The PKCS#11 standard enables easy integration of hardware tokens with a wide range of software applications, including document suites, web browsers, and password managers. In this talk, we will introduce the fundamentals of PKCS#11 v2 and review a year-long journey of developing an open-source PKCS#11 module for Serbian eID cards. We will present three black-box techniques that were used to analyze proprietary software, and explain how they helped us understand the original PKCS#11 module for Serbian eID cards. The talk does not require prior knowledge of PKCS#11 or smart cards, but basic familiarity with public-key cryptography, web services, and shared libraries is recommended.