diff --git a/lib/crypto/OlmDevice.js b/lib/crypto/OlmDevice.js
index 01a710580..a4d564362 100644
--- a/lib/crypto/OlmDevice.js
+++ b/lib/crypto/OlmDevice.js
@@ -514,21 +514,23 @@ OlmDevice.prototype.getOutboundGroupSessionKey = function(sessionId) {
  * store an InboundGroupSession in the session store
  *
  * @param {string} roomId
- * @param {string} senderKey
+ * @param {string} senderCurve25519Key
  * @param {string} sessionId
  * @param {Olm.InboundGroupSession} session
+ * @param {object} keysClaimed Other keys the sender claims.
  * @private
  */
 OlmDevice.prototype._saveInboundGroupSession = function(
-    roomId, senderKey, sessionId, session
+    roomId, senderCurve25519Key, sessionId, session, keysClaimed
 ) {
     var r = {
         room_id: roomId,
         session: session.pickle(this._pickleKey),
+        keysClaimed: keysClaimed,
     };
 
     this._sessionStore.storeEndToEndInboundGroupSession(
-        senderKey, sessionId, JSON.stringify(r)
+        senderKey, senderCurve25519Key, sessionId, JSON.stringify(r)
     );
 };
 
@@ -569,7 +571,12 @@ OlmDevice.prototype._getInboundGroupSession = function(
     var session = new Olm.InboundGroupSession();
     try {
         session.unpickle(this._pickleKey, r.session);
-        return {sessionExists: true, result: func(session)};
+        return {
+            sessionExists: true,
+            result: func(session),
+            keysProved: {curve25519: senderKey},
+            keysClaimed: r.keysClaimed || {},
+        };
     } finally {
         session.free();
     }
diff --git a/lib/crypto/algorithms/megolm.js b/lib/crypto/algorithms/megolm.js
index 78bafdffd..d082ecdb3 100644
--- a/lib/crypto/algorithms/megolm.js
+++ b/lib/crypto/algorithms/megolm.js
@@ -360,7 +360,7 @@ utils.inherits(MegolmDecryption, base.DecryptionAlgorithm);
  * @param {object} event raw event
  *
  * @return {object} object with 'result' key with decrypted payload (with
- *  properties 'type', 'content') and a 'sessionKey' key.
+ *  properties 'type', 'content') and a 'sessionExists' key.
  *
  * @throws {module:crypto/algorithms/base.DecryptionError} if there is a
  *   problem decrypting the event
@@ -382,7 +382,8 @@ MegolmDecryption.prototype.decryptEvent = function(event) {
             event.room_id, content.sender_key, content.session_id, content.ciphertext
         );
         if (res.sessionExists) {
-            return {result: JSON.parse(res.result), sessionExists: true};
+            res.result = JSON.parse(res.result);
+            return res;
         } else {
             return {sessionExists: false};
         }
@@ -411,7 +412,7 @@ MegolmDecryption.prototype.onRoomKeyEvent = function(event) {
 
     this._olmDevice.addInboundGroupSession(
         content.room_id, event.getSenderKey(), content.session_id,
-        content.session_key, content.chain_index
+        content.session_key, content.chain_index, event.getKeysClaimed()
     );
 };
 
diff --git a/lib/crypto/algorithms/olm.js b/lib/crypto/algorithms/olm.js
index e75877cdf..df889766b 100644
--- a/lib/crypto/algorithms/olm.js
+++ b/lib/crypto/algorithms/olm.js
@@ -119,6 +119,17 @@ OlmEncryption.prototype.encryptMessage = function(room, eventType, content) {
                 room_id: room.roomId,
                 type: eventType,
                 content: content,
+                // Include the ED25519 key so that the recipient knows what
+                // device this message came from.
+                // We don't need to include the curve25519 key since the
+                // recipient will already know this from the olm headers.
+                // When combined with the device keys retrieved from the
+                // homeserver signed by the ed25519 key this proves that
+                // the curve25519 key and the ed25519 key are owned by
+                // the same device.
+                keys: {
+                    "ed25519": self._olmDevice.deviceEd25519Key
+                },
             }
         );
     });
@@ -200,7 +211,13 @@ OlmDecryption.prototype.decryptEvent = function(event) {
     // TODO: Check the sender user id matches the sender key.
     // TODO: check the room_id and fingerprint
     if (payloadString !== null) {
-        return {result: JSON.parse(payloadString), sessionExists: true};
+        var payload = JSON.parse(payloadString);
+        return {
+            result: payload,
+            sessionExists: true,
+            keysProved: {curve25519: deviceKey},
+            keysClaimed: payload.keys || {}
+        };
     } else {
         throw new base.DecryptionError("Bad Encrypted Message");
     }
diff --git a/lib/crypto/index.js b/lib/crypto/index.js
index b0a519ff6..e650308f8 100644
--- a/lib/crypto/index.js
+++ b/lib/crypto/index.js
@@ -823,8 +823,11 @@ Crypto.prototype.decryptEvent = function(event) {
         olmDevice: this._olmDevice,
     });
     var r = alg.decryptEvent(event);
+    var payload = r.result;
+    payload.keysClaimed = r.keysClaimed;
+    payload.keysProved = r.keysProved;
     if (r.sessionExists) {
-        return r.result;
+        return payload;
     } else {
         // We've got a message for a session we don't have.
         // Maybe the sender forgot to tell us about the session.
diff --git a/lib/models/event.js b/lib/models/event.js
index 90e8a39b4..859c2b488 100644
--- a/lib/models/event.js
+++ b/lib/models/event.js
@@ -233,12 +233,27 @@ module.exports.MatrixEvent.prototype = {
         return Boolean(this._clearEvent.type);
     },
 
+    /**
+     * Returns the curve25519 key that sent this event
+     */
     getSenderKey: function() {
-        if (!this.isEncrypted()) {
-            return null;
-        }
-        var c = this.getWireContent();
-        return c.sender_key;
+        return this.getKeysProved().curve25519 || null;
+    },
+
+    /**
+     * The keys that must have been owned by the sender of this encrypted event.
+     * @return {object}
+     */
+    getKeysProved: function() {
+        return this._clearEvent.keysProved || {};
+    },
+
+    /**
+     * The additional keys the sender of this encrypted event claims to possess
+     * @return {object}
+     */
+    getKeysClaimed: function() {
+        return this._clearEvent.keysClaimed || {};
     },
 
     getUnsigned: function() {