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Symmetric Encryption

One Key to Rule Them All

12 min read Updated 2024

How It Works

Symmetric encryption uses the same key for both encryption and decryption. It's fast and efficient, making it ideal for encrypting large amounts of data.

Symmetric Process
Plaintext + Key → [Encryption] → Ciphertext
Ciphertext + Key → [Decryption] → Plaintext

Same key used for both operations!

Common Algorithms

AES

Advanced Encryption Standard - gold standard

Block Cipher

ChaCha20

Fast stream cipher, great for mobile

Stream Cipher

3DES

Legacy, being phased out

Legacy

Blowfish/Twofish

Schneier designs, still secure

Alternative

Modes of Operation

GCMGalois/Counter Mode - authenticated encryption (recommended)
CBCCipher Block Chaining - common but needs careful implementation
ECBElectronic Codebook - NEVER use (patterns visible)
CTRCounter mode - parallelizable stream cipher mode

The Key Distribution Problem

!

Challenge: How do you securely share the key? If you could securely send the key, you could securely send the message! This is why asymmetric encryption is used for key exchange.

Best Practices

  • Use AES-256-GCM or ChaCha20-Poly1305
  • Never reuse nonces/IVs
  • Use authenticated encryption (AEAD)
  • Derive keys properly with KDFs
  • Rotate keys periodically