Which of the following is the encryption subsystem of the NTFS file system?

IIS (Internet Information Services) is Microsoft's web and application server platform and has no relationship to NTFS encryption functionality.

RSA is a public-key cryptographic algorithm used broadly in security protocols, but it is not itself an NTFS subsystem or filesystem feature.

ECC (Elliptic Curve Cryptography) is a mathematical approach to asymmetric cryptography and is not an NTFS subsystem.

EFS (Encrypting File System) is a component of the NTFS file system on Windows that provides filesystem-level encryption for files and folders. It operates transparently to the user, using public-key cryptography tied to user certificates so that only authorized accounts can decrypt the protected data.