Modern public-key cryptography relies extensively on modular multiplication with long operands. We investigate the opportunities to optimize this operation in a heterogeneous multiprocessing platform such as TI OMAP3530. By migrating the long operand modular multiplication from a general-purpose ARM Cortex A8 to a specialized C64x+ VLIW DSP, we are able to exploit the XOR-Multiply instruction and the inherent parallelism of the DSP. The proposed multiplication utilizes Multi-Precision Binary Polynomial Multiplication with Unbalanced Exponent Modular Reduction. The resulting DSP implementation performs a GF(2^233) multiplication in less than 1.31us, which is over a seven times speed up when compared with the ARM implementation on the same chip. We present several strategies for different field sizes and field polynomials, and show that a 360MHz DSP easily outperforms the 500MHz ARM.