Which of the following is NOT an advantage of a stream cipher?

A.
The same equipment can be used for encryption and decryption.

B.
It is amenable to hardware implementations that result in higher
speeds.

C.
Since encryption takes place bit by bit, there is no error propagation.

D.
The receiver and transmitter must be synchronized.

Explanation:
The transmitter and receiver must be synchronized since they must
use the same keystream bits for the same bits of the text that are to be
enciphered and deciphered. Usually, synchronizing frames must be sent
to effect the synchronization and, thus, additional overhead is required
for the transmissions.
* Answer “The same equipment can be used for encryption and decryption” describes an

advantage since stream ciphers commonly use Linear Feedback Shift Registers (LFSRs) to
generate the keystream and use XORs to operate on the plaintext input stream.
Because of the characteristics of the XOR, the same XOR gates and LFSRs
can also decrypt the message. Since LFSRs and XORs are used in a stream
cipher to encrypt and decrypt, these components are amenable to hardware
implementation, which means higher speeds of operation. Thus,
answer “It is amenable to hardware implementations that result in higher
speeds” describes an advantage.
For answer “Since encryption takes place bit by bit, there is no error propagation”, stream ciphers
encrypt individual bits with no feedback of the generated ciphertext bits and, therefore, errors do
not propagate.