use crate::error::{Context, Error, bail, ensure};
use crate::format::{ContentType, RecordKind, Urma, chunk_count};
use aes::cipher::{KeyIvInit, StreamCipher};
use hkdf::Hkdf;
use hmac::{Hmac, Mac};
use rand::{CryptoRng, RngCore};
use sha2::{Digest, Sha256};
use std::collections::BTreeMap;
use zeroize::Zeroizing;
type Cipher = ctr::Ctr128BE<aes::Aes256>;
type Authenticator = Hmac<Sha256>;
pub fn random_secret<R: RngCore + CryptoRng>(rng: &mut R) -> Result<Zeroizing<[u8; 32]>, Error> {
let mut key = Zeroizing::new([0; 32]);
rng.try_fill_bytes(key.as_mut())?;
Ok(key)
}
fn derive(root: &[u8; 32], id: &[u8; 32], purpose: &[u8], output: &mut [u8]) -> Result<(), Error> {
Hkdf::<Sha256>::new(Some(id), root)
.expand(purpose, output)
.map_err(|error| Error::Invalid(format!("HKDF expansion: {error}")))?;
Ok(())
}
fn discovery_tag(root: &[u8; 32], id: &[u8; 32]) -> Result<[u8; 16], Error> {
let mut tag = [0; 16];
derive(root, id, Urma::DISCOVERY_DOMAIN, &mut tag)?;
Ok(tag)
}
fn cipher(root: &[u8; 32], id: &[u8; 32], iv: &[u8; 16]) -> Result<Cipher, Error> {
let mut key = Zeroizing::new([0; 32]);
derive(root, id, Urma::CONTENT_DOMAIN, key.as_mut())?;
Ok(Cipher::new((&*key).into(), iv.into()))
}
fn nonce(index: u32) -> [u8; 16] {
let mut iv = [0; 16];
iv[..8].copy_from_slice(&u64::from(index).to_be_bytes());
iv
}
fn authenticator(root: &[u8; 32], id: &[u8; 32]) -> Result<Authenticator, Error> {
let mut key = Zeroizing::new([0; 32]);
derive(root, id, Urma::AUTHENTICATION_DOMAIN, key.as_mut())?;
Ok(Authenticator::new_from_slice(key.as_ref())?)
}
pub fn seal<R: RngCore + CryptoRng>(
root: &[u8; 32],
plaintext: &[u8],
content_type: ContentType,
rng: &mut R,
) -> Result<Vec<Vec<u8>>, Error> {
let count = chunk_count(u64::try_from(plaintext.len())?)?;
let id = *random_secret(rng)?;
let tag = discovery_tag(root, &id)?;
let digest: [u8; 32] = Sha256::digest(plaintext).into();
let mut records = Vec::new();
records.try_reserve_exact(usize::try_from(count)?)?;
for (position, chunk) in plaintext.chunks(Urma::CHUNK_BYTES).enumerate() {
let index = u32::try_from(position)?;
let mut record = Vec::with_capacity(Urma::PRIVATE_RECORD_BYTES);
record.extend_from_slice(&RecordKind::Private.prefix());
record.extend_from_slice(&id);
record.extend_from_slice(&tag);
record.extend_from_slice(&index.to_le_bytes());
record.extend_from_slice(&count.to_le_bytes());
let iv = nonce(index);
record.extend_from_slice(&iv);
let mut body = Zeroizing::new(vec![0; Urma::BODY_BYTES]);
body[..32].copy_from_slice(&digest);
body[32..40].copy_from_slice(&u64::try_from(plaintext.len())?.to_le_bytes());
body[40..44].copy_from_slice(&content_type.code().to_le_bytes());
body[Urma::METADATA_BYTES..Urma::METADATA_BYTES + chunk.len()].copy_from_slice(chunk);
rng.try_fill_bytes(&mut body[Urma::METADATA_BYTES + chunk.len()..])?;
cipher(root, &id, &iv)?.apply_keystream(&mut body);
record.extend_from_slice(&body);
let mut mac = authenticator(root, &id)?;
mac.update(&record);
record.extend_from_slice(&mac.finalize().into_bytes());
records.push(record);
}
Ok(records)
}
pub struct PrivateChunk {
pub id: [u8; 32],
pub index: u32,
pub count: u32,
pub total: u64,
pub digest: [u8; 32],
pub content_type: ContentType,
pub bytes: Zeroizing<Vec<u8>>,
record_digest: [u8; 32],
}
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct PrivateRecordHeader {
pub id: [u8; 32],
pub discovery_tag: [u8; 16],
pub index: u32,
pub count: u32,
}
pub enum RecordMatch {
Unrelated,
Authenticated(PrivateChunk),
}
pub fn inspect_header(record: &[u8]) -> Result<PrivateRecordHeader, Error> {
ensure!(
record.len() == Urma::PRIVATE_RECORD_BYTES,
"invalid private record length"
);
ensure!(
RecordKind::parse(record)? == RecordKind::Private,
"not a private record"
);
let header = PrivateRecordHeader {
id: record[8..40].try_into()?,
discovery_tag: record[40..56].try_into()?,
index: u32::from_le_bytes(record[56..60].try_into()?),
count: u32::from_le_bytes(record[60..64].try_into()?),
};
ensure!(
header.count > 0 && header.index < header.count,
"invalid chunk bounds"
);
Ok(header)
}
pub fn open_record(root: &[u8; 32], record: &[u8]) -> Result<RecordMatch, Error> {
if !record.starts_with(&Urma::MAGIC) {
return Ok(RecordMatch::Unrelated);
}
match RecordKind::parse(record)? {
RecordKind::Private => {}
RecordKind::Post
| RecordKind::Reply
| RecordKind::Profile
| RecordKind::Avatar
| RecordKind::Container
| RecordKind::DataPart
| RecordKind::LeafManifest
| RecordKind::WirePost
| RecordKind::WireReply
| RecordKind::RootManifest => return Ok(RecordMatch::Unrelated),
}
let header = inspect_header(record)?;
if header.discovery_tag != discovery_tag(root, &header.id)? {
return Ok(RecordMatch::Unrelated);
}
let mut mac = authenticator(root, &header.id)?;
mac.update(&record[..Urma::MAC_OFFSET]);
mac.verify_slice(&record[Urma::MAC_OFFSET..])
.map_err(|error| Error::Invalid(format!("record authentication failed: {error}")))?;
let iv = nonce(header.index);
ensure!(
record[Urma::PRIVATE_HEADER_BYTES..Urma::BODY_OFFSET] == iv,
"noncanonical counter IV"
);
let mut body = Zeroizing::new(record[Urma::BODY_OFFSET..Urma::MAC_OFFSET].to_vec());
cipher(root, &header.id, &iv)?.apply_keystream(&mut body);
let total = u64::from_le_bytes(body[32..40].try_into()?);
ensure!(
chunk_count(total)? == header.count,
"chunk count does not match encrypted file length"
);
let content_type = ContentType::from_code(u32::from_le_bytes(body[40..44].try_into()?))?;
if body[44..48] != [0; 4] {
return Err(Error::Unsupported(
"unsupported private metadata flags".into(),
));
}
let remaining = total
.checked_sub(u64::from(header.index) * u64::try_from(Urma::CHUNK_BYTES)?)
.context("chunk offset exceeds original length")?;
let size = usize::try_from(remaining.min(u64::try_from(Urma::CHUNK_BYTES)?))?;
Ok(RecordMatch::Authenticated(PrivateChunk {
id: header.id,
index: header.index,
count: header.count,
total,
digest: body[..32].try_into()?,
content_type,
bytes: Zeroizing::new(body[Urma::METADATA_BYTES..Urma::METADATA_BYTES + size].to_vec()),
record_digest: Sha256::digest(record).into(),
}))
}
pub struct PrivateObject {
pub id: [u8; 32],
pub count: u32,
pub total: u64,
pub content_type: ContentType,
digest: [u8; 32],
chunks: BTreeMap<u32, PrivateChunk>,
conflict: bool,
}
impl PrivateObject {
pub fn new(chunk: PrivateChunk) -> Self {
Self {
id: chunk.id,
count: chunk.count,
total: chunk.total,
content_type: chunk.content_type,
digest: chunk.digest,
chunks: BTreeMap::from([(chunk.index, chunk)]),
conflict: false,
}
}
pub fn insert(&mut self, chunk: PrivateChunk) -> Result<(), Error> {
if self.id != chunk.id
|| self.count != chunk.count
|| self.total != chunk.total
|| self.digest != chunk.digest
|| self.content_type != chunk.content_type
{
self.conflict = true;
bail!("conflicting authenticated object metadata");
}
match self.chunks.entry(chunk.index) {
std::collections::btree_map::Entry::Occupied(previous) => {
if previous.get().record_digest != chunk.record_digest {
self.conflict = true;
bail!("conflicting authenticated record");
}
}
std::collections::btree_map::Entry::Vacant(slot) => {
slot.insert(chunk);
}
}
Ok(())
}
pub fn received(&self) -> usize {
self.chunks.len()
}
pub fn is_conflicted(&self) -> bool {
self.conflict
}
pub fn is_complete(&self) -> bool {
match u32::try_from(self.chunks.len()) {
Ok(count) => !self.conflict && count == self.count,
Err(error) => panic!("chunk map exceeds u32 key space: {error}"),
}
}
pub fn finish(&self) -> Result<Zeroizing<Vec<u8>>, Error> {
ensure!(!self.conflict, "conflicting authenticated object");
ensure!(
u32::try_from(self.chunks.len())? == self.count,
"incomplete object: {} of {} chunks",
self.chunks.len(),
self.count
);
let mut bytes = Zeroizing::new(Vec::new());
bytes.try_reserve_exact(
usize::try_from(self.total).context("object exceeds host capacity")?,
)?;
for index in 0..self.count {
bytes.extend_from_slice(&self.chunks.get(&index).context("missing chunk")?.bytes);
}
ensure!(
u64::try_from(bytes.len())? == self.total
&& Sha256::digest(&bytes).as_slice() == self.digest,
"whole-file integrity failed"
);
Ok(bytes)
}
}
pub fn pack(records: &[Vec<u8>]) -> Result<Vec<u8>, Error> {
let count = u32::try_from(records.len())?;
ensure!(count > 0, "empty container");
let first = inspect_header(&records[0])?;
let capacity = records
.len()
.checked_mul(Urma::PRIVATE_RECORD_BYTES + 4)
.and_then(|n| n.checked_add(Urma::CONTAINER_HEADER_BYTES))
.context("container size overflow")?;
let mut bytes = Vec::new();
bytes.try_reserve_exact(capacity)?;
bytes.extend_from_slice(&RecordKind::Container.prefix());
bytes.extend_from_slice(&count.to_le_bytes());
for record in records {
ensure!(inspect_header(record)?.id == first.id, "mixed objects");
bytes.extend_from_slice(&u32::try_from(record.len())?.to_le_bytes());
bytes.extend_from_slice(record);
}
Ok(bytes)
}
pub fn unpack(bytes: &[u8]) -> Result<Vec<Vec<u8>>, Error> {
ensure!(
RecordKind::parse(bytes)? == RecordKind::Container,
"not an offline container"
);
ensure!(
bytes.len() >= Urma::CONTAINER_HEADER_BYTES,
"truncated container"
);
let count = usize::try_from(u32::from_le_bytes(bytes[8..12].try_into()?))?;
ensure!(count > 0, "empty container");
let size = count
.checked_mul(Urma::PRIVATE_RECORD_BYTES + 4)
.and_then(|n| n.checked_add(Urma::CONTAINER_HEADER_BYTES))
.context("container size overflow")?;
ensure!(bytes.len() == size, "truncated or trailing container data");
let mut records = Vec::new();
records.try_reserve_exact(count)?;
for entry in bytes[Urma::CONTAINER_HEADER_BYTES..]
.as_chunks::<{ Urma::PRIVATE_RECORD_BYTES + 4 }>()
.0
{
ensure!(
u32::from_le_bytes(entry[..4].try_into()?)
== u32::try_from(Urma::PRIVATE_RECORD_BYTES)?,
"invalid container record length"
);
inspect_header(&entry[4..])?;
records.push(entry[4..].to_vec());
}
let id = inspect_header(&records[0])?.id;
for record in &records {
ensure!(inspect_header(record)?.id == id, "mixed objects");
}
Ok(records)
}
fn required_chunk(root: &[u8; 32], record: &[u8]) -> Result<PrivateChunk, Error> {
match open_record(root, record)? {
RecordMatch::Authenticated(chunk) => Ok(chunk),
RecordMatch::Unrelated => bail!("wrong key or unrelated record"),
}
}
pub fn open(root: &[u8; 32], records: &[Vec<u8>]) -> Result<Zeroizing<Vec<u8>>, Error> {
let (first, rest) = records.split_first().context("no records")?;
let mut object = PrivateObject::new(required_chunk(root, first)?);
for record in rest {
object.insert(required_chunk(root, record)?)?;
}
object.finish()
}