security goals of a problem. We then discussed various cryptographic techniques and also looked at the details of the PKI. Finally, we looked at the different ways of protecting a trained machine learning model against common attacks. Now, you should be able to understand the fundamentals of security algorithms used to protect modern IT infrastructures.

In the next chapter, we will look at designing large-scale algorithms. We will study the challenges and trade-offs involved in designing and selecting large algorithms. We will also look at the use of a GPU and clusters to solve complex problems.

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