Digital signatures. Whom do you trust?

This paper describes the current status of the efforts to attribute a level of confidence in the use of public key cryptography especially when used for digital signatures. In particular it focuses on the standardization efforts, both international and national, to define the framework for an infrastructure that allow digital signatures to be used in place of a paper signature for business transactions. That framework encompasses technical, business, and legal issues that must be addressed to enable such electronic commerce. This paper describes the initial definition of a public key certificate (known as X.509), the early efforts to use that definition, and the recent extensions to the definition to address problems found in those early efforts.