Hashing Basics

Consider the scenario where you just downloaded a 6 GB file and want to know whether the copy you downloaded is identical to the original file, bit for bit. How would you do that? Or if a good Samaritan handed you this 6 GB file on a USB memory drive, how can you be sure it is identical to the file you want to download?

The answer to both of the above questions lies in comparing the hash values of the two files; if two hash values are equal, you can say with very high certainty that the two files are identical. But what is a hash value?

A hash value is a fixed-size string or characters that is computed by a hash function. A hash function takes an input of an arbitrary size and returns an output of fixed length, i.e., a hash value. We will cover various exciting and clever uses of hash functions and values in this room.

Note about terminology: We favoured the terms hash function and hash value. However, we occasionally use the word hash as a verb to mean calculate the hash value; moreover, we occasionally use the word hash by itself as a noun to refer to the hash value.

Room Prerequisites

This room is the third of three introductory rooms about cryptography. Because we will reference the topics in the previous two rooms, it is recommended that you finish the last two rooms before attempting this one.

• Cryptography Basics
• Public Key Cryptography Basics
• Hashing Basics (this room)

Learning Objectives

Upon the completion of this room, you will learn about:

• Hash functions and collisions
• The role of hashing in authentication systems
• Recognizing stored hash values
• Cracking hash values
• The use of hashing for integrity protection

To follow along, first, let’s start the Virtual Machine by pressing the Start Machine button below.

The machine will start in Split-Screen view. In case the VM is not visible, use the blue Show Split View button at the top of the page.

You can also access the virtual machine using SSH at the IP address MACHINE_IP using the following credentials:

• Username: user
• Password: Tryhackme123!