Text Message Encryption: Best Algorithms

TL;DR

For most text message encryption needs, AES-256 is the best choice. It’s widely supported, very secure, and efficient. However, consider Signal Protocol if you need end-to-end encryption with forward secrecy (like WhatsApp or Signal).

1. Understanding Encryption Basics

Encryption turns readable text (plaintext) into unreadable code (ciphertext). Decryption does the reverse.

• Symmetric Encryption: Uses the same key for encryption and decryption. Faster, but key distribution is tricky.
• Asymmetric Encryption: Uses different keys – a public key for encryption and a private key for decryption. Slower, but solves the key distribution problem.

2. Popular Encryption Algorithms

Here’s a breakdown of common algorithms:

• AES (Advanced Encryption Standard): A symmetric block cipher. Available in different key sizes (128-bit, 192-bit, 256-bit).
• DES (Data Encryption Standard): Older and now considered insecure due to its small key size. Avoid using it.
• 3DES (Triple DES): An improvement over DES but still slower and less secure than AES. Not recommended for new applications.
• RSA: A widely used asymmetric algorithm. Good for key exchange, digital signatures, and encrypting small amounts of data.
• ChaCha20-Poly1305: A symmetric stream cipher often preferred when AES hardware acceleration isn’t available (e.g., on some mobile devices).
• Signal Protocol: Not a single algorithm, but a complete end-to-end encryption protocol built on top of other algorithms like Curve25519 and AES.

3. Choosing the Right Algorithm for Text Messages

Here’s how to decide:

1. AES-256: Best overall choice for most applications. It’s fast, secure, and well-supported in many programming languages and libraries.
   • Example using Python with the cryptography library:

     from cryptography.fernet import Fernet
     key = Fernet.generate_key()
     f = Fernet(key)
     token = f.encrypt(b"My secret message!")
     decrypted = f.decrypt(token)

2. ChaCha20-Poly1305: Good alternative if AES hardware acceleration isn’t available on your target devices.
   • Often used in TLS 1.3 and is becoming more common.
3. Signal Protocol: If you need end-to-end encryption with forward secrecy (meaning past messages remain secure even if a key is compromised), use the Signal Protocol.
   • Implementing this yourself is complex; it’s best to use an existing library like libsignal.

4. Key Management

The biggest challenge isn’t the algorithm itself, but how you manage the encryption keys.

• Never hardcode keys into your application!
• Key Exchange: How do you securely share the key between sender and receiver? Options include:
  • Diffie-Hellman Key Exchange: Allows two parties to establish a shared secret key over an insecure channel.
  • Pre-shared Keys: Simplest, but requires a secure way to initially distribute the key.
  • Asymmetric Encryption (RSA): Use the receiver’s public key to encrypt the symmetric key and send it to them.
• Key Storage: Protect the keys on both sender and receiver devices.
  • Use secure storage mechanisms provided by the operating system (e.g., Keychain on iOS, KeyStore on Android).

5. Important Considerations

• Library Choice: Use well-vetted cryptography libraries like:
  • Python: cryptography
  • Java: Bouncy Castle, Java Cryptography Extension (JCE)
  • JavaScript: Web Crypto API, crypto-js
• Random Number Generation: Use a cryptographically secure pseudo-random number generator (CSPRNG) for key generation.
• Padding: When using block ciphers like AES, use appropriate padding schemes (e.g., PKCS#7).