Question $39(0\mathrm{.}5$ points$)$

In which of the following attack the adversary just observes a ciphertext $($or multiple ciphertexts$)$ and attempts to determine information about the underlying plaintext $($or plaintexts$).?$

Ciphertext$-$only attack

Known$-$plaintext attack

Chosen$-$plaintext attack

osen$-$ciphertext attack