Classification of Robotics

Digital Signatures

Requirements

Message authentication protects two parties who exchange messages from any third party. However, it does not protect the two parties against each other.

In situations where there is not complete trust between sender and receiver, something more than authentication is needed. The most attractive solution to this problem is the digital signature. The digital signature is analogous to the handwritten signature. It must have the following properties:

• It must verify the author and the date and time of the signature. • It must to authenticate the contents at the time of the signature. • It must be verifiable by third parties, to resolve disputes.

Thus, the digital signature function includes the authentication function.
On the basis of these properties, we can formulate the following requirements for a digital signature:

• The signature must be a bit pattern that depends on the message being signed. • The signature must use some information unique to the sender, to prevent both forgery and denial. • It must be relatively easy to produce the digital signature. • It must be relatively easy to recognize and verify the digital signature. • It must be computationally infeasible to forge a digital signature, either by constructing a new message for an existing digital signature or by constructing a fraudulent digital signature for a given message. • It must be practical to retain a copy of the digital signature in storage.

A variety of approaches has been proposed for the digital signature function. These approaches fall into two categories: direct and arbitrated.

Direct Digital Signature

The direct digital signature involves only the communicating parties (source, destination). It is assumed that the destination knows the public key of the source. A digital signature may be formed by encrypting the entire message with the sender's private key or by encrypting a hash code