Which component of EFS uses CryptoAPI to encode the File Encryption Key (FEK)?

The EFS Service, or Encrypting File System Service, is the component responsible for utilizing the CryptoAPI to encode the File Encryption Key (FEK). This process is essential for ensuring that the data being encrypted is secured by the FEK, which in turn is protected using a stronger key. The CryptoAPI provides cryptographic services, including encryption and decryption functions that the EFS Service leverages to encapsulate the FEK securely. This allows for the safe storage and transmission of the FEK associated with the encrypted files.

When a file is encrypted, the FEK is generated and then encrypted with the user’s public key, which is part of the user's EFS certificate. The encrypted FEK is stored alongside the encrypted file, allowing the corresponding private key to decrypt it when needed to access the file. This architecture enhances security, as even if an attacker gains access to the encrypted file, they still require the user's private key to retrieve the FEK and, consequently, decrypt the file contents.

The other components mentioned do not directly perform the action of encoding the FEK using CryptoAPI, which solidifies the EFS Service's role in this process.