12.16. Ensure Data Integrity Using a Keyed Hash Code

Problem

You need to transmit a file to someone and provide the recipient with a means to verify the integrity of the file and its source.

Solution

Share a secret key with the intended recipient. This key would ideally be a randomly generated number, but it could also be a phrase that you and the recipient agree to use. Use the key with one of the keyed hashing algorithm classes derived from the System.Security.Cryptography.KeyedHashAlgorithm class to create a keyed hash code. Send the hash code with the file. On receipt of the file, the recipient will generate the keyed hash code of the file using the shared secret key. If the hash codes are equal, the recipient knows that the file is from ...

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