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// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// Copyright by contributors to this project.
// SPDX-License-Identifier: (Apache-2.0 OR MIT)
use mls_rs_core::{
crypto::{HpkeContextR, HpkeContextS},
error::IntoAnyError,
};
use mls_rs_crypto_traits::{AeadType, KdfType};
use crate::{hpke::HpkeError, kdf::HpkeKdf};
use alloc::vec::Vec;
use core::fmt::{self, Debug};
/// A type representing an HPKE context
#[derive(Clone)]
pub(super) struct Context<KDF: KdfType, AEAD: AeadType> {
exporter_secret: Vec<u8>,
encryption_context: Option<EncryptionContext<AEAD>>,
kdf: HpkeKdf<KDF>,
}
impl<KDF: KdfType + Debug, AEAD: AeadType + Debug> Debug for Context<KDF, AEAD> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Context")
.field(
"exporter_secret",
&mls_rs_core::debug::pretty_bytes(&self.exporter_secret),
)
.field("encryption_context", &self.encryption_context)
.field("kdf", &self.kdf)
.finish()
}
}
impl<KDF: KdfType, AEAD: AeadType> Context<KDF, AEAD> {
#[inline]
pub(super) fn new(
encryption_context: Option<EncryptionContext<AEAD>>,
exporter_secret: Vec<u8>,
kdf: HpkeKdf<KDF>,
) -> Self {
Self {
exporter_secret,
encryption_context,
kdf,
}
}
}
impl<KDF: KdfType, AEAD: AeadType> Context<KDF, AEAD> {
#[cfg_attr(not(mls_build_async), maybe_async::must_be_sync)]
async fn seal(&mut self, aad: Option<&[u8]>, data: &[u8]) -> Result<Vec<u8>, HpkeError> {
self.encryption_context
.as_mut()
.ok_or(HpkeError::ExportOnlyMode)?
.seal(aad, data)
.await
}
#[cfg_attr(not(mls_build_async), maybe_async::must_be_sync)]
async fn open(&mut self, aad: Option<&[u8]>, ciphertext: &[u8]) -> Result<Vec<u8>, HpkeError> {
self.encryption_context
.as_mut()
.ok_or(HpkeError::ExportOnlyMode)?
.open(aad, ciphertext)
.await
}
#[cfg_attr(not(mls_build_async), maybe_async::must_be_sync)]
async fn export(&self, exporter_context: &[u8], len: usize) -> Result<Vec<u8>, HpkeError> {
self.kdf
.labeled_expand(&self.exporter_secret, b"sec", exporter_context, len)
.await
.map_err(|e| HpkeError::KdfError(e.into_any_error()))
}
}
#[derive(Debug, Clone)]
pub struct ContextS<KDF: KdfType, AEAD: AeadType>(pub(super) Context<KDF, AEAD>);
#[cfg_attr(not(mls_build_async), maybe_async::must_be_sync)]
#[cfg_attr(all(target_arch = "wasm32", mls_build_async), maybe_async::must_be_async(?Send))]
#[cfg_attr(
all(not(target_arch = "wasm32"), mls_build_async),
maybe_async::must_be_async
)]
impl<KDF: KdfType, AEAD: AeadType> HpkeContextS for ContextS<KDF, AEAD> {
type Error = HpkeError;
async fn export(&self, exporter_context: &[u8], len: usize) -> Result<Vec<u8>, Self::Error> {
self.0.export(exporter_context, len).await
}
/// # Errors
///
/// Returns [SequenceNumberOverflow](HpkeError::SequenceNumberOverflow)
/// in the event that the sequence number overflows. The sequence number is a u64 and starts
/// at 0.
async fn seal(&mut self, aad: Option<&[u8]>, data: &[u8]) -> Result<Vec<u8>, Self::Error> {
self.0.seal(aad, data).await
}
}
#[derive(Debug, Clone)]
pub struct ContextR<KDF: KdfType, AEAD: AeadType>(pub(super) Context<KDF, AEAD>);
#[cfg_attr(not(mls_build_async), maybe_async::must_be_sync)]
#[cfg_attr(all(target_arch = "wasm32", mls_build_async), maybe_async::must_be_async(?Send))]
#[cfg_attr(
all(not(target_arch = "wasm32"), mls_build_async),
maybe_async::must_be_async
)]
impl<KDF: KdfType, AEAD: AeadType> HpkeContextR for ContextR<KDF, AEAD> {
type Error = HpkeError;
async fn export(&self, exporter_context: &[u8], len: usize) -> Result<Vec<u8>, Self::Error> {
self.0.export(exporter_context, len).await
}
/// # Errors
///
/// Returns [SequenceNumberOverflow](HpkeError::SequenceNumberOverflow)
/// in the event that the sequence number overflows. The sequence number is a u64 and starts
/// at 0.
///
/// Returns [AeadError](HpkeError::AeadError) if decryption fails due to either an invalid
/// `aad` value, or incorrect cipher key.
async fn open(
&mut self,
aad: Option<&[u8]>,
ciphertext: &[u8],
) -> Result<Vec<u8>, Self::Error> {
self.0.open(aad, ciphertext).await
}
}
#[derive(PartialEq, Eq, Clone)]
pub(super) struct EncryptionContext<AEAD: AeadType> {
base_nonce: Vec<u8>,
seq_number: u64,
aead: AEAD,
aead_key: Vec<u8>,
}
impl<AEAD: AeadType + Debug> Debug for EncryptionContext<AEAD> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("EncryptionContext")
.field(
"base_nonce",
&mls_rs_core::debug::pretty_bytes(&self.base_nonce),
)
.field("seq_number", &self.seq_number)
.field("aead", &self.aead)
.field(
"aead_key",
&mls_rs_core::debug::pretty_bytes(&self.aead_key),
)
.finish()
}
}
impl<AEAD: AeadType> EncryptionContext<AEAD> {
pub fn new(base_nonce: Vec<u8>, aead: AEAD, aead_key: Vec<u8>) -> Result<Self, HpkeError> {
(base_nonce.len() == aead.nonce_size())
.then_some(())
.ok_or(HpkeError::IncorrectNonceLen(
base_nonce.len(),
aead.nonce_size(),
))?;
(aead_key.len() == aead.key_size())
.then_some(())
.ok_or(HpkeError::IncorrectKeyLen(aead_key.len(), aead.key_size()))?;
Ok(EncryptionContext {
base_nonce,
seq_number: 0,
aead,
aead_key,
})
}
}
impl<AEAD: AeadType> EncryptionContext<AEAD> {
//draft-irtf-cfrg-hpke Section 5.2. Encryption and Decryption
fn compute_nonce(&self) -> Vec<u8> {
let mut nonce = self.base_nonce.clone();
// XOR the sequence number into the last 4 bytes of the nonce
nonce
.iter_mut()
.rev()
.zip(self.seq_number.to_le_bytes())
.for_each(|(n, s)| *n ^= s);
nonce
}
#[inline]
fn increment_seq(&mut self) -> Result<(), HpkeError> {
// If the sequence number is going to roll over just throw an error
self.seq_number = self
.seq_number
.checked_add(1)
.ok_or(HpkeError::SequenceNumberOverflow)?;
Ok(())
}
#[cfg_attr(not(mls_build_async), maybe_async::must_be_sync)]
pub async fn seal(&mut self, aad: Option<&[u8]>, pt: &[u8]) -> Result<Vec<u8>, HpkeError> {
let ct = self
.aead
.seal(&self.aead_key, pt, aad, &self.compute_nonce())
.await
.map_err(|e| HpkeError::AeadError(e.into_any_error()))?;
self.increment_seq()?;
Ok(ct)
}
#[cfg_attr(not(mls_build_async), maybe_async::must_be_sync)]
pub async fn open(&mut self, aad: Option<&[u8]>, ct: &[u8]) -> Result<Vec<u8>, HpkeError> {
let pt = self
.aead
.open(&self.aead_key, ct, aad, &self.compute_nonce())
.await
.map_err(|e| HpkeError::AeadError(e.into_any_error()))?;
self.increment_seq()?;
Ok(pt)
}
}