nonextractable

Nonextractable describes a security property of secrets, such as cryptographic keys, indicating that the secret cannot be retrieved in plain form from the system or device where it resides. In practice, nonextractability is achieved by isolating the secret in hardware or in a protected software environment that enforces internal operations without exposing the secret material to the host system.

Common implementations include secure elements (SE) in smart cards and smartphones, trusted platform modules (TPMs), and hardware security modules (HSMs). These components are designed to store keys in tamper-resistant, isolated storage and to perform cryptographic operations internally, often with device-bound credentials and attestation that proves the origin and integrity of the environment. In the field of cryptocurrencies and digital wallets, nonextractable private keys are used so that signing of transactions can occur without exporting the key material to the host computer, reducing exposure to malware.

Nonextractability is not an absolute guarantee of security. It reduces the risk of key theft but does not eliminate all attack vectors. Potential weaknesses include side-channel attacks, firmware or supply chain compromises, misconfigurations, or flaws in the cryptographic protocol that could enable indirect leakage or misuse. Some devices may allow constrained or controlled export under specific conditions, or reveal ancillary data such as public keys or attestation evidence, which is different from exporting the secret itself.

Overall, nonextractability is a defense-in-depth concept that enhances secrecy by preventing straightforward retrieval of sensitive material, rather than an imitation of universal security.