DESX is a variant of DES in which:

A.
The output of DES is bitwise XORed with 64 bits of key material.

B.
Input plaintext is bitwise XORed with 64 bits of additional key material before encryption with
DES, and the output of DES is also bitwise XORed with another 64 bits of key material.

C.
The input plaintext is encrypted X times with the DES algorithm using different keys for each
encryption.

D.
Input plaintext is bitwise XORed with 64 bits of additional key material before encryption with
DES.

Explanation:
DESX was developed by Ron Rivest to increase the resistance of DES to brute force key search
attacks; however, the resistance of DESX to differential and linear attacks is equivalent to that of DES
with independent subkeys.