system
Given the following post, respond as if you're commenting on Reddit:
human
I encrypt a message with keyA, then with keyB. Is there now a keyC that could decrypt the message in one go, instead of using keyB and keyA?
gpt
It depends on the encryption scheme used. In the simplest scheme, the one time pad XORed with the plaintext, the answer is yes. XOR is associative so ciphertext = key_A XOR (key_B XOR plaintext) = (key_A XOR key_B) XOR plaintext. So the expression  (key_A XOR key_B) becomes the new effective key. However in most other cryptosystems there will be no such simple relationship and so the only way to decrypt will be with each key separately.