What Is Digital Signature?

PKI Tutorials - Herong's Tutorial Examples - Version 2.10, by Dr. Herong Yang

PKI Tutorials - Herong's Tutorial Examples

∟What Is Digital Signature?

This section describes the digital signature of a digital document. A digital signature is the message digest of the document encrypted by sender's private key. Receiver can decrypt the digital signature with sender's public key and compare it with the message digest of the received document.

In earlier part of the book, we discussed one important application area of the PKI (Public Key Infrastructure) technology. That is the HTTPS (Hypertext Transfer Protocol Secure) to provide encrypted communication and secure identification of Web servers.

Now we can look at another application area of the PKI technology, digital signature.

What Is Digital Signature? I like the definition from wikipedia.org: "A digital signature or digital signature scheme is a mathematical scheme for demonstrating the authenticity of a digital message or document. A valid digital signature gives a recipient reason to believe that the message was created by a known sender, and that it was not altered in transit."

The digital signature scheme is shown in this picture from globus.org:

The diagram shows you that:

The sender must have a private-public pair.
The sender generates a digital signature, shown as the Encrypted Message Digest in the picture, using the private key and a message digest of the original document.
The receiver decrypts the digital signature using the sender's public key and compares with the message digest of the received document.
The receiver knows that received document has been tampered with by a third party if the message digest does not match the decrypted digital signature.

Note that the picture above only verifies the integrity of the received document. It does not cover the verification of sender's identity. See next section for details on this.

Last update: 2011.

Table of Contents

About This Book

Introduction of PKI (Public Key Infrastructure)

Introduction of HTTPS (Hypertext Transfer Protocol Secure)

Using HTTPS with Google Chrome

Using HTTPS with Mozilla Firefox

HTTPS with IE (Internet Explorer)

Perl Scripts Communicating with HTTPS Servers

PHP Scripts Communicating with HTTPS Servers

Java Programs Communicating with HTTPS Servers

Windows Certificate Stores and Console