Which of the following refers to a symmetric key cipher which operates on fixedlength groups of bits with an unvarying transformation?

A. stream cipher

B. block cipher

C. check cipher

D. string cipher

E. None of the choices.

Explanation:

In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation.

A stream cipher, on the other hand, operates on individual digits one at a time.