This paper presents a systematic investigation of electromagnetic (EM) side-channel leakage from CMOS devices. The study shows that EM emanations consist of multiple signals, each leaking different information about the underlying computation. These signals can be used to attack cryptographic devices even when the power side-channel is unavailable, and can even break power analysis countermeasures. The paper explores the causes and types of EM signals, the equipment needed to capture and extract them, and the results of experiments on various types of EM emanations. EM signals can be direct or unintentional. Direct emanations result from intentional current flows, while unintentional emanations are due to coupling and circuit geometry. These signals can be modulated in various ways, such as amplitude modulation (AM) and angle modulation (FM or phase modulation). The paper demonstrates that EM signals can be captured using near-field and far-field sensors, and that the quality of the received signal can be improved by shielding from interfering EM emanations. The paper presents experimental results showing that EM signals can be used to perform attacks such as simple and differential electromagnetic attacks (SEMA and DEMA) on cryptographic devices. It also shows that EM side-channels can be more effective than power side-channels in certain cases, particularly when the power side-channel is unavailable. The paper also discusses the use of EM side-channels to break power analysis countermeasures, particularly those based on secret-sharing. The paper highlights the importance of separating signals early in the acquisition process to avoid loss of low-energy signals. It also discusses the use of unintentional emanations, which can be more effective than direct emanations. The paper concludes that EM side-channels are a powerful tool for side-channel attacks and that further research is needed to develop effective countermeasures.This paper presents a systematic investigation of electromagnetic (EM) side-channel leakage from CMOS devices. The study shows that EM emanations consist of multiple signals, each leaking different information about the underlying computation. These signals can be used to attack cryptographic devices even when the power side-channel is unavailable, and can even break power analysis countermeasures. The paper explores the causes and types of EM signals, the equipment needed to capture and extract them, and the results of experiments on various types of EM emanations. EM signals can be direct or unintentional. Direct emanations result from intentional current flows, while unintentional emanations are due to coupling and circuit geometry. These signals can be modulated in various ways, such as amplitude modulation (AM) and angle modulation (FM or phase modulation). The paper demonstrates that EM signals can be captured using near-field and far-field sensors, and that the quality of the received signal can be improved by shielding from interfering EM emanations. The paper presents experimental results showing that EM signals can be used to perform attacks such as simple and differential electromagnetic attacks (SEMA and DEMA) on cryptographic devices. It also shows that EM side-channels can be more effective than power side-channels in certain cases, particularly when the power side-channel is unavailable. The paper also discusses the use of EM side-channels to break power analysis countermeasures, particularly those based on secret-sharing. The paper highlights the importance of separating signals early in the acquisition process to avoid loss of low-energy signals. It also discusses the use of unintentional emanations, which can be more effective than direct emanations. The paper concludes that EM side-channels are a powerful tool for side-channel attacks and that further research is needed to develop effective countermeasures.