ChaCha20 is like the agile ninja of modern encryption—fast, stealthy, and built to dodge many of the pitfalls older ciphers stumbled over. Let’s unlock what makes it so effective:

🧠 What Is ChaCha20?

ChaCha20 is a stream cipher developed by Daniel J. Bernstein as an improvement on his earlier Salsa20 algorithm. It encrypts data by generating a stream of pseudorandom bytes (called a keystream) and XORing it with the plaintext—classic stream cipher style.

⚙️ Key Features

• Key Size: 256 bits (very secure)
• Nonce Size: 96 bits, used to ensure each message is encrypted uniquely
• Block Size: 512 bits of keystream generated at a time
• Designed For: High speed, strong security, and simplicity on both hardware and software

🔄 How It Works (Simplified Flow)

1. Setup: Combines the key, nonce, and a counter into a 512-bit input.
2. Rounds of Mixing: The core operation involves 20 rounds of permutations using addition, rotation, and XOR—called ARX operations.
3. Keystream Generation: Transforms the input into a pseudorandom output block (keystream).
4. Encryption: Each byte of the plaintext is XORed with the corresponding byte of the keystream.

🛡️ Strengths

• 🚀 Speed: Faster than AES in many software environments, especially on mobile devices.
• 🧠 Simplicity: Avoids complex tables and memory-intensive operations.
• 🧱 Strong Security: Resistant to known attacks; cryptographers haven’t found any practical weaknesses.
• 🔒 Used In: TLS 1.3, SSH, WireGuard VPN, and secure messaging apps like Signal.

⚠️ Considerations

• Since it’s a stream cipher, nonce reuse can be catastrophic—it must never encrypt two messages with the same key and nonce combination.
• It doesn’t provide authentication on its own, but it’s often paired with Poly1305, creating the ChaCha20-Poly1305 authenticated encryption scheme.