The Schlage Primus is one of the most common high-security locks in the United States. We reverse-engineered the operation of this lock, constructed a parameterized 3d model of a working key, and constructed a software tool to produce such a 3d model given the code number for any key. We then used this tool to 3d print working Primus keys with a variety of 3d printing processes. In our talk, we will discuss the reverse-engineering process, demonstrate our software tool, examine the working 3d printed keys, and discuss the security ramifications of this process. dlaw, ervanalb, and robj study electrical engineering and computer science at the Massachusetts Institute of Technology, where they spend most of their time hacking on projects unrelated to their studies. They have taught seminars on lockpicking and security vulnerabilities to various audiences at the Institute.