Bug 1539578 - Add telemetry for DH use in WebCrypto API r=keeler

Our WebCrypto implementation supports using DH as an algorithm in generateKey,
which is not one of the recognized algorithms in the published specification [0].

We should seek to remove it from Firefox, but before we do, it'd be good to
gather some telemetry on whether it's used at all, even in its' non-standard
form.

[0] https://www.w3.org/TR/WebCryptoAPI/#algorithm-overview

Differential Revision: https://phabricator.services.mozilla.com/D25291

--HG--
extra : moz-landing-system : lando

dom/crypto/WebCryptoTask.cpp

@@ -85,6 +85,7 @@ enum TelemetryAlgorithm {
   TA_PBKDF2 = 21,
   TA_ECDSA = 22,
   TA_HKDF = 23,
+  TA_DH = 24,
 };
 
 // Convenience functions for extracting / converting information
@@ -2883,6 +2884,7 @@ class DeriveDhBitsTask : public ReturnArrayBufferViewTask {
   }
 
   void Init(JSContext* aCx, const ObjectOrString& aAlgorithm, CryptoKey& aKey) {
+    Telemetry::Accumulate(Telemetry::WEBCRYPTO_ALG, TA_DH);
     CHECK_KEY_ALGORITHM(aKey.Algorithm(), WEBCRYPTO_ALG_DH);
 
     // Check that we have a private key.

dom/crypto/moz.build

@@ -34,3 +34,4 @@ LOCAL_INCLUDES += [
 ]
 
 MOCHITEST_MANIFESTS += ['test/mochitest.ini']
+BROWSER_CHROME_MANIFESTS += ['test/browser/browser.ini']

dom/crypto/test/browser/browser.ini

@@ -0,0 +1,7 @@
+[DEFAULT]
+support-files =
+  head.js
+  ../test-vectors.js
+  ../util.js
+
+[browser_WebCrypto_telemetry.js]

dom/crypto/test/browser/browser_WebCrypto_telemetry.js

@@ -0,0 +1,60 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+/* global tv */
+
+const WEBCRYPTO_ALG_PROBE = "WEBCRYPTO_ALG";
+
+ChromeUtils.defineModuleGetter(this, "TelemetryTestUtils",
+  "resource://testing-common/TelemetryTestUtils.jsm");
+
+function validateHistogramEntryCount(aHistogramName, aExpectedTotalCount, aBucketCounts) {
+  let hist = Services.telemetry.getHistogramById(aHistogramName);
+  let resultIndexes = hist.snapshot();
+
+  let entriesSeen = Object.values(resultIndexes.values).reduce((a, b) => a + b, 0);
+
+  is(entriesSeen, aExpectedTotalCount, `Expecting ${aExpectedTotalCount} histogram entries in ` +
+     aHistogramName);
+
+  for (let bucket in aBucketCounts) {
+    is(resultIndexes.values[bucket], aBucketCounts[bucket], `Expecting bucket ${bucket} to be ` +
+      aBucketCounts[bucket]);
+  }
+}
+
+function cleanupTelemetry() {
+  Services.telemetry.clearScalars();
+  Services.telemetry.clearEvents();
+  Services.telemetry.getHistogramById(WEBCRYPTO_ALG_PROBE).clear();
+}
+
+add_task(async function ecdh_key() {
+  cleanupTelemetry();
+
+  var alg = { name: "ECDH", namedCurve: "P-256" };
+
+  let x = await crypto.subtle.generateKey(alg, false, ["deriveKey", "deriveBits"]);
+  await crypto.subtle.deriveBits({ name: "ECDH", public: x.publicKey }, x.privateKey, 128);
+
+  validateHistogramEntryCount(WEBCRYPTO_ALG_PROBE, 1, {20: 1});
+});
+
+
+add_task(async function dh_key() {
+  cleanupTelemetry();
+
+  var alg = {
+    name: "DH",
+    prime: tv.dh.prime,
+    generator: new Uint8Array([0x02]),
+  };
+
+  let x = await crypto.subtle.generateKey(alg, false, ["deriveKey", "deriveBits"]);
+  await crypto.subtle.deriveBits({ name: "DH", public: x.publicKey }, x.privateKey, 128);
+
+  validateHistogramEntryCount(WEBCRYPTO_ALG_PROBE, 1, {24: 1});
+});

dom/crypto/test/browser/head.js

@@ -0,0 +1,18 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+let exports = this;
+
+const scripts = [
+  "util.js",
+  "test-vectors.js",
+];
+
+for (let script of scripts) {
+  Services.scriptloader.loadSubScript(
+    `chrome://mochitests/content/browser/dom/crypto/test/browser/${script}`,
+    this);
+}