Data mining often causes privacy concerns. To ease the concerns, various privacy preserving data mining techniques have been proposed. However, those techniques are often too computationally intensive to be deployed in practice. Efficiency becomes a major challenge in privacy preserving data mining. In this paper, the authors present an efficient secure dot product protocol and show its application in privacy preserving association rule mining, one of the most widely used data mining techniques. The protocol is orders of magnitude faster than previous protocols because it employs mostly cheap cryptographic operations, e.g. hashing and modular multiplication. The performance has been further improved by parallelization.