Which of the following two cryptography methods are used by NTFS Encrypting File System (EFS) to encrypt
the data stored on a disk on a file-by-file basis?

A.
Twofish

B.
Digital certificates

C.
Public key

D.
RSA

Explanation:
EFS uses public key cryptography and digital certificates to encrypt the data stored on a
disk on a file-by-file basis.
Public key encryption is one of the encryption types, which uses a public key that is known to
everyone and a private key that is known only
to the recipient of the message. When a user wants to send a secure message to another user, the
sending user uses the target user’s
public key to encrypt the message, and the target user then decrypts the message using his private
key, which is known only to the target
user. If a public key is used to encrypt a message, only the corresponding private key can be used to
decrypt it.
A digital certificate is used to identify the user logged into the system. It provides authentication
showing that the person is authorized to
access the data. EFS uses digital certificates that are associated with the user account.
Answer option A is incorrect. Twofish is a symmetric key block cipher. It operates on 128-bits block
size and uses key sizes up to 256 bits. It
uses pre-computed key-dependent S-boxes, and a relatively complex key schedule. One half of an nbit key is used as the actual encryption
key and the other half the key is used to modify the encryption algorithm. It borrows some elements
from the pseudo-Hadamard transform
(PHT) from the SAFER family of ciphers.
Answer option D is incorrect. The RSA algorithm is an example of the public key algorithm in which
the public key is generated from the private
key. In the RSA algorithm, public and private keys are generated as follows:
1.Choose two large prime numbers p and q of equal lengths, and compute n=p*q.
2.Choose a random public key e such that e and (p-1)*(q-1) are relatively prime.
3.Calculate e*d=1*mod[(p-1)*(q-1)]. Here, d is a private key.
4.Calculate d=e^(-1)*mod[(p-1)*(q-1)].
5.Now (e,n) and (d,n) are the public and private keys respectively.