InformationThis policy setting determines whether users' private keys (such as their S-MIME keys) require a password to be used.
The recommended state for this setting is: User is prompted when the key is first used. Configuring this setting to User must enter a password each time they use a key also conforms to the benchmark.
If a user's account is compromised or their computer is inadvertently left unsecured the malicious user can use the keys stored for the user to access protected resources. You can configure this policy setting so that users must provide a password that is distinct from their domain password every time they use a key. This configuration makes it more difficult for an attacker to access locally stored user keys, even if the attacker takes control of the user's computer and determines their logon password.
SolutionTo establish the recommended configuration via GP, set the following UI path to User is prompted when the key is first used (configuring to User must enter a password each time they use a key also conforms to the benchmark):
Computer Configuration\Policies\Windows Settings\Security Settings\Local Policies\Security Options\System cryptography: Force strong key protection for user keys stored on the computer
Users will have to enter their password the first time they access a key that is stored on their computer. For example, if users use an S-MIME certificate to digitally sign their e-mail they will be forced to enter the password for that certificate the first time that they send a signed e-mail message. For even stronger security, the value User must enter a password each time they use a key can be set, but the overhead that is involved using this configuration may be too high for some organizations.
Microsoft does not recommend enforcing this setting on servers due to the significant impact on manageability. For example, you may not be able to configure Remote Desktop Services to use SSL certificates. More information is available in the Windows PKI TechNet Blog here: What is a strong key protection in Windows?.
User input is not required when new keys are stored and used.