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Data Protection API

The Windows Data Protection API (DPAPI) is mainly used to symmetrically encrypt asymmetric private keys using a user or system secret as a significant contribution of entropy.
The DPAPI keys to encrypt a user's RSI keys are stored under %appdata%\Microsoft\Protect\S-1-5-21-….

See also

DPAPI is used for example to encrypt the the database master key of SQL Server.

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