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use super::{
chacha::{self, *},
chacha20_poly1305::derive_poly1305_key,
poly1305, Nonce, Tag,
};
use crate::{constant_time, endian::*, error};
use core::convert::TryInto;
pub struct SealingKey {
key: Key,
}
impl SealingKey {
pub fn new(key_material: &[u8; KEY_LEN]) -> SealingKey {
SealingKey {
key: Key::new(key_material),
}
}
pub fn seal_in_place(
&self,
sequence_number: u32,
plaintext_in_ciphertext_out: &mut [u8],
tag_out: &mut [u8; TAG_LEN],
) {
let mut counter = make_counter(sequence_number);
let poly_key = derive_poly1305_key(&self.key.k_2, counter.increment());
{
let (len_in_out, data_and_padding_in_out) =
plaintext_in_ciphertext_out.split_at_mut(PACKET_LENGTH_LEN);
self.key
.k_1
.encrypt_in_place(make_counter(sequence_number), len_in_out);
self.key
.k_2
.encrypt_in_place(counter, data_and_padding_in_out);
}
let Tag(tag) = poly1305::sign(poly_key, plaintext_in_ciphertext_out);
tag_out.copy_from_slice(tag.as_ref());
}
}
pub struct OpeningKey {
key: Key,
}
impl OpeningKey {
pub fn new(key_material: &[u8; KEY_LEN]) -> OpeningKey {
OpeningKey {
key: Key::new(key_material),
}
}
pub fn decrypt_packet_length(
&self,
sequence_number: u32,
encrypted_packet_length: [u8; PACKET_LENGTH_LEN],
) -> [u8; PACKET_LENGTH_LEN] {
let mut packet_length = encrypted_packet_length;
let counter = make_counter(sequence_number);
self.key.k_1.encrypt_in_place(counter, &mut packet_length);
packet_length
}
pub fn open_in_place<'a>(
&self,
sequence_number: u32,
ciphertext_in_plaintext_out: &'a mut [u8],
tag: &[u8; TAG_LEN],
) -> Result<&'a [u8], error::Unspecified> {
let mut counter = make_counter(sequence_number);
let poly_key = derive_poly1305_key(&self.key.k_2, counter.increment());
verify(poly_key, ciphertext_in_plaintext_out, tag)?;
let plaintext_in_ciphertext_out = &mut ciphertext_in_plaintext_out[PACKET_LENGTH_LEN..];
self.key
.k_2
.encrypt_in_place(counter, plaintext_in_ciphertext_out);
Ok(plaintext_in_ciphertext_out)
}
}
struct Key {
k_1: chacha::Key,
k_2: chacha::Key,
}
impl Key {
pub fn new(key_material: &[u8; KEY_LEN]) -> Key {
let (k_2, k_1) = key_material.split_at(chacha::KEY_LEN);
Key {
k_1: chacha::Key::from(k_1.try_into().unwrap()),
k_2: chacha::Key::from(k_2.try_into().unwrap()),
}
}
}
fn make_counter(sequence_number: u32) -> Counter {
let nonce = [
BigEndian::ZERO,
BigEndian::ZERO,
BigEndian::from(sequence_number),
];
Counter::zero(Nonce::try_assume_unique_for_key(as_bytes(&nonce)).unwrap())
}
pub const KEY_LEN: usize = chacha::KEY_LEN * 2;
pub const PACKET_LENGTH_LEN: usize = 4;
pub const TAG_LEN: usize = super::BLOCK_LEN;
fn verify(key: poly1305::Key, msg: &[u8], tag: &[u8; TAG_LEN]) -> Result<(), error::Unspecified> {
let Tag(calculated_tag) = poly1305::sign(key, msg);
constant_time::verify_slices_are_equal(calculated_tag.as_ref(), tag)
}