ChaCha20 is a stream cipher designed by Daniel J. Bernstein as a variant of the Salsa20 cipher. It is known for its speed and security, making it suitable for various applications, including secure communications and data encryption. ChaCha20 operates on 64-byte blocks and uses a 256-bit key, providing a high level of security against cryptographic attacks. The cipher employs a series of mathematical operations, including addition, XOR, and rotation, to transform plaintext into ciphertext. Its design allows for efficient implementation on both software and hardware platforms, making it a popular choice in modern cryptographic protocols, such as TLS and VPNs.