Signal reconstruction is the process of converting a captured trace, emission, or waveform back into usable information such as speech, text, or device activity. In cyber security, the source signal is often not a file or network packet, but a byproduct: electromagnetic leakage, acoustic noise, timing variation, or power fluctuations. The attacker records that weak signal and then filters, amplifies, and decodes it until the hidden content becomes readable or audible.
This matters because reconstruction can recover data without breaking encryption or touching the target system directly. It appears in side-channel attacks, where device emissions reveal what the hardware is doing, and in defenses such as signal masking, shielding, and noise injection, which aim to make reconstruction unreliable. The practical challenge is that the usefulness of a trace depends on distance, device design, environment, and the quality of the capture equipment.