Constant time only reduces the chance of 'simple power analysis' (SPA) which is predominantly what the authors perform ('simple' is misleading but it's just the

Constant time only reduces the chance of 'simple power analysis' (SPA) which is predominantly what the authors perform ('simple' is misleading but it's just the name for it). There are a number of works that perform 'differential power analysis' (DPA) attacks on mobile devices that target symmetric crypto. These are generally both constant time and constant execution path. In this instance, attackers can attack the data dependancy in the EM emanations. Simple example! a program that XORs two registers: r1 = r1 XOR r2 If r2 has all the bits set to 1, then this will completely invert the contents of r1. This in turn consumes more energy (and hence emit more EM) in comparison to if r2 was all 0's. Hope that clarifies.