A digital signature or digital signature scheme is a type of asymmetric cryptography used to simulate the security properties of a handwritten signature on paper.

Digital signature schemes consist of at least three algorithms: a key generation algorithm, a signature algorithm, and a verification algorithm. A signature provides authentication of a “message”. Messages may be anything, from electronic mail to a contract, or even a message sent in a more complicated cryptographic protocol.

Digital signatures are often used to implement electronic signatures, a broader term that refers to any electronic data that carries the intent of a signature, but not all electronic signatures use digital signatures. In some countries, including the United States, and in the European Union, electronic signatures have legal significance. However, laws concerning electronic signatures do not always make clear their applicability towards cryptographic digital signatures, leaving their legal importance somewhat unspecified.

How It Works

Assume you were going to send the draft of a will to your lawyer in another town. You want to give your lawyer the assurance that it was unchanged from what you sent and that it is really from you.

You copy-and-paste the will into an e-mail note.
Using special software, you obtain a message (mathematical summary) of the will.

You then use a private key that you have previously obtained from a public-private key authority to encrypt the hash.

The encrypted hash becomes your digital signature of the message. (Note that it will be different each time you send a message.)

At the other end, your lawyer receives the message.
To make sure it’s intact and from you, your lawyer makes a hash of the received message.

Your lawyer then uses your public key to decrypt the message hash or summary.

If the hashes match, the received message is valid.

See also…

Internet Law – Forum