Question $2\mathrm{.}1$

What is the main issue that allows for Padding Oracle Attacks to work on block ciphers?

Choose one $1$ point

A system that does not behave differently depending on whether the padding in a CBC$-$encrypted ciphertext is valid.

A system that behaves differently depending on whether the padding in a ECB$-$encrypted ciphertext is valid.

A system that behaves consistantly depending on whether the padding in a ECB$-$encrypted ciphertext is valid.

A system that behaves differently depending on whether the padding in a CBC$-$encrypted ciphertext is valid.