What is digital signature and how it works?

[danisara]

Hi,

I am trying to find out what a digital signature is and how it works. I am really confused. Can anyone help with this and explain, please?

Thanks.

Dani

[atari]

Let's assume you and I are going to exchange email.

YOU:
Using special software, you obtain a message hash (mathematical summary) of the your email.
You then use a private key that you have previously obtained from a public-private key authority to encrypt your email hash.
The encrypted hash becomes your digital signature of the message.

ME:
I make a hash of the received message.
Then I use your public key to decrypt the message hash.
If the hash and hash match, the received message is valid.

One thing that might get confusing, digital signature are not to encrypt the email so that nobody can read it, they are just to make sure that a message that comes to me from you is intact and from you.