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//! XChaCha20-Poly1305 authenticated encryption.
//!
//! Uses OS-provided randomness (`arc4random_buf`) via
//! `tesseras_dht::sys::random_bytes` for key and nonce
//! generation.
use chacha20poly1305::{
XChaCha20Poly1305, XNonce,
aead::{Aead, KeyInit},
};
/// XChaCha20 extended nonce size (24 bytes).
const NONCE_SIZE: usize = 24;
/// XChaCha20-Poly1305 key size (32 bytes).
pub const KEY_SIZE: usize = 32;
/// Generate a random 32-byte encryption key.
pub fn generate_key() -> [u8; KEY_SIZE] {
let mut key = [0u8; KEY_SIZE];
tesseras_dht::sys::random_bytes(&mut key);
key
}
/// Encrypt plaintext with a random nonce. Returns `nonce || ciphertext`.
pub fn encrypt(key: &[u8; KEY_SIZE], plaintext: &[u8]) -> Vec<u8> {
let cipher = XChaCha20Poly1305::new(key.into());
let mut nonce_bytes = [0u8; NONCE_SIZE];
tesseras_dht::sys::random_bytes(&mut nonce_bytes);
let nonce = XNonce::from(nonce_bytes);
let ciphertext = cipher
.encrypt(&nonce, plaintext)
.expect("encryption should not fail");
let mut out = Vec::with_capacity(NONCE_SIZE + ciphertext.len());
out.extend_from_slice(&nonce_bytes);
out.extend_from_slice(&ciphertext);
out
}
/// Decrypt `nonce || ciphertext`. Returns `None` if authentication fails.
pub fn decrypt(key: &[u8; KEY_SIZE], data: &[u8]) -> Option<Vec<u8>> {
if data.len() < NONCE_SIZE {
return None;
}
let (nonce_bytes, ciphertext) = data.split_at(NONCE_SIZE);
let nonce = XNonce::from_slice(nonce_bytes);
let cipher = XChaCha20Poly1305::new(key.into());
cipher.decrypt(nonce, ciphertext).ok()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn round_trip() {
let key = generate_key();
let sealed = encrypt(&key, b"hello");
let opened = decrypt(&key, &sealed).unwrap();
assert_eq!(opened, b"hello");
}
#[test]
fn wrong_key_fails() {
let key = generate_key();
let wrong = generate_key();
let sealed = encrypt(&key, b"secret");
assert!(decrypt(&wrong, &sealed).is_none());
}
#[test]
fn truncated_fails() {
let key = generate_key();
assert!(decrypt(&key, &[0u8; 10]).is_none());
}
#[test]
fn different_nonces() {
let key = generate_key();
let a = encrypt(&key, b"same");
let b = encrypt(&key, b"same");
assert_ne!(a, b);
}
}
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