This paper proposes a configurable architecture for dual moduli multi-operand modular addition (MOMA) based on the diminished-one number representation. This architecture accomplishes the MOMA operations for the two most frequently used moduli, 2/sup n/-1 and 2/sup n/+1 by sharing a common tree of CSA-like elements. Multi-function reconfigurability is made possible by the introduction of the composite carry save adders (CCSA). Although area overhead is incurred due to the multiplexers for switching between CEAC and EAC and two-operand modulo adders, there is very little speed penalty. Synthesis results in TSMC 0.18 /spl mu/m CMOS technology show that in stand alone operation, the proposed diminished-one modulo 2/sup n/+1 MOMA based on the CCSA outperforms the normal binary modulo 2/sup n/+1 MOMA in both area and delay. The speed up is more prominent with long operands.