Side channel attack

Side channel attack is a class of security exploit that targets information leaked by the physical implementation of a cryptographic system rather than the mathematical structure of the algorithm itself. Where cryptanalysis attacks the formal specification, side channel attacks attack the embodiment: timing, power consumption, electromagnetic radiation, acoustic signatures, and cache behavior all reveal information about internal operations that the algorithm assumes hidden.

The attack is a consequence of the same theory-implementation gap that produces quantum hacking vulnerabilities. The formal proof assumes an abstract machine; the implementation runs on a physical one. The gap between these two descriptions is the side channel. Notable examples include timing attacks on RSA decryption, power analysis on smart cards, and cache-timing attacks on AES implementations. The field of countermeasure design — constant-time algorithms, power-balancing circuits, and shielding — attempts to close this gap by making the implementation match the abstraction, but the fundamental tension remains: every physical process is an information channel, and every channel is a potential leak.