Sign first and then encrypt. Otherwise, after being intercepted by hackers in the transmission process, you can forge your own signature and continue to send it, although you don't know the specific content of the plaintext corresponding to the ciphertext information. In this way, the receiver will think that the message was sent by a hacker. For example, if the original plain text is a paper and the recipient is a magazine, then the magazine will assume that the paper was sent to him by a hacker.