What Is a Message Integrity?

Message integrity ensures that a message has not been changed.

Let's say you need to transmit a private key from your computer to your phone. Because your network connection isn't great, there's a chance that information is lost in transit. You want to be sure that the private key makes it to your phone in pristine condition. If there is data loss, you'll want to know about it so you can try again.

To accomplish this, we can take a hash of the private key, and send it alongside the key. When the private key is transmitted, you'll be able to check on your phone by hashing the private key and checking if the hashes match.

Checksums

This "hash and check" method is called a checksum.

1. checksum = hash(data)
2. send data
3. send checksum
4. if (hash(data) == checksum) then the message has not been altered

Assignment

Complete the checksumMatches function.

Convert the message to a slice of bytes and hash it using sha256. Check if the lowercase hexadecimal encoding of the hash matches the checksum argument. If it does, return true. Otherwise, return false.