Fast scalar multiplication operations are disclosed for use in an elliptic curve cryptographic system The operations use binary representations of a secret key and points on an elliptic curve defined over a prime field expressed in a coordinate system (e.g., Jacobian coordinates). The operations can be based on a modified Montgomery ladder that uses modified Meloni addition formulas. The operations can be more efficient than a double-and-add operation, and can be more resistant to side-channel attacks by hackers.