diff --git a/src/crypto/device.rs b/src/crypto/device.rs
index cf1ddf49..c5d50a32 100644
--- a/src/crypto/device.rs
+++ b/src/crypto/device.rs
@@ -20,11 +20,12 @@ use atomic::Atomic;
 
 use ruma_client_api::r0::keys::{DeviceKeys, KeyAlgorithm};
 use ruma_events::Algorithm;
+use ruma_identifiers::{DeviceId, UserId};
 
 #[derive(Debug, Clone)]
 pub struct Device {
-    user_id: Arc<String>,
-    device_id: Arc<String>,
+    user_id: Arc<UserId>,
+    device_id: Arc<DeviceId>,
     algorithms: Arc<Vec<Algorithm>>,
     keys: Arc<HashMap<KeyAlgorithm, String>>,
     display_name: Arc<Option<String>>,
@@ -47,11 +48,11 @@ pub enum TrustState {
 }
 
 impl Device {
-    pub fn device_id(&self) -> &str {
+    pub fn device_id(&self) -> &DeviceId {
         &self.device_id
     }
 
-    pub fn user_id(&self) -> &str {
+    pub fn user_id(&self) -> &UserId {
         &self.user_id
     }
 }
@@ -66,7 +67,7 @@ impl From<&DeviceKeys> for Device {
         }
 
         Device {
-            user_id: Arc::new(device_keys.user_id.to_string()),
+            user_id: Arc::new(device_keys.user_id.clone()),
             device_id: Arc::new(device_keys.device_id.clone()),
             algorithms: Arc::new(device_keys.algorithms.clone()),
             keys: Arc::new(keys),
diff --git a/src/crypto/machine.rs b/src/crypto/machine.rs
index 98554cbf..dd8d49dc 100644
--- a/src/crypto/machine.rs
+++ b/src/crypto/machine.rs
@@ -20,7 +20,7 @@ use std::result::Result as StdResult;
 use std::sync::Arc;
 
 use super::error::{OlmError, Result, SignatureError, VerificationResult};
-use super::olm::{Account, InboundGroupSession, OutboundGroupSession};
+use super::olm::{Account, InboundGroupSession, OutboundGroupSession, Session};
 use super::store::memorystore::MemoryStore;
 #[cfg(feature = "sqlite-cryptostore")]
 use super::store::sqlite::SqliteStore;
@@ -35,19 +35,25 @@ use serde_json::{json, Value};
 use tokio::sync::Mutex;
 use tracing::{debug, error, info, instrument, trace, warn};
 
-use ruma_client_api::r0::client_exchange::DeviceIdOrAllDevices;
+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::{Event, RoomEvent},
-    room::encrypted::{EncryptedEvent, EncryptedEventContent},
+    collections::all::RoomEvent,
+    room::encrypted::{
+        CiphertextInfo, EncryptedEvent, EncryptedEventContent, MegolmV1AesSha2Content,
+        OlmV1Curve25519AesSha2Content,
+    },
+    room::message::MessageEventContent,
     to_device::{
         AnyToDeviceEvent as ToDeviceEvent, ToDeviceEncrypted, ToDeviceForwardedRoomKey,
         ToDeviceRoomKey, ToDeviceRoomKeyRequest,
     },
-    Algorithm, EventResult,
+    Algorithm, EventResult, EventType,
 };
 use ruma_identifiers::RoomId;
 use ruma_identifiers::{DeviceId, UserId};
@@ -409,9 +415,9 @@ impl OlmMachine {
                 }
             }
 
-            let current_devices: HashSet<&String> = device_map.keys().collect();
+            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<&String> = stored_devices.keys().collect();
+            let stored_devices_set: HashSet<&DeviceId> = stored_devices.keys().collect();
 
             let deleted_devices = stored_devices_set.difference(&current_devices);
 
diff --git a/src/crypto/memory_stores.rs b/src/crypto/memory_stores.rs
index dee2378f..de2e67e3 100644
--- a/src/crypto/memory_stores.rs
+++ b/src/crypto/memory_stores.rs
@@ -13,7 +13,6 @@
 // limitations under the License.
 
 use std::collections::HashMap;
-use std::convert::TryFrom;
 use std::sync::Arc;
 
 use dashmap::{DashMap, ReadOnlyView};
@@ -21,7 +20,7 @@ use tokio::sync::Mutex;
 
 use super::device::Device;
 use super::olm::{InboundGroupSession, Session};
-use crate::identifiers::{RoomId, UserId};
+use crate::identifiers::{DeviceId, RoomId, UserId};
 
 #[derive(Debug)]
 pub struct SessionStore {
@@ -107,7 +106,7 @@ pub struct DeviceStore {
 }
 
 pub struct UserDevices {
-    entries: ReadOnlyView<String, Device>,
+    entries: ReadOnlyView<DeviceId, Device>,
 }
 
 impl UserDevices {
@@ -115,7 +114,7 @@ impl UserDevices {
         self.entries.get(device_id).cloned()
     }
 
-    pub fn keys(&self) -> impl Iterator<Item = &String> {
+    pub fn keys(&self) -> impl Iterator<Item = &DeviceId> {
         self.entries.keys()
     }
 
@@ -132,7 +131,7 @@ impl DeviceStore {
     }
 
     pub fn add(&self, device: Device) -> bool {
-        let user_id = UserId::try_from(device.user_id()).unwrap();
+        let user_id = device.user_id();
 
         if !self.entries.contains_key(&user_id) {
             self.entries.insert(user_id.clone(), DashMap::new());
diff --git a/src/crypto/olm.rs b/src/crypto/olm.rs
index f8259873..bafd2d56 100644
--- a/src/crypto/olm.rs
+++ b/src/crypto/olm.rs
@@ -292,6 +292,7 @@ impl OutboundGroupSession {
     pub fn new(room_id: &RoomId) -> Self {
         let session = OlmOutboundGroupSession::new();
         let session_id = session.session_id();
+
         OutboundGroupSession {
             inner: Arc::new(Mutex::new(session)),
             room_id: Arc::new(room_id.to_owned()),