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use crate::{error, hmac};
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Algorithm(hmac::Algorithm);
impl Algorithm {
#[inline]
pub fn hmac_algorithm(&self) -> hmac::Algorithm {
self.0
}
}
pub static HKDF_SHA1_FOR_LEGACY_USE_ONLY: Algorithm =
Algorithm(hmac::HMAC_SHA1_FOR_LEGACY_USE_ONLY);
pub static HKDF_SHA256: Algorithm = Algorithm(hmac::HMAC_SHA256);
pub static HKDF_SHA384: Algorithm = Algorithm(hmac::HMAC_SHA384);
pub static HKDF_SHA512: Algorithm = Algorithm(hmac::HMAC_SHA512);
impl KeyType for Algorithm {
fn len(&self) -> usize {
self.0.digest_algorithm().output_len
}
}
#[derive(Debug)]
pub struct Salt(hmac::Key);
impl Salt {
pub fn new(algorithm: Algorithm, value: &[u8]) -> Self {
Salt(hmac::Key::new(algorithm.0, value))
}
pub fn extract(&self, secret: &[u8]) -> Prk {
let salt = &self.0;
let prk = hmac::sign(salt, secret);
Prk(hmac::Key::new(salt.algorithm(), prk.as_ref()))
}
#[inline]
pub fn algorithm(&self) -> Algorithm {
Algorithm(self.0.algorithm())
}
}
impl From<Okm<'_, Algorithm>> for Salt {
fn from(okm: Okm<'_, Algorithm>) -> Self {
Self(hmac::Key::from(Okm {
prk: okm.prk,
info: okm.info,
len: okm.len().0,
len_cached: okm.len_cached,
}))
}
}
pub trait KeyType {
fn len(&self) -> usize;
}
#[derive(Clone, Debug)]
pub struct Prk(hmac::Key);
impl Prk {
pub fn new_less_safe(algorithm: Algorithm, value: &[u8]) -> Self {
Self(hmac::Key::new(algorithm.hmac_algorithm(), value))
}
#[inline]
pub fn expand<'a, L: KeyType>(
&'a self,
info: &'a [&'a [u8]],
len: L,
) -> Result<Okm<'a, L>, error::Unspecified> {
let len_cached = len.len();
if len_cached > 255 * self.0.algorithm().digest_algorithm().output_len {
return Err(error::Unspecified);
}
Ok(Okm {
prk: self,
info,
len,
len_cached,
})
}
}
impl From<Okm<'_, Algorithm>> for Prk {
fn from(okm: Okm<Algorithm>) -> Self {
Self(hmac::Key::from(Okm {
prk: okm.prk,
info: okm.info,
len: okm.len().0,
len_cached: okm.len_cached,
}))
}
}
#[derive(Debug)]
pub struct Okm<'a, L: KeyType> {
prk: &'a Prk,
info: &'a [&'a [u8]],
len: L,
len_cached: usize,
}
impl<L: KeyType> Okm<'_, L> {
#[inline]
pub fn len(&self) -> &L {
&self.len
}
#[inline]
pub fn fill(self, out: &mut [u8]) -> Result<(), error::Unspecified> {
fill_okm(self.prk, self.info, out, self.len_cached)
}
}
fn fill_okm(
prk: &Prk,
info: &[&[u8]],
out: &mut [u8],
len: usize,
) -> Result<(), error::Unspecified> {
if out.len() != len {
return Err(error::Unspecified);
}
let digest_alg = prk.0.algorithm().digest_algorithm();
assert!(digest_alg.block_len >= digest_alg.output_len);
let mut ctx = hmac::Context::with_key(&prk.0);
let mut n = 1u8;
let mut out = out;
loop {
for info in info {
ctx.update(info);
}
ctx.update(&[n]);
let t = ctx.sign();
let t = t.as_ref();
out = if out.len() < digest_alg.output_len {
let len = out.len();
out.copy_from_slice(&t[..len]);
&mut []
} else {
let (this_chunk, rest) = out.split_at_mut(digest_alg.output_len);
this_chunk.copy_from_slice(t);
rest
};
if out.is_empty() {
return Ok(());
}
ctx = hmac::Context::with_key(&prk.0);
ctx.update(t);
n = n.checked_add(1).unwrap();
}
}