This chapter is from the book
This chapter is from the book
This chapter is from the book
1.10 Key Escrow for Law Enforcement
Law enforcement would like to preserve its ability to wiretap otherwise secure communication. (Also, sometimes companies want to be able to read all data of their employees, either to enforce company policies, or to ensure data is not lost when an employee forgets a password or leaves the company.)
In order for the government to ensure it can always wiretap, it must prevent use of encryption, break the codes used for encryption (as it did in a military context during World War II), or somehow learn everyone's cryptographic keys. The Clipper proposal was proposed in the mid-90's and attempted the third option. It allows the government to reconstruct your key (only upon court order and with legitimate cause of course). This is made possible through the use of a device known as the Clipper chip. A lot about Clipper was classified by the government as secret (and classified by a lot of other people as evil). We describe the basic technical design of Clipper in §24.9 Clipper. Although the Clipper proposal appears to have been a failure, and the government appears to have for the moment at least given up on attempting to control cryptography, the Clipper design was fascinating, and is worth learning about. The simple concept is that encryption is done with a special chip (the Clipper chip). Each chip manufactured has a unique key, and the government keeps a record of the serial number/encryption key correspondence of every chip manufactured. Because not all people have complete trust in the government, rather than keeping the key in one place, each key is broken into two quantities which must be 'd in order to obtain the actual key. Each piece is completely useless without the other. Since each piece is kept with a separate government agency, it would require two U.S. government agencies to cooperate in order to cheat and obtain the key for your Clipper chip without a valid court order. The government assures us, and evidence of past experience supports its claim, that cooperation between U.S. government agencies is unlikely.
The Clipper proposal was always controversial, starting with its name (which violated someone's trademark on something unrelated). Why would anyone use Clipper when alternative methods should be cheaper and more secure? The reason alternatives would be cheaper is that enforcing the ability of the U.S. government to wiretap adds a lot of complexity over a design that simply encrypts the data. Proponents of Clipper gave several answers to this question:
The government would buy a lot of Clipper chips, bringing the cost down because of volume production, so Clipper would wind up being the most cost-effective solution.
Encryption technology is only useful if both parties have compatible equipment. Since the U.S. government would use Clipper, to talk securely to the U.S. government, you would have to use Clipper. So any other mechanism would have to be implemented in addition to Clipper.
Again, since encryption technology is only useful if both parties have compatible equipment, if Clipper took over enough market share, it would essentially own the market (just like VHS, a technically inferior standard supposedly, beat out Beta in the VCR marketplace). Since Clipper would be one of the earliest standards, it might take over the marketplace before any other standards have an opportunity to become entrenched. The argument was that most people wouldn't care that Clipper enables wiretapping, because they'll assume they have nothing to fear from the U.S. government wiretapping them.
The government claimed that the cryptographic algorithm in Clipper was stronger than you could get from a commercial source.
Civil libertarians feared Clipper was a first step towards outlawing untappable cryptography. Clipper proponents say it was not. It's true that outlawing alternatives was not part of the Clipper proposal. However, there have been independent efforts to outlaw cryptography. Those efforts have been thwarted in part with the argument that industry needs security. But if Clipper were deployed, that argument would have gone away.
Clipper was designed for telephones, fax, and other low-speed applications, and in some sense is not relevant to computer networking. Many people regard it, however, as a first step and a model for taking the same approach for computer networks.
The Clipper proposal was a commercial failure, and export controls are currently relaxed. However, the technical aspects of such designs are fascinating, laws can change at any time, and export controls have created other fascinating and arcane designs that we will describe throughout the book, for instance, §19.13 Exportability.