# The ChaCha family of stream ciphers

## Features

- pure Rust implementation
- supports the RustCrypto API
- builds on stable Rust
- portable
- fast: within 15% of throughput of a hand-optimized ASM SIMD implementation
  (floodberry/chacha-opt) on my machine (a Xeon X5650, using ppv-lite86)
- no-std compatible (std required only for runtime algorithm selection)

## Supported Variants

ChaCha20: used in chacha20-poly1305 in TLS, OpenSSH; arc4random in the BSDs,
Linux /dev/urandom since 4.8.

Ietf: IETF RFC 7539. Longer nonce, short block counter.

XChaCha20: constructed analogously to XSalsa20; a mixing step during
initialization allows using a long nonce and along with a full-sized block
counter.

ChaCha12, ChaCha8: faster; lower security margin of safety.