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Next: 3.3.6 What about authenticity? Up: 3.3 Data Security: Cryptography Previous: 3.3.4 How does someone

3.3.5 How is information integrity assured?

When you put together your message to me and encrypt it with my public key, you also have your computer calculate something called a ``message digest'' and attach it to the message. The message digest is a small piece of data that results from performing a particular mathematical calculation on your message. It acts as the digital fingerprint of your message -- the message digest of every message is different.

When I receive your message and decrypt it with my private key, I also calculate the message digest of your message. Then, I compare the digest I generated to the one you sent with your message. If they match, then I know that I received exactly what you sent.

Denis Arnaud