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// Copyright 2023 Cryspen Sarl
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//! This module contains the trait and related errors for a KEM that takes array references as
//! arguments and returns values as arrays.
//!
use super::arrayref;
pub use arrayref::{DecapsError, EncapsError, KeyGenError};
/// A Key Encapsulation Mechanismd (KEM) that returns values insteaf of writing the results to
/// `&mut` arguments.
pub trait Kem<
const EK_LEN: usize,
const DK_LEN: usize,
const CT_LEN: usize,
const SS_LEN: usize,
const RAND_KEYGEN_LEN: usize,
const RAND_ENCAPS_LEN: usize,
>
{
/// Generate a pair of encapsulation and decapsulation keys.
/// It is the responsibility of the caller to ensure that the `rand` argument is actually
/// random.
fn keygen(rand: &[u8; RAND_KEYGEN_LEN]) -> Result<([u8; DK_LEN], [u8; EK_LEN]), KeyGenError>;
/// Encapsulate a shared secret towards a given encapsulation key.
/// It is the responsibility of the caller to ensure that the `rand` argument is actually
/// random.
fn encaps(
ek: &[u8; EK_LEN],
rand: &[u8; RAND_ENCAPS_LEN],
) -> Result<([u8; SS_LEN], [u8; CT_LEN]), EncapsError>;
/// Decapsulate a shared secret.
fn decaps(ct: &[u8; CT_LEN], dk: &[u8; DK_LEN]) -> Result<[u8; SS_LEN], DecapsError>;
}
impl<
const EK_LEN: usize,
const DK_LEN: usize,
const CT_LEN: usize,
const SS_LEN: usize,
const RAND_KEYGEN_LEN: usize,
const RAND_ENCAPS_LEN: usize,
T: arrayref::Kem<EK_LEN, DK_LEN, CT_LEN, SS_LEN, RAND_KEYGEN_LEN, RAND_ENCAPS_LEN>,
> Kem<EK_LEN, DK_LEN, CT_LEN, SS_LEN, RAND_KEYGEN_LEN, RAND_ENCAPS_LEN> for T
{
fn keygen(rand: &[u8; RAND_KEYGEN_LEN]) -> Result<([u8; DK_LEN], [u8; EK_LEN]), KeyGenError> {
let mut dk = [0u8; DK_LEN];
let mut ek = [0u8; EK_LEN];
<Self as arrayref::Kem<
EK_LEN,
DK_LEN,
CT_LEN,
SS_LEN,
RAND_KEYGEN_LEN,
RAND_ENCAPS_LEN,
>>::keygen(&mut ek, &mut dk, rand)?;
Ok((dk, ek))
}
fn encaps(
ek: &[u8; EK_LEN],
rand: &[u8; RAND_ENCAPS_LEN],
) -> Result<([u8; SS_LEN], [u8; CT_LEN]), EncapsError> {
let mut ss = [0u8; SS_LEN];
let mut ct = [0u8; CT_LEN];
<Self as arrayref::Kem<
EK_LEN,
DK_LEN,
CT_LEN,
SS_LEN,
RAND_KEYGEN_LEN,
RAND_ENCAPS_LEN,
>>::encaps(&mut ct, &mut ss, ek, rand)?;
Ok((ss, ct))
}
fn decaps(ct: &[u8; CT_LEN], dk: &[u8; DK_LEN]) -> Result<[u8; SS_LEN], DecapsError> {
let mut ss = [0u8; SS_LEN];
<Self as arrayref::Kem<
EK_LEN,
DK_LEN,
CT_LEN,
SS_LEN,
RAND_KEYGEN_LEN,
RAND_ENCAPS_LEN,
>>::decaps(&mut ss, ct, dk)?;
Ok(ss)
}
}