This is from http://mondediplo.com/2000/06/15publicgood: "What is a public good? This question can best be answered by looking at the counterpart, a private good. Private goods are typically traded in markets. Buyers and sellers meet through the price mechanism. If they agree on a price, the ownership or use of the good (or service) can be transferred. Thus private goods tend to be excludable. They have clearly identified owners; and they tend to be rival. For example, others cannot enjoy a piece of cake, once consumed. "Public goods have just the opposite qualities. They are non-excludable and non-rival in consumption. An example is a street sign. It will not wear out, even if large numbers of people are looking at it; and it would be extremely difficult, costly and highly inefficient to limit its use to only one or a few persons and try to prevent others from looking at it, too. A traffic light or clean air is a further example. " Robert Hettinga writes:

A signed, much less encrypted, copy of a piece of digital information, or even a digital service, for that matter, (teleoperated machine commands, or a live video feed answering a question, and, of course, computation and bandwidth) is, in fact, an "ordinary, private" good.

How can a signed piece of digital information be a private good, by the definitions above? It is non-rival: if someone enjoys the good, he can give it to others and he will still be able to enjoy it. And it is non-excludable: if you give it to some people, they can share it with others and you can't prevent that, as Napster proved. Even encrypting the information won't help (unless to a key embedded in some DRM related hardware). The recipient can still decrypt it and share it. It is still non-rival and non-excludable. Digital services, on the other hand, may well be rival and excludable, and so do qualify as private goods. Hence there is no need for DRM mechanisms to control services. Most observers believe this is a big reason for the software industry's interest in "web services", that they will not be vulnerable to software piracy. Since such services are excludable they are not relevant to our debate over DRM and TCPA. But you claimed that signed pieces of digital information were private goods. Please explain. Are you using standard economic definitions, or are you inventing your own terminology?