Digital Signature Schemes based on RSA

We now discuss what most people regard as ‘true’ digital signature schemes based on public-key cryptography. Indeed, Whit Diffie, one of the authors of the seminal research paper proposing public-key cryptography, has indicated that his motivation for the idea was substantially driven by a desire to find a means of creating ‘digital signatures’ and not public-key encryption. We’ll present a basic model of a digital signature scheme and describe two digital signature schemes based on RSA.

Complementary requirements

Keeping in mind our concerns about arbitrated digital signature schemes, it’s preferable to avoid the direct involvement of a third party in the generation of digital signatures. This leads us to some very simple requirements for a digital signature scheme, which we indicate in the table below. As can be seen, these requirements have more than a passing resemblance to the basic requirements for a public-key encryption scheme.