Cryptanalysis knows several methods in which changes in the supply voltage or in the time sequence are determined and the encryption algorithm and the secret key are derived from them. Attacks based on the analysis of the supply voltage are called Simple Power Analysis(SPA), Differential Power Analysis( DPA) and Differential Fault Analysis( DFA).
Simple Power Analysis (SPA) records the power consumption of the encryption processor during encryption. Since the energy consumption of the microprocessor changes depending on its computing power, conclusions about the encryption method and the secret key can be drawn from the energy consumption, its timing and the resulting pattern. With more computing operations, the calculation takes longer. The recorded patterns are compared with correct calculations and provide information about the crypto method.