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#![no_std]
#![warn(rust_2018_idioms)]
#[cfg(feature = "std")]
extern crate std;
use core::fmt;
use digest::generic_array::{self, ArrayLength, GenericArray};
use digest::{BlockInput, FixedOutput, Reset, Update};
use hmac::{Hmac, Mac, NewMac};
#[derive(Copy, Clone, Eq, PartialEq, Debug)]
pub struct InvalidPrkLength;
#[derive(Copy, Clone, Eq, PartialEq, Debug)]
pub struct InvalidLength;
#[derive(Clone)]
pub struct Hkdf<D>
where
D: Update + BlockInput + FixedOutput + Reset + Default + Clone,
D::BlockSize: ArrayLength<u8>,
D::OutputSize: ArrayLength<u8>,
{
hmac: Hmac<D>,
}
impl<D> Hkdf<D>
where
D: Update + BlockInput + FixedOutput + Reset + Default + Clone,
D::BlockSize: ArrayLength<u8>,
D::OutputSize: ArrayLength<u8>,
{
pub fn new(salt: Option<&[u8]>, ikm: &[u8]) -> Hkdf<D> {
let (_, hkdf) = Hkdf::extract(salt, ikm);
hkdf
}
pub fn from_prk(prk: &[u8]) -> Result<Hkdf<D>, InvalidPrkLength> {
use crate::generic_array::typenum::Unsigned;
if prk.len() < D::OutputSize::to_usize() {
return Err(InvalidPrkLength);
}
Ok(Hkdf {
hmac: Hmac::new_varkey(prk).expect("HMAC can take a key of any size"),
})
}
pub fn extract(salt: Option<&[u8]>, ikm: &[u8]) -> (GenericArray<u8, D::OutputSize>, Hkdf<D>) {
let mut hmac = match salt {
Some(s) => Hmac::<D>::new_varkey(s).expect("HMAC can take a key of any size"),
None => Hmac::<D>::new(&Default::default()),
};
hmac.update(ikm);
let prk = hmac.finalize().into_bytes();
let hkdf = Hkdf::from_prk(&prk).expect("PRK size is correct");
(prk, hkdf)
}
pub fn expand(&self, info: &[u8], okm: &mut [u8]) -> Result<(), InvalidLength> {
use crate::generic_array::typenum::Unsigned;
let mut prev: Option<GenericArray<u8, <D as digest::FixedOutput>::OutputSize>> = None;
let hmac_output_bytes = D::OutputSize::to_usize();
if okm.len() > hmac_output_bytes * 255 {
return Err(InvalidLength);
}
let mut hmac = self.hmac.clone();
for (blocknum, okm_block) in okm.chunks_mut(hmac_output_bytes).enumerate() {
let block_len = okm_block.len();
if let Some(ref prev) = prev {
hmac.update(prev)
};
hmac.update(info);
hmac.update(&[blocknum as u8 + 1]);
let output = hmac.finalize_reset().into_bytes();
okm_block.copy_from_slice(&output[..block_len]);
prev = Some(output);
}
Ok(())
}
}
impl fmt::Display for InvalidPrkLength {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
f.write_str("invalid pseudorandom key length, too short")
}
}
#[cfg(feature = "std")]
impl ::std::error::Error for InvalidPrkLength {}
impl fmt::Display for InvalidLength {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
f.write_str("invalid number of blocks, too large output")
}
}
#[cfg(feature = "std")]
impl ::std::error::Error for InvalidLength {}