Modular Exponentiation

Modular exponentiation is the computation of the remainder when an integer base is raised to a power and then divided by a modulus, written c equals b to the e mod m, where the result c always satisfies 0 less than or equal to c less than m. It can be computed efficiently even for very large numbers through repeated squaring, while the reverse problem, finding the exponent from the result, called the discrete logarithm, is believed to be computationally difficult. This one way property, easy to compute forward but hard to reverse, makes modular exponentiation central to cryptographic systems such as Diffie-Hellman key exchange and the RSA public key cryptosystem.