matrix-rust-sdk/src/crypto/machine.rs

// Copyright 2020 The Matrix.org Foundation C.I.C.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::collections::{HashMap, HashSet};
use std::convert::TryInto;
#[cfg(feature = "sqlite-cryptostore")]
use std::path::Path;
use std::result::Result as StdResult;
use std::sync::Arc;
use uuid::Uuid;

use super::error::{OlmError, Result, SignatureError, VerificationResult};
use super::olm::{Account, GroupSessionKey, InboundGroupSession, OutboundGroupSession, Session};
use super::store::memorystore::MemoryStore;
#[cfg(feature = "sqlite-cryptostore")]
use super::store::sqlite::SqliteStore;
use super::{device::Device, CryptoStore};
use crate::api;

use api::r0::keys;

use cjson;
use olm_rs::{session::OlmMessage, utility::OlmUtility};
use serde_json::{json, Value};
use tokio::sync::Mutex;
use tracing::{debug, error, info, instrument, trace, warn};

use ruma_client_api::r0::client_exchange::{
    send_event_to_device::Request as ToDeviceRequest, DeviceIdOrAllDevices,
};
use ruma_client_api::r0::keys::{
    AlgorithmAndDeviceId, DeviceKeys, KeyAlgorithm, OneTimeKey, SignedKey,
};
use ruma_client_api::r0::sync::sync_events::IncomingResponse as SyncResponse;
use ruma_events::{
    collections::all::RoomEvent,
    room::encrypted::{
        CiphertextInfo, EncryptedEvent, EncryptedEventContent, MegolmV1AesSha2Content,
        OlmV1Curve25519AesSha2Content,
    },
    room::message::MessageEventContent,
    to_device::{
        AnyToDeviceEvent as ToDeviceEvent, ToDeviceEncrypted, ToDeviceForwardedRoomKey,
        ToDeviceRoomKey, ToDeviceRoomKeyRequest,
    },
    Algorithm, EventResult, EventType,
};
use ruma_identifiers::RoomId;
use ruma_identifiers::{DeviceId, UserId};

pub type OneTimeKeys = HashMap<AlgorithmAndDeviceId, OneTimeKey>;

#[derive(Debug)]
pub struct OlmMachine {
    /// The unique user id that owns this account.
    user_id: UserId,
    /// The unique device id of the device that holds this account.
    device_id: DeviceId,
    /// Our underlying Olm Account holding our identity keys.
    account: Account,
    /// The number of signed one-time keys we have uploaded to the server. If
    /// this is None, no action will be taken. After a sync request the client
    /// needs to set this for us, depending on the count we will suggest the
    /// client to upload new keys.
    uploaded_signed_key_count: Option<u64>,
    /// Store for the encryption keys.
    /// Persists all the encrytpion keys so a client can resume the session
    /// without the need to create new keys.
    store: Box<dyn CryptoStore>,
    /// Set of users that we need to query keys for. This is a subset of
    /// the tracked users in the CryptoStore.
    users_for_key_query: HashSet<UserId>,
    /// The currently active outbound group sessions.
    outbound_group_session: HashMap<RoomId, OutboundGroupSession>,
}

impl OlmMachine {
    const ALGORITHMS: &'static [&'static ruma_events::Algorithm] = &[
        &Algorithm::OlmV1Curve25519AesSha2,
        &Algorithm::MegolmV1AesSha2,
    ];

    const MAX_TO_DEVICE_MESSAGES: usize = 20;

    /// Create a new account.
    pub fn new(user_id: &UserId, device_id: &str) -> Result<Self> {
        Ok(OlmMachine {
            user_id: user_id.clone(),
            device_id: device_id.to_owned(),
            account: Account::new(),
            uploaded_signed_key_count: None,
            store: Box::new(MemoryStore::new()),
            users_for_key_query: HashSet::new(),
            outbound_group_session: HashMap::new(),
        })
    }

    #[cfg(feature = "sqlite-cryptostore")]
    #[instrument(skip(path, passphrase))]
    pub async fn new_with_sqlite_store<P: AsRef<Path>>(
        user_id: &UserId,
        device_id: &str,
        path: P,
        passphrase: String,
    ) -> Result<Self> {
        let mut store =
            SqliteStore::open_with_passphrase(&user_id, device_id, path, passphrase).await?;

        let account = match store.load_account().await? {
            Some(a) => {
                debug!("Restored account");
                a
            }
            None => {
                debug!("Creating a new account");
                Account::new()
            }
        };

        // TODO load the tracked users here.
        Ok(OlmMachine {
            user_id: user_id.clone(),
            device_id: device_id.to_owned(),
            account,
            uploaded_signed_key_count: None,
            store: Box::new(store),
            users_for_key_query: HashSet::new(),
            outbound_group_session: HashMap::new(),
        })
    }

    /// Should account or one-time keys be uploaded to the server.
    pub async fn should_upload_keys(&self) -> bool {
        if !self.account.shared() {
            return true;
        }

        // If we have a known key count, check that we have more than
        // max_one_time_Keys() / 2, otherwise tell the client to upload more.
        match self.uploaded_signed_key_count {
            Some(count) => {
                let max_keys = self.account.max_one_time_keys().await as u64;
                let key_count = (max_keys / 2) - count;
                key_count > 0
            }
            None => false,
        }
    }

    /// Receive a successful keys upload response.
    ///
    /// # Arguments
    ///
    /// * `response` - The keys upload response of the request that the client
    /// performed.
    #[instrument]
    pub async fn receive_keys_upload_response(
        &mut self,
        response: &keys::upload_keys::Response,
    ) -> Result<()> {
        if !self.account.shared() {
            debug!("Marking account as shared");
        }
        self.account.mark_as_shared();

        let one_time_key_count = response
            .one_time_key_counts
            .get(&keys::KeyAlgorithm::SignedCurve25519);

        let count: u64 = one_time_key_count.map_or(0, |c| (*c).into());
        debug!(
            "Updated uploaded one-time key count {} -> {}, marking keys as published",
            self.uploaded_signed_key_count.as_ref().map_or(0, |c| *c),
            count
        );
        self.uploaded_signed_key_count = Some(count);

        self.account.mark_keys_as_published().await;

        // self.store.save_account(self.account.clone()).await?;

        Ok(())
    }

    pub async fn get_missing_sessions(
        &mut self,
        users: impl Iterator<Item = &UserId>,
    ) -> HashMap<UserId, HashMap<DeviceId, KeyAlgorithm>> {
        let mut missing = HashMap::new();

        for user_id in users {
            let user_devices = self.store.get_user_devices(user_id).await.unwrap();

            for device in user_devices.devices() {
                let sender_key = if let Some(k) = device.keys(&KeyAlgorithm::Curve25519) {
                    k
                } else {
                    continue;
                };

                let sessions = self.store.get_sessions(sender_key).await.unwrap();

                let is_missing = if let Some(sessions) = sessions {
                    sessions.lock().await.is_empty()
                } else {
                    true
                };

                if is_missing {
                    if !missing.contains_key(user_id) {
                        missing.insert(user_id.clone(), HashMap::new());
                    }

                    let user_map = missing.get_mut(user_id).unwrap();
                    user_map.insert(
                        device.device_id().to_owned(),
                        KeyAlgorithm::SignedCurve25519,
                    );
                }
            }
        }

        missing
    }

    pub async fn receive_keys_claim_response(
        &mut self,
        response: &keys::claim_keys::Response,
    ) -> Result<()> {
        // TODO log the failures here

        for (user_id, user_devices) in &response.one_time_keys {
            for (device_id, key_map) in user_devices {
                let device = if let Some(d) = self
                    .store
                    .get_device(&user_id, device_id)
                    .await
                    .expect("Can't get devices")
                {
                    d
                } else {
                    warn!(
                        "Tried to create an Olm session for {} {}, but the device is unknown",
                        user_id, device_id
                    );
                    continue;
                };

                let one_time_key = if let Some(k) = key_map.values().nth(0) {
                    match k {
                        OneTimeKey::SignedKey(k) => k,
                        OneTimeKey::Key(_) => {
                            warn!(
                                "Tried to create an Olm session for {} {}, but
                                   the requested key isn't a signed curve key",
                                user_id, device_id
                            );
                            continue;
                        }
                    }
                } else {
                    warn!(
                        "Tried to create an Olm session for {} {}, but the
                           signed one-time key is missing",
                        user_id, device_id
                    );
                    continue;
                };

                let signing_key = if let Some(k) = device.keys(&KeyAlgorithm::Ed25519) {
                    k
                } else {
                    warn!(
                        "Tried to create an Olm session for {} {}, but the
                           device is missing the signing key",
                        user_id, device_id
                    );
                    continue;
                };

                if self
                    .verify_json(user_id, device_id, signing_key, &mut json!(&one_time_key))
                    .is_err()
                {
                    warn!(
                        "Failed to verify the one-time key signatures for {} {}",
                        user_id, device_id
                    );
                    continue;
                }

                let curve_key = if let Some(k) = device.keys(&KeyAlgorithm::Curve25519) {
                    k
                } else {
                    warn!(
                        "Tried to create an Olm session for {} {}, but the
                           device is missing the curve key",
                        user_id, device_id
                    );
                    continue;
                };

                info!("Creating outbound Session for {} {}", user_id, device_id);

                let session = match self
                    .account
                    .create_outbound_session(curve_key, &one_time_key)
                    .await
                {
                    Ok(s) => s,
                    Err(e) => {
                        warn!(
                            "Error creating new Olm session for {} {}: {}",
                            user_id, device_id, e
                        );
                        continue;
                    }
                };

                if let Err(e) = self.store.add_and_save_session(session).await {
                    error!("Failed to store newly created Olm session {}", e);
                    continue;
                }

                // TODO if this session was created because a previous one was
                // wedged queue up a dummy event to be sent out.
                // TODO if this session was created because of a key request,
                // mark the forwarding keys to be sent out
            }
        }
        Ok(())
    }

    /// Receive a successful keys query response.
    ///
    /// # Arguments
    ///
    /// * `response` - The keys query response of the request that the client
    /// performed.
    // TODO this should return a list of changed devices.
    pub async fn receive_keys_query_response(
        &mut self,
        response: &keys::get_keys::Response,
    ) -> Result<()> {
        let mut changed_devices = Vec::new();

        for (user_id, device_map) in &response.device_keys {
            self.users_for_key_query.remove(&user_id);

            for (device_id, device_keys) in device_map.iter() {
                // We don't need our own device in the device store.
                if user_id == &self.user_id && device_id == &self.device_id {
                    continue;
                }

                if user_id != &device_keys.user_id || device_id != &device_keys.device_id {
                    warn!(
                        "Mismatch in device keys payload of device {} from user {}",
                        device_keys.device_id, device_keys.user_id
                    );
                    continue;
                }

                // let curve_key_id =
                //     AlgorithmAndDeviceId(KeyAlgorithm::Curve25519, device_id.to_owned());
                let ed_key_id = AlgorithmAndDeviceId(KeyAlgorithm::Ed25519, device_id.to_owned());

                // TODO check if the curve key changed for an existing device.
                // let sender_key = if let Some(k) = device_keys.keys.get(&curve_key_id) {
                //     k
                // } else {
                //     continue;
                // };

                let signing_key = if let Some(k) = device_keys.keys.get(&ed_key_id) {
                    k
                } else {
                    continue;
                };

                if self
                    .verify_json(user_id, device_id, signing_key, &mut json!(&device_keys))
                    .is_err()
                {
                    warn!(
                        "Failed to verify the device key signatures for {} {}",
                        user_id, device_id
                    );
                    continue;
                }

                let device = self
                    .store
                    .get_device(&user_id, device_id)
                    .await
                    .expect("Can't load device");

                if let Some(_d) = device {
                    // TODO check what and if anything changed for the device.
                } else {
                    let device = Device::from(device_keys);
                    info!("Found new device {:?}", device);
                    changed_devices.push(device);
                }
            }

            let current_devices: HashSet<&DeviceId> = device_map.keys().collect();
            let stored_devices = self.store.get_user_devices(&user_id).await.unwrap();
            let stored_devices_set: HashSet<&DeviceId> = stored_devices.keys().collect();

            let deleted_devices = stored_devices_set.difference(&current_devices);

            for _device_id in deleted_devices {
                // TODO delete devices here.
            }
        }

        for device in changed_devices {
            self.store.save_device(device).await.unwrap();
        }

        Ok(())
    }

    /// Generate new one-time keys.
    ///
    /// Returns the number of newly generated one-time keys. If no keys can be
    /// generated returns an empty error.
    async fn generate_one_time_keys(&self) -> StdResult<u64, ()> {
        match self.uploaded_signed_key_count {
            Some(count) => {
                let max_keys = self.account.max_one_time_keys().await as u64;
                let max_on_server = max_keys / 2;

                if count >= (max_on_server) {
                    return Err(());
                }

                let key_count = (max_on_server) - count;

                let max_keys = self.account.max_one_time_keys().await;

                let key_count: usize = key_count.try_into().unwrap_or(max_keys);

                self.account.generate_one_time_keys(key_count).await;
                Ok(key_count as u64)
            }
            None => Err(()),
        }
    }

    /// Sign the device keys and return a JSON Value to upload them.
    async fn device_keys(&self) -> DeviceKeys {
        let identity_keys = self.account.identity_keys();

        let mut keys = HashMap::new();

        keys.insert(
            AlgorithmAndDeviceId(KeyAlgorithm::Curve25519, self.device_id.clone()),
            identity_keys.curve25519().to_owned(),
        );
        keys.insert(
            AlgorithmAndDeviceId(KeyAlgorithm::Ed25519, self.device_id.clone()),
            identity_keys.ed25519().to_owned(),
        );

        let device_keys = json!({
            "user_id": self.user_id,
            "device_id": self.device_id,
            "algorithms": OlmMachine::ALGORITHMS,
            "keys": keys,
        });

        let mut signatures = HashMap::new();

        let mut signature = HashMap::new();
        signature.insert(
            AlgorithmAndDeviceId(KeyAlgorithm::Ed25519, self.device_id.clone()),
            self.sign_json(&device_keys).await,
        );
        signatures.insert(self.user_id.clone(), signature);

        DeviceKeys {
            user_id: self.user_id.clone(),
            device_id: self.device_id.clone(),
            algorithms: vec![
                Algorithm::OlmV1Curve25519AesSha2,
                Algorithm::MegolmV1AesSha2,
            ],
            keys,
            signatures,
            unsigned: None,
        }
    }

    /// Generate, sign and prepare one-time keys to be uploaded.
    ///
    /// If no one-time keys need to be uploaded returns an empty error.
    async fn signed_one_time_keys(&self) -> StdResult<OneTimeKeys, ()> {
        let _ = self.generate_one_time_keys().await?;
        let one_time_keys = self.account.one_time_keys().await;
        let mut one_time_key_map = HashMap::new();

        for (key_id, key) in one_time_keys.curve25519().iter() {
            let key_json = json!({
                "key": key,
            });

            let signature = self.sign_json(&key_json).await;

            let mut signature_map = HashMap::new();

            signature_map.insert(
                AlgorithmAndDeviceId(KeyAlgorithm::Ed25519, self.device_id.clone()),
                signature,
            );

            let mut signatures = HashMap::new();
            signatures.insert(self.user_id.clone(), signature_map);

            let signed_key = SignedKey {
                key: key.to_owned(),
                signatures,
            };

            one_time_key_map.insert(
                AlgorithmAndDeviceId(KeyAlgorithm::SignedCurve25519, key_id.to_owned()),
                OneTimeKey::SignedKey(signed_key),
            );
        }

        Ok(one_time_key_map)
    }

    /// Convert a JSON value to the canonical representation and sign the JSON
    /// string.
    ///
    /// # Arguments
    ///
    /// * `json` - The value that should be converted into a canonical JSON
    /// string.
    async fn sign_json(&self, json: &Value) -> String {
        let canonical_json = cjson::to_string(json)
            .unwrap_or_else(|_| panic!(format!("Can't serialize {} to canonical JSON", json)));
        self.account.sign(&canonical_json).await
    }

    /// Verify a signed JSON object.
    ///
    /// The object must have a signatures key associated  with an object of the
    /// form `user_id: {key_id: signature}`.
    ///
    /// Returns Ok if the signature was successfully verified, otherwise an
    /// SignatureError.
    ///
    /// # Arguments
    ///
    /// * `user_id` - The user who signed the JSON object.
    ///
    /// * `device_id` - The device that signed the JSON object.
    ///
    /// * `user_key` - The public ed25519 key which was used to sign the JSON
    ///     object.
    ///
    /// * `json` - The JSON object that should be verified.
    fn verify_json(
        &self,
        user_id: &UserId,
        device_id: &str,
        user_key: &str,
        json: &mut Value,
    ) -> VerificationResult<()> {
        let json_object = json.as_object_mut().ok_or(SignatureError::NotAnObject)?;
        let unsigned = json_object.remove("unsigned");
        let signatures = json_object.remove("signatures");

        let canonical_json = cjson::to_string(json_object)?;

        if let Some(u) = unsigned {
            json_object.insert("unsigned".to_string(), u);
        }

        // TODO this should be part of ruma-client-api.
        let key_id_string = format!("{}:{}", KeyAlgorithm::Ed25519, device_id);

        let signatures = signatures.ok_or(SignatureError::NoSignatureFound)?;
        let signature_object = signatures
            .as_object()
            .ok_or(SignatureError::NoSignatureFound)?;
        let signature = signature_object
            .get(&user_id.to_string())
            .ok_or(SignatureError::NoSignatureFound)?;
        let signature = signature
            .get(key_id_string)
            .ok_or(SignatureError::NoSignatureFound)?;
        let signature = signature.as_str().ok_or(SignatureError::NoSignatureFound)?;

        let utility = OlmUtility::new();

        let ret = if utility
            .ed25519_verify(&user_key, &canonical_json, signature)
            .is_ok()
        {
            Ok(())
        } else {
            Err(SignatureError::VerificationError)
        };

        json_object.insert("signatures".to_string(), signatures);

        ret
    }

    /// Get a tuple of device and one-time keys that need to be uploaded.
    ///
    /// Returns an empty error if no keys need to be uploaded.
    pub async fn keys_for_upload(
        &self,
    ) -> StdResult<(Option<DeviceKeys>, Option<OneTimeKeys>), ()> {
        if !self.should_upload_keys().await {
            return Err(());
        }

        let shared = self.account.shared();

        let device_keys = if !shared {
            Some(self.device_keys().await)
        } else {
            None
        };

        let one_time_keys: Option<OneTimeKeys> = self.signed_one_time_keys().await.ok();

        Ok((device_keys, one_time_keys))
    }

    async fn try_decrypt_olm_event(
        &mut self,
        sender_key: &str,
        message: &OlmMessage,
    ) -> Result<Option<String>> {
        let s = self.store.get_sessions(sender_key).await?;

        let sessions = if let Some(s) = s {
            s
        } else {
            return Ok(None);
        };

        for session in &*sessions.lock().await {
            let mut matches = false;

            let mut session_lock = session.lock().await;

            if let OlmMessage::PreKey(m) = &message {
                matches = session_lock.matches(sender_key, m.clone())?;
                if !matches {
                    continue;
                }
            }

            let ret = session_lock.decrypt(message.clone());

            if let Ok(p) = ret {
                self.store.save_session(session.clone()).await?;
                return Ok(Some(p));
            } else {
                if matches {
                    return Err(OlmError::SessionWedged);
                }
            }
        }

        Ok(None)
    }

    async fn decrypt_olm_message(
        &mut self,
        _sender: &str,
        sender_key: &str,
        message: OlmMessage,
    ) -> Result<EventResult<ToDeviceEvent>> {
        let plaintext = if let Some(p) = self.try_decrypt_olm_event(sender_key, &message).await? {
            p
        } else {
            let mut session = match &message {
                OlmMessage::Message(_) => return Err(OlmError::SessionWedged),
                OlmMessage::PreKey(m) => {
                    self.account
                        .create_inbound_session(sender_key, m.clone())
                        .await?
                }
            };

            let plaintext = session.decrypt(message)?;
            self.store.add_and_save_session(session).await?;
            plaintext
        };

        trace!("Successfully decrypted a Olm message: {}", plaintext);
        Ok(serde_json::from_str::<EventResult<ToDeviceEvent>>(
            &plaintext,
        )?)
    }

    /// Decrypt a to-device event.
    ///
    /// Returns a decrypted `ToDeviceEvent` if the decryption was successful,
    /// an error indicating why decryption failed otherwise.
    ///
    /// # Arguments
    ///
    /// * `event` - The to-device event that should be decrypted.
    #[instrument]
    async fn decrypt_to_device_event(
        &mut self,
        event: &ToDeviceEncrypted,
    ) -> Result<EventResult<ToDeviceEvent>> {
        info!("Decrypting to-device event");

        let content = if let EncryptedEventContent::OlmV1Curve25519AesSha2(c) = &event.content {
            c
        } else {
            warn!("Error, unsupported encryption algorithm");
            return Err(OlmError::UnsupportedAlgorithm);
        };

        let identity_keys = self.account.identity_keys();
        let own_key = identity_keys.curve25519();
        let own_ciphertext = content.ciphertext.get(own_key);

        if let Some(ciphertext) = own_ciphertext {
            let message_type: u8 = ciphertext
                .message_type
                .try_into()
                .map_err(|_| OlmError::UnsupportedOlmType)?;
            let message =
                OlmMessage::from_type_and_ciphertext(message_type.into(), ciphertext.body.clone())
                    .map_err(|_| OlmError::UnsupportedOlmType)?;

            let decrypted_event = self
                .decrypt_olm_message(&event.sender.to_string(), &content.sender_key, message)
                .await?;
            debug!("Decrypted a to-device event {:?}", decrypted_event);
            self.handle_decrypted_to_device_event(&content.sender_key, &decrypted_event)
                .await?;

            Ok(decrypted_event)
        } else {
            warn!("Olm event doesn't contain a ciphertext for our key");
            Err(OlmError::MissingCiphertext)
        }
    }

    async fn add_room_key(&mut self, sender_key: &str, event: &ToDeviceRoomKey) -> Result<()> {
        match event.content.algorithm {
            Algorithm::MegolmV1AesSha2 => {
                // TODO check for all the valid fields.
                let signing_key = event
                    .keys
                    .get("ed25519")
                    .ok_or(OlmError::MissingSigningKey)?;

                let session_key = GroupSessionKey(event.content.session_key.to_owned());

                let session = InboundGroupSession::new(
                    sender_key,
                    signing_key,
                    &event.content.room_id,
                    session_key,
                )?;
                self.store.save_inbound_group_session(session).await?;
                Ok(())
            }
            _ => {
                warn!(
                    "Received room key with unsupported key algorithm {}",
                    event.content.algorithm
                );
                Ok(())
            }
        }
    }

    async fn create_outbound_group_session(&mut self, room_id: &RoomId) -> Result<()> {
        let session = OutboundGroupSession::new(room_id);
        let identity_keys = self.account.identity_keys();

        let sender_key = identity_keys.curve25519();
        let signing_key = identity_keys.ed25519();

        let inbound_session = InboundGroupSession::new(
            sender_key,
            signing_key,
            &room_id,
            session.session_key().await,
        )?;
        self.store
            .save_inbound_group_session(inbound_session)
            .await?;

        self.outbound_group_session
            .insert(room_id.to_owned(), session);
        Ok(())
    }

    pub async fn encrypt(
        &self,
        room_id: &RoomId,
        content: MessageEventContent,
    ) -> Result<MegolmV1AesSha2Content> {
        let session = self.outbound_group_session.get(room_id);

        let session = if let Some(s) = session {
            s
        } else {
            panic!("Session wasn't created nor shared");
        };

        if session.expired() {
            panic!("Session is expired");
        }

        let json_content = json!({
            "content": content,
            "room_id": room_id,
            "type": EventType::RoomMessage,
        });

        let plaintext = cjson::to_string(&json_content).unwrap_or_else(|_| {
            panic!(format!(
                "Can't serialize {} to canonical JSON",
                json_content
            ))
        });

        let ciphertext = session.encrypt(plaintext).await;

        Ok(MegolmV1AesSha2Content {
            algorithm: Algorithm::MegolmV1AesSha2,
            ciphertext,
            sender_key: self.account.identity_keys().curve25519().to_owned(),
            session_id: session.session_id().to_owned(),
            device_id: self.device_id.to_owned(),
        })
    }

    async fn olm_encrypt(
        &mut self,
        session: Arc<Mutex<Session>>,
        recipient_device: &Device,
        event_type: EventType,
        content: Value,
    ) -> Result<OlmV1Curve25519AesSha2Content> {
        let identity_keys = self.account.identity_keys();

        let recipient_signing_key = recipient_device
            .keys(&KeyAlgorithm::Ed25519)
            .ok_or(OlmError::MissingSigningKey)?;
        let recipient_sender_key = recipient_device
            .keys(&KeyAlgorithm::Curve25519)
            .ok_or(OlmError::MissingSigningKey)?;

        let payload = json!({
            "sender": self.user_id,
            "sender_device": self.device_id,
            "keys": {
                "ed25519": identity_keys.ed25519(),
            },
            "recipient": recipient_device.user_id(),
            "recipient_keys": {
                "ed25519": recipient_signing_key,
            },
            "type": event_type,
            "content": content,
        });

        let plaintext = cjson::to_string(&payload)
            .unwrap_or_else(|_| panic!(format!("Can't serialize {} to canonical JSON", payload)));

        let ciphertext = session.lock().await.encrypt(&plaintext).to_tuple();
        self.store.save_session(session).await?;

        let message_type: usize = ciphertext.0.into();

        let ciphertext = CiphertextInfo {
            body: ciphertext.1,
            message_type: (message_type as u32).into(),
        };

        let mut content = HashMap::new();

        content.insert(recipient_sender_key.to_owned(), ciphertext);

        Ok(OlmV1Curve25519AesSha2Content {
            algorithm: Algorithm::OlmV1Curve25519AesSha2,
            sender_key: identity_keys.curve25519().to_owned(),
            ciphertext: content,
        })
    }

    /// Should the client share a group session for the given room.
    ///
    /// Returns true if a session needs to be shared before room messages can be
    /// encrypted, false if one is already shared and ready to encrypt room
    /// messages.
    ///
    /// This should be called every time a new room message wants to be sent out
    /// since group sessions can expire at any time.
    pub fn should_share_group_session(&self, room_id: &RoomId) -> bool {
        let session = self.outbound_group_session.get(room_id);

        match session {
            Some(s) => !s.shared() || s.expired(),
            None => true,
        }
    }

    // TODO accept an algorithm here
    pub(crate) async fn share_group_session<'a, I>(
        &mut self,
        room_id: &RoomId,
        users: I,
    ) -> Result<Vec<ToDeviceRequest>>
    where
        I: IntoIterator<Item = &'a UserId>,
    {
        self.create_outbound_group_session(room_id).await?;
        let megolm_session = self.outbound_group_session.get(room_id).unwrap();

        if megolm_session.shared() {
            panic!("Session is already shared");
        }

        let session_id = megolm_session.session_id().to_owned();
        megolm_session.mark_as_shared();

        let key_content = json!({
            "algorithm": Algorithm::MegolmV1AesSha2,
            "room_id": room_id,
            "session_id": session_id.clone(),
            "session_key": megolm_session.session_key().await,
            "chain_index": megolm_session.message_index().await,
        });

        let mut user_map = Vec::new();

        for user_id in users {
            for device in self.store.get_user_devices(user_id).await?.devices() {
                let sender_key = if let Some(k) = device.keys(&KeyAlgorithm::Curve25519) {
                    k
                } else {
                    warn!(
                        "The device {} of user {} doesn't have a curve 25519 key",
                        user_id,
                        device.device_id()
                    );
                    // TODO mark the user for a key query.
                    continue;
                };

                // TODO abort if the device isn't verified
                let sessions = self.store.get_sessions(sender_key).await?;

                if let Some(s) = sessions {
                    let session = &s.lock().await[0];
                    user_map.push((session.clone(), device.clone()));
                } else {
                    warn!(
                        "Trying to encrypt a megolm session for user
                          {} on device {}, but no Olm session is found",
                        user_id,
                        device.device_id()
                    );
                }
            }
        }

        let mut message_vec = Vec::new();

        for user_map_chunk in user_map.chunks(OlmMachine::MAX_TO_DEVICE_MESSAGES) {
            let mut messages = HashMap::new();

            for (session, device) in user_map_chunk {
                if !messages.contains_key(device.user_id()) {
                    messages.insert(device.user_id().clone(), HashMap::new());
                };

                let user_messages = messages.get_mut(device.user_id()).unwrap();

                let encrypted_content = self
                    .olm_encrypt(
                        session.clone(),
                        &device,
                        EventType::RoomKey,
                        key_content.clone(),
                    )
                    .await?;

                user_messages.insert(
                    DeviceIdOrAllDevices::DeviceId(device.device_id().clone()),
                    encrypted_content,
                );
            }

            message_vec.push(ToDeviceRequest {
                event_type: "m.room.encrypted".to_owned(),
                txn_id: Uuid::new_v4().to_string(),
                messages,
            });
        }

        Ok(message_vec)
    }

    fn add_forwarded_room_key(
        &self,
        _sender_key: &str,
        _event: &ToDeviceForwardedRoomKey,
    ) -> Result<()> {
        Ok(())
        // TODO
    }

    async fn handle_decrypted_to_device_event(
        &mut self,
        sender_key: &str,
        event: &EventResult<ToDeviceEvent>,
    ) -> Result<()> {
        let event = if let EventResult::Ok(e) = event {
            e
        } else {
            warn!("Decrypted to-device event failed to be parsed correctly");
            return Ok(());
        };

        match event {
            ToDeviceEvent::RoomKey(e) => self.add_room_key(sender_key, e).await,
            ToDeviceEvent::ForwardedRoomKey(e) => self.add_forwarded_room_key(sender_key, e),
            _ => {
                warn!("Received a unexpected encrypted to-device event");
                Ok(())
            }
        }
    }

    fn handle_room_key_request(&self, _: &ToDeviceRoomKeyRequest) {
        // TODO handle room key requests here.
    }

    fn handle_verification_event(&self, _: &ToDeviceEvent) {
        // TODO handle to-device verification events here.
    }

    #[instrument(skip(response))]
    /// Handle a sync response and update the internal state of the Olm machine.
    ///
    /// This will decrypt to-device events but will not touch room messages.
    ///
    /// # Arguments
    ///
    /// * `response` - The sync latest sync response.
    pub async fn receive_sync_response(&mut self, response: &mut SyncResponse) {
        let one_time_key_count = response
            .device_one_time_keys_count
            .get(&keys::KeyAlgorithm::SignedCurve25519);

        let count: u64 = one_time_key_count.map_or(0, |c| (*c).into());
        self.uploaded_signed_key_count = Some(count);

        for event_result in &mut response.to_device.events {
            let event = if let EventResult::Ok(e) = &event_result {
                e
            } else {
                // Skip invalid events.
                warn!("Received an invalid to-device event {:?}", event_result);
                continue;
            };

            info!("Received a to-device event {:?}", event);

            match event {
                ToDeviceEvent::RoomEncrypted(e) => {
                    let decrypted_event = match self.decrypt_to_device_event(e).await {
                        Ok(e) => e,
                        Err(err) => {
                            warn!(
                                "Failed to decrypt to-device event from {} {}",
                                e.sender, err
                            );
                            // TODO if the session is wedged mark it for
                            // unwedging.
                            continue;
                        }
                    };

                    // TODO make sure private keys are cleared from the event
                    // before we replace the result.
                    *event_result = decrypted_event;
                }
                ToDeviceEvent::RoomKeyRequest(e) => self.handle_room_key_request(e),
                ToDeviceEvent::KeyVerificationAccept(..)
                | ToDeviceEvent::KeyVerificationCancel(..)
                | ToDeviceEvent::KeyVerificationKey(..)
                | ToDeviceEvent::KeyVerificationMac(..)
                | ToDeviceEvent::KeyVerificationRequest(..)
                | ToDeviceEvent::KeyVerificationStart(..) => self.handle_verification_event(event),
                _ => continue,
            }
        }
    }

    pub async fn decrypt_room_event(
        &mut self,
        event: &EncryptedEvent,
    ) -> Result<EventResult<RoomEvent>> {
        let content = match &event.content {
            EncryptedEventContent::MegolmV1AesSha2(c) => c,
            _ => return Err(OlmError::UnsupportedAlgorithm),
        };

        let room_id = event.room_id.as_ref().unwrap();

        let session = self
            .store
            .get_inbound_group_session(&room_id, &content.sender_key, &content.session_id)
            .await?;
        // TODO check if the olm session is wedged and re-request the key.
        let session = session.ok_or(OlmError::MissingSession)?;

        let (plaintext, _) = session.decrypt(content.ciphertext.clone()).await?;
        // TODO check the message index.
        // TODO check if this is from a verified device.

        let mut decrypted_value = serde_json::from_str::<Value>(&plaintext)?;
        let decrypted_object = decrypted_value
            .as_object_mut()
            .ok_or(OlmError::NotAnObject)?;

        let server_ts: u64 = event.origin_server_ts.into();

        decrypted_object.insert("sender".to_owned(), event.sender.to_string().into());
        decrypted_object.insert("event_id".to_owned(), event.event_id.to_string().into());
        decrypted_object.insert("origin_server_ts".to_owned(), server_ts.into());

        decrypted_object.insert("unsigned".to_owned(), event.unsigned.clone().into());

        let decrypted_event = serde_json::from_value::<EventResult<RoomEvent>>(decrypted_value)?;
        trace!("Successfully decrypted megolm event {:?}", decrypted_event);
        // TODO set the encryption info on the event (is it verified, was it
        // decrypted, sender key...)

        Ok(decrypted_event)
    }

    /// Update the tracked users.
    ///
    /// This will only not already seen users for a key query and user tracking.
    /// If the user is already known to the Olm machine it will not be
    /// considered for a key query.
    ///
    /// Use the `mark_user_as_changed()` if the user really needs a key query.
    pub async fn update_tracked_users<'a, I>(&mut self, users: I)
    where
        I: IntoIterator<Item = &'a UserId>,
    {
        for user in users {
            let ret = self.store.add_user_for_tracking(user).await;

            match ret {
                Ok(newly_added) => {
                    if newly_added {
                        self.users_for_key_query.insert(user.clone());
                    }
                }
                Err(e) => {
                    warn!("Error storing users for tracking {}", e);
                    self.users_for_key_query.insert(user.clone());
                }
            }
        }
    }

    /// Should a key query be done.
    pub fn should_query_keys(&self) -> bool {
        !self.users_for_key_query.is_empty()
    }

    /// Get the set of users that we need to query keys for.
    pub fn users_for_key_query(&self) -> HashSet<UserId> {
        self.users_for_key_query.clone()
    }
}

#[cfg(test)]
mod test {
    static USER_ID: &str = "@test:example.org";
    const DEVICE_ID: &str = "DEVICEID";

    use js_int::UInt;
    use std::convert::TryFrom;
    use std::fs::File;
    use std::io::prelude::*;

    use ruma_identifiers::UserId;
    use serde_json::json;

    use crate::api::r0::keys;
    use crate::crypto::machine::OlmMachine;
    use http::Response;

    fn user_id() -> UserId {
        UserId::try_from(USER_ID).unwrap()
    }

    fn response_from_file(path: &str) -> Response<Vec<u8>> {
        let mut file = File::open(path)
            .unwrap_or_else(|_| panic!(format!("No such data file found {}", path)));
        let mut contents = Vec::new();
        file.read_to_end(&mut contents)
            .unwrap_or_else(|_| panic!(format!("Can't read data file {}", path)));

        Response::builder().status(200).body(contents).unwrap()
    }

    fn keys_upload_response() -> keys::upload_keys::Response {
        let data = response_from_file("tests/data/keys_upload.json");
        keys::upload_keys::Response::try_from(data).expect("Can't parse the keys upload response")
    }

    #[tokio::test]
    async fn create_olm_machine() {
        let machine = OlmMachine::new(&user_id(), DEVICE_ID).unwrap();
        assert!(machine.should_upload_keys().await);
    }

    #[tokio::test]
    async fn receive_keys_upload_response() {
        let mut machine = OlmMachine::new(&user_id(), DEVICE_ID).unwrap();
        let mut response = keys_upload_response();

        response
            .one_time_key_counts
            .remove(&keys::KeyAlgorithm::SignedCurve25519)
            .unwrap();

        assert!(machine.should_upload_keys().await);
        machine
            .receive_keys_upload_response(&response)
            .await
            .unwrap();
        assert!(machine.should_upload_keys().await);

        response.one_time_key_counts.insert(
            keys::KeyAlgorithm::SignedCurve25519,
            UInt::try_from(10).unwrap(),
        );
        machine
            .receive_keys_upload_response(&response)
            .await
            .unwrap();
        assert!(machine.should_upload_keys().await);

        response.one_time_key_counts.insert(
            keys::KeyAlgorithm::SignedCurve25519,
            UInt::try_from(50).unwrap(),
        );
        machine
            .receive_keys_upload_response(&response)
            .await
            .unwrap();
        assert!(!machine.should_upload_keys().await);
    }

    #[tokio::test]
    async fn generate_one_time_keys() {
        let mut machine = OlmMachine::new(&user_id(), DEVICE_ID).unwrap();

        let mut response = keys_upload_response();

        assert!(machine.should_upload_keys().await);
        assert!(machine.generate_one_time_keys().await.is_err());

        machine
            .receive_keys_upload_response(&response)
            .await
            .unwrap();
        assert!(machine.should_upload_keys().await);
        assert!(machine.generate_one_time_keys().await.is_ok());

        response.one_time_key_counts.insert(
            keys::KeyAlgorithm::SignedCurve25519,
            UInt::try_from(50).unwrap(),
        );
        machine
            .receive_keys_upload_response(&response)
            .await
            .unwrap();
        assert!(machine.generate_one_time_keys().await.is_err());
    }

    #[tokio::test]
    async fn test_device_key_signing() {
        let machine = OlmMachine::new(&user_id(), DEVICE_ID).unwrap();

        let mut device_keys = machine.device_keys().await;
        let identity_keys = machine.account.identity_keys();
        let ed25519_key = identity_keys.ed25519();

        let ret = machine.verify_json(
            &machine.user_id,
            &machine.device_id,
            ed25519_key,
            &mut json!(&mut device_keys),
        );
        assert!(ret.is_ok());
    }

    #[tokio::test]
    async fn test_invalid_signature() {
        let machine = OlmMachine::new(&user_id(), DEVICE_ID).unwrap();

        let mut device_keys = machine.device_keys().await;

        let ret = machine.verify_json(
            &machine.user_id,
            &machine.device_id,
            "fake_key",
            &mut json!(&mut device_keys),
        );
        assert!(ret.is_err());
    }

    #[tokio::test]
    async fn test_one_time_key_signing() {
        let mut machine = OlmMachine::new(&user_id(), DEVICE_ID).unwrap();
        machine.uploaded_signed_key_count = Some(49);

        let mut one_time_keys = machine.signed_one_time_keys().await.unwrap();
        let identity_keys = machine.account.identity_keys();
        let ed25519_key = identity_keys.ed25519();

        let mut one_time_key = one_time_keys.values_mut().nth(0).unwrap();

        let ret = machine.verify_json(
            &machine.user_id,
            &machine.device_id,
            ed25519_key,
            &mut json!(&mut one_time_key),
        );
        assert!(ret.is_ok());
    }

    #[tokio::test]
    async fn test_keys_for_upload() {
        let mut machine = OlmMachine::new(&user_id(), DEVICE_ID).unwrap();
        machine.uploaded_signed_key_count = Some(0);

        let identity_keys = machine.account.identity_keys();
        let ed25519_key = identity_keys.ed25519();

        let (device_keys, mut one_time_keys) = machine
            .keys_for_upload()
            .await
            .expect("Can't prepare initial key upload");

        let ret = machine.verify_json(
            &machine.user_id,
            &machine.device_id,
            ed25519_key,
            &mut json!(&mut one_time_keys.as_mut().unwrap().values_mut().nth(0)),
        );
        assert!(ret.is_ok());

        let ret = machine.verify_json(
            &machine.user_id,
            &machine.device_id,
            ed25519_key,
            &mut json!(&mut device_keys.unwrap()),
        );
        assert!(ret.is_ok());

        let mut response = keys_upload_response();
        response.one_time_key_counts.insert(
            keys::KeyAlgorithm::SignedCurve25519,
            UInt::new_wrapping(one_time_keys.unwrap().len() as u64),
        );

        machine
            .receive_keys_upload_response(&response)
            .await
            .unwrap();

        let ret = machine.keys_for_upload().await;
        assert!(ret.is_err());
    }
}