Checking data integrity using a hashing function to prevent a MITM attack

Question

I recently discovered a way to ensure that a message was not tampered by someone in the middle using a hash function like SHA-256. For my knolage the sender sends the original message with the original message summerized using hash function, Which ensure that a man in the middle cannot change the data because the hashes will not match. The part that I do not understand is that if there is a man in the middle that is tampering the messages why can't he just change the hash as well to match to the changed message?.

Answer 1

It is possible that the man in the middle can modify the body of the request and then calculate the hash as per the new tempered data. but that is only possible when the attacker knows what kind of hashing function is used and what salt is utilized. So to avoid this thing always use public key cryptography to share the salt becuase in this case the salt is considered to be a key and if you hardcode the key at the client side as well server side then at the server side we can consider it secure but the attacker can fetch the hardcoded key and use it for malicious purposes.

So make sure you use the Defie Helman key exchange mechanism for key sharing before applying the hash function on the data for which you want the integrity to be intact.

Hope this answers your question.