Message Authentication Code (MAC) is essentially a cryptographic hash that, in addition to verifying the integrity of the message (

), also has an important additional task: to verify the 

 of the message, i.e., to verify that the 

message really originates from the expected sender

The operating principle of MAC is quite simple.

First, there must be a shared symmetric encryption key between the sender and receiver.

Then the sender creates a MAC value. MAC is created, simplistically, by combining a secret key with the contents of the message and calculating a cryptographic digest of these.

The recipient itself calculates the MAC value of the incoming message in exactly the same way and with the secret key known to the recipient.

Then the recipient compares the MAC value it calculated itself with the MAC value sent by the sender.

If the content of the message changes, for example by an attacker, along the way, the MAC value no longer matches the value calculated by the recipient.

You have shared the encryption key with Alice: 

 (hex) and agreed to use the HMAC-SHA256 MAC algorithm.

Alice sends you the coordinates of the secret meeting place with a message: 

bc31e702151483ab8ce821519bf10dbde09a66fd930a03cadccef7bc1c72eae1

 to verify the authenticity of the message!

## What is MAC?

Message Authentication Code (MAC) is essentially a cryptographic hash that, in addition to verifying the integrity of the message (**message has remained unchanged**), also has an important additional task: to verify the *authenticity* of the message, i.e., to verify that the **message really originates from the expected sender**.

---

## How Does MAC Work?

The operating principle of MAC is quite simple.

- First, there must be a shared symmetric encryption key between the sender and receiver.
- Then the sender creates a MAC value. MAC is created, simplistically, by combining a secret key with the contents of the message and calculating a cryptographic digest of these.
- The recipient itself calculates the MAC value of the incoming message in exactly the same way and with the secret key known to the recipient.
- Then the recipient compares the MAC value it calculated itself with the MAC value sent by the sender.
- If the content of the message changes, for example by an attacker, along the way, the MAC value no longer matches the value calculated by the recipient.

---

## Exercise

You have shared the encryption key with Alice: **01:02:03** (hex) and agreed to use the HMAC-SHA256 MAC algorithm.

- Alice sends you the coordinates of the secret meeting place with a message: **51.848637, -0.55462**
- Message includes MAC: **bc31e702151483ab8ce821519bf10dbde09a66fd930a03cadccef7bc1c72eae1**

Use [CyberChef's HMAC module](https://gchq.github.io/CyberChef/#recipe=HMAC(%7B'option':'Hex','string':'010203'%7D,'SHA256')) to verify the authenticity of the message!

@exercise 003acfc87073

@exercise 4ee60b1b512c


What is MAC and why is it needed?

From the history of cryptography to current use, the basics of encryption, technologies, applications and their impact on security.

Welcome to Hakatemia's cryptography course!

In this course, we will go through the basics of cryptography, the most important encryption algorithms, and their modern applications. The course is beginner-friendly and practical.

The goal is that after the course you will know what cryptography is, what it is used for, and how to choose the right encryption techniques and settings for different purposes.

What is cryptography? Basic concepts and uses

Introduction to Cryptography

Caesar Cipher: The Ancient Code That Changed Communication

The Enigma Machine: How WWII Codebreakers Unlocked the Greatest Mystery of the War

Historical encryption techniques

Checksums

What are hash functions and what are they used for?

Cracking Hashes: How Does It Work?

MD5 hash - a broken classic

PBKDF2, BCrypt, SCrypt and Argon2

SHA2 vs SHA3 vs PBKDF2 vs bcrypt vs SCrypt vs Argon2: Which to choose for password storage?

Diversion functions

Different MAC algorithms

MAC algorithms

What is MAC and why is it needed?

What is MAC?

Learn to hack — start here