We report for the first time the use of the well-known coherence modulation of light in two-dimensional arithmetic operations. This method, which allows several signals to be multiplexed on a single light beam, permits parallel real-time all optical subtractions and additions. In the context of an increased need of security, a major application of our multiplexed approach could be the optical encryption of images and multi-modalities techniques in biometric domain. The single-channel optical architecture, which allows carrying out single and multiple arithmetic operations, is described and more results are presented to show the effectiveness of our technique. We have evaluated the performance of the processor in terms of noise level as a function of the continuous optical path-difference ratio.