Personal tools


Diffie Testimony

Whitfield Diffie Testimony

The Impact of a Secret Cryptographic Standard on Encryption, Privacy, Law Enforcement and Technology

Whitfield Diffie
Sun Microsystems
11 May 1993

I'd like to begin by expressing my thanks to Congressman Boucher, the other members of the committee, and the committee staff for giving us the opportunity to appear before the committee and express our views.

On Friday, the 16th of April, a sweeping new proposal for both the promotion and control of cryptography was made public on the front page of the New York Times and in press releases from the White House and other organizations.

This proposal was to adopt a new cryptographic system as a federal standard, but at the same time to keep the system's functioning secret. The standard would call for the use of a tamper resistant chip, called Clipper, and embody a `back door' that will allow the government to decrypt the traffic for law enforcement and national security purposes.

So far, available information about the chip is minimal and to some extent contradictory, but the essence appears to be this: When a Clipper chip prepares to encrypt a message, it generates a short preliminary signal rather candidly entitled the Law Enforcement Exploitation Field. Before another Clipper chip will decrypt the message, this signal must be fed into it. The Law Enforcement Exploitation Field or LEEF is tied to the key in use and the two must match for decryption to be successful. The LEEF in turn, when decrypted by a government held key that is unique to the chip, will reveal the key used to encrypt the message.

The effect is very much like that of the little keyhole in the back of the combination locks used on the lockers of school children. The children open the locks with the combinations, which is supposed to keep the other children out, but the teachers can always look in the lockers by using the key.

In the month that has elapsed since the announcement, we have studied the Clipper chip proposal as carefully as the available information permits. We conclude that such a proposal is at best premature and at worst will have a damaging effect on both business security and civil rights without making any improvement in law enforcement.

To give you some idea of the importance of the issues this raises, I'd like to suggest that you think about what are the most essential security mechanisms in your daily life and work. I believe you will realize that the most important things any of you ever do by way of security have nothing to do with guards, fences, badges, or safes. Far and away the most important element of your security is that you recognize your family, your friends, and your colleagues. Probably second to that is that you sign your signature, which provides the people to whom you give letters, checks, or documents, with a way of proving to third parties that you have said or promised something. Finally you engage in private conversations, saying things to your loved ones, your friends, or your staff that you do not wish to be overheard by anyone else.

These three mechanisms lean heavily on the physical: face to face contact between people or the exchange of written messages. At this moment in history, however, we are transferring our medium of social interaction from the physical to the electronic at a pace limited only by the development of our technology. Many of us spend half the day on the telephone talking to people we may visit in person at most a few times a year and the other half exchanging electronic mail with people we never meet in person.

Communication security has traditionally been seen as an arcane security technology of real concern only to the military and perhaps the banks and oil companies. Viewed in light of the observations above, however, it is revealed as nothing less than the transplantation of fundamental social mechanisms from the world of face to face meetings and pen and ink communication into a world of electronic mail, video conferences, electronic funds transfers, electronic data interchange, and, in the not too distant future, digital money and electronic voting.

No right of private conversation was enumerated in the constitution. I don't suppose it occurred to anyone at the time that it could be prevented. Now, however, we are on the verge of a world in which electronic communication is both so good and so inexpensive that intimate business and personal relationships will flourish between parties who can at most occasionally afford the luxury of traveling to visit each other. If we do not accept the right of these people to protect the privacy of their communication, we take a long step in the direction of a world in which privacy will belong only to the rich.

The import of this is clear: The decisions we make about communication security today will determine the kind of society we live in tomorrow.

The objective of the administration's proposal can be simply stated:
They want to provide a high level of security to their friends, while being sure that the equipment cannot be used to prevent them from spying on their enemies.
Within a command society like the military, a mechanism of this sort that allows soldiers' communications to be protected from the enemy, but not necessarily from the Inspector General, is an entirely natural objective. Its imposition on a free society, however, is quite another matter.

Let us begin by examining the monitoring requirement and ask both whether it is essential to future law enforcement and what measures would be required to make it work as planned.

Eavesdropping, as its name reminds us, is not a new phenomenon. But in spite of the fact that police and spies have been doing it for a long time, it has acquired a whole new dimension since the invention of the telegraph. Prior to electronic communication, it was a hit or miss affair. Postal services as we know them today are a fairly new phenomenon and messages were carried by a variety of couriers, travelers, and merchants. Sensitive messages in particular, did not necessarily go by standardized channels. Paul Revere, who is generally remembered for only one short ride, was the American Revolution's courier, traveling routinely from Boston to Philadelphia with his saddle bags full of political broadsides.

Even when a letter was intercepted, opened, and read, there was no guarantee, despite some people's great skill with flaps and seals, that the victim would not notice the intrusion.

The development of the telephone, telegraph, and radio have given the spies a systematic way of intercepting messages. The telephone provides a means of communication so effective and convenient that even people who are aware of the danger routinely put aside their caution and use it to convey sensitive information. Digital switching has helped eavesdroppers immensely in automating their activities and made it possible for them to do their listening a long way from the target with negligible chance of detection.

Police work was not born with the invention of wiretapping and at present the significance of wiretaps as an investigative tool is quite limited. Even if their phone calls were perfectly secure, criminals would still be vulnerable to bugs in their offices, body wires on agents, betrayal by co-conspirators who saw a brighter future in cooperating with the police, and ordinary forensic inquiry.

Moreover, cryptography, even without intentional back doors, will no more guarantee that a criminal's communications are secure than the Enigma guaranteed that German communications were secure in World War II. Traditionally, the richest source of success in communications intelligence is the ubiquity of busts: failures to use the equipment correctly.

Even if the best cryptographic equipment we know how to build is available to them, criminal communications will only be secure to the degree that the criminals energetically pursue that goal. The question thus becomes, ``If criminals energetically pursue secure communications, will a government standard with a built in inspection port, stop them.

It goes without saying that unless unapproved cryptography is outlawed, and probably even if it is, users bent on not having their communications read by the state will implement their own encryption. If this requires them to forgo a broad variety of approved products, it will be an expensive route taken only by the dedicated, but this sacrifice does not appear to be necessary.

The law enforcement function of the Clipper system, as it has been described, is not difficult to bypass. Users who have faith in the secret Skipjack algorithm and merely want to protect themselves from compromise via the Law Enforcement Exploitation Field, need only encrypt that one item at the start of transmission. In many systems, this would require very small changes to supporting programs already present. This makes it likely that if Clipper chips become as freely available as has been suggested, many products will employ them in ways that defeat a major objective of the plan.

What then is the alternative? In order to guarantee that the government can always read Clipper traffic when it feels the need, the construction of equipment will have to be carefully controlled to prevent non-conforming implementations. A major incentive that has been cited for industry to implement products using the new standard is that these will be required for communication with the government. If this strategy is successful, it is a club that few manufacturers will be able to resist. The program therefore threatens to bring communications manufacturers under an all encompassing regulatory regime.

It is noteworthy that such a regime already exists to govern the manufacture of equipment designed to protect `unclassified but sensitive' government information, the application for which Clipper is to be mandated. The program, called the Type II Commercial COMSEC Endorsement Program, requires facility clearances, memoranda of agreement with NSA, and access to secret `Functional Security Requirements Specifications.' Under this program member companies submit designs to NSA and refine them in an iterative process before they are approved for manufacture.

The rationale for this onerous procedure has always been, and with much justification, that even though these manufacturers build equipment around approved tamper resistant modules analogous to the Clipper chip, the equipment must be carefully vetted to assure that it provides adequate security. One requirement that would likely be imposed on conforming Clipper applications is that they offer no alternative or additional encryption mechanisms.

Beyond the damaging effects that such regulation would have on innovation in the communications and computer industries, we must also consider the fact that the public cryptographic community has been the principal source of innovation in cryptography. Despite NSA's undocumented claim to have discovered public key cryptography, evidence suggests that, although they may have been aware of the mathematics, they entirely failed to understand the significance. The fact that public key is now widely used in government as well as commercial cryptographic equipment is a consequence of the public community being there to show the way.

Farsightedness continues to characterize public research in cryptography, with steady progress toward acceptable schemes for digital money, electronic voting, distributed contract negotiation, and other elements of the computer mediated infrastructure of the future.

Even in the absence of a draconian regulatory framework, the effect of a secret standard, available only in a tamper resistant chip, will be a profound increase in the prices of many computing devices. Cryptography is often embodied in microcode, mingled on chips with other functions, or implemented in dedicated, but standard, microprocessors at a tiny fraction of the tens of dollars per chip that Clipper is predicted to cost.

What will be the effect of giving one or a small number of companies a monopoly on tamper resistant parts? Will there come a time, as occurred with DES, when NSA wants the standard changed even though industry still finds it adequate for many applications? If that occurs will industry have any recourse but to do what it is told? And who will pay for the conversion?

One of the little noticed aspects of this proposal is the arrival of tamper resistant chips in the commercial arena. Is this tamper resistant part merely the precursor to many? Will the open competition to improve semiconductor computing that has characterized the past twenty-years give way to an era of trade secrecy? Is it perhaps tamper resistance technology rather than cryptography that should be regulated?

Recent years have seen a succession of technological developments that diminish the privacy available to the individual. Cameras watch us in the stores, x-ray machines search us at the airport, magnetometers look to see that we are not stealing from the merchants, and databases record our actions and transactions. Among the gems of this invasion is the British Rafter technology that enables observers to determine what station a radio or TV is receiving. Except for the continuing but ineffectual controversy surrounding databases, these technologies flourish without so much as talk of regulation.

Cryptography is perhaps alone in its promise to give us more privacy rather than less, but here we are told that we should forgo this technical benefit and accept a solution in which the government will retain the power to intercept our ever more valuable and intimate communications and will allow that power to be limited only by policy.

In discussion of the FBI's Digital Telephony Proposal --- which would have required communication providers, at great expense to themselves, to build eavesdropping into their switches --- it was continually emphasized that wiretaps were an exceptional investigative measure only authorized when other measures had failed. Absent was any sense that were the country to make the proposed quarter billion dollar inventment in intercept equipment, courts could hardly fail to accept the police argument that a wiretap would save the people thousands of dollars over other options. As Don Cotter, at one time director of Sandia National Laboratories, said in respect to military strategy: ``Hardware makes policy.''

Law, technology, and economics are three central elements of society that must all be kept in harmony if freedom is to be secure. An essential element of that freedom is the right to privacy, a right that cannot be expected to stand against unremitting technological attack. Where technology has the capacity to support individual rights, we must enlist that support rather than rejecting it on the grounds that rights can be abused by criminals. If we put the desires of the police ahead of the rights of the citizens often enough, we will shortly find that we are living in police state. We must instead assure that the rights recognized by law are supported rather than undermined by technology.

At NSA they believe in something they call `security in depth.' Their most valuable secret may lie encrypted on a tamper resistant chip, inside a safe, within a locked office, in a guarded building, surrounded by barbed wire, on a military base. I submit to you that the most valuable secret in the world is the secret of democracy; that technology and policy should go hand in hand in guarding that secret; that it must be protected by security in depth.


There is a crying need for improved security in American communication and computing equipment and the Administration is largely correct when it blames the problem on a lack of standards. One essential standard that is missing is a more secure conventional algorithm to replace DES, an area of cryptography in which NSA's expertise is probably second to none.

I urge the committee to take what is good in the Administration's proposal and reject what is bad.

  • The Skipjack algorithm and every other aspect of this proposal should be made public, not only to expose them to public scrutiny but to guarantee that once made available as standards they will not be prematurely withdrawn. Configuration control techniques pioneered by the public community can be used to verify that some pieces of equipment conform to government standards stricter than the commercial where that is appropriate.

  • I likewise urge the committee to recognize that the right to private conversation must not be sacrificed as we move into a telecommunicated world and reject the Law Enforcement Exploitation Function and the draconian regulation that would necessarily come with it.

  • I further urge the committee to press the Administration to accept the need for a sound international security technology appropriate to the increasingly international character of the world's economy.

Return to main Clipper page.

Return to the CPSR home page.

Send mail to webmaster.

Archived CPSR Information
Created before October 2004

Sign up for CPSR announcements emails


International Chapters -

> Canada
> Japan
> Peru
> Spain

USA Chapters -

> Chicago, IL
> Pittsburgh, PA
> San Francisco Bay Area
> Seattle, WA
Why did you join CPSR?

My professor recommended me to join CPSR.