Differential fault analysis (DFA) is a type of active side-channel attack in the field of cryptography, specifically cryptanalysis.
The principle is to induce faults—unexpected environmental conditions—into cryptographic operations to reveal their internal states.
Taking a smartcard containing an embedded processor as an example, some unexpected environmental conditions it could experience include being subjected to high temperature, receiving unsupported supply voltage or current, being excessively overclocked, experiencing strong electric or magnetic fields, or even receiving ionizing radiation to influence the operation of the processor.
Practical fault injection consists of using an electromagnetic probe connected to a pulser or a laser generating a disturbance of a similar length to the processor's cycle time (of the order of a nanosecond).
For greater precision, the chips are often decapsulated (chemically eroded to expose the bare silicon).