Recently, handheld devices have become one of the most popular computing tools. Although handheld devices are able to perform anything that a PC can do, their lack of computing power makes it next to impossible to perform some heavy calculations. Hence it appears very useful to have a combination of a handheld with a PC, where the PC can perform heavy calculations to assist the handheld. However, we must be assured that the PC will not have learnt anything from the interaction. In this paper, we show two schemes which involve some server-aided computation where the server has not learnt anything from the interaction with the handheld device. The first scheme is to generate a strong prime number in a handheld, which can be used as a candidate for the RSA algorithm. The second scheme is to allow the server to behave as an authentication oracle on behalf of the hand-held. The handheld will prepare a message that needs to be authenticated by sending it to the server in a blinded form, so that the server will not learn about the message. On the other hand, the handheld will not learn about the server's secret.