Factor out a function for doing olm encryption

Make a library file with some constants and a function to pack olm-encrypted
events (which we are going to use from megolm)

lib/OlmDevice.js

@@ -294,6 +294,22 @@ OlmDevice.prototype.getSessionIdsForDevice = function(theirDeviceIdentityKey) {
     return utils.keys(sessions);
 };
 
+/**
+ * Get the right olm session id for encrypting messages to the given identity key
+ *
+ * @param {string} theirDeviceIdentityKey Curve25519 identity key for the
+ *     remote device
+ * @return {string?}  session id, or null if no established session
+ */
+OlmDevice.prototype.getSessionIdForDevice = function(theirDeviceIdentityKey) {
+    var sessionIds = this.getSessionIdsForDevice(theirDeviceIdentityKey);
+    if (sessionIds.length === 0) {
+        return null;
+    }
+    // Use the session with the lowest ID.
+    sessionIds.sort();
+    return sessionIds[0];
+};
 
 /**
  * Encrypt an outgoing message using an existing session

lib/crypto-algorithms/megolm.js

@@ -24,10 +24,9 @@ limitations under the License.
 var q = require("q");
 
 var utils = require("../utils");
+var olmlib = require("../olmlib");
 var base = require("./base");
 
-var MEGOLM_ALGORITHM = "m.megolm.v1.aes-sha2";
-
 /**
  * Megolm encryption implementation
  *
@@ -114,7 +113,7 @@ MegolmEncryption.prototype.encryptMessage = function(room, eventType, content) {
         );
 
         var encryptedContent = {
-            algorithm: MEGOLM_ALGORITHM,
+            algorithm: olmlib.MEGOLM_ALGORITHM,
             sender_key: self._olmDevice.deviceCurve25519Key,
             body: ciphertext,
             session_id: self._outboundSessionId,
@@ -171,4 +170,6 @@ MegolmDecryption.prototype.decryptEvent = function(event) {
     }
 };
 
-base.registerAlgorithm(MEGOLM_ALGORITHM, MegolmEncryption, MegolmDecryption);
+base.registerAlgorithm(
+    olmlib.MEGOLM_ALGORITHM, MegolmEncryption, MegolmDecryption
+);

lib/crypto-algorithms/olm.js

@@ -23,11 +23,10 @@ limitations under the License.
 var q = require('q');
 
 var utils = require("../utils");
+var olmlib = require("../olmlib");
 
 var base = require("./base");
 
-var OLM_ALGORITHM = "m.olm.v1.curve25519-aes-sha2";
-
 /**
  * Olm encryption implementation
  *
@@ -89,47 +88,27 @@ OlmEncryption.prototype.encryptMessage = function(room, eventType, content) {
 
             for (var keyId in dev.keys) {
                 if (keyId.indexOf("curve25519:") === 0) {
-                    participantKeys.push(dev.keys[keyId]);
+                    var key = dev.keys[keyId];
+
+                    // don't send to ourselves.
+                    if (key != this._olmDevice.deviceCurve25519Key) {
+                        participantKeys.push(key);
                     }
                 }
             }
         }
-    participantKeys.sort();
-    var participantHash = ""; // Olm.sha256(participantKeys.join());
-    var payloadJson = {
+    }
+
+    return q(
+        olmlib.encryptMessageForDevices(
+            this._deviceId, this._olmDevice, participantKeys, {
                 room_id: room.roomId,
                 type: eventType,
-        fingerprint: participantHash,
-        sender_device: this._deviceId,
-        content: content
-    };
-    var ciphertext = {};
-    var payloadString = JSON.stringify(payloadJson);
-    for (i = 0; i < participantKeys.length; ++i) {
-        var deviceKey = participantKeys[i];
-        if (deviceKey == this._olmDevice.deviceCurve25519Key) {
-            continue;
+                content: content,
             }
-        var sessionIds = this._olmDevice.getSessionIdsForDevice(deviceKey);
-        // Use the session with the lowest ID.
-        sessionIds.sort();
-        if (sessionIds.length === 0) {
-            // If we don't have a session for a device then
-            // we can't encrypt a message for it.
-            continue;
-        }
-        var sessionId = sessionIds[0];
-        console.log("Using sessionid " + sessionId + " for device " + deviceKey);
-        ciphertext[deviceKey] = this._olmDevice.encryptMessage(
-            deviceKey, sessionId, payloadString
+        )
     );
-    }
-    var encryptedContent = {
-        algorithm: OLM_ALGORITHM,
-        sender_key: this._olmDevice.deviceCurve25519Key,
-        ciphertext: ciphertext
-    };
-    return q(encryptedContent);
+
 };
 
 /**
@@ -211,4 +190,4 @@ OlmDecryption.prototype.decryptEvent = function(event) {
     }
 };
 
-base.registerAlgorithm(OLM_ALGORITHM, OlmEncryption, OlmDecryption);
+base.registerAlgorithm(olmlib.OLM_ALGORITHM, OlmEncryption, OlmDecryption);

lib/crypto.js

@@ -24,11 +24,10 @@ var anotherjson = require('another-json');
 var q = require("q");
 
 var OlmDevice = require("./OlmDevice");
+var olmlib = require("./olmlib");
 
 var algorithms = require("./crypto-algorithms");
 
-var OLM_ALGORITHM = "m.olm.v1.curve25519-aes-sha2";
-
 var DeviceInfo = require("./crypto-deviceinfo");
 var DeviceVerification = DeviceInfo.DeviceVerification;
 
@@ -69,7 +68,7 @@ function Crypto(baseApis, sessionStore, userId, deviceId) {
     // add our own deviceinfo to the sessionstore
     var deviceInfo = {
         keys: this._deviceKeys,
-        algorithms: [OLM_ALGORITHM],
+        algorithms: [olmlib.OLM_ALGORITHM],
         verified: DeviceVerification.VERIFIED,
     };
     var myDevices = this._sessionStore.getEndToEndDevicesForUser(
@@ -122,7 +121,7 @@ function _uploadDeviceKeys(crypto) {
     var deviceId = crypto._deviceId;
 
     var deviceKeys = {
-        algorithms: [OLM_ALGORITHM],
+        algorithms: [olmlib.OLM_ALGORITHM],
         device_id: deviceId,
         keys: crypto._deviceKeys,
         user_id: userId,
@@ -411,7 +410,7 @@ Crypto.prototype.listDeviceKeys = function(userId) {
  * @return {module:crypto-deviceinfo?}
  */
 Crypto.prototype.getDeviceByIdentityKey = function(userId, algorithm, sender_key) {
-    if (algorithm !== OLM_ALGORITHM) {
+    if (algorithm !== olmlib.OLM_ALGORITHM) {
         // we only deal in olm keys
         return null;
     }

lib/olmlib.js

@@ -0,0 +1,78 @@
+/*
+Copyright 2016 OpenMarket Ltd
+
+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.
+*/
+
+/**
+ * @module olmlib
+ *
+ * Utilities common to olm encryption algorithms
+ */
+
+var utils = require("./utils");
+
+/**
+ * matrix algorithm tag for olm
+ */
+module.exports.OLM_ALGORITHM = "m.olm.v1.curve25519-aes-sha2";
+
+/**
+ * matrix algorithm tag for megolm
+ */
+module.exports.MEGOLM_ALGORITHM = "m.megolm.v1.aes-sha2";
+
+
+/**
+ * Encrypt an event payload for a list of devices
+ *
+ * @param {string} ourDeviceId
+ * @param {module:OlmDevice} olmDevice olm.js wrapper
+ * @param {string[]} participantKeys list of curve25519 keys to encrypt for
+ * @param {object} payloadFields fields to include in the encrypted payload
+ *
+ * @return {object} content for an m.room.encrypted event
+ */
+module.exports.encryptMessageForDevices = function(
+    ourDeviceId, olmDevice, participantKeys, payloadFields
+) {
+    participantKeys.sort();
+    var participantHash = ""; // Olm.sha256(participantKeys.join());
+    var payloadJson = {
+        fingerprint: participantHash,
+        sender_device: ourDeviceId,
+    };
+    utils.extend(payloadJson, payloadFields);
+
+    var ciphertext = {};
+    var payloadString = JSON.stringify(payloadJson);
+    for (var i = 0; i < participantKeys.length; ++i) {
+        var deviceKey = participantKeys[i];
+        var sessionId = olmDevice.getSessionIdForDevice(deviceKey);
+        if (sessionId === null) {
+            // If we don't have a session for a device then
+            // we can't encrypt a message for it.
+            continue;
+        }
+        console.log("Using sessionid " + sessionId + " for device " + deviceKey);
+        ciphertext[deviceKey] = olmDevice.encryptMessage(
+            deviceKey, sessionId, payloadString
+        );
+    }
+    var encryptedContent = {
+        algorithm: module.exports.OLM_ALGORITHM,
+        sender_key: olmDevice.deviceCurve25519Key,
+        ciphertext: ciphertext
+    };
+    return encryptedContent;
+};