What are Digital Signatures? - Computerphile?

A digital signature is like a special sticker that proves someone really sent a message.

Imagine you're sending a letter to your friend. To make sure it's really from you, you could put a unique sticker on the envelope, maybe one only you have. That’s like a digital signature: it shows who sent the message and makes sure no one changed it along the way.

Think of writing a letter as typing a message on a computer. A digital signature is created using a special tool called a private key, which only you have. When you send your message, you attach this digital sticker, your signature, to it.

Your friend gets the message and uses another special tool, like a public key, to check if the sticker really came from you. If everything matches up, they know it’s truly from you and no one tampered with it.

It's just like when you use a fingerprint scanner on your phone, only your finger can unlock it. A digital signature works in a similar way, but with messages instead of phones!