Modular multiplication is basic operation in public key cryptosystems like RSA. Montgomery modular multiplication being efficient is widely used. It is based on additions and shift operations. Each iteration requires a right shift, therefore in a word based architecture a complete word is not formed at end of iteration.
This paper presents compute early word based scalable Montgomery architecture. It computes the most significant bit of word by applying 2 XOR operations. Also compute early scheme for common multiplicand Montgomery is proposed. Both the architectures are compared with previous architectures in literature.