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Use the dehydrated device format implemented by vodozemac #4421

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Use the dehydrated device format implemented by vodozemac #4421

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b5563c2
use the dehydrated device format implemented by vodozemac
uhoreg Dec 16, 2024
0323681
Merge branch 'main' into dehydration_format
uhoreg Dec 16, 2024
b0dd695
make it work with latest main, and fmt
uhoreg Dec 17, 2024
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3 changes: 1 addition & 2 deletions Cargo.lock
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2 changes: 2 additions & 0 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -145,6 +145,8 @@ tracing-core = { git = "https://github.com/element-hq/tracing.git", rev = "ca943
tracing-subscriber = { git = "https://github.com/element-hq/tracing.git", rev = "ca9431f74d37c9d3b5e6a9f35b2c706711dab7dd" }
tracing-appender = { git = "https://github.com/element-hq/tracing.git", rev = "ca9431f74d37c9d3b5e6a9f35b2c706711dab7dd" }
paranoid-android = { git = "https://github.com/element-hq/paranoid-android.git", rev = "69388ac5b4afeed7be4401c70ce17f6d9a2cf19b" }
vodozemac = { git = "https://github.com/uhoreg/vodozemac.git", branch = "dehydration_format" }


[workspace.lints.rust]
rust_2018_idioms = "warn"
Expand Down
40 changes: 3 additions & 37 deletions crates/matrix-sdk-crypto/src/dehydrated_devices.rs
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Expand Up @@ -43,15 +43,13 @@

use std::sync::Arc;

use hkdf::Hkdf;
use ruma::{
api::client::dehydrated_device::{put_dehydrated_device, DehydratedDeviceData},
assign,
events::AnyToDeviceEvent,
serde::Raw,
DeviceId,
};
use sha2::Sha256;
use thiserror::Error;
use tracing::{instrument, trace};
use vodozemac::LibolmPickleError;
Expand Down Expand Up @@ -136,8 +134,8 @@ impl DehydratedDevices {
device_id: &DeviceId,
device_data: Raw<DehydratedDeviceData>,
) -> Result<RehydratedDevice, DehydrationError> {
let pickle_key = expand_pickle_key(pickle_key.inner.as_ref(), device_id);
let rehydrated = self.inner.rehydrate(&pickle_key, device_id, device_data).await?;
let rehydrated =
self.inner.rehydrate(pickle_key.inner.as_ref(), device_id, device_data).await?;

Ok(RehydratedDevice { rehydrated, original: self.inner.to_owned() })
}
Expand Down Expand Up @@ -369,10 +367,8 @@ impl DehydratedDevice {

trace!("Creating an upload request for a dehydrated device");

let pickle_key =
expand_pickle_key(pickle_key.inner.as_ref(), &self.store.static_account().device_id);
let device_id = self.store.static_account().device_id.clone();
let device_data = account.dehydrate(&pickle_key);
let device_data = account.dehydrate(pickle_key.inner.as_ref());
let initial_device_display_name = Some(initial_device_display_name);

transaction.commit().await?;
Expand All @@ -385,36 +381,6 @@ impl DehydratedDevice {
}
}

/// We're using the libolm-compatible pickle format and its encryption scheme.
///
/// The libolm pickle encryption scheme uses HKDF to deterministically expand an
/// input key material, usually 32 bytes, into a AES key, MAC key, and the
/// initialization vector (IV).
///
/// This means that the same input key material will always end up producing the
/// same AES key, and IV.
///
/// This encryption scheme is used in the Olm double ratchet and was designed to
/// minimize the size of the ciphertext. As a tradeof, it requires a unique
/// input key material for each plaintext that gets encrypted, otherwise IV
/// reuse happens.
///
/// To combat the IV reuse, we're going to create a per-dehydrated-device unique
/// pickle key by expanding the key itself with the device ID used as the salt.
fn expand_pickle_key(key: &[u8; 32], device_id: &DeviceId) -> Box<[u8; 32]> {
// TODO: Perhaps we should put this into vodozemac with a new pickle
// minimalistic pickle format using the [`matrix_pickle`] crate.
//
// [`matrix_pickle`]: https://docs.rs/matrix-pickle/latest/matrix_pickle/
let kdf: Hkdf<Sha256> = Hkdf::new(Some(device_id.as_bytes()), key);
let mut key = Box::new([0u8; 32]);

kdf.expand(b"dehydrated-device-pickle-key", key.as_mut_slice())
.expect("We should be able to expand the 32 byte pickle key");

key
}

#[cfg(test)]
mod tests {
use std::{collections::BTreeMap, iter};
Expand Down
8 changes: 6 additions & 2 deletions crates/matrix-sdk-crypto/src/olm/account.rs
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Expand Up @@ -694,7 +694,7 @@ impl Account {
pub(crate) fn dehydrate(&self, pickle_key: &[u8; 32]) -> Raw<DehydratedDeviceData> {
let device_pickle = self
.inner
.to_libolm_pickle(pickle_key)
.to_dehydrated_device(pickle_key)
.expect("We should be able to convert a freshly created Account into a libolm pickle");

let data = DehydratedDeviceData::V1(DehydratedDeviceV1::new(device_pickle));
Expand All @@ -711,7 +711,11 @@ impl Account {

match data {
DehydratedDeviceData::V1(d) => {
let account = InnerAccount::from_libolm_pickle(&d.device_pickle, pickle_key)?;
let account = InnerAccount::from_dehydrated_device(
&d.device_pickle,
device_id.as_str(),
pickle_key,
)?;
Ok(Self::new_helper(account, user_id, device_id))
}
_ => Err(DehydrationError::Json(serde_json::Error::custom(format!(
Expand Down
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