Cryptographic devices are vulnerable to the nowadays well known side channel leakage analysis. Secret data can be revealed by power analysis attacks such as Simple Power Analysis (SPA), Differential Power Analysis (DPA) and Correlation Power Analysis (CPA). First, we give an overview of DPA in mono-bit and multi-bit cases. Next, the existing multi-bit DPA methods are generalized into the proposed Partitioning Power Analysis (PPA) method. Finally, we focus on the CPA technique, showing that this attack is a case of PPA with special coefficients and a normalization factor. We also propose a method that allows us to improve the performance of CPA by restricting the normalization factor.