How message authentication and digital signatures work

　・In Japanese
Premise knowledge
　・Hash function
　・Encryption

■What is message authentication?

Message authentication is one of the encryption technologies for checking whether a message has been tampered with, and a message authentication code (MAC) is a ciphertext.

＜How message authentication works＞
When sending a message, the sender sends the message and the MAC created by the following procedure. The receiving side also uses the received message to create a MAC in the same procedure. If the received MAC matches the generated MAC, the message is correct.

＜MAC generation procedure＞
・ Create a hash value from a message using a hash function.
・ Generate MAC from hash value by encryption algorithm.

　

■What is a digital signature?

A digital signature is an encryption technique that verifies that a message has been tampered with and whose message it is.

＜How digital signatures work＞
The basic mechanism is the same as message authentication. The difference is that the cryptography is public-key cryptography, which vouches for the sender of the message.

　

■Differences between message authentication and digital signatures

Message authentication can confirm that the message has not been tampered with, but it does not guarantee who sent it, but digital signatures can tell who sent it. You may think that message authentication is not necessary, but the advantage of message authentication is that the calculation speed is faster than that of digital signatures (due to the difference between public key cryptography and common key cryptography). Therefore, if you don't need to guarantee who sent the message, message authentication should be fine.

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