Which
of the following encryption algorithms are based on block ciphers?

A.
RC4

B.
Twofish

C.
Rijndael

D.
RC5

Explanation:
The following encryption algorithms are based on block ciphers:
RC5
Rijndael
Twofish
In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of
bits, termed as ‘blocks’, with an unvarying

transformation. When encrypting, a block cipher might take (for example) a 128-bit block of plain
text as input, and output a corresponding
128-bit block of cipher text.