Power attacks are serious threats to cryptographic devices, and most countermeasures against power attacks result in a large time overhead for hardware implementation. This work presents an efficient countermeasure against power attacks for elliptic curve cryptography over GF(p). The proposed algorithm adopts the Montgomery ladder scalar multiplication algorithm as a basic framework to protect SPA. Then, a new scheme is presented to effectively manipulate the key so as to reduce the resulting time overhead for preventing differential power attack (DPA) and zero power attack (ZPA). Particularly, the base point blinding technique and half key splitting scheme are used to protect the upper and the lower halves of the key, respectively. Experimental results show the proposed countermeasure exhibit a time advantage over related works. Compared to other countermeasures against SPA, DPA, and ZPA, the proposed one can achieve up to 15% time improvement for accomplishing one 160-bit GF(p) scalar multiplication.