In this paper we show that, paradoxically, what looks like a “universal improvement” or a “straight-forward improvement” which
enables better security and better reliability on a theoretical level, may in fact, within certain operational contexts, introduce
new exposures and attacks, resulting in a weaker operational cryptosystem. We demonstrate a number of such dangerous “improvements”.
This implies that careful considerations should be given to the fact that an implemented cryptosystem exists within certain
operational environments (which may enable certain types of tampering and other observed information channels via faults,
side-channel attacks or behavior of system operators). We use our case studies to draw conclusions about certain investigations
required in studying implementations and suggested improvements of cryptosystems; looking at them in the context of their
operating environments (combined with their potential adversarial settings). We call these investigations observability analysis.
Keywords Security analysis - observability - cryptanalysis - implementations - side-channel attacks - fault analysis - robustness - cryptosystems
Supported in part by the Computer & Communication Research Laboratories, Industrial Technology Research Institute, Republic
of China.