Cryptography Reference
In-Depth Information
Digital Signature
Schemes
7
In this chapter we consider digital signature schemes, which are the main
cryptographic mechanisms for providing non-repudiation. We start by looking at
general requirements for a digital signature scheme.We then examine several ways
in which a digital signature scheme could be realised. We also discuss important
issues concerning the adoption and use of digital signatures.
At the end of this chapter you should be able to:
• Explain general requirements for a digital signature scheme.
• Recognise that not all digital signature schemes rely on public-key
cryptography.
• Appreciate the important role that hash functions play in creating some types
of digital signature scheme.
• Explain two different methods of creating a digital signature scheme based
on RSA.
• Compare the various properties of digital and handwritten signatures.
• Identify some points of vulnerability in any practical digital signature scheme.
The term
digital signature
is somewhat provocative in the sense that it infers
a digital analogue of handwritten signatures. We will later discuss the precise
extent to which this is true. For now, we will use this loose connection to motivate
a cryptographic perspective on what it means to provide non-repudiation.
7.1.1
The basic idea
In Section 1.3.1 we defined non-repudiation to be the assurance that an entity
cannot deny a previous commitment or action. Non-repudiation is a vital service
for any application which requires evidence that a particular entity has generated
