Non-repudiation is one of the most important security services. In this paper we present a novel non-repudiation technique, called server-supported signatures, S 3 . It is based on one-way hash functions and traditional digital signatures. One of its highlights is that for ordinary users the use of asymmetric cryptography is limited to signature verification. S 3 is efficient in terms of computational, communication and storage costs. It also offers a degree of security comparable to that of existing techniques based on asymmetric cryptography.