Computer Science and Artificial Intelligence Laboratory
Technical Report
MIT-CSAIL-TR-2015-026

July 6, 2015

Keys Under Doormats: Mandating
insecurity by requiring government
access to all data and communications
Harold Abelson, Ross Anderson, Steven M.
Bellovin, Josh Benaloh, Matt Blaze, Whitfield Diffie,
John Gilmore, Matthew Green, Susan Landau,
Peter G. Neumann, Ronald L. Rivest, Jeffrey I.
Schiller, Bruce Schneier, Michael Specter, and
Daniel J. Weitzner

m a ss a c h u se t t s i n st i t u t e o f t e c h n o l o g y, c a m b ri d g e , m a 02139 u s a — w w w. c s a il . m i t . e d u

 Keys Under Doormats:
mandating insecurity by requiring government access to all
data and communications
Harold Abelson, Ross Anderson, Steven M. Bellovin, Josh Benaloh, Matt Blaze,
Whitfield Diffie, John Gilmore, Matthew Green, Susan Landau, Peter G. Neumann,
Ronald L. Rivest, Jeffrey I. Schiller, Bruce Schneier, Michael Specter, Daniel J. Weitzner
Abstract
Twenty years ago, law enforcement organizations lobbied to require data and
communication services to engineer their products to guarantee law enforcement
access to all data. After lengthy debate and vigorous predictions of enforcement
channels “going dark,” these attempts to regulate the emerging Internet were abandoned. In the intervening years, innovation on the Internet flourished, and law
enforcement agencies found new and more effective means of accessing vastly larger
quantities of data. Today we are again hearing calls for regulation to mandate the
provision of exceptional access mechanisms. In this report, a group of computer
scientists and security experts, many of whom participated in a 1997 study of these
same topics, has convened to explore the likely effects of imposing extraordinary
access mandates.
We have found that the damage that could be caused by law enforcement exceptional access requirements would be even greater today than it would have been 20
years ago. In the wake of the growing economic and social cost of the fundamental
insecurity of today’s Internet environment, any proposals that alter the security dynamics online should be approached with caution. Exceptional access would force
Internet system developers to reverse “forward secrecy” design practices that seek to
minimize the impact on user privacy when systems are breached. The complexity of
today’s Internet environment, with millions of apps and globally connected services,
means that new law enforcement requirements are likely to introduce unanticipated,
hard to detect security flaws. Beyond these and other technical vulnerabilities, the
prospect of globally deployed exceptional access systems raises difficult problems
about how such an environment would be governed and how to ensure that such
systems would respect human rights and the rule of law.

July 7, 2015

 Executive Summary
Political and law enforcement leaders in the United States and the United Kingdom have
called for Internet systems to be redesigned to ensure government access to information —
even encrypted information. They argue that the growing use of encryption will neutralize their investigative capabilities. They propose that data storage and communications
systems must be designed for exceptional access by law enforcement agencies. These proposals are unworkable in practice, raise enormous legal and ethical questions, and would
undo progress on security at a time when Internet vulnerabilities are causing extreme
economic harm.
As computer scientists with extensive security and systems experience, we believe that
law enforcement has failed to account for the risks inherent in exceptional access systems.
Based on our considerable expertise in real-world applications, we know that such risks
lurk in the technical details. In this report we examine whether it is technically and
operationally feasible to meet law enforcement’s call for exceptional access without causing
large-scale security vulnerabilities. We take no issue here with law enforcement’s desire to
execute lawful surveillance orders when they meet the requirements of human rights and
the rule of law. Our strong recommendation is that anyone proposing regulations should
first present concrete technical requirements, which industry, academics, and the public
can analyze for technical weaknesses and for hidden costs.
Many of us worked together in 1997 in response to a similar but narrower and betterdefined proposal called the Clipper Chip [1]. The Clipper proposal sought to have all
strong encryption systems retain a copy of keys necessary to decrypt information with
a trusted third party who would turn over keys to law enforcement upon proper legal
authorization. We found at that time that it was beyond the technical state of the
art to build key escrow systems at scale. Governments kept pressing for key escrow,
but Internet firms successfully resisted on the grounds of the enormous expense, the
governance issues, and the risk. The Clipper Chip was eventually abandoned. A much
more narrow set of law enforcement access requirements have been imposed, but only on
regulated telecommunications systems. Still, in a small but troubling number of cases,
weakness related to these requirements have emerged and been exploited by state actors
and others. Those problems would have been worse had key escrow been widely deployed.
And if all information applications had had to be designed and certified for exceptional
access, it is doubtful that companies like Facebook and Twitter would even exist. Another
important lesson from the 1990’s is that the decline in surveillance capacity predicted by
law enforcement 20 years ago did not happen. Indeed, in 1992, the FBI’s Advanced
Telephony Unit warned that within three years Title III wiretaps would be useless: no
1

 more than 40% would be intelligible and that in the worst case all might be rendered
useless [2]. The world did not “go dark.” On the contrary, law enforcement has much
better and more effective surveillance capabilities now than it did then.
The goal of this report is to similarly analyze the newly proposed requirement of
exceptional access to communications in today’s more complex, global information infrastructure. We find that it would pose far more grave security risks, imperil innovation,
and raise thorny issues for human rights and international relations.
There are three general problems. First, providing exceptional access to communications would force a U-turn from the best practices now being deployed to make the
Internet more secure. These practices include forward secrecy — where decryption keys
are deleted immediately after use, so that stealing the encryption key used by a communications server would not compromise earlier or later communications. A related technique,
authenticated encryption, uses the same temporary key to guarantee confidentiality and
to verify that the message has not been forged or tampered with.
Second, building in exceptional access would substantially increase system complexity.
Security researchers inside and outside government agree that complexity is the enemy of
security — every new feature can interact with others to create vulnerabilities. To achieve
widespread exceptional access, new technology features would have to be deployed and
tested with literally hundreds of thousands of developers all around the world. This is a far
more complex environment than the electronic surveillance now deployed in telecommunications and Internet access services, which tend to use similar technologies and are more
likely to have the resources to manage vulnerabilities that may arise from new features.
Features to permit law enforcement exceptional access across a wide range of Internet and
mobile computing applications could be particularly problematic because their typical use
would be surreptitious — making security testing difficult and less effective.
Third, exceptional access would create concentrated targets that could attract bad
actors. Security credentials that unlock the data would have to be retained by the platform
provider, law enforcement agencies, or some other trusted third party. If law enforcement’s
keys guaranteed access to everything, an attacker who gained access to these keys would
enjoy the same privilege. Moreover, law enforcement’s stated need for rapid access to data
would make it impractical to store keys offline or split keys among multiple keyholders,
as security engineers would normally do with extremely high-value credentials. Recent
attacks on the United States Government Office of Personnel Management (OPM) show
how much harm can arise when many organizations rely on a single institution that itself
has security vulnerabilities. In the case of OPM, numerous federal agencies lost sensitive
data because OPM had insecure infrastructure. If service providers implement exceptional
2

 access requirements incorrectly, the security of all of their users will be at risk.
Our analysis applies not just to systems providing access to encrypted data but also to
systems providing access directly to plaintext. For example, law enforcement has called
for social networks to allow automated, rapid access to their data. A law enforcement
backdoor into a social network is also a vulnerability open to attack and abuse. Indeed,
Google’s database of surveillance targets was surveilled by Chinese agents who hacked
into its systems, presumably for counterintelligence purposes [3].
The greatest impediment to exceptional access may be jurisdiction. Building in exceptional access would be risky enough even if only one law enforcement agency in the
world had it. But this is not only a US issue. The UK government promises legislation
this fall to compel communications service providers, including US-based corporations,
to grant access to UK law enforcement agencies, and other countries would certainly
follow suit. China has already intimated that it may require exceptional access. If a
British-based developer deploys a messaging application used by citizens of China, must
it provide exceptional access to Chinese law enforcement? Which countries have sufficient
respect for the rule of law to participate in an international exceptional access framework?
How would such determinations be made? How would timely approvals be given for the
millions of new products with communications capabilities? And how would this new
surveillance ecosystem be funded and supervised? The US and UK governments have
fought long and hard to keep the governance of the Internet open, in the face of demands
from authoritarian countries that it be brought under state control. Does not the push
for exceptional access represent a breathtaking policy reversal?
The need to grapple with these legal and policy concerns could move the Internet
overnight from its current open and entrepreneurial model to becoming a highly regulated
industry. Tackling these questions requires more than our technical expertise as computer
scientists, but they must be answered before anyone can embark on the technical design
of an exceptional access system.
In the body of this report, we seek to set the basis for the needed debate by presenting
the historical background to exceptional access, summarizing law enforcement demands
as we understand them, and then discussing them in the context of the two most popular
and rapidly growing types of platform: a messaging service and a personal electronic
device such as a smartphone or tablet. Finally, we set out in detail the questions for
which policymakers should require answers if the demand for exceptional access is to be
taken seriously. Absent a concrete technical proposal, and without adequate answers to
the questions raised in this report, legislators should reject out of hand any proposal to
return to the failed cryptography control policy of the 1990s.
3

 Contents
1 Background of today’s debate on exceptional access
1.1 Summary of the current debate . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Findings from the 1997 analysis of key escrow systems . . . . . . . . . . .
1.3 What has changed and what remains the same since 1990s? . . . . . . . .

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2 Scenarios
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2.1 Scenario 1: Providing exceptional access to globally distributed, encrypted
messaging applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 Scenario 2: Exceptional access to plaintext on encrypted devices such as
smartphones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3 Summary of risks from the two scenarios . . . . . . . . . . . . . . . . . . . 15
3 Security impact of common law enforcement requirements with
tional access
3.1 Access to communications content . . . . . . . . . . . . . . . . . . .
3.2 Access to communications data . . . . . . . . . . . . . . . . . . . .
3.3 Access to data at rest . . . . . . . . . . . . . . . . . . . . . . . . .
4 Principles at stake and unanswered questions
4.1 Scope, limitations, and freedoms . . . . . . . .
4.2 Planning and design . . . . . . . . . . . . . .
4.3 Deployment and operation . . . . . . . . . . .
4.4 Evaluation, assessment, and evolution . . . . .

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5 Conclusion

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6 Author Biographies

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7 Acknowledgments

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4

 1

Background of today’s debate on exceptional access

The encryption debate has been reopened in the last year with both FBI Director James
Comey and UK Prime Minister David Cameron warning, as in the early 1990s, that
encryption threatens law enforcement capabilities, and advocating that the providers of
services that use encryption be compelled by law to provide access to keys or to plaintext in
response to duly authorized warrants. We have therefore reconvened our expert group to
re-examine the impact of mandatory exceptional access in today’s Internet environment.1
In the 1990s, the governments of United States and a number of other industrialized
countries advocated weakening encryption. Claiming that widespread encryption would
be disastrous for law enforcement, the US government proposed the use of the Clipper
Chip, an encryption device that contained a government master key to give the government
access to encrypted communications. Other governments followed suit with proposals for
encryption licensing that would require copies of keys to be held in escrow by trusted third
parties — companies that would be trusted to hand over keys in response to warrants.
The debate engaged industry, NGOs, academia, and others. Most of the authors of the
present paper wrote a report on the issues raised by key escrow or trusted-third-party
encryption that analyzed the technical difficulties, the added risks, and the likely costs of
such an escrow system[1]. That push for key escrow was abandoned in 2000 because of
pressure from industry during the dotcom boom and because of political resistance from
the European Union, among others.

1.1

Summary of the current debate

The current public policy debate is hampered by the fact that law enforcement has not
provided a sufficiently complete statement of their requirements for technical experts or
lawmakers to analyze. The following exhortation from United States FBI Director James
Comey is as close as we come:
“We aren’t seeking a back-door approach. We want to use the front door,
with clarity and transparency, and with clear guidance provided by law. We
are completely comfortable with court orders and legal process — front doors
that provide the evidence and information we need to investigate crime and
1

We follow the 1996 National Academies CRISIS report in using the phrase “exceptional access”
to “stress that the situation is not one that was included within the intended bounds of the original
transaction.” [4, p. 80]

5

 prevent terrorist attacks.”
“Cyber adversaries will exploit any vulnerability they find. But it makes more
sense to address any security risks by developing intercept solutions during
the design phase, rather than resorting to a patchwork solution when law
enforcement comes knocking after the fact. And with sophisticated encryption,
there might be no solution, leaving the government at a dead end — all in the
name of privacy and network security.” [5]
Prime Minister David Cameron simply wants the police to have access to everything.
Speaking in the wake of the Charlie Hebdo murders in Paris, he said:
“In our country, do we want to allow a means of communication between
people which, even in extremis, with a signed warrant from the home secretary
personally, that we cannot read? . . . The question remains: are we going to
allow a means of communications where it simply is not possible to do that?
My answer to that question is: no, we must not.” [6]
So, we must ask, is it possible to build in such exceptional access without creating
unacceptable risk? In order to understand the technical and operational issues, we first
review the results of our 1997 report and consider what has changed since then. We next
try to clarify ideal law enforcement requirements and understand the kinds of risks that
are likely to arise if these generic requirements are imposed broadly in the global Internet
environment. Then, we present two technology scenarios typical of the landscape facing
modern electronic surveillance. Combining what is publicly known about surveillance
practices today, along with common legal requirements, we are able to present scenarios
that illustrate many of the key risks that exceptional access will entail.
We do not suggest that our own interpretation of Comey’s stated requirements serve
as a basis for regulation but merely as a starting point for discussion. If officials in the UK
or US disagree with our interpretation, we urge them to state their requirements clearly.
Only then can a rigorous technical analysis be conducted in an open, transparent manner.
Such analysis is crucial in a world that is so completely reliant on secure communications
for every aspect of daily lives, from nations’ critical infrastructure, to government, to
personal privacy in daily life, to all matters of business from the trivial to the global.

1.2

Findings from the 1997 analysis of key escrow systems

We begin by reviewing the findings on the risks of key recovery/key escrow systems from
a paper that many of us wrote almost 20 years ago[1]. Many of us came together then to
6

 examine the security risks of ensuring law enforcement access to encrypted information.
We found that any key escrow system had basic requirements that placed substantial
costs on end users, and that these costs would have been too difficult and expensive to
implement. For law enforcement to have quick and reliable access to plaintext, every key
escrow system required the existence of highly sensitive yet perennially available secret
keys. This requirement alone inevitably leads to an increased risk of exposure, inflated
software complexity, and high economic costs.
The first downside is increased risk of a security incident. An organization that holds
an escrow key could have a malicious insider that abuses its power or leaks that organization’s key. Even assuming an honest agency, there is an issue of competence: cyberattacks
on keyholders could easily result in catastrophic loss.
The additional complexity of a key escrow system compounds these risks. At the time,
all openly proposed key escrow solutions had major flaws that could be exploited; even
normal encryption was difficult to implement well, and key escrow made things much
harder. Another source of complexity was the scale of a universal key recovery system
— the number of agents, products, and users involved would be immense, requiring an
escrow system well beyond the technology of the time. Further, key escrow threatened
to increase operational complexity: a very large number of institutions would have to
securely and safely negotiate targeting, authentication, validity, and information transfer
for lawful information access.
All of the above factors raise costs. Risks of exposure, for instance, change the threat
landscape for organizations, which must then worry about mistaken or fraudulent disclosures. The government would have increased bureaucracy to test and approve key
recovery systems. Software vendors would have to bear the burden of increased engineering costs. In 1997, we found that systems enabling exceptional access to keys would be
inherently less secure, more expensive, and much more complex than those without. This
result helped policymakers decide against mandated exceptional access.

1.3

What has changed and what remains the same since 1990s?

It is impossible to operate the commercial Internet or other widely deployed global communications network with even modest security without the use of encryption. An extensive
debate in the 1980s and 1990s about the role of encryption came to this conclusion once
before. Today, the fundamental technical importance of strong cryptography and the difficulties inherent in limiting its use to meet law enforcement purposes remain the same.
What has changed is that the scale and scope of systems dependent on strong encryption
are far greater, and our society is far more reliant on far-flung digital networks that are
7

 under daily attack.
In the early 1990s, the commercialization of the Internet was being thwarted by US
government controls on encryption — controls that were in many ways counterproductive to long-term commercial and national security interests. A 1996 United States National Academy of Science study concluded that, “On balance, the advantages of more
widespread use of cryptography outweigh the disadvantages” [4, p. 6]. Four years later,
partly in response to pressures from industry, partly in response to the loosening of cryptographic export controls by the European Union, partly because crypto export controls
were declared unconstitutional by US Circuit Courts, and partly because of increasing
reliance on electronic communications and commerce, the US relaxed export controls on
encryption [7].
The Crypto Wars actually began in the 1970s, with conflicts over whether computer
companies such as IBM and Digital Equipment Corporation could export hardware and
software with strong encryption, and over whether academics could publish cryptographic
research freely. They continued through the 1980s over whether the NSA or the National
Institute of Standards and Technology (NIST) would control the development of cryptographic standards for the non-national security side of the government (NIST was given
the authority under the 1987 Computer Security Act). They came to full force during
the 1990s, when the US government, largely through the use of export controls, sought
to prevent companies such as Microsoft and Netscape from using strong cryptography in
web browsers and other software that was at the heart of the growing Internet. The end
of the wars — or the apparent end — came because of the Internet boom.
In many ways, the arguments are the same as two decades ago. US government
cryptographic standards — the Data Encryption Standard then, the Advanced Encryption Standard now — are widely used both domestically and abroad. We know more
now about how to build strong cryptosystems, though periodically we are surprised by a
break. However, the real security challenge is not the mathematics of cryptosystems; it
is engineering, specifically the design and implementation of complex software systems.
Two large government efforts, healthcare.gov and the FBI Trilogy program, demonstrate
the difficulties that scale and system integration pose in building large software systems.
Healthcare.gov, the website implementing the president’s signature healthcare program,
failed badly in its initial days, unable to serve more than a tiny percentage of users [8].
A decade earlier, five years of effort spent building an electronic case file system for the
FBI — an effort that cost $170 million — was abandoned as unworkable [9].
At one level, the worst has not come to pass — the power grid, the financial system,
critical infrastructure in general, and many other systems all function reliably using com8

 plex software. On another level, the worst is occurring daily. Recent breaches for financial
gain include: T.J. Maxx, theft of 45 million credit card records [10]; Heartland Payment
Systems, compromise of 100 million credit cards [11]; Target, compromise of 40 million
credit cards; Anthem, collection of names, addresses, birthdates, employment and income
information, and Social Security numbers of 80 million people that could result in identity
theft [12].
Attacks on government agencies are also increasing. A set of 2003 intrusions targeting
US military sites collected such sensitive data as specifications for Army helicopter mission
planning systems, Army and Air Force flight-planning software, and schematics for the
Mars Orbiter Lander [13]. Such theft has not only been from the defense industrial base,
but has included the pharmaceuticals, Internet, biotechnology and energy industries. In
2010, then Deputy Secretary of Defense William Lynn concluded, “Although the threat
to intellectual property is less dramatic than the threat to critical national infrastructure,
it may be the most significant cyberthreat that the United States will face over the long
term” [14].
The December 2014 North Korean cyberattacks against Sony, the first such by a
nation-state, resulted in large headlines. But the 2011 theft from RSA/EMC of the seed
keys — initial keys used to generate other keys — in hardware tokens used to provide
two-factor authentication [15], and the recent theft of personnel records from the US
Office of Personnel Management are far more serious issues. The former undermined the
technical infrastructure for secure systems, while the latter, by providing outsiders with
personal information of government users, creates leverage for many years to come for
potential insider attacks, undermining the social infrastructure needed to support secure
governmental systems — including any future system for exceptional access. And while
attacks against critical infrastructure have not been significant, the potential to do so has
been demonstrated in test cases [16] and in an actual attack on German steel mill that
caused significant damage to a blast furnace [17].
As exceptional access puts the security of Internet infrastructure at risk, the effects
will be felt every bit as much by government agencies as by the private sector. Because
of cost and Silicon Valley’s speed of innovation, beginning in the mid-1990s, the US government moved to a commercial off the shelf (COTS) strategy for information technology
equipment, including communications devices. In 2002, Information Assurance Technical
Director Richard George told a Black Hat audience that “NSA has a COTS strategy,
which is: when COTS products exist with the needed capabilities, we will encourage their
use whenever and wherever appropriate . . . ”[18]. Such a COTS solution makes sense, of
course, only if the private sector technologies the government uses are secure.
9

 Communications technologies designed to comply with government requirements for
backdoors for legal access have turned out to be insecure. For ten months in 2004 and
2005, 100 senior members of the Greek government (including the Prime Minister, the
head of the Ministry of National Defense and the head of the Ministry of Justice) were
wiretapped by unknown parties through lawful access built into a telephone switch owned
by Vodafone Greece [19]. In 2010 an IBM researcher observed that a Cisco architecture
for enabling lawful interception in IP networks was insecure.2 This architecture had
been public for several years, and insecure versions had been implemented by several
carriers in Europe [20]. And when the NSA examined telephone switches built to comply
with government-mandated access for wiretapping, it discovered security problems with
all the switches submitted for testing[21]. Embedding exceptional access requirements
into communications technology will ensure even more such problems, putting not only
private-sector systems, but government ones, at risk.
Speaking on the topic of law enforcement access and systems security, Vice Chairman
of the Joint Chiefs of Staff Admiral James A. Winnefeld recently remarked, “But I think
we would all win if our networks are more secure. And I think I would rather live on the
side of secure networks and a harder problem for Mike [NSA Director Mike Rogers] on the
intelligence side than very vulnerable networks and an easy problem for Mike and part of
that, it’s not only is the right thing to do, but part of that goes to the fact that we are
more vulnerable than any other country in the world, on our dependence on cyber. I’m
also very confident that Mike has some very clever people working for him, who might
actually still be able to get some good work done.”
While the debate over mandated law enforcement access is not new, it does take on
added urgency in today’s world. Given our growing dependence on the Internet, and the
urgent need to make this and other digital infrastructures more secure, any move in the
direction of decreased security should be looked upon with extreme skepticism. Once
before, when considering this issue, governments around the world came to the conclusion
that designing in exceptional access provisions to vital systems would increase security
risk and thwart innovation. As the remainder of this paper will show, such measures are
even riskier today.
2

It is worth noting that the router’s design was based on standards put forth by the European Telecommunications Standards Institute.

10

 2

Scenarios

Law enforcement authorities have stated a very broad requirement for exceptional access.
Yet there are many details lacking including the range of systems to which such requirements would apply, the extraterritorial application, whether anonymous communications
would be allowed, and many other variables. To analyze the range of security risks that
may arise in commonly used applications and services, we examine two popular scenarios:
encrypted real-time messaging services and devices such as smartphones that use strong
encryption to lock access to the device.

2.1

Scenario 1: Providing exceptional access to globally distributed, encrypted messaging applications

Imagine a massively distributed global messaging application on the Internet currently
using end-to-end encryption. Many examples of such systems actually exist, including
Signal, which is available on iPhone and Android, Off-the-Record (OTR), a cryptographyenabling plug-in for many popular computer chat programs, and the often cited TextSecure and WhatsApp. Could one provide a secure application while meeting law enforcement exceptional access requirements?
To provide law enforcement access to encrypted data, one natural approach is to
provide law enforcement direct access to keys that can be used to decrypt the data, and
there is a frequently suggested and seemingly quite attractive mechanism for escrowing
decryption keys. Data is typically encrypted — either for storage or transmission —
with a symmetric key,3 and many data transmission protocols (e.g., the Transport Layer
Security (TLS) protocol) can operate in a mode where the data to be sent is encrypted
with a symmetric key that is in turn encrypted with a public key4 associated with the
intended recipient. This encrypted symmetric key then travels with the encrypted data,
and the recipient accesses the data by first using its private key to decrypt the symmetric
key and then using the symmetric key to decrypt the data.
A common suggestion is to augment this approach by encrypting the symmetric key
a second time — this time with a special escrowing public key. If the data is then
transmitted, two encryptions of the symmetric key accompany the data — one with the
public key of the intended recipient and one with a public key associated with an escrow
agent. If the data has been encrypted with a symmetric key for storage rather than
3

A symmetric key is one that is used for both encryption and decryption.
A public key is used to encrypt data that can then be decrypted only by an entity in possession of
an associated private key.
4

11

 transmission, the symmetric key might be encrypted with the public key of an escrow
agent and this escrowed key could remain with the encrypted data. If a law enforcement
entity obtains this encrypted data either during transmission or from storage the escrow
agent could be enlisted to decrypt the symmetric key, which could then be used to decrypt
the data.
There are, however, three principal impediments to using this approach for third-party
escrow. Two are technical and the third is procedural.
The first technical obstacle is that although the mode of encrypting a symmetric key
with a public key is in common use, companies are aggressively moving away from it
because of a significant practical vulnerability: if an entity’s private key is ever breached,
all data ever secured with this public key is immediately compromised. Because it is unwise
to assume a network will never be breached, a single failure should never compromise all
data that was ever encrypted.
Thus, companies are moving towards forward secrecy, an approach that greatly reduces
the exposure of an entity that has been compromised. With forward secrecy, a new key
is negotiated with each transaction, and long-term keys are used only for authentication.
These transaction (or session) keys are discarded after each transaction — leaving much
less for an attacker to work with. When a system with forward secrecy is used, an attacker
who breaches a network and gains access to keys can only decrypt data from the time of the
breach until the breach is discovered and rectified; historic data remains safe. In addition,
since session keys are destroyed immediately after the completion of each transaction, an
attacker must interject itself into the process of each transaction in real time to obtain
the keys and compromise the data.5
The security benefits make clear why companies are rapidly switching to systems that
provide forward secrecy.6 However, the requirement of key escrow creates a long-term
vulnerability: if any of the private escrowing keys are ever compromised, then all data
that ever made use of the compromised key is permanently compromised. That is, in
order to accommodate the need for surreptitious, third-party access by law enforcement
agencies, messages will have to be left open to attack by anyone who can obtain a copy of
one of the many copies of the law enforcement keys. Thus all known methods of achieving
third-party escrow are incompatible with forward secrecy.
Innovations providing better forward secrecy also support a broad social trend: users
are moving en masse to more ephemeral communications. Reasons for moving to ephemeral
communications range from practical decisions by corporations to protect proprietary in5

Lack of forward secrecy was identified in the 1997 paper [1] as a weakness of key escrow systems then.
Since that time, the need for forward secrecy has grown substantially.
6
See [22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32].

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 formation from industrial espionage to individuals seeking to protect their ability to communicate anonymously and avoid attack by repressive governments. Many corporations
delete email after 90 days, while individuals are moving from email to chat and using
services like Snapchat where messages vanish after reading. Leading companies such as
Twitter, Microsoft, and Facebook are supporting the move to transient messaging, and
using modern security mechanisms to support it. This social and technical development
is not compatible with retaining the means to provide exceptional access.
The second technical obstacle is that current best practice is often to use authenticated
encryption, which provides authentication (ensuring that the entity at the other end of
the communication is who you expect, and that the message has not been modified since
being sent) as well as confidentiality (protecting the privacy of communications, including
financial, medical, and other personal data). However, disclosure of the key for authenticated encryption to a third party means the message recipient is no longer provided
with technical assurance of the communication’s integrity; disclosure of the key allows the
third party not only to read the encrypted traffic but also to forge traffic to the recipient
and make it look as if it is coming from the original sender. Thus disclosing the key to a
third party creates a new security vulnerability. Going back to the encryption methods
of the 1990s, with separate keys for encryption and authentication, would not only double the computational effort required, but introduce many opportunities for design and
implementation errors that would cause vulnerabilities.
The third principal obstacle to third-party key escrow is procedural and comes down
to a simple question: who would control the escrowed keys? Within the US, one could
postulate that the FBI or some other designated federal entity would hold the private key
necessary to obtain access to data and that judicial mechanisms would be constructed
to enable its use by the plethora of federal, state, and local law enforcement entities.
However, this leaves unanswered the question of what happens outside a nation’s borders.
Would German and French public- and private-sector organizations be willing to use
systems that gave the US government access to their data — especially when they could
instead use locally built systems that do not? What about Russia? Would encrypted data
transmitted between the US and China need to have keys escrowed by both governments?
Could a single escrow agent be found that would be acceptable to both governments? If
so, would access be granted to just one of the two governments or would both need to
agree to a request?
These difficult questions must be answered before any system of exceptional access can
be implemented. Such an architecture would require global agreements on how escrow
would be structured, often against the best interests of certain countries’ domestic goals,
13

 together with mandates in virtually all nations to only sell and use compliant systems.

2.2

Scenario 2: Exceptional access to plaintext on encrypted
devices such as smartphones

Imagine a smartphone platform vendor that seeks to accommodate law enforcement exceptional demands. When law enforcement comes into possession of a device, perhaps at
a crime scene, and then obtains the necessary legal authorization (in the US this would
be a warrant as a result of Riley v. California), the agent collects a unique identifying
number from the device through some service mechanism, and then sends a request to
the platform vendor to unlock the device remotely or provide the keys necessary for law
enforcement to unlock the device locally.
At first glance, providing access to plaintext on devices — laptop hard drives, smartphones, tablets — is straightforward. Indeed, many corporations already escrow device
encryption keys. However, and as is frequently the case, scaling up a corporate mechanism
to a global one is hard.
When encrypting device storage, the user-entered passphrase is generally not used directly as an encryption key. There are many reasons for this; from a usability perspective,
the most important one is to make it easier for the user to change the passphrase. If the
key were used directly, it would be a time-consuming process to decrypt and re-encrypt
the entire device when the passphrase is changed. Instead, a random key is used for bulk
encryption; the user-supplied key (called the Key-Encrypting Key, or KEK) is used to
encrypt the random key.
To protect against brute-force attacks against the user’s passphrase, the device vendor
may go a step further and combine it with a device-specific unique identifier to produce
the KEK. In the iPhone, the KEK is stored in a special tamper-resistant processor that
limits the guess rate to once every 80 milliseconds. This protects device owners against,
for example, sophisticated thieves who might try to gain access to things like banking
passwords. But regardless of how the KEK is generated, obtaining access to the plaintext
requires that the device-encrypting key be encrypted under some additional key or keys.
These could be manufacturer-owned keys or keys belonging to one or more law enforcement
agencies. Either choice is problematic[33].
If a vendor-supplied key is used, some sort of network protocol to decrypt the device
key is necessary. This request must be authenticated, but how? How can the vendor
have secure credentials for all of the thousands of law enforcement agencies around the
world? How can the result be strongly bound to the device, to prevent unscrupulous
agencies from requesting keys to devices not in their lawful possession? These are not
14

 easy requirements to meet, especially for devices that will not even boot without a valid
key. They are likely to require changes to security hardware or to the software that drives
it; both are difficult to do properly. Fixing glitches — especially security glitches — in
deployed hardware is expensive and often infeasible.
Providing devices with law enforcement keys is equally difficult. Again, how can the
vendor know who supplied the keys? How are these keys to be changed? 7 How many
keys can be installed without causing unacceptable slowdowns? Another alternative is
to require that law enforcement ship devices back to the vendor for exceptional access
decryption. However, it will still be necessary to store over long periods of time keys that
can decrypt all of the sensitive data on devices. This only shifts the risks of protecting
these keys to the device manufacturers.
Some would argue that per-country keys could be a sales requirement. That is, all
devices sold within the US would be required to have, say, a preinstalled FBI-supplied
key. That, however, does not suffice for devices brought in by travelers — and those
are the devices likely to be of interest in terrorism investigations. A requirement that
keys be installed at the border is also problematic. There are no standard input ports
or key-loading mechanisms; furthermore, it would expose American travelers to malware
installed by border guards in other countries [34, 35].

2.3

Summary of risks from the two scenarios

Designing exceptional access into today’s information services and applications will give
rise to a range of critical security risks. First, major efforts that the industry is making
to improve security will be undermined and reversed. Providing access over any period
of time to thousands of law enforcement agencies will necessarily increase the risk that
intruders will hijack the exceptional access mechanisms. If law enforcement needs to look
backwards at encrypted data for one year, then one year’s worth of data will be put at
risk. If law enforcement wants to assure itself real time access to communications streams,
then intruders will have an easier time getting access in real time, too. This is a trade-off
space in which law enforcement cannot be guaranteed access without creating serious risk
that criminal intruders will gain the same access.
Second, the challenge of guaranteeing access to multiple law enforcement agencies in
multiple countries is enormously complex. It is likely to be prohibitively expensive and
also an intractable foreign affairs problem.
Simple requirements can yield simple solutions (e.g. a door lock). But the requirements
7

We note that some pieces of malware, such as Stuxnet and Duqu 2, have relied on code-signing keys
issued to legitimate companies. When a key is compromised, it must be replaced.

15

 of law enforcement access to encrypted data are inherently complex and, as we have
already shown, nearly contradictory. Complex or nearly contradictory requirements yield
brittle, often-insecure solutions. As NSA’s former head of research testified in 2013:
“When it comes to security, complexity is not your friend. Indeed it has been
said that complexity is the enemy of security. This is a point that has been
made often about cybersecurity in a variety of contexts including, technology,
coding and policy. The basic idea is simple: as software systems grow more
complex, they will contain more flaws and these flaws will be exploited by
cyber adversaries.” [36]
We have a very real illustration of the problem of complexity in a recent analysis of
one of the most important security systems on the Internet: SSL/TLS. Transport Layer
Security (TLS) and its predecessor Secure Socket Layer (SSL) are the mechanisms by
which the majority of the web encrypts its traffic — every time a user logs into a bank
account, makes an electronic purchase, or communicates over a social network, that user is
trusting SSL/TLS to function properly. All a user needs to know of all of this complexity
is that the lock or key icon shows up in the browser window. This indicates that the
communication between the user and the remote website is secure from interception.
Unfortunately, writing code that correctly implements such cryptographic protocols
has proven difficult; weakened protections makes it harder still. For instance, OpenSSL,
the software used by about two-thirds of websites to do TLS encryption, has been plagued
with systems-level bugs resulting in catastrophic vulnerabilities. The now-infamous Heartbleed bug was caused by a missing bounds check, an elementary programming error that
lurked in the code for two years, leaving 17% of all websites vulnerable to data theft.
More recent vulnerabilities, however, were caused by legacy restrictions on the exportation of cryptographic algorithms, dating back to the Crypto Wars. The fact that there
are so many different implementations of TLS, all of which have to interoperate to make
the Web secure, has proven to be a real source of security risk [37]. Website operators
are reluctant to switch to more secure protocols if this will lose them even a few percent
of prospective customers who are still using old software, so vulnerabilities introduced
deliberately during the Crypto Wars have persisted to this day. Introducing complex new
exceptional access requirements will similarly add more security bugs that will lurk in our
software infrastructure for decades to come.
Third, there are broader risks for poorly deployed surveillance technology. Exceptional
access mechanisms designed for law enforcement use have been exploited by hostile actors
in the past. Between 1996 and 2006, it appears that insiders at Telecom Italia enabled the
16

 wiretapping of 6,000 people, including business, financial, and political leaders, judges,
and journalists [38]. In a country of 60 million, this means that no major business or
political deal was truly private. The motivation here appeared to be money, including the
possibility of blackmail. As we mentioned earlier, from 2004 to 2005, the cell phones of 100
senior members of the Greek government, including the Prime Minister, the head of the
Ministry of National Defense, the head of the Ministry of Justice, and others. Vodafone
Greece had purchased a telephone switch from Ericsson. The Greek phone company had
not purchased wiretapping capabilities, but these were added during a switch upgrade
in 2003. Because Vodafone Greece had not arranged for interception capabilities, the
company did not have the ability to access related features, such as auditing. Nevertheless,
someone acting without legal authorization was able to activate the intercept features and
keep them running for ten months without being detected. The surveillance was uncovered
only when some text messages went awry. Although the techniques of how it was done
are understood, who was behind the surveillance remains unknown[19].
Next, there are the broader costs to the economy. Economic growth comes largely
from innovation in science, technology, and business processes. At present, technological progress is largely about embedding intelligence — software and communications —
everywhere. Products and services that used to be standalone now come with a mobile
phone app, an online web service, and business models that involve either ads or a subscription. Increasingly these are also “social”, so you can chat to your friends and draw
them into the vendor’s marketing web. Countries that require these new apps and web
services to have their user-to-user communications functions authorized by the government will be at a significant disadvantage. At present, the world largely uses US apps
and services, rather than the government-approved ones from Russia and China. This
provides enormous leverage to US businesses.
Finally, this market advantage gives real benefits not just economically but in terms
of soft power and moral leadership. The open Internet has long been a foreign policy goal
of the US and its allies for a lot of good reasons. The West’s credibility on this issue was
damaged by the Snowden revelations, but can and must recover. Lawmakers should not
risk the real economic, geopolitical, and strategic benefits of an open and secure Internet
for law enforcement gains that are at best minor and tactical.

17

 3

Security impact of common law enforcement requirements with exceptional access

Since there is no specific statement of law enforcement requirements for exceptional access, we consider what we understand to be a very general set of electronic surveillance
needs applicable in multiple jurisdictions around the world. Our goal here is to understand the general nature of security risks associated with the application of exceptional
access requirements in the context of traditional categories of electronic surveillance. Law
enforcement agencies in different countries have presented different requirements at different times, which we will treat under four headings: access to communications content,
access to communications data, access to content at rest, and covert endpoint access.
All types of access must be controlled and capable of being audited according to local
legal requirements; for example, under the requirements of US law, one must respect the
security and privacy of non-targeted communications.8

3.1

Access to communications content

Most police forces are permitted to access suspect data. In countries with respect for the
rule of law, such access is carefully regulated by statute and supervised by an independent
judiciary, though most of the world’s population do not enjoy such legal protections. Law
enforcement access might be to a central database of unencrypted messages where this
exists at a central provider. Where there is no central database, such as for a telephone
or video call, the police must tap the communication as it happens. How might an
exceptional access requirement be implemented to enable for access to communications
content? If the data is encrypted, the most obvious mechanism to allow for police access
would require that traffic between Alice in country X and Bob in country Y would have
its session key also encrypted under the public keys of the police forces in both X and Y,
or of third parties trusted by them. This, however, raises serious issues.
First, any escrow requirement will restrict other important security functionality such
as forward secrecy, the use of transient identities, and strong location privacy. As illustrated in the scenario analysis above, an exceptional access requirement overlaid on the
traditional content surveillance will put the security of the content at risk. To the extent
that capabilities exist to provide law enforcement exceptional access, they can be abused
by others.
Second, the global nature of Internet services makes compliance with exceptional access
8

In the USA, 47 USC 1002(a)(4)

18

 rules both hard to define and hard to enforce. If software sold in country X will copy
all keys to that country’s government, criminals might simply buy their software from
countries that don’t cooperate; thus, US crooks might buy their software from Russia.
And if software automatically chooses which governments to copy using a technique such
as IP geolocation, how does one prevent attacks based on location spoofing? While it
is possible to design mobile phone systems so that the host jurisdictions have access to
the traffic (so long as the users do not resort to VoIP), this is a much harder task for
general-purpose messaging applications.
Third, one might have to detect or deter firms that do not provide exceptional access,
leading to issues around certification and enforcement. For example, if the US or the
UK were to forbid the use of messaging apps that are not certified under a new escrow
law, will such apps be blocked at the national firewall? Will Tor then be blocked, as in
China? Or will it simply become a crime to use such software? And what is the effect on
innovation if every new communications product must go through government-supervised
evaluation against some new key escrow protection profile?

3.2

Access to communications data

Communications data traditionally meant call detail records and (since mobile phones
became common) caller location history; it was obtained by subpoena from phone companies, and is used in the investigation of most serious violent crimes such as murder, rape,
and robbery. Communications data remains widely available as service providers keep it
for some time for internal purposes. However, police forces outside the US complain that
the move to globalized messaging services makes a lot of data harder to obtain. For example, emails are now typically encrypted using TLS; that is, the message is encrypted
between the user’s computer and the service provider (e.g., Google for Gmail, Microsoft
for Hotmail, etc.). Thus, to acquire the communications in plaintext, law enforcement
must serve the email provider with a court order. A new UK surveillance law may require message service firms like Apple, Google, and Microsoft to honor such requests
expeditiously and directly as a condition of doing business in the UK. So will there be
uniform provisions for access to communications data subject to provisions for warrants
or subpoenas, transparency, and jurisdiction?
As already noted, determining location is not trivial, and cheating (using foreign
software, VPNs, and other proxies) could be easy. Criminals would turn to noncompliant
messaging apps, raising issues of enforcement; aggressive enforcement might impose real
costs on innovation and on industry generally.

19

 3.3

Access to data at rest

Communications data are one instance of the general problem of access to data at rest.
Almost all countries allow their police forces access to data. Where basic rule of law
is in place, access is under the authority of a legal instrument such as a warrant or
subpoena, subject to certain limits. Many corporations already insist on escrowing keys
used to protect corporate data at rest (such as BitLocker on corporate laptops). So this
is one field with an already deployed escrow “solution”: a fraud investigator wanting
access to a London rogue trader’s laptop can simply get a law enforcement officer to
serve a decryption notice on the bank’s CEO. But still, many of the same problems
arise. Suspects may use encryption software that does not have escrow capability, or may
fail to escrow the key properly, or may claim they have forgotten the password, or may
actually have forgotten it. The escrow authority may be in another jurisdiction, or may
be a counterparty in litigation. In other words, what works tolerably well for corporate
purposes or in a reasonably well-regulated industry in a single jurisdiction simply does
not scale to a global ecosystem of highly diverse technologies, services, and legal systems.
Another thorny case of access to data at rest arises when the data is only present on,
or accessible via, a suspect’s personal laptop, tablet, or mobile phone. At present, police
officers who want to catch a suspect using Tor services may have to arrest him while his
laptop is open and a session is live. Law enforcement agencies in some countries can get a
warrant to install malware on a suspect’s computer. Such agencies would prefer antivirus
companies not to detect their malware; some might even want the vendors to help them,
perhaps via a warrant to install an upgrade with a remote monitoring tool on a device
with a specific serial number. The same issues arise with this kind of exceptional access,
along with the issues familiar from covert police access to a suspect’s home to conduct
a surreptitious search or plant a listening device. Such exceptional access would gravely
undermine trust and would be resisted vigorously by vendors.

4

Principles at stake and unanswered questions

With people’s lives and liberties increasingly online, the question of whether to support law
enforcement demands for guaranteed access to private information has a special urgency,
and must be evaluated with clarity. From a public policy perspective, there is an argument
for giving law enforcement the best possible tools to investigate crime, subject to due
process and the rule of law. But a careful scientific analysis of the likely impact of such
demands must distinguish what might be desirable from what is technically possible.
In this regard, a proposal to regulate encryption and guarantee law enforcement access
20

 centrally feels rather like a proposal to require that all airplanes can be controlled from
the ground. While this might be desirable in the case of a hijacking or a suicidal pilot, a
clear-eyed assessment of how one could design such a capability reveals enormous technical
and operational complexity, international scope, large costs, and massive risks — so much
so that such proposals, though occasionally made, are not really taken seriously.
We have shown that current law enforcement demands for exceptional access would
likely entail very substantial security risks, engineering costs, and collateral damage. If
policy-makers believe it is still necessary to consider exceptional access mandates, there
are technical, operational, and legal questions that must be answered in detail before
legislation is drafted. From our analysis of the two scenarios and general law enforcement
access requirements presented earlier in the paper, we offer this set of questions.

4.1

Scope, limitations, and freedoms

The first set of questions that an exceptional access proposal must address concerns the
scope of applicability of the exceptional access requirement, any limitations on the mandate, and what user freedoms would remain protected under such proposals. Questions
such as these arise in this category:
1. Are all systems that use encryption covered, or just some? Which ones?
2. Do all online communications and information platforms have to provide access to
plain text, or merely provide keys to agencies that had already collected ciphertext
using technical means?
3. Would individuals, corporations, nonprofit institutions, or governments be allowed
to deploy additional encryption services on top of those systems with exceptional
access? Would those user-installed systems also have to meet exceptional access
requirements?
4. Would machine-to-machine systems be covered? What about Internet of Things
and industrial control (SCADA) systems? Much information exchange is from one
machine to another, such as communicating personal health data from a sensor to
a smartphone, field-based agricultural sensing devices to tractors, or load balancing
controls in electric power, gas, oil and water distribution systems.
5. How would cross-border regulatory differences be resolved? Would technology developers have to meet different exceptional access requirements in each jurisdiction
where their systems are used? Or would there be a globally harmonized set of
regulatory requirements?
21

 6. How can the technical design of an exceptional access system prevent mass surveillance that would covertly violate the rights of entire populations, while still allowing
covert targeted surveillance of small numbers of suspects as an actual ”exception”
to a general rule of citizen privacy?
7. Would there be an exception for research and teaching?
8. Could companies refuse to comply with exceptional access rules based on a fear of
violating human rights?
9. Would anonymous communications, widely recognized as vital to democratic societies, be allowed?

4.2

Planning and design

Designing the technology and planning the administrative procedures that would be
needed to implement a comprehensive exceptional access system raises many questions:
1. What are the target cost and benefit estimates for such a program? No system is
cost-free and this one could be very expensive, especially if it has to accommodate
a large number of providers, such as today’s millions of app developers.
2. What security and reliability measures would be established for the design? How
would system prototypes be tested? How long would companies have to comply
with exceptional access rules?
3. How would existing services and products be treated if they do not comply with
exceptional access rules? Would providers have to redesign their systems? What if
those systems cannot accommodate exceptional access requirements?
4. Who would be involved in the design of the systems and procedures — just the US
government, or would other governments be invited to participate? Could foreign
technology providers such as Huawei participate in the design discussions?
5. Would the technical details of the program be made public and open for technical
review? What level of assurance would be provided for the design?
6. We note that it generally takes many years after a cryptographic protocol is published before it is deemed secure enough for actual use. For example, the NeedhamSchroeder public-key protocol, first published in 1978 [39], was discovered to have
security flaw only in 1995 by Gavin Lowe (17 later!) [40].
22

 4.3

Deployment and operation

Once regulations are established and technical design parameters set, there would remain
questions about how systems would be deployed, who would supervise and regulate compliance, and how the design of the system would evolve to address inevitable technical
and operational bugs that emerge. We know of no system that is designed perfectly the
first time, and it is well understood that maintenance, support, and evolution of existing
systems constitutes a major expense.
1. Who would supervise compliance? Would an existing regulatory agency such as
the FCC be given jurisdiction over the entire process? How would other countries
regulate US domestic and foreign services? Would there be a global harmonization
of rules regulation and enforcement? Would the International Telecommunications
Union have a role in setting and enforcing requirements?
2. Would global technical standards be required? How would these be developed and
enforced? How would be such standards be changed/improved/patched? Would traditional standards bodies such as the UN International Telecommunications Union
T-sector or ISO set standards, or would the world look to Internet standards bodies
such as the IETF and the World Wide Web Consortium? How would the world
converge on one set of standards?
3. Would the US government provide reference software libraries implementing the
desired functionality?
4. Would programs and apps need to be certified before they were allowed to be sold?
Who would test or certify that programs produced operate as intended?
5. Who would be liable if the plaintext-disclosure mechanisms were buggy (either in
design or in implementation), causing the disclosure of all citizens’ information?
More generally, what would happen when (not if) critical secret information was
revealed, such as the private keys that allow encrypted data to be read by anyone,
that destroyed the privileged position of law enforcement?
6. How many companies would withdraw all but local sales staff from markets where
exceptional access was mandated in ways that clashed with their business strategies
or the rights of users in other countries, as Google already has done from China and
Russia?

23

 4.4

Evaluation, assessment, and evolution

Large systems exist because successful systems evolve and grow. Typically, this evolution
happens through interaction guided by the institution (software company, government
agency, or open-source community) responsible for the system. A system that evolves
subject to a set of constraints, such as medical systems that need to maintain a safety case
or flight control systems that need to maintain not just a safety case but also need to meet
real-time performance requirements, evolve less quickly and at more cost. If all systems
that communicate must in future evolve subject to an exceptional access constraint, there
will be real costs, which are hard to quantify, since the question of who exactly would
be responsible for establishing and policing the exceptional access constraint is not clear.
However that question is answered, the following further issues will arise.
1. What oversight program would be required to monitor the effectiveness, cost, benefits, and abuse of exceptional access?
2. What sunset provisions would be build into legislation for such a program? What
conditions would be in place for its termination (e.g., for lack of sufficient benefit,
for excessive cost, or for excessive abuse)?
3. One unintended consequence of such a program may be a much-reduced use of crypto
altogether. This would further weaken our already fragile and insecure information
infrastructure, so how do we incentivize companies to continue encrypting sensitive
user communications?
4. A further unintended consequence of such a program might be to make the US and
other participating countries less welcoming to technological innovation; diminishing
or displacing innovation may have consequences for economic growth and national
security. How will these economic impacts be assessed before an exceptional access
program is mandated? Further, what economic effect would be considered too
impactful for exceptional access to be considered worthwhile?

5

Conclusion

Even as citizens need law enforcement to protect themselves in the digital world, all
policy-makers, companies, researchers, individuals, and law enforcement have an obligation to work to make our global information infrastructure more secure, trustworthy, and
resilient. This report’s analysis of law enforcement demands for exceptional access to
private communications and data shows that such access will open doors through which
24

 criminals and malicious nation-states can attack the very individuals law enforcement
seeks to defend. The costs would be substantial, the damage to innovation severe, and
the consequences to economic growth difficult to predict. The costs to developed countries’ soft power and to our moral authority would also be considerable. Policy-makers
need to be clear-eyed in evaluating the likely costs and benefits. It is no surprise that this
report has ended with more questions than answers, as the requirements for exceptional
access are still vague. If law enforcement wishes to prioritize exceptional access, we suggest that they need to provide evidence to document their requirements and then develop
genuine, detailed specifications for what they expect exceptional access mechanisms to
do. As computer scientists and security experts, we are committed to remaining engaged
in the dialogue with all parts of our governments, to help discern the best path through
these complex questions.

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 6

Author Biographies

Harold “Hal” Abelson is a Professor of Electrical Engineering and Computer Science at
MIT, a fellow of the IEEE, and a founding director of both Creative Commons and the
Free Software Foundation.
Ross Anderson is Professor of Security Engineering at the University of Cambridge.
Steven M. Bellovin is the Percy K. and Vida L.W. Hudson Professor of Computer Science
at Columbia University.
Josh Benaloh is Senior Cryptographer at Microsoft Research where his research focuses
on verifiable election protocols and related technologies
Matt Blaze is Associate Professor of Computer and Information Science at the University
of Pennsylvania where he directs the Distributed Systems Lab.
Whitfield “Whit” Diffie is an American cryptographer whose 1975 discovery of the concept
of public-key cryptography opened up the possibility of secure, Internet-scale communications.
John Gilmore is an entrepreneur and civil libertarian. He was an early employee of Sun
Microsystems, and co-founded Cygnus Solutions, the Electronic Frontier Foundation, the
Cypherpunks, and the Internet’s alt newsgroups.
Matthew Green is a Research Professor at the Johns Hopkins University Information Security Institute. His research focus is on cryptographic techniques for maintaining users’
privacy, and on new techniques for deploying secure messaging protocols.
Peter G. Neumann, Senior Principal Scientist at the SRI International Computer Science
Lab, and moderator of the ACM Risks Forum for thirty years.
Susan Landau is a professor of cybersecurity policy at Worcester Polytechnic Institute.
She is the author of Surveillance or Security? The Risks Posed by New Wiretapping Technologies (MIT Press, 2011) and co-author, with Whitfield Diffie, of Privacy on the Line:
The Politics of Wiretapping and Encryption (MIT Press, 1998).

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 Ronald L. Rivest is an MIT Institute Professor, and well known for his co-invention of
the RSA public-key cryptosystem, as well for founding RSA Security and Verisign.
Jeffrey I. Schiller was the Internet Engineering Steering Group Area Director for Security
(1994–2003).
Bruce Schneier is a security technologist, author, Fellow at the Berkman Center for Internet and Society at Harvard Law School, and the CTO of Resilient Systems, Inc. He has
written a number of books, including Data and Goliath: The Hidden Battles to Collect
Your Data and Control Your World (Norton, 2015).
Michael A. Specter is a security researcher and PhD candidate in Computer Science at
MIT’s Computer Science and Artificial Intelligence Laboratory.
Daniel J. Weitzner is Principal Research Scientist at the MIT Computer Science and
Artificial Intelligence Lab and Founding Director, MIT Cybersecurity and Internet Policy
Research Initiative. From 2011–2012, he was United States Deputy Chief Technology
Officer in the White House.

7

Acknowledgments

The authors thank several individuals who were extremely helpful in the production of
this report. Alan Davidson was instrumental in the early discussions that led to this
report while he was Vice President and Director of the Open Technology Institute at the
New America Foundation. Beth Friedman, Technical Communicator at Resilient Systems,
provided invaluable editing support. The MIT Cybersecurity and Internet Policy Research
Initiative helped with convening the authors and producing the final version of the report.

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