A method for computation, including defining a sequence of n bits that encodes an exponent d, such that no more than a specified number of successive bits in the sequence are the same, initializing first and second registers using a value of a base x that is to be exponentiated, whereby the first and second registers hold respective first and second values, which are successively updated during the computation, successively, for each bit in the sequence computing a product of the first and second values, depending on whether the bit is one or zero, selecting one of the first and second registers, and storing the product in the selected one of the registers, whereby the first and second registers hold respective first and second final values upon completion of the sequence, and returning xd based on the first and second final values. Related apparatus and methods are also described.