In terms of data security, what action is a subscriber expected to take with their private signing key?

A subscriber is expected to keep their private signing key confidential and secure because the private key is a critical component of the public key infrastructure (PKI) system. The integrity and security of the PKI depend significantly on how well subscribers manage their private keys. If a private key is compromised, it allows unauthorized individuals to create signatures that appear valid, thus undermining the trust in the digital signatures associated with that private key.

Maintaining confidentiality ensures that only the subscriber can use the key for signing data or documents, thereby protecting against fraud and ensuring the authenticity of communications. In scenarios where sensitive information is involved, such as military operations or confidential communications, the security of the private key is paramount to prevent unauthorized access or manipulation.

The other options suggest practices that could lead to various security compromises. Sharing the key with a supervisor does not guarantee reasonable security measures and can increase the risk of exposure. Documenting it in a secure place may seem prudent, but if the documentation is not managed correctly, it could also become a vulnerability. Storing the key on an unsecured device directly contradicts best practices in cybersecurity, as this invites potential unauthorized access and exploitation.