eID, or electronic identity, is a digital credential used to prove who a user is during online authentication. It may be tied to a national identity system, a smart card, a mobile app, or a local signing component that confirms the user’s identity before access is granted.
In cyber security, eID systems matter because they sit at a trusted boundary between the browser, the device, and the service being accessed. If that boundary is weak, an attacker may try to abuse login flows, trigger fake approval prompts, or influence signing requests without the user realizing it. Defenders protect eID by enforcing strict origin checks, validating messages, patching client software quickly, and monitoring for unusual authentication or signature activity. In practice, eID is often the layer that makes high-value services usable, which also makes it a high-value target.