The MIST algorithm is a randomized version of the division chain exponentiation algorithm and is a side-channel countermeasure. When analyzing the MIST algorithm by ordinary simple power analysis (with only one square-multiply sequence obtained), an attacker cannot retrieve the secret exponent due to the ambiguous relationship between the square-multiply sequence and the computation. We point out the MIST algorithm is still vulnerable to simple power analysis observing multiple power consumption traces and propose a practical method with detailed steps to deduce the secret exponent from multiple square-multiply sequences. Further countermeasures such as exponent blinding are required to prevent the analysis proposed in this paper.