Next: 3.3.6 What about authenticity?
Up: 3.3 Data Security: Cryptography
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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.