Side-channel attacks (SCA) can be used to reveal the security key stored in cryptographic implementations by monitoring characteristics such as power consumption and subsequently applying statistical analysis techniques. However, cryptographic algorithms, such as SHACAL-2, which do not have any S-Box operations, are more resistant to SCA than algorithms that do contain S-Box operations, such as the S-box computation in DES or AES. In this paper, the advantages of SHACAL-2 in relation to its resistance to differential power analysis (DPA) are outlined. The first reported DPA attack of a SHACAL-2 encryption algorithm FPGA implementation is also presented. Finally, the effect of using different power models in the DPA attack of SHACAL-2 is discussed.