Add simple test for scalarMult timing variations

test/timing/timing.js

@@ -0,0 +1,59 @@
+// Measures timing variations and displays them
+var nacl = (typeof window !== 'undefined') ? window.nacl : require('../../' + (process.env.NACL_SRC || 'nacl.min.js'));
+nacl.util = require('tweetnacl-util');
+var test = require('tape');
+
+var hex = function(x) { return Buffer.from(x).toString('hex'); }
+
+test('nacl.scalarMult timings', function(t) {
+  function measure(x, prev) {
+    var avgdiff = 0;
+    for (var k = 0; k < 10; k++) {
+      var t0 = Date.now();
+      for (var j = 0; j < 100; j++) {
+        z = nacl.scalarMult.base(x);
+        nacl.scalarMult(x, prev);
+      }
+      var t1 = Date.now();
+      avgdiff += t1 - t0;
+    }
+    avgdiff /= 10;
+    return avgdiff;
+  }
+
+  var diffs = [];
+  var z, prev = nacl.scalarMult.base(nacl.randomBytes(32));
+  for (var i = 0; i < 10; i++) {
+    var x = nacl.randomBytes(32);
+    if (i % 2 === 0) {
+      for (var k = 0; k < 16; k++) x[k] = 0;
+    } else if (i % 2 === 3) {
+      for (var k = 16; k < 32; k++) x[k] = 0;
+    }
+    var diff = measure(x, prev);
+    console.log(i + ': ' + diff + 'ms');
+    prev = z;
+    diffs.push({
+      diff: diff,
+      x: x,
+      prev: prev
+    });
+  }
+  diffs.sort(function (a, b) { return a.diff - b.diff; })
+  var lo = diffs[0], hi = diffs[diffs.length-1];
+  console.log('Lowest : ' + lo.diff + 'ms');
+  console.log(hex(lo.x), hex(lo.prev));
+  console.log('Highest: ' + hi.diff + 'ms');
+  console.log(hex(hi.x), hex(hi.prev));
+  console.log('Difference: ' + (hi.diff - lo.diff) + 'ms');
+
+  /* Retest low and high */
+  console.log('* Retesting low and high');
+  var rlo = measure(lo.x, lo.prev);
+  var rhi = measure(hi.x, hi.prev);
+  console.log('Re-test low: ' + rlo + 'ms');
+  console.log('Re-test high: ' + rhi + 'ms');
+  console.log('New difference: ' + (rhi - rlo) + 'ms');
+
+  t.end();
+});