Fix constantTimeCompare.

group/client.go

@@ -35,7 +35,7 @@ var hashSemaphore = make(chan struct{}, runtime.GOMAXPROCS(-1))
 func constantTimeCompare(a, b string) bool {
 	as := []byte(a)
 	bs := make([]byte, len(as))
-	copy(bs, a)
+	copy(bs, b)
 	equal := subtle.ConstantTimeCompare(as, bs) == 1
 	return len(a) == len(b) && equal
 }

group/client_test.go

@@ -58,7 +58,10 @@ func TestGood(t *testing.T) {
 
 func TestBad(t *testing.T) {
 	if match, err := pw2.Match("bad"); err != nil || match {
-		t.Errorf("pw2 matches")
+		t.Errorf("pw2 matches bad")
+	}
+	if match, err := pw2.Match("bad1"); err != nil || match {
+		t.Errorf("pw2 matches bad1")
 	}
 	if match, err := pw3.Match("bad"); err != nil || match {
 		t.Errorf("pw3 matches")