How useful are digital signatures?
There's one article that anyone interested in the business use of PKI should read. This is "Legislating Market Winners: Digital Signature Laws and the Electronic Commerce Marketplace" by Bradford Biddle. Biddle is a lawyer, and this article was first published in the San Diego Law Review in 1997. It's also available from Biddle's web site here.
The abstract of the article nicely sums up the legal arguments about using PKI. Here's what it says:
Abstract: "Legislating Market Winners" argues that certain enacted digital signature laws are premised upon false assumptions, and inappropriately enshrine a business model which would not evolve naturally in the marketplace. In attempting to solve an unsolvable liability allocation problem, such legislation harms consumers and the future evolution of electronic commerce. The article points out that alternative business models can solve the liability allocation problem. Despite obvious flaws, legislation of this type continues to be proposed, partly because the infrastructure created by these laws coincides with the needs of key escrow proponents. Ultimately the article argues that digital signature laws, which impose a particular view of electronic commerce, should be abandoned, in favor of laws which remove specific, well-defined barriers to electronic commerce and which allow the electronic commerce marketplace to evolve unfettered.
This article goes on to essentially argue that the type of PKI envisioned by digital signature laws simply isn't viable, and that the only viable PKI is one in which the CA is essentially totally absolved of any liability. Similarly, a problem with individuals using PKI is that digital signature laws try to give an end user much more liability that any other legal framework in existence. Because of these problems, digital signatures that try to be anything more that a cryptographic checksum are almost certainly doomed to fail.
Anyone who is thinking about using PKI in one of their business processes would do well to read this article and think about what it says. Some things are feasible with digital signatures. Some things aren't. Confusing the two can be a source of all sorts of problems.