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.