[verb ない-form 〜ない → 〜] + ずとも する → せずとも [verb ない-form 〜ない → 〜] + ずともよい
ずとも means "even without doing": the main clause holds whether or not the action happens. Take the ない-form of a verb and replace ない with ずとも – 言わない gives いわ言わずとも. It is literary, the written counterpart of 〜~なくても, and you meet it in writing, speeches and a handful of set phrases.
In conversation the same sentence takes なくても.
Followed by よい or いい, ずとも gives permission not to do something: "you need not". It is the literary form of なくてもいい, and sounds old-fashioned or stiff.