In cryptography, the Pointcheval–Stern signature algorithm is a digital signature scheme based on the closely related ElGamal signature scheme. It changes the ElGamal scheme slightly to produce an algorithm which has been proven secure in a strong sense against adaptive chosen-message attacks. That is, if the discrete logarithm problem is intractable in a strong sense.David Pointcheval and Jacques Stern developed the forking lemma technique in constructing their proof for this algorithm.