An RSA private key is the secret half of an RSA key pair. It is used to decrypt data, create digital signatures, or prove ownership of the matching public key. Because the private key must remain confidential, it should be generated securely, stored with strong access controls, and never shared between devices or users.
In cyber security, exposure of an RSA private key can break trust quickly. An attacker who steals it may decrypt protected traffic, impersonate a trusted service, or bypass authentication flows that rely on RSA-based checks. Risks rise further when the same key is hard-coded into firmware or reused across products, because one leak can affect many systems. Defenders reduce this risk by keeping private keys off exposed paths, using unique per-device keys, and rotating credentials when key handling is suspected to be weak.