Struct chacha20poly1305::XChaCha20Poly1305

pub struct XChaCha20Poly1305 { /* private fields */ }

ChaCha20Poly1305 variant with an extended 192-bit (24-byte) nonce.

The xchacha20poly1305 Cargo feature must be enabled in order to use this (which it is by default).

The construction is an adaptation of the same techniques used by XSalsa20 as described in the paper “Extending the Salsa20 Nonce” to the 96-bit nonce variant of ChaCha20, which derive a separate subkey/nonce for each extended nonce:

https://cr.yp.to/snuffle/xsalsa-20081128.pdf

No authoritative specification exists for XChaCha20Poly1305, however the construction has “rough consensus and running code” in the form of several interoperable libraries and protocols (e.g. libsodium, WireGuard) and is documented in an (expired) IETF draft, which also applies the proof from the XSalsa20 paper to the construction in order to demonstrate that XChaCha20 is secure if ChaCha20 is secure (see Section 3.1):

https://tools.ietf.org/html/draft-arciszewski-xchacha-03

It is worth noting that NaCl/libsodium’s default “secretbox” algorithm is XSalsa20Poly1305, not XChaCha20Poly1305, and thus not compatible with this library. If you are interested in that construction, please see the xsalsa20poly1305 crate:

https://docs.rs/xsalsa20poly1305/

Usage

use chacha20poly1305::{XChaCha20Poly1305, Key, XNonce};
use chacha20poly1305::aead::{Aead, NewAead};

let key = Key::from_slice(b"an example very very secret key."); // 32-bytes
let aead = XChaCha20Poly1305::new(key);

let nonce = XNonce::from_slice(b"extra long unique nonce!"); // 24-bytes; unique
let ciphertext = aead.encrypt(nonce, b"plaintext message".as_ref()).expect("encryption failure!");
let plaintext = aead.decrypt(nonce, ciphertext.as_ref()).expect("decryption failure!");
assert_eq!(&plaintext, b"plaintext message");

Trait Implementations

impl AeadInPlace for XChaCha20Poly1305

type NonceSize = U24

The length of a nonce.

type TagSize = U16

The maximum length of the nonce.

type CiphertextOverhead = U0

The upper bound amount of additional space required to support a ciphertext vs. a plaintext.

fn encrypt_in_place_detached(
    &self,
    nonce: &XNonce,
    associated_data: &[u8],
    buffer: &mut [u8]
) -> Result<Tag, Error>

Encrypt the data in-place, returning the authentication tag

fn decrypt_in_place_detached(
    &self,
    nonce: &XNonce,
    associated_data: &[u8],
    buffer: &mut [u8],
    tag: &Tag
) -> Result<(), Error>

Decrypt the message in-place, returning an error in the event the provided authentication tag does not match the given ciphertext (i.e. ciphertext is modified/unauthentic)

fn encrypt_in_place(
    &self,
    nonce: &GenericArray<u8, Self::NonceSize>,
    associated_data: &[u8],
    buffer: &mut dyn Buffer
) -> Result<(), Error>

Encrypt the given buffer containing a plaintext message in-place.

fn decrypt_in_place(
    &self,
    nonce: &GenericArray<u8, Self::NonceSize>,
    associated_data: &[u8],
    buffer: &mut dyn Buffer
) -> Result<(), Error>

Decrypt the message in-place, returning an error in the event the provided authentication tag does not match the given ciphertext.

impl Clone for XChaCha20Poly1305

fn clone(&self) -> XChaCha20Poly1305

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Drop for XChaCha20Poly1305

fn drop(&mut self)

Executes the destructor for this type.

impl NewAead for XChaCha20Poly1305

type KeySize = U32

The size of the key array required by this algorithm.

fn new(key: &Key) -> Self

Create a new AEAD instance with the given key.

fn new_varkey(key: &[u8]) -> Result<Self, Error>

Create new AEAD instance from key with variable size.