Nadine wants to protect and manage her RSA keys while using a mobile device. What kind of solution could she buy to guarantee that the keys remain secure, allowing her to perform public key authentication?

Hardware security modules are offered as smartcards, microSD cards, and USB thumb drives, as well as in the form of appliances for enterprise use. To secure her keys in a safe manner, Nadine could purchase a certified and tested HSM based on a microSD card. An application-based public key infrastructure (PKI) would not provide comparable security on most mobile devices without specialized hardware, which is not mentioned in this scenario. OPAL is an encryption standard that relies on hardware and does not offer key management functionality. An offline certificate authority (CA) would also not be beneficial in this situation.