Authentication encryption working mode

Encryption and authentication are the two major topics in the field of information security. Encryption ensures the secrecy of data and authentication signature ensures the integrity of data. The two are often inseparable. There are three main working modes:

1. Encrypt and then sign the ciphertext (encrypt-then-mac)

2. Sign the plaintext first, then encrypt the plaintext and the signature (mac-then-encrypt)

3. First sign the plaintext, then encrypt the plaintext, and finally attach the signature to the ciphertext (mac-and-encrypt)

All three methods can ensure the secrecy and integrity of information to a certain extent, but each has its own characteristics. The analysis of the next three modes, the first is 1, which can ensure that the receiver verifies the integrity of the data before decryption, and discards the data that cannot be verified by HMAC directly, which improves the processing speed. However, once the HMAC key is disclosed, it will threaten the security of the communication, because the receiver can send a random piece of data to the receiver after HMAC, and can pass the authentication of the receiver. As a result, the receiver thinks this is a legitimate piece of data. However, this will not happen in 2 and 3. Even if the HMAC key is leaked, solution 2 can guarantee the security of the communication as well as 3, because the user does not know the encryption key and cannot forge the authenticated data. However, scheme 2 and 3 will be slower than 1 in application.