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//! [Authenticated Encryption with Associated Data] (AEAD) traits
//!
//! This crate provides an abstract interface for AEAD ciphers, which guarantee
//! both confidentiality and integrity, even from a powerful attacker who is
//! able to execute [chosen-ciphertext attacks]. The resulting security property,
//! [ciphertext indistinguishability], is considered a basic requirement for
//! modern cryptographic implementations.
//!
//! See [RustCrypto/AEADs] for cipher implementations which use this trait.
//!
//! [Authenticated Encryption with Associated Data]: https://en.wikipedia.org/wiki/Authenticated_encryption
//! [chosen-ciphertext attacks]: https://en.wikipedia.org/wiki/Chosen-ciphertext_attack
//! [ciphertext indistinguishability]: https://en.wikipedia.org/wiki/Ciphertext_indistinguishability
//! [RustCrypto/AEADs]: https://github.com/RustCrypto/AEADs
#![no_std]
#![cfg_attr(docsrs, feature(doc_cfg))]
#![doc(
html_logo_url = "https://raw.githubusercontent.com/RustCrypto/media/8f1a9894/logo.svg",
html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/media/8f1a9894/logo.svg"
)]
#![forbid(unsafe_code)]
#![warn(clippy::unwrap_used, missing_docs, rust_2018_idioms)]
#[cfg(feature = "alloc")]
extern crate alloc;
#[cfg(feature = "std")]
extern crate std;
#[cfg(feature = "dev")]
#[cfg_attr(docsrs, doc(cfg(feature = "dev")))]
pub mod dev;
#[cfg(feature = "stream")]
#[cfg_attr(docsrs, doc(cfg(feature = "stream")))]
pub mod stream;
pub use crypto_common::{Key, KeyInit, KeySizeUser};
pub use generic_array::{self, typenum::consts};
#[cfg(feature = "arrayvec")]
#[cfg_attr(docsrs, doc(cfg(feature = "arrayvec")))]
pub use arrayvec;
#[cfg(feature = "bytes")]
#[cfg_attr(docsrs, doc(cfg(feature = "bytes")))]
pub use bytes;
#[cfg(feature = "getrandom")]
#[cfg_attr(docsrs, doc(cfg(feature = "getrandom")))]
pub use crypto_common::rand_core::OsRng;
#[cfg(feature = "heapless")]
#[cfg_attr(docsrs, doc(cfg(feature = "heapless")))]
pub use heapless;
#[cfg(feature = "rand_core")]
#[cfg_attr(docsrs, doc(cfg(feature = "rand_core")))]
pub use crypto_common::rand_core;
use core::fmt;
use generic_array::{typenum::Unsigned, ArrayLength, GenericArray};
#[cfg(feature = "alloc")]
use alloc::vec::Vec;
#[cfg(feature = "bytes")]
use bytes::BytesMut;
#[cfg(feature = "rand_core")]
use rand_core::{CryptoRng, RngCore};
/// Error type.
///
/// This type is deliberately opaque as to avoid potential side-channel
/// leakage (e.g. padding oracle).
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct Error;
/// Result type alias with [`Error`].
pub type Result<T> = core::result::Result<T, Error>;
impl fmt::Display for Error {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str("aead::Error")
}
}
#[cfg(feature = "std")]
impl std::error::Error for Error {}
/// Nonce: single-use value for ensuring ciphertexts are unique
pub type Nonce<A> = GenericArray<u8, <A as AeadCore>::NonceSize>;
/// Tag: authentication code which ensures ciphertexts are authentic
pub type Tag<A> = GenericArray<u8, <A as AeadCore>::TagSize>;
/// Authenticated Encryption with Associated Data (AEAD) algorithm core trait.
///
/// Defines nonce, tag, and overhead sizes that are consumed by various other
/// `Aead*` traits.
pub trait AeadCore {
/// The length of a nonce.
type NonceSize: ArrayLength<u8>;
/// The maximum length of the nonce.
type TagSize: ArrayLength<u8>;
/// The upper bound amount of additional space required to support a
/// ciphertext vs. a plaintext.
type CiphertextOverhead: ArrayLength<u8> + Unsigned;
/// Generate a random nonce for this AEAD algorithm.
///
/// AEAD algorithms accept a parameter to encryption/decryption called
/// a "nonce" which must be unique every time encryption is performed and
/// never repeated for the same key. The nonce is often prepended to the
/// ciphertext. The nonce used to produce a given ciphertext must be passed
/// to the decryption function in order for it to decrypt correctly.
///
/// Nonces don't necessarily have to be random, but it is one strategy
/// which is implemented by this function.
///
/// # ⚠️Security Warning
///
/// AEAD algorithms often fail catastrophically if nonces are ever repeated
/// (with SIV modes being an exception).
///
/// Using random nonces runs the risk of repeating them unless the nonce
/// size is particularly large (e.g. 192-bit extended nonces used by the
/// `XChaCha20Poly1305` and `XSalsa20Poly1305` constructions.
///
/// [NIST SP 800-38D] recommends the following:
///
/// > The total number of invocations of the authenticated encryption
/// > function shall not exceed 2^32, including all IV lengths and all
/// > instances of the authenticated encryption function with the given key.
///
/// Following this guideline, only 4,294,967,296 messages with random
/// nonces can be encrypted under a given key. While this bound is high,
/// it's possible to encounter in practice, and systems which might
/// reach it should consider alternatives to purely random nonces, like
/// a counter or a combination of a random nonce + counter.
///
/// See the [`stream`] module for a ready-made implementation of the latter.
///
/// [NIST SP 800-38D]: https://csrc.nist.gov/publications/detail/sp/800-38d/final
#[cfg(feature = "rand_core")]
#[cfg_attr(docsrs, doc(cfg(feature = "rand_core")))]
fn generate_nonce(mut rng: impl CryptoRng + RngCore) -> Nonce<Self>
where
Nonce<Self>: Default,
{
let mut nonce = Nonce::<Self>::default();
rng.fill_bytes(&mut nonce);
nonce
}
}
/// Authenticated Encryption with Associated Data (AEAD) algorithm.
///
/// This trait is intended for use with stateless AEAD algorithms. The
/// [`AeadMut`] trait provides a stateful interface.
#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
pub trait Aead: AeadCore {
/// Encrypt the given plaintext payload, and return the resulting
/// ciphertext as a vector of bytes.
///
/// The [`Payload`] type can be used to provide Additional Associated Data
/// (AAD) along with the message: this is an optional bytestring which is
/// not encrypted, but *is* authenticated along with the message. Failure
/// to pass the same AAD that was used during encryption will cause
/// decryption to fail, which is useful if you would like to "bind" the
/// ciphertext to some other identifier, like a digital signature key
/// or other identifier.
///
/// If you don't care about AAD and just want to encrypt a plaintext
/// message, `&[u8]` will automatically be coerced into a `Payload`:
///
/// ```nobuild
/// let plaintext = b"Top secret message, handle with care";
/// let ciphertext = cipher.encrypt(nonce, plaintext);
/// ```
///
/// The default implementation assumes a postfix tag (ala AES-GCM,
/// AES-GCM-SIV, ChaCha20Poly1305). [`Aead`] implementations which do not
/// use a postfix tag will need to override this to correctly assemble the
/// ciphertext message.
fn encrypt<'msg, 'aad>(
&self,
nonce: &Nonce<Self>,
plaintext: impl Into<Payload<'msg, 'aad>>,
) -> Result<Vec<u8>>;
/// Decrypt the given ciphertext slice, and return the resulting plaintext
/// as a vector of bytes.
///
/// See notes on [`Aead::encrypt()`] about allowable message payloads and
/// Associated Additional Data (AAD).
///
/// If you have no AAD, you can call this as follows:
///
/// ```nobuild
/// let ciphertext = b"...";
/// let plaintext = cipher.decrypt(nonce, ciphertext)?;
/// ```
///
/// The default implementation assumes a postfix tag (ala AES-GCM,
/// AES-GCM-SIV, ChaCha20Poly1305). [`Aead`] implementations which do not
/// use a postfix tag will need to override this to correctly parse the
/// ciphertext message.
fn decrypt<'msg, 'aad>(
&self,
nonce: &Nonce<Self>,
ciphertext: impl Into<Payload<'msg, 'aad>>,
) -> Result<Vec<u8>>;
}
/// Stateful Authenticated Encryption with Associated Data algorithm.
#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
pub trait AeadMut: AeadCore {
/// Encrypt the given plaintext slice, and return the resulting ciphertext
/// as a vector of bytes.
///
/// See notes on [`Aead::encrypt()`] about allowable message payloads and
/// Associated Additional Data (AAD).
fn encrypt<'msg, 'aad>(
&mut self,
nonce: &Nonce<Self>,
plaintext: impl Into<Payload<'msg, 'aad>>,
) -> Result<Vec<u8>>;
/// Decrypt the given ciphertext slice, and return the resulting plaintext
/// as a vector of bytes.
///
/// See notes on [`Aead::encrypt()`] and [`Aead::decrypt()`] about allowable
/// message payloads and Associated Additional Data (AAD).
fn decrypt<'msg, 'aad>(
&mut self,
nonce: &Nonce<Self>,
ciphertext: impl Into<Payload<'msg, 'aad>>,
) -> Result<Vec<u8>>;
}
/// Implement the `decrypt_in_place` method on [`AeadInPlace`] and
/// [`AeadMutInPlace]`, using a macro to gloss over the `&self` vs `&mut self`.
///
/// Assumes a postfix authentication tag. AEAD ciphers which do not use a
/// postfix authentication tag will need to define their own implementation.
macro_rules! impl_decrypt_in_place {
($aead:expr, $nonce:expr, $aad:expr, $buffer:expr) => {{
if $buffer.len() < Self::TagSize::to_usize() {
return Err(Error);
}
let tag_pos = $buffer.len() - Self::TagSize::to_usize();
let (msg, tag) = $buffer.as_mut().split_at_mut(tag_pos);
$aead.decrypt_in_place_detached($nonce, $aad, msg, Tag::<Self>::from_slice(tag))?;
$buffer.truncate(tag_pos);
Ok(())
}};
}
/// In-place stateless AEAD trait.
///
/// This trait is both object safe and has no dependencies on `alloc` or `std`.
pub trait AeadInPlace: AeadCore {
/// Encrypt the given buffer containing a plaintext message in-place.
///
/// The buffer must have sufficient capacity to store the ciphertext
/// message, which will always be larger than the original plaintext.
/// The exact size needed is cipher-dependent, but generally includes
/// the size of an authentication tag.
///
/// Returns an error if the buffer has insufficient capacity to store the
/// resulting ciphertext message.
fn encrypt_in_place(
&self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut dyn Buffer,
) -> Result<()> {
let tag = self.encrypt_in_place_detached(nonce, associated_data, buffer.as_mut())?;
buffer.extend_from_slice(tag.as_slice())?;
Ok(())
}
/// Encrypt the data in-place, returning the authentication tag
fn encrypt_in_place_detached(
&self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut [u8],
) -> Result<Tag<Self>>;
/// Decrypt the message in-place, returning an error in the event the
/// provided authentication tag does not match the given ciphertext.
///
/// The buffer will be truncated to the length of the original plaintext
/// message upon success.
fn decrypt_in_place(
&self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut dyn Buffer,
) -> Result<()> {
impl_decrypt_in_place!(self, nonce, associated_data, buffer)
}
/// 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 decrypt_in_place_detached(
&self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut [u8],
tag: &Tag<Self>,
) -> Result<()>;
}
/// In-place stateful AEAD trait.
///
/// This trait is both object safe and has no dependencies on `alloc` or `std`.
pub trait AeadMutInPlace: AeadCore {
/// Encrypt the given buffer containing a plaintext message in-place.
///
/// The buffer must have sufficient capacity to store the ciphertext
/// message, which will always be larger than the original plaintext.
/// The exact size needed is cipher-dependent, but generally includes
/// the size of an authentication tag.
///
/// Returns an error if the buffer has insufficient capacity to store the
/// resulting ciphertext message.
fn encrypt_in_place(
&mut self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut impl Buffer,
) -> Result<()> {
let tag = self.encrypt_in_place_detached(nonce, associated_data, buffer.as_mut())?;
buffer.extend_from_slice(tag.as_slice())?;
Ok(())
}
/// Encrypt the data in-place, returning the authentication tag
fn encrypt_in_place_detached(
&mut self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut [u8],
) -> Result<Tag<Self>>;
/// Decrypt the message in-place, returning an error in the event the
/// provided authentication tag does not match the given ciphertext.
///
/// The buffer will be truncated to the length of the original plaintext
/// message upon success.
fn decrypt_in_place(
&mut self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut impl Buffer,
) -> Result<()> {
impl_decrypt_in_place!(self, nonce, associated_data, buffer)
}
/// Decrypt the data 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 decrypt_in_place_detached(
&mut self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut [u8],
tag: &Tag<Self>,
) -> Result<()>;
}
#[cfg(feature = "alloc")]
impl<Alg: AeadInPlace> Aead for Alg {
fn encrypt<'msg, 'aad>(
&self,
nonce: &Nonce<Self>,
plaintext: impl Into<Payload<'msg, 'aad>>,
) -> Result<Vec<u8>> {
let payload = plaintext.into();
let mut buffer = Vec::with_capacity(payload.msg.len() + Self::TagSize::to_usize());
buffer.extend_from_slice(payload.msg);
self.encrypt_in_place(nonce, payload.aad, &mut buffer)?;
Ok(buffer)
}
fn decrypt<'msg, 'aad>(
&self,
nonce: &Nonce<Self>,
ciphertext: impl Into<Payload<'msg, 'aad>>,
) -> Result<Vec<u8>> {
let payload = ciphertext.into();
let mut buffer = Vec::from(payload.msg);
self.decrypt_in_place(nonce, payload.aad, &mut buffer)?;
Ok(buffer)
}
}
#[cfg(feature = "alloc")]
impl<Alg: AeadMutInPlace> AeadMut for Alg {
fn encrypt<'msg, 'aad>(
&mut self,
nonce: &Nonce<Self>,
plaintext: impl Into<Payload<'msg, 'aad>>,
) -> Result<Vec<u8>> {
let payload = plaintext.into();
let mut buffer = Vec::with_capacity(payload.msg.len() + Self::TagSize::to_usize());
buffer.extend_from_slice(payload.msg);
self.encrypt_in_place(nonce, payload.aad, &mut buffer)?;
Ok(buffer)
}
fn decrypt<'msg, 'aad>(
&mut self,
nonce: &Nonce<Self>,
ciphertext: impl Into<Payload<'msg, 'aad>>,
) -> Result<Vec<u8>> {
let payload = ciphertext.into();
let mut buffer = Vec::from(payload.msg);
self.decrypt_in_place(nonce, payload.aad, &mut buffer)?;
Ok(buffer)
}
}
impl<Alg: AeadInPlace> AeadMutInPlace for Alg {
fn encrypt_in_place(
&mut self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut impl Buffer,
) -> Result<()> {
<Self as AeadInPlace>::encrypt_in_place(self, nonce, associated_data, buffer)
}
fn encrypt_in_place_detached(
&mut self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut [u8],
) -> Result<Tag<Self>> {
<Self as AeadInPlace>::encrypt_in_place_detached(self, nonce, associated_data, buffer)
}
fn decrypt_in_place(
&mut self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut impl Buffer,
) -> Result<()> {
<Self as AeadInPlace>::decrypt_in_place(self, nonce, associated_data, buffer)
}
fn decrypt_in_place_detached(
&mut self,
nonce: &Nonce<Self>,
associated_data: &[u8],
buffer: &mut [u8],
tag: &Tag<Self>,
) -> Result<()> {
<Self as AeadInPlace>::decrypt_in_place_detached(self, nonce, associated_data, buffer, tag)
}
}
/// AEAD payloads (message + AAD).
///
/// Combination of a message (plaintext or ciphertext) and
/// "additional associated data" (AAD) to be authenticated (in cleartext)
/// along with the message.
///
/// If you don't care about AAD, you can pass a `&[u8]` as the payload to
/// `encrypt`/`decrypt` and it will automatically be coerced to this type.
#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
pub struct Payload<'msg, 'aad> {
/// Message to be encrypted/decrypted
pub msg: &'msg [u8],
/// Optional "additional associated data" to authenticate along with
/// this message. If AAD is provided at the time the message is encrypted,
/// the same AAD *MUST* be provided at the time the message is decrypted,
/// or decryption will fail.
pub aad: &'aad [u8],
}
#[cfg(feature = "alloc")]
impl<'msg, 'aad> From<&'msg [u8]> for Payload<'msg, 'aad> {
fn from(msg: &'msg [u8]) -> Self {
Self { msg, aad: b"" }
}
}
/// In-place encryption/decryption byte buffers.
///
/// This trait defines the set of methods needed to support in-place operations
/// on a `Vec`-like data type.
pub trait Buffer: AsRef<[u8]> + AsMut<[u8]> {
/// Get the length of the buffer
fn len(&self) -> usize {
self.as_ref().len()
}
/// Is the buffer empty?
fn is_empty(&self) -> bool {
self.as_ref().is_empty()
}
/// Extend this buffer from the given slice
fn extend_from_slice(&mut self, other: &[u8]) -> Result<()>;
/// Truncate this buffer to the given size
fn truncate(&mut self, len: usize);
}
#[cfg(feature = "alloc")]
impl Buffer for Vec<u8> {
fn extend_from_slice(&mut self, other: &[u8]) -> Result<()> {
Vec::extend_from_slice(self, other);
Ok(())
}
fn truncate(&mut self, len: usize) {
Vec::truncate(self, len);
}
}
#[cfg(feature = "bytes")]
impl Buffer for BytesMut {
fn len(&self) -> usize {
BytesMut::len(self)
}
fn is_empty(&self) -> bool {
BytesMut::is_empty(self)
}
fn extend_from_slice(&mut self, other: &[u8]) -> Result<()> {
BytesMut::extend_from_slice(self, other);
Ok(())
}
fn truncate(&mut self, len: usize) {
BytesMut::truncate(self, len);
}
}
#[cfg(feature = "arrayvec")]
impl<const N: usize> Buffer for arrayvec::ArrayVec<u8, N> {
fn extend_from_slice(&mut self, other: &[u8]) -> Result<()> {
arrayvec::ArrayVec::try_extend_from_slice(self, other).map_err(|_| Error)
}
fn truncate(&mut self, len: usize) {
arrayvec::ArrayVec::truncate(self, len);
}
}
#[cfg(feature = "heapless")]
impl<const N: usize> Buffer for heapless::Vec<u8, N> {
fn extend_from_slice(&mut self, other: &[u8]) -> Result<()> {
heapless::Vec::extend_from_slice(self, other).map_err(|_| Error)
}
fn truncate(&mut self, len: usize) {
heapless::Vec::truncate(self, len);
}
}
#[cfg(test)]
mod tests {
use super::*;
/// Ensure that `AeadInPlace` is object-safe
#[allow(dead_code)]
type DynAeadInPlace<N, T, O> =
dyn AeadInPlace<NonceSize = N, TagSize = T, CiphertextOverhead = O>;
/// Ensure that `AeadMutInPlace` is object-safe
#[allow(dead_code)]
type DynAeadMutInPlace<N, T, O> =
dyn AeadMutInPlace<NonceSize = N, TagSize = T, CiphertextOverhead = O>;
}