crypto: Add initial support to decrypt megolm encrypted events.

Makefile

@@ -1,3 +1,7 @@
+all: build
+
+build:
+	cargo build --features 'encryption sqlite-cryptostore'
 test:
 	cargo test --features 'encryption sqlite-cryptostore'
 

src/async_client.rs

@@ -25,7 +25,6 @@ use tracing::{debug, info, instrument, trace};
 
 use http::Method as HttpMethod;
 use http::Response as HttpResponse;
-use js_int::UInt;
 use reqwest::header::{HeaderValue, InvalidHeaderValue};
 use url::Url;
 
@@ -382,28 +381,33 @@ impl AsyncClient {
 
         let mut response = self.send(request).await?;
 
-        for (room_id, room) in &response.rooms.join {
+        for (room_id, room) in &mut response.rooms.join {
-            let room_id = room_id.to_string();
+            let room_id_string = room_id.to_string();
 
             let matrix_room = {
                 let mut client = self.base_client.write().await;
 
                 for event in &room.state.events {
                     if let EventResult::Ok(e) = event {
-                        client.receive_joined_state_event(&room_id, &e);
+                        client.receive_joined_state_event(&room_id_string, &e);
                     }
                 }
 
-                client.get_or_create_room(&room_id).clone()
+                client.get_or_create_room(&room_id_string).clone()
             };
 
-            for event in &room.timeline.events {
+            for mut event in &mut room.timeline.events {
-                {
+                let decrypted_event = {
                     let mut client = self.base_client.write().await;
-                    client.receive_joined_timeline_event(&room_id, &event);
+                    client
-                }
+                        .receive_joined_timeline_event(room_id, &mut event)
+                        .await
+                };
 
-                let event = Arc::new(event.clone());
+                let event = match decrypted_event {
+                    Some(e) => Arc::new(e.clone()),
+                    None => Arc::new(event.clone()),
+                };
 
                 let callbacks = {
                     let mut cb_futures = self.event_callbacks.lock().unwrap();

src/base_client.rs

@@ -33,9 +33,9 @@ use tokio::sync::Mutex;
 use crate::crypto::{OlmMachine, OneTimeKeys};
 #[cfg(feature = "encryption")]
 use ruma_client_api::r0::keys::{upload_keys::Response as KeysUploadResponse, DeviceKeys};
+use ruma_identifiers::RoomId;
 
 pub type Token = String;
-pub type RoomId = String;
 pub type UserId = String;
 
 #[derive(Debug)]
@@ -55,7 +55,7 @@ pub struct RoomMember {
 /// A Matrix rooom.
 pub struct Room {
     /// The unique id of the room.
-    pub room_id: RoomId,
+    pub room_id: String,
     /// The mxid of our own user.
     pub own_user_id: UserId,
     /// The mxid of the room creator.
@@ -191,7 +191,7 @@ pub struct Client {
     /// The current sync token that should be used for the next sync call.
     pub sync_token: Option<Token>,
     /// A map of the rooms our user is joined in.
-    pub joined_rooms: HashMap<RoomId, Arc<RwLock<Room>>>,
+    pub joined_rooms: HashMap<String, Arc<RwLock<Room>>>,
     #[cfg(feature = "encryption")]
     olm: Arc<Mutex<Option<OlmMachine>>>,
 }
@@ -267,25 +267,49 @@ impl Client {
 
     /// Receive a timeline event for a joined room and update the client state.
     ///
-    /// Returns true if the membership list of the room changed, false
+    /// If the event was a encrypted room event and decryption was successful
-    /// otherwise.
+    /// the decrypted event will be returned, otherwise None.
     ///
     /// # Arguments
     ///
     /// * `room_id` - The unique id of the room the event belongs to.
     ///
     /// * `event` - The event that should be handled by the client.
-    pub fn receive_joined_timeline_event(
+    pub async fn receive_joined_timeline_event(
         &mut self,
-        room_id: &str,
+        room_id: &RoomId,
-        event: &EventResult<RoomEvent>,
+        event: &mut EventResult<RoomEvent>,
-    ) -> bool {
+    ) -> Option<EventResult<RoomEvent>> {
         match event {
             EventResult::Ok(e) => {
-                let mut room = self.get_or_create_room(room_id).write().unwrap();
+                #[cfg(feature = "encryption")]
-                room.receive_timeline_event(e)
+                let mut decrypted_event = None;
+                #[cfg(not(feature = "encryption"))]
+                let decrypted_event = None;
+
+                #[cfg(feature = "encryption")]
+                {
+                    match e {
+                        RoomEvent::RoomEncrypted(e) => {
+                            e.room_id = Some(room_id.to_owned());
+                            let mut olm = self.olm.lock().await;
+
+                            if let Some(o) = &mut *olm {
+                                decrypted_event = o.decrypt_room_event(e).await.ok();
                             }
-            _ => false,
+                        }
+                        _ => (),
+                    }
+                }
+
+                let mut room = self
+                    .get_or_create_room(&room_id.to_string())
+                    .write()
+                    .unwrap();
+                room.receive_timeline_event(e);
+                decrypted_event
+            }
+            _ => None,
         }
     }
 

src/crypto/error.rs

@@ -35,6 +35,8 @@ pub enum OlmError {
     UnsupportedAlgorithm,
     #[error("the Encrypted message doesn't contain a ciphertext for our device")]
     MissingCiphertext,
+    #[error("decryption failed because the session to decrypt the message is missing")]
+    MissingSession,
     #[error("can't finish Olm Session operation {0}")]
     OlmSession(#[from] OlmSessionError),
     #[error("can't finish Olm Session operation {0}")]

src/crypto/machine.rs

@@ -41,7 +41,8 @@ use ruma_client_api::r0::keys::{
 };
 use ruma_client_api::r0::sync::sync_events::IncomingResponse as SyncResponse;
 use ruma_events::{
-    room::encrypted::EncryptedEventContent,
+    collections::all::RoomEvent,
+    room::encrypted::{EncryptedEvent, EncryptedEventContent},
     to_device::{
         AnyToDeviceEvent as ToDeviceEvent, ToDeviceEncrypted, ToDeviceForwardedRoomKey,
         ToDeviceRoomKey, ToDeviceRoomKeyRequest,
@@ -623,6 +624,52 @@ impl OlmMachine {
             }
         }
     }
+
+    pub async fn decrypt_room_event(
+        &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.inbound_group_sessions.get(
+            &room_id.to_string(),
+            &content.sender_key,
+            &content.session_id,
+        );
+        // 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())?;
+        // 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());
+
+        if let Some(unsigned) = &event.unsigned {
+            decrypted_object.insert("unsigned".to_owned(), unsigned.clone());
+        }
+
+        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)
+    }
 }
 
 #[cfg(test)]