Digital Signatures

Chapter 13 DIGITAL  SIGNATURES

o Digital Signatures

·        Properties

·        Attacks and Forgeries

·        Digital Signature Requirements Direct Digital Signature

o ElGamal Digital Signature Scheme

o Schnorr Digital Signature Scheme

o Digital Signature Standard

·        The DSS Approach

·        The Digital Signature Algorithm

KEY POINTS

◆             A digital signature is an authentication mechanism that enables the creator of a message to attach a code that acts as a signature. Typically the signature is formed by taking the hash of the message and encrypting the message with the creator’s private key. The signature guarantees the source and integrity of the message.

◆             The digital signature standard (DSS) is an NIST standard that uses the secure hash algorithm (SHA).

The most important development from the work on public-key cryptography is the digital signature. The digital signature provides a set of security capabilities that would be difficult to implement in any other way.

Figure 13.1 is a generic model of the process of making and using digital signa- tures. Bob can sign a message using a digital signature generation algorithm.The inputs to the algorithm are the message and Bob’s private key. Any other user, say Alice, can verify the signature using a verification algorithm, whose inputs are the message, the signature, and Bob’s public key. In simplified terms, the essence of the digital signature mechanism is shown in Figure 13.2. This repeats the logic shown in Figure 11.3. A worked-out example, using RSA, is available at this book’s Web site.

We begin this chapter with an overview of digital signatures. Then, we introduce the Digital Signature Standard (DSS).