Symmetric cryptography is an encryption method where the same key is used for both encrypting and decrypting data. It is fast and efficient, and is widely used on the internet and computer systems.

In symmetric cryptography, it is always necessary to solve how to distribute the key to the parties.

If, for example, Liisa wants to send a message to Jaska, they would meet in advance and agree on an encryption key. However, this is not very convenient, so there are smarter solutions for key exchange in the realm of asymmetric cryptography, which we will cover later in the course!

Symmetric encryption uses two types of algorithms for encrypting and decrypting data: stream ciphers and block ciphers. Both use the same encryption key, but the amount of data they handle and their operating principles differ from each other.

Uses a key stream encryption, combined with XOR operation, to encrypt plaintext data, producing ciphertext.

The encryption key is usually a pseudorandom number sequence that is difficult to predict.

The encryption algorithm takes one block at a time and produces a corresponding-sized ciphertext block.

Often iteration (repetitive application) is used to ensure security.

This is sufficient for now! Next, let's continue to explore block ciphers in more detail.

## What is symmetric cryptography?

Symmetric cryptography is an encryption method where the same key is used for both encrypting and decrypting data. It is fast and efficient, and is widely used on the internet and computer systems.

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## Key Exchange

In symmetric cryptography, it is always necessary to solve how to distribute the key to the parties.

If, for example, Liisa wants to send a message to Jaska, they would meet in advance and agree on an encryption key. However, this is not very convenient, so there are smarter solutions for key exchange in the realm of asymmetric cryptography, which we will cover later in the course!

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## Two types of symmetric cryptography

Symmetric encryption uses two types of algorithms for encrypting and decrypting data: stream ciphers and block ciphers. Both use the same encryption key, but the amount of data they handle and their operating principles differ from each other.

### Virran salausta

- Encrypt the data **one bit at a time**.
- Uses a key stream encryption, combined with XOR operation, to encrypt plaintext data, producing ciphertext.
- The encryption key is usually a pseudorandom number sequence that is difficult to predict.

### Block Cipher

- Encrypt data in **fixed-size blocks** (e.g. 64 bits).
- The encryption algorithm takes one block at a time and produces a corresponding-sized ciphertext block.
- Often iteration (repetitive application) is used to ensure security.

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## Bottom line

This is sufficient for now! Next, let's continue to explore block ciphers in more detail.


What is symmetric cryptography?

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

What is MAC and why is it needed?

Different MAC algorithms

MAC algorithms

Random numbers in cryptography

Random numbers

What is symmetric cryptography?

What is symmetric cryptography?

Learn to hack — start here