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lib.rs
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lib.rs
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//! This crate provides trait for Message Authentication Code (MAC) algorithms.
#![no_std]
#![doc(html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo_small.png")]
#![forbid(unsafe_code)]
#![warn(missing_docs, rust_2018_idioms)]
#[cfg(feature = "std")]
extern crate std;
#[cfg(feature = "dev")]
pub mod dev;
mod errors;
pub use crate::errors::{InvalidKeyLength, MacError};
pub use generic_array::{self, typenum::consts};
use generic_array::typenum::Unsigned;
use generic_array::{ArrayLength, GenericArray};
use subtle::{Choice, ConstantTimeEq};
/// The [`Mac`] trait defines methods for a Message Authentication algorithm.
pub trait Mac: Clone {
/// Output size of the [[`Mac`]]
type OutputSize: ArrayLength<u8>;
/// Keys size of the [[`Mac`]]
type KeySize: ArrayLength<u8>;
/// Initialize new MAC instance from key with fixed size.
fn new(key: &GenericArray<u8, Self::KeySize>) -> Self;
/// Initialize new MAC instance from key with variable size.
///
/// Default implementation will accept only keys with length equal to
/// `KeySize`, but some MACs can accept range of key lengths.
fn new_varkey(key: &[u8]) -> Result<Self, InvalidKeyLength> {
if key.len() != Self::KeySize::to_usize() {
Err(InvalidKeyLength)
} else {
Ok(Self::new(GenericArray::from_slice(key)))
}
}
/// Update MAC state with the given data.
fn update(&mut self, data: &[u8]);
/// Reset [`Mac`] instance.
fn reset(&mut self);
/// Obtain the result of a [`Mac`] computation as a [`Output`] and consume
/// [`Mac`] instance.
fn result(self) -> Output<Self::OutputSize>;
/// Obtain the result of a [`Mac`] computation as a [`Output`] and reset
/// [`Mac`] instance.
fn result_reset(&mut self) -> Output<Self::OutputSize> {
let res = self.clone().result();
self.reset();
res
}
/// Check if code is correct for the processed input.
fn verify(self, code: &[u8]) -> Result<(), MacError> {
let choice = self.result().code.ct_eq(code);
if choice.unwrap_u8() == 1 {
Ok(())
} else {
Err(MacError)
}
}
}
/// [`Output`] is a thin wrapper around bytes array which provides a safe `Eq`
/// implementation that runs in a fixed time.
#[derive(Clone)]
pub struct Output<N: ArrayLength<u8>> {
code: GenericArray<u8, N>,
}
impl<N> Output<N>
where
N: ArrayLength<u8>,
{
/// Create a new MAC [`Output`].
pub fn new(code: GenericArray<u8, N>) -> Output<N> {
Output { code }
}
/// Get the MAC code/tag value as a byte array.
///
/// Be very careful using this method, since incorrect use of the code value
/// may permit timing attacks which defeat the security provided by the
/// [`Mac`] trait.
pub fn into_bytes(self) -> GenericArray<u8, N> {
self.code
}
}
impl<N> ConstantTimeEq for Output<N>
where
N: ArrayLength<u8>,
{
fn ct_eq(&self, other: &Self) -> Choice {
self.code.ct_eq(&other.code)
}
}
impl<N> PartialEq for Output<N>
where
N: ArrayLength<u8>,
{
fn eq(&self, x: &Output<N>) -> bool {
self.ct_eq(x).unwrap_u8() == 1
}
}
impl<N> Eq for Output<N> where N: ArrayLength<u8> {}