Bug 1654520 - Concat the networkID to the clientID and SHA256 the result before including in telemetry. r=mossop

Differential Revision: https://phabricator.services.mozilla.com/D84859

browser/components/doh/DoHController.jsm

@@ -18,6 +18,7 @@ const { XPCOMUtils } = ChromeUtils.import(
 
 XPCOMUtils.defineLazyModuleGetters(this, {
   AsyncShutdown: "resource://gre/modules/AsyncShutdown.jsm",
+  ClientID: "resource://gre/modules/ClientID.jsm",
   ExtensionStorageIDB: "resource://gre/modules/ExtensionStorageIDB.jsm",
   Heuristics: "resource:///modules/DoHHeuristics.jsm",
   Preferences: "resource://gre/modules/Preferences.jsm",
@@ -93,6 +94,28 @@ const kLinkStatusChangedTopic = "network:link-status-changed";
 const kConnectivityTopic = "network:captive-portal-connectivity";
 const kPrefChangedTopic = "nsPref:changed";
 
+// Helper function to hash the network ID concatenated with telemetry client ID.
+// This prevents us from being able to tell if 2 clients are on the same network.
+function getHashedNetworkID() {
+  let currentNetworkID = gNetworkLinkService.networkID;
+  if (!currentNetworkID) {
+    return "";
+  }
+
+  let hasher = Cc["@mozilla.org/security/hash;1"].createInstance(
+    Ci.nsICryptoHash
+  );
+
+  hasher.init(Ci.nsICryptoHash.SHA256);
+  // Concat the client ID with the network ID before hashing.
+  let clientNetworkID = ClientID.getClientID() + currentNetworkID;
+  hasher.update(
+    clientNetworkID.split("").map(c => c.charCodeAt(0)),
+    clientNetworkID.length
+  );
+  return hasher.finish(true);
+}
+
 const DoHController = {
   _heuristicsAreEnabled: false,
 
@@ -317,7 +340,7 @@ const DoHController = {
       // care about the startup case though - we want to look at whether the
       // heuristics result is consistent for networkIDs often seen at startup.
       // TODO: Use this data to implement cached results to use early at startup.
-      networkID: gNetworkLinkService.networkID,
+      networkID: getHashedNetworkID(),
     };
 
     if (results.steeredProvider) {