I was going through this question and intuition came that same message can be used to break security but I an not able formalize it well...can someone help how to create chosen ciphertext attack formally so that adversary wins with significant probability.
Not getting idea how to formally chose chosen cipher attack so adversay wins with non-negligible probability
$\begingroup$ Hint: consider the malleability of countermode; that is, given the encryption of $E_k(P_1)$, you can convert it into the encryption $E_k(P_2)$ (assuming that you know both $P_1$ and $P_2$, and they're the same length...) $\endgroup$– ponchoMar 22, 2021 at 21:09
$\begingroup$ can you please more elaborate.. $\endgroup$– SamMar 22, 2021 at 21:21
$\begingroup$ If this is homework, you're supposed to figure it out... $\endgroup$– ponchoMar 22, 2021 at 21:51
$\begingroup$ it is not a homework i am solving chapter 9 of boneh shoup book and it is 9.4 of that book .....just that i am stuck at this ..i thought for 1 day.....but i am not getting idea of it $\endgroup$– SamMar 22, 2021 at 22:06