So in summary, here are some key properties that we should keep in mind.
These are essential properties of digital signature schemes that are enabled by the functionality that we went over just now with Alice sending a message to Bob.
First, given a message and a signature, as well as a copy of the sender’s public key, the recipient should be able to identify the message origin.
Since the message has been signed by the sender’s private key, this shows that the original sender has authorized this message.
There’s also non-repudiation, meaning that the original sender should not be able to backtrack.
Since they have already signed the message with their private key, there should not be away to undo that signature, or to nullify it.
And changing the message would make it such that signature wouldn’t match up with it anymore.
Finally, message recipients should also be able to verify message integrity.
And this is what we saw earlier: that signatures can be used so that messages can’t be modified by anyone after signing.