Small, embedded integrated circuits (ICs) such as smart cards are vulnerable to so-called side-channel attacks (SCAs). The attacker can gain information by monitoring the power consumption, execution time, electromagnetic radiation and other information that is leaked by the switching behavior of digital CMOS gates. Ever since power attacks have been introduced in 1999, many countermeasures have been proposed. Often a significant increase in security has been touted. We will show that in order to assess the effectiveness of a countermeasure, a correct simulation model of the side-channel information leaks is vital. We will show that seemingly correct approximations can lead to completely flawed results. Categories and Subject Descriptors B.5 [Hardware]: Register-Transfer-Level Implementation; B.6 [Hardware]: Logic Design; B.7 [Hardware]: Integrated Circuits; E.3 [Data]: Data encryption. General Terms Design, Security, Verification. Keywords Simulation Model, Countermeasure, Side-Chann...