Q: Generate a question which can yield the answer mentioned in the input. Generated question must be answered by the answer provided in input, without using any extra knowledge.
Context : In cryptography, DES-X (or DESX) is a variant on the DES (Data Encryption Standard) symmetric-key block cipher intended to increase the complexity of a brute force attack using a technique called key whitening.
Answer : Data Encryption Standard
A:
Which is the basis of DES-X?