Security+ Academy · Lesson

Symmetric Encryption Algorithms

Explore AES, DES, and 3DES — how shared-key encryption works, key lengths, and when to use each algorithm.

How Symmetric Encryption Works

Symmetric encryption uses a single shared key for both encrypting and decrypting data. The sender and receiver must both possess the same secret key, and keeping that key secure is critical — anyone with the key can decrypt the data. Symmetric encryption is computationally fast and efficient, making it ideal for encrypting large volumes of data. The core challenge of symmetric encryption is key distribution: how do two parties securely share a key before they have a secure channel?

AES: The Gold Standard

Advanced Encryption Standard (AES) is the most widely used symmetric encryption algorithm today, adopted by NIST in 2001 as the successor to DES. AES operates on 128-bit blocks and supports three key sizes: AES-128, AES-192, and AES-256, where the number indicates key length in bits. AES-256 provides the strongest security margin. AES is used in TLS for HTTPS, full-disk encryption (BitLocker), file encryption, and virtually every secure modern application. It has no known practical weaknesses when properly implemented.

# Encrypting a file with AES-256 using OpenSSL
openssl enc -aes-256-cbc -pbkdf2 -in plaintext.txt -out encrypted.bin -k 'mysecretpassword'

# Decrypting
openssl enc -aes-256-cbc -pbkdf2 -d -in encrypted.bin -out decrypted.txt -k 'mysecretpassword'

# AES-256 key: 256 bits = 32 bytes = extremely secure

All lessons in this course

← Back to Security+ Academy