Encryption shields private information from malicious eavesdroppers. After years of slow adoption, encryption is finally becoming widespread in consumer- oriented electronic devices and communications services. Consumer-oriented encryption software is now more user-friendly, and much of it turns on encryption by default. However, encryption also poses an impediment to law enforcement’s ability to gather electronic evidence. Law enforcement calls this the “going dark” problem. U.S. law enforcement agencies have responded through both legal and technological means to encryption’s perceived threat to their capabilities. One means of doing so is through a “side-channel attack.” Our electronic devices are always radiating something—electromagnetic emissions, heat, and so forth. Those emissions reveal information, called “side channel information,” about the device. The physical implementation of a cryptosystem leaks electromagnetic emissions from which academic researchers have shown it is possible to extract the system’s secret encryption keys. Side-channel cryptanalysis is not a known law enforcement tactic at present, but that may change in time.