I have this question I am trying to figure out the answer about RSA. I'd be grateful if someone could actually help me understand how the procedure would work. I am new to cryptography and with all the maths in it, I am barely understanding it.
Assuming that we have a sender A and 2 recipients B and C. This sender wants to send 12 messages.
If A wants to send to B he'd use B's public key $(n_B,e_B)$. Meaning: $$\text{ciphertext}_i = (\text{plaintext}_i)^{e_B} \bmod n_B$$
If A wants to send to C he'd use C's public key $(n_C,e_C)$. Meaning: $$\text{ciphertext}_i = (\text{plaintext}_i)^{e_C} \bmod n_C$$
An attacker gets the 12 ciphertexts A encrypted. He also knows the public key of B and C.
How can he determine whether A sent her messages to B or C?