ssamparn/digital-signature

Digital Signature

Digital Signature is a technique for ensuring:

1. Integrity: The message hasn't been altered in transit.
2. Authenticity: The author of the message is really who they claim to be.
3. Non-repudiation: The author of the message can't later deny that they were the source.

Sending a Message with a Digital Signature

Technically speaking, a digital signature is the encrypted hash (digest, checksum) of a message. That means we generate a hash from a message and encrypt it with a private key according to a chosen algorithm.

The message, the encrypted hash, the corresponding public key, and the algorithm are all then sent. This is classified as a message with its digital signature.

Receiving and Checking a Digital Signature

To check the digital signature, the message receiver generates a new hash from the received message, decrypts the received encrypted hash using the public key, and compares them. If they match, the Digital Signature is said to be verified.

We should note that we only encrypt the message hash, and not the message itself. In other words, Digital Signature doesn't try to keep the message secret. Our digital signature only proves that the message was not altered in transit.

When the signature is verified, we're sure that only the owner of the private key could be the author of the message.

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