Encryption Algorithms Compared: AES, ChaCha20, and RSA Explained
Understand the differences between symmetric and asymmetric encryption, when to use AES-256 vs ChaCha20-Poly1305, and how RSA fits into modern cryptographic systems. A practical guide for non-cryptographers making security decisions.
Key Takeaways
- Symmetric encryption uses the same key for encryption and decryption — fast but requires secure key exchange.
- The Advanced Encryption Standard with 256-bit keys is the most widely deployed symmetric cipher.
- Designed by Daniel Bernstein, ChaCha20 is a stream cipher paired with the Poly1305 authenticator.
- RSA remains widely used for digital signatures and key exchange, though newer elliptic curve algorithms (ECDH, Ed25519) provide equivalent security with smaller keys.
AES Encrypt / Decrypt
Encrypt and decrypt text with AES-256-GCM
Symmetric vs Asymmetric Encryption
Symmetric encryption uses the same key for encryption and decryption — fast but requires secure key exchange. Asymmetric encryption uses a public/private key pair — slower but solves the key distribution problem. Modern systems combine both: asymmetric encryption exchanges a symmetric session key, then symmetric encryption handles the bulk data transfer.
AES-256: The Industry Standard
The Advanced Encryption Standard with 256-bit keys is the most widely deployed symmetric cipher. It operates on 128-bit blocks and uses 14 rounds of substitution and permutation. AES-GCM mode provides both encryption and authentication in a single operation. Hardware acceleration (AES-NI instructions) makes it extremely fast on modern processors — often exceeding 10 GB/s.
ChaCha20-Poly1305: The Mobile-Friendly Alternative
Designed by Daniel Bernstein, ChaCha20 is a stream cipher paired with the Poly1305 authenticator. It performs exceptionally well on devices without AES hardware acceleration — particularly older smartphones and IoT devices. ChaCha20 is also resistant to timing attacks by design, whereas some AES implementations require careful countermeasures.
| Feature | AES-256-GCM | ChaCha20-Poly1305 |
|---|---|---|
| Type | Block cipher | Stream cipher |
| Key size | 256 bits | 256 bits |
| Speed (hardware) | Very fast | Fast |
| Speed (software) | Medium | Very fast |
| Nonce size | 96 bits | 96 bits |
RSA and Modern Key Exchange
RSA remains widely used for digital signatures and key exchange, though newer elliptic curve algorithms (ECDH, Ed25519) provide equivalent security with smaller keys. A 256-bit elliptic curve key offers comparable strength to a 3072-bit RSA key. For file encryption tools, the choice of symmetric cipher matters most — use AES-GCM when hardware acceleration is available, or ChaCha20-Poly1305 for universal compatibility.