Internet DRAFT - draft-arkko-dns-confidential
draft-arkko-dns-confidential
Network Working Group J. Arkko
Internet-Draft J. Novotny
Intended status: Informational Ericsson
Expires: 3 January 2022 2 July 2021
Privacy Improvements for DNS Resolution with Confidential Computing
draft-arkko-dns-confidential-02
Abstract
Data leaks are a serious privacy problem for Internet users. Data in
flight and at rest can be protected with traditional communications
security and data encryption. Protecting data in use is more
difficult. In addition, failure to protect data in use can lead to
disclosing session or encryption keys needed for protecting data in
flight or at rest.
This document discusses the use of Confidential Computing, to reduce
the risk of leaks from data in use. Our example use case is in the
context of DNS resolution services. The document looks at the
operational implications of running services in a way that even the
owner of the service or compute platform cannot access user-specific
information produced by the resolution process.
Status of This Memo
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This Internet-Draft will expire on 3 January 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Prerequisities . . . . . . . . . . . . . . . . . . . . . . . 5
5. Confidential Computing . . . . . . . . . . . . . . . . . . . 6
6. Using Confidential Computing for DNS Resolution . . . . . . . 7
7. Operational Considerations . . . . . . . . . . . . . . . . . 9
7.1. Operations . . . . . . . . . . . . . . . . . . . . . . . 9
7.2. Debugging . . . . . . . . . . . . . . . . . . . . . . . . 11
7.3. Dependencies . . . . . . . . . . . . . . . . . . . . . . 11
7.4. Additional services . . . . . . . . . . . . . . . . . . . 12
7.5. Performance . . . . . . . . . . . . . . . . . . . . . . . 12
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8.1. Observations from outside the TEE . . . . . . . . . . . . 13
8.2. Trust Relationships . . . . . . . . . . . . . . . . . . . 13
8.3. Denial-of-Service Attacks . . . . . . . . . . . . . . . . 14
8.4. Other vulnerabilities . . . . . . . . . . . . . . . . . . 15
9. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 16
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
DNS privacy has been a popular topic in the last few years, and
continues to be. The issues with regards to privacy are first that
domain name meta-data is visible on the wire, even when the actual
communications are encryped. This is being addressed with better
technology.
But even if the meta-data is hidden inside communications, any DNS
resolvers still have the potential too see users' entire browsing
history. This is particularly problematic, given that commonly used
large public or operator resolver services are an obviously
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attractive target, for both attacks and for commercial or other use
of information visible to them.
A lot of work is ongoing in the industry and the IETF to address some
of these issues:
* Work on encrypted DNS query protocols to hide the meta-data
related to domain names.
* Discovery mechanisms. These may enable a bigger fraction of DNS
query traffic to move to encrypted protocols, and may also help
distributed queries to different parties to avoid concentrating
all information in one place.
* Practices, expectations, contracts (e.g., [RFC8932], Mozilla's
trusted recursive resolver requirements [MozTRR])
* Improvements outside DNS (e.g., encrypted Server Name Indication
(eSNI) [I-D.ietf-tls-esni]).
* General technology developments (e.g., confidential computing,
attestations, remote attestation work at the IETF RATS WG, and so
on)
The goal of this document is to build on all that work - and assume
all communications are or become encrypted, including the DNS
traffic. Our question is what problems remain? Is there a next
step?
Our worry is that resolvers can be a major remaining source of leaks,
e.g., through accidents, attacks, commercial use, or requests from
the authorities. We need to protect user's data in flight, at rest,
or in use - we wanted to experiment with technology that could reduce
leaks on the last two cases. Confidential Computing is one such
potential technology, but it is important to talk about it and get
broader feedback. The use of this technology does have some
operational impacts.
Our primary conclusions are that data held by servers should receive
at least as much security attention as communications do. The
authors feel that this is particularly crucial for DNS, due to the
potential to leak of users' browsing histories, but principles apply
also to other services.
As a result, all applicable tools should be considered, including
confidential computing that is discussed in this document. However,
the operational and business implications of such tools should be
considered. Feedback to us is very welcome. Are these approaches
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feasible or infeasible? What aspects need to be taken into account
to successfully apply them?
2. Background
Communications security has been at the center of many security
improvements in the Internet. The goal has been to ensure that
communications are protected against outside observers and attackers
[RFC3552] [RFC7258]. Communications security is, however, not
sufficient by itself, and continuing success in better protection of
communications is highlighting the need to address other issues.
In particular, more attention needs to be paid to protecting data not
just in flight but also at rest or in use. User data leaks that can
occur from servers and other systems, through accidents, attacks,
commercial use of data, and requests for information by authorities.
Both data at rest and data in use needs to be protected. Being able
to protect data in use provides also benefits to protecting keys used
for protecting data in flight and at rest.
Data leaks are very common, and include highly publicized ones or
ones with significant consequences, such as [Cambridge]. Data leaks
are also not limited to traditional computer applications, but can
also impact anything from private health data [Vastaamo] to
children's toys [Toys] or smart TVs [SmartTV].
The general issue and possible solutions have been discussed
extensively elsewhere, e.g., [Digging], [Mem], [Comparison],
[Innovative], [AMD], [Efficient], [CCC-Deepdive], [CC], and so on.
The Internet-relevant angle has also been discussed in few documents,
e.g., [I-D.lazanski-smart-users-internet], [I-D.iab-dedr-report]
[I-D.arkko-farrell-arch-model-t-redux], and so on. The topic is also
related to best practices for protocol and network architecture
design, and what information can be provided to what participants in
a system, see, e.g. [RFC8558] [I-D.thomson-tmi]
[I-D.arkko-arch-infrastructure-centralisation].
Data leaks can occur in user-visible services that user has chosen to
use and agreed to provide information to (at least in theory
[Unread]). But leaks can also occur in other types of services, that
are part of the infrastructure, such as DNS resolution services or
parts of the communication infrastructure.
This document looks at the possibility of using a specific technical
solution, Confidential Computing [CCC-Deepdive], to reduce the risk
of leaks from data in use. We consider the operational implications
of running services in a way that even the owner of the service or
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compute platform cannot access user-specific information that is
produced as a side-effect of the service.
We explore the use of Confidential Computing in the context of DNS
resolution services [RFC1035]. This is a nice and relatively simple
example, but there are of course potential other applications as
well.
DNS resolution services are of course also an important case where
privacy matters a lot for the users. Threats against the resolution
process could prevent the user from accessing services. Data leaks
from the process have the potential to expose the user's entire
browsing history.
The use of Confidential Computing in the DNS context has been also
discussed in other documents, e.g., [PDoT] and
[I-D.reddy-add-server-policy-selection].
The DNS privacy issues have been also discussed in multiple
documents, such as [RFC7626] [RFC8324] and so on.
3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
4. Prerequisities
The primary sources of leaks are as follows:
* Communications interception. This threat can be addressed by
encrypted communications, such as the use of DNS-over-TLS (DoT)
[RFC7858], DNS-over-HTTPS (DoH) [RFC8484], or DNS-over-QUIC (DoQ)
[I-D.ietf-dprive-dnsoquic] instead of traditional DNS protocols.
* Data leakage from the server or service, either from data at rest
or in use. This can be addressed by encrypting the data while at
rest and employing the techniques discussed in this document for
data in use.
The specific information that is privacy sensitive depends on the
application. In DNS resolution application it is clear that the
users' browsing histories, i.e., which users asked for what names is
privacy sensitive, and protecting that information is the primary
focus in this document. In contrast, the domains themselves or the
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associated address information is in the general case public and not
privacy sensitive. However, in some cases even this information may
be sensitive, such as in the case of internal domains of a corporate
network. Information not related to individuals may also be
sensitive in some cases, e.g., the collective browsing destinations
of an entire organization.
The above was also observed in [RFC7626] which stated the following:
"DNS data and the results of a DNS query are public [...], and may
not have any confidentiality requirements. However, the same is
not true of a single transaction or a sequence of transactions;
that transaction is not / should not be public."
Nevertheless, it should be noted that technology can help only
insofar as there is commercial willingness to provide the best
possible service and to protect the users' information.
Similarly, the techniques discussed in this document are not the
sole, or full answer to all problems. There are a lot of technical,
operational, and governance issues that also matter and practices
that help. A good compilation of some best practices can be found in
[RFC8932], and particularly Section 5.2 that discusses data at rest.
5. Confidential Computing
Confidential Computing is about protecting data in use by performing
computation in a hardware enforced Trusted Execution Environment
(TEE) [CCC-Deepdive]. It addresses the need to protect data in use,
which traditionally has been hard to achieve. It may also help
improve the encryption of data in flight and at rest, by helping
protect session keys and other security information used in that
process.
For our purposes, we focus on Trusted Execution Environments that use
computer hardware to provide the following characteristics:
* Attestability: The environment can provide verifiable evidence to
others (such as client using services running on it) about the
environment, its characteristics, and the software it runs.
* Code integrity: Unauthorized entities cannot modify software being
run within the environment.
* Data confidentiality and integrity: Unauthorized entities cannot
view or modify data while it is in use within the TEE.
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These characteristics have been paraphrased from [CCC-Deepdive]. See
also [I-D.ietf-rats-architecture] for details of attestation. There
are additional characteristics that matter in some situations, but
for our purposes the above ones are central.
Specific technologies to perform Confidential Computing or run TEEs
are becoming common in CPUs, operating systems, and other supporting
software. For instance, Intel's Software Guard Extension (SGX) [SGX]
is one CPU manufacturer's approach to this technology. SGX allows
application developers to run software protected in a secure enclave
protected by the CPU, including for instance encrypting all memory
accesses outside the CPU and being able to provide remote attestation
to outsiders about which software image is being run. These secure
enclaves are the SGX approach to providing a TEE.
Confidential Computing is also becoming available on commonly
available cloud computing services. When a user employs these
services, they have the ability to run software and process data that
even the owner of the cloud system does not have access to.
Interestingly, that is quite a contrast to the worries expressed some
years ago about Trusted Computing technology, when it was feared that
it enabled running software in users' computers that could act
against the interests of the user in some cases, such as when
protecting media files [Stallman]. While those concerns may apply
even today in some cases, it is clear that whe the user can get
secure information about services running somewhere in the network,
this is an advantage for the users.
Note that availability might be another desirable characteristic for
Confidential Computing systems, but it is one that is not in any
special way supported by current technology. Ultimately, the owner
of the computer still has the ability to choose when to switch the
computer off, for instance. There is also no particular hardware
technology at this time to deal with Denial-of-Service attacks. Some
of the software techniques related to dealing with Denial-of-Service
attacks are discussed in the Security Considerations section.
6. Using Confidential Computing for DNS Resolution
Confidential Computing can be used to provide a privacy-friendly
resolution service in a server.
The basic arrangement is two-fold:
* User's computer and the DNS resolution server communicate using an
encrypted and integrity protected transport protocol, such as DoT
or DoH [RFC7858] [RFC8484].
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* The secure connection terminates inside a TEE running in the the
DNS resolution server. This TEE performs all the necessary
processing to respond to the user's query. The TEE will not
provide any user-specific information outside of the TEE, such as
logs of what names specific clients queried for.
The TEE may need to contact other local servers or in the Internet
to resolve a query that has no recently cached answer. We will
discuss later how this can be done securely: it is necessary to
prevent the linking any external actions such as receiving a
client request and observing a query going out to other DNS
servers in the Internet.
The arrangement is shown in Figure 1.
+------------------+ +----------------+
| User's | | Server |
| Computer | | Computer |
| | | |
| | | +----------+ |
| | | | A TEE, | |
| +------------+ | | | running | | other DNS
| | DNS Client |-|-------------|--| a DNS |--|------ servers
| +------------+ | | | resolver | | (if needed)
| | | +----------+ |
| | | |
+------------------+ +----------------+
Figure 1: Confidential Computing for DNS Resoluton
In this application, we strive to have no data at rest at all, at
least nothing that relates directly to users. Data in flight and
data in use are both protected by encryption. As a result of running
the resolution service in this manner, any user-specific information
should remain within the TEE, and not exposed to outsiders or even
the owner of the service or the compute platform where the service is
running in.
The authors believe that this is a desirable property. However, it
remains to assure users and clients that the service is actually run
in this manner. This can be done in two ways:
* Through off-line reliance on a particular service, i.e., a human
decision to use a particular system. Once there is a decision to
use a particular system, cryptographic means such as public keys
may be used to ensure that the client is indeed connected to the
expected server. However, there is no guarantee that the human-
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space statements about the practices used in running the server
are valid.
* Cryptographic check that the service is actually running inside a
valid TEE and that it runs the expected software. Such checks
needs to rely on third parties. The attestation verification is
performed by a verifier - that can be either user's computer or a
designated verifier as discussed in [I-D.ietf-rats-architecture]
and [I-D.voit-rats-attestation-results] The verifier checks that
(a) the cryptographic attestation refers to a server machine that
is acceptable to the user (e.g., manufactured by a manufacturer it
trusts, CPU features considered secure are used, features
considered insecure are turned off, etc.) (b) that the software
image designated as being run in the attestation is a software
image that the relying party (end user) is willing to use (e.g.,
has a hash that matches a known software that does not log user
actions, or is vouched as trustworthy by another party that the
relying party trusts).
7. Operational Considerations
This section discusses some aspects of the Confidential Computing
arrangement for DNS, based on the authors' experience with these
systems.
7.1. Operations
Given that the service executes confidentially, and is not observable
even by the owner of the hardware, the operations model becomes
different. Some different models may be applied:
* The service executes on a hardware platform (such as a commercial
cloud service) that has no access to information, but there is
some other management entity that does have access. The control
functions of this entity can communicate with the service
instances running in TEEs, and have access to the internal state
and statistics of the service instances.
* Truly confidential operations where the service and hardware
owners have decided to deploy a service that really does not
expose private user information to anyone, including themselves.
It is not clear how the first model differs from currently deployed
service models. It merely makes it possible to run a service without
exposing information to, say, the cloud provider, but any data
collection about user behaviours would still be possible for the
service owner.
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As a result, this document focuses mostly on the second model. For
some functions, such as DNS resolution, it is possible to hide all
user-related information, and our document argues that we should do
so.
Of course, the owners of a service do need some information to run
the service, from an efficiency, scaling, problem tracking, and
security monitoring point of view. The service operator may even
benefit from seeing some overall trend information about various
queries and traffic. This does not have to mean exposing individual
user behaviours, however.
The authors have worked with aggregate statistics to be able to
provide load, performance, memory usage, cache statistics, error, and
other information out of the confidential processes. This helps the
operator understand the health and status of various service
instances. Even with aggregate statistics, there are some danger of
revealing private information. For instance, even a sum of counters
across all clients can reveal counters associated with an individual
user, if the aggregate counters can be sampled at any time with
arbitrary precision. For instance, the actions of a single client
can be determined by sampling the statistics before and after that
client sent a message.
A simplistic approach to producing safer statistics in such cases is
to truncate and/or obfuscate the least significant bits of the
statistics. It is often necessary to tailor such truncation to the
types of measurements, e.g., number of requests is typically a very
large number while the number of specific errors is usually small.
Truncation could of course be done dynamically. More generally, the
set of information provided to the operator about the confidential
process could be viewed in light of differential privacy.
Another complementary approach is to provide statistics only at set
intervals, or after a sufficient amount of new traffic has been
received.
Another complementary technique to monitor the health of confidential
services is the use of probes to ensure that the services function
correctly. Probes can also measure the performance of the services.
The case of excessive service conditions due to Denial-of-Service
attacks is discussed further under the Security Considerations
section.
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7.2. Debugging
Various error conditions and software issues may occur, as is usual
with any service. There is a need to monitor problems that occur
inside the service or at the client. This can be done, for instance,
with the help of various statistics discussed earlier.
Some of the monitored conditions should include:
* All major (or preferably even minor) error conditions should have
an associated counter. This is necessary as no traditional
logging can be reasonably provided that would otherwise have
entries for, say, "client IP 203.0.113.0 sent a malformed
request". While some errors can be expected at any time, a major
increase in specific issues can indicate a problem. As a result,
the counters need to be monitored and issues investigated as
needed.
* Client connection failures, which might indicate software version,
trust root or other configuration problems.
Of course, for dedicated software testing purposes (such as debugging
interoperability problems), even confidential services need to be run
in a mode that exposes everything. Actual clients and users MUST be
able to ensure that they are connected to a production service
instance. This can be be done by providing debugging status as part
of the remote attestation, so that clients can verify it is off.
Alternatively, testing versions of the service are simply not listed
as trusted software versions.
7.3. Dependencies
The use of Confidential Computing introduces three additional
dependencies to the system:
There is a need to be able to verify that the CPU executing the
service is a legitimate CPU with the right hardware, and that the
software being run for the service is acceptable. While this can be
hard coded information in the service clients, in practice there is
often a need to rely on other parties for scalability. As a result,
there are two dependencies for legitimate CPU verification and for
checking acceptable software versions. These are services that need
to be run, and/or their use need to be agreed and possibly contracted
for. The CPU manufacturer often plays a role in the CPU
verification.
The third dependency is on the client. Depending on specific
protocol arrangements, Confidential Computing services often can
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serve unmodified clients, but for the full benefits and for
validating attestations or software images, client changes are
necessary. The necessary communications may happen as part of TLS
negotiations or other general purpose protocols
[I-D.mandyam-tokbind-attest], [I-D.ietf-rats-eat].
7.4. Additional services
Many services employ information that can be used to perform
additional services beyond the basic task. For instance, knowledge
about what the users requests or who the user is can be used for
various optimizations or additional information that can be delivered
to the user. Or the user can provide some additional information
that is taken into account by the service.
One concern with these types of additional services is that the
information used by them can be privacy sensitive. But Confidential
Computing can assist in this as well, as long as the relevant
information stays only within the TEE, it is better protected than
by, e.g., providing that extra information to a regular service on
the Internet.
Conversely, care needs to be taken whenever the service needs to
relay some information outside the TEE. Some specific situations
where this is needed with DNS are discussed in Section 7.1.
One example of additional services is that aggregate, privacy-
sensitive data may be produced about trends in a confidentially run
service, if it will not be possible to separate individual users from
that data. For instance, it would be difficult sell information
about individual users to help with targeted advertising, but the
overall popularity of some websites could be measured.
7.5. Performance
Confidential Computing technology may impact performance. Nakatsuka
et al. [PDoT] report on DNS resolution within a TEE where their
solution could outperform the open source Unbound DNS server in
certain scenarios, especially in situations where there are not a lot
of DNS client connections. We concur their suggestion that at
current stage of Confidential Computing technology, possible
implementations may be more suited for local DNS resolution services
rather than global scale implementation, where the performance hit
would be much more significant. Nonetheless with Confidential
Computing technology ever evolving we believe the low performance
overhead solutions will be possible in foreseeable future.
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Other things being equal there's likely some performance hit, as
current Confidential Computing technology typically involves
separating a server into two parts, the trusted and untrusted parts.
In practice, all communications need to go through both, and the
communication between the two parts consumes some cycles. There are
also current limitations on amount of memory or threads supported by
these technologies. However, newer virtualization-based confidential
computing TEE approaches are likely going to improve these aspects.
Another performance hit comes from the overhead related to running
the attestation process, and passing the necessary extra information
in the communications protocols with the clients. In general, this
works best when the cost of the setup is amortized over a long-lived
session. Such sessions may exist between DoT/DoH-enabled clients and
resolvers. Also, there are many possible arrangements and possible
parties involved in attestation, see [I-D.ietf-rats-architecture].
8. Security Considerations
Security issues in this arrangement are discussed below.
8.1. Observations from outside the TEE
While a TEE is considered to be secure and not observable, there may
be signs outside the TEE that can reveal information.
For instance, a server may receive a request from a client and
immediately send out a question to a server in the Internet about a
particular domain name. Observers - such as the owner of the server
computer or the cloud farm - may be able to link incoming user
queries to outgoing questions
Caching, randomly made other traffic, and timing obfuscation can
deter such attacks, at least to an extent.
8.2. Trust Relationships
For scaling reasons, the arrangement typically depends on the ability
to have trusted parties (a) for attesting the validity of a
particular CPU being manufactured by a CPU manufacturer, and (b) for
determining whether a particular software image hash is acceptable
for the task it is advertising to do.
Such trusted parties need to be configured, which presents an
additional operational burden. The information can of course be
provided as part of a device manufacturer's or application's initial
configuration, or be provided independently similar to how, for
instance, certificate authorities are run.
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It is important to recognize that mere use of technology is not
sufficient to make the system secure. With communications,
establishing a secure, encrypted channel is of no use if it is not
with the intended party due to a certificate authority that proved to
be untrustworthy. With confidential computing, the same applies: one
has to have someone who can assert that a CPU is capable of
performing the confidential computing task and that the indicated
software is good for performing the task that the user expects it to
perform. That being said, when such trusted parties can be found,
the service performed by the server can become much more privacy
friendly.
8.3. Denial-of-Service Attacks
To paraphrase an old philosophical question, "If an evil packet is
sent behind the veil of encryption and no one is around to lift it,
did an attack happen?" [Chautauquan]
Denial-of-Service attacks are a more serious form of the problems
with operating services that the operator (intentionally) does not
fully see. There needs to be means to deal with these attacks.
Attacks that can be identified by particularly high traffic flows
from externally observable sources (e.g., source IP address) can of
course still be dealt with in similar ways as we do in more open
server designs.
But this is often not enough, and for this purpose some additional
support is needed in the systems, for both detection of attacks and
reacting to them.
One detection technique is to use the aggregate/truncated statistics
to analyze anomalous behaviour. Another technique is to have the
confidential part of the service produce extra information about
events that cross a threshold. For instance, a particular error may
occur exceptionally frequently, say among millions of requests, and
this could warrant exposing either something about the request (e.g.,
the associated domain name) or something about the client (e.g.,
connection type, protocol details, or sender address).
The operator of the services needs to be able to react to possible
attacks as well. One technique is to be able to provide instruction
to the confidential part of the service to refuse service for
specific requests (e.g., specific domain names) or for specific
clients (e.g., coming from specific addresses). Alternatively, the
service can also dynamically react to issues, e.g., by starting to
reduce the amount of resources dedicated to some classes of requests
that for some reason are starting to require exceptionally high
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amount of resources. These techniques do not endanger user privacy,
but may of course impact provided service.
8.4. Other vulnerabilities
Like all security mechanisms, this solution is not a panacea. It
relies on the correct operation of a number of technologies and
entities. For instance, CPU bugs or side channel vulnerabilities can
cause information leaks to become possible. While confidential
computing offers a layer of protection against attacks even from the
owner of the computer hardware or the operating system, it is
believed that this protection does not extend to sophisticated
physical attacks, such being able to study chips with an electron
microscope.
And as discussed above, it is also critical to check what software is
being run, as otherwise any possible benefit would be negated by the
possibly negligent or nefarious actions the unchecked software makes.
The mechanism does offer an additional layer of defense, however. It
allows some of the trust that we place on our cloud platform owners,
CPUs, and software applications to be verified and controlled with
technical means. It may have some remaining vulnerabilities, but we
obviously already depend on, for instance, the correct operation of
our computing platforms. As such, Confidential Computing works to
reduce some of the vulnerabilities in this area.
It should also be a desirable feature for users. A service that
offers Confidential Computing-based protection of user data and can
show that its software does not leak user-specific information is
likely going to be more attractive to users than one that provides no
such assurances. Of course, overall user choice depends on many
factors beyond privacy, such as cost, ease of use, switching costs,
and so on.
There is also a danger of attacks or pressure from intelligence
agencies that could result in, e.g., the use of unpublicized
vulnerabilities in an attempt to dwarf the protections in
Confidential Computing. This could be used to perform pervasive
monitoring, for instance [RFC7258]. Even so, it is always beneficial
to push the costs and difficulty for attackers. Requiring parties
who perform pervasive monitoring to employ complex technical attacks
rather than being able to request logs from a service provider
significantly increases the difficulty and risk associated with such
monitoring.
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9. Recommendations
Data held by servers SHOULD receive at least as much security
attention as communications do.
The authors would like to draw attention to the problem of data
leaks, particularly for data in use, and RECOMMEND the application of
all available tools to prevent inappropriate access to users'
information.
This is particularly crucial for DNS resolution services that have
the potential to learn user's browsing histories. But the principles
apply also to other services.
While using Confidential Computing without other modifications to the
service in question is possible, real benefits can only be realized
when the actual service is built for the purpose of avoiding data
leaks or user data capture. Systems may need to be tuned or
modified, for instance they MUST NOT produce logs that would negate
purpose of running them inside a TEE to begin with. Mechanisms
SHOULD be found to enable debugging and the detection of fault
situations and attacks, again without exposing private information
relating to individual users.
Some computing services can proceed on their own and require no
interaction with the rest of the world. These are easier to secure.
Even then, care SHOULD be taken to avoid request-response timing to
provide information useful for side-channel attacks. If so, the
owner of the server hardware can not determine much about what was
going on.
However, other services may require interaction with other systems,
such as is the case with a DNS resolver needing to find out a
particular name that is not in a cache or whose cache entry has
expired. This is because the resolution service is not a self-
contained computation task but ultimately needs, at least in some
cases, interaction with the rest of the world.
Consequently, the resolver needs to collaborate with other network
nodes that are not even in the same administrative domain and cannot
be guaranteed to subscribe to the same principles of protecting
user's information. In this case, even if communications to other
entities are encrypted, the potentially untrusted party at the other
end of the communications may leak information.
In such communications, care SHOULD be taken to avoid exposing any
information that would identify users, or allow fingerprinting the
capabilities of those users' systems. Similarly, care SHOULD be
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taken to avoid exposing any timing information that would allow the
owner of the server hardware to determine what is going on, e.g.,
which users are asking for what names. Even so, vulnerabilities may
appear if the attacker can force the system to behave in a particular
way, by, e.g., forcing cache overflow, overloading it with traffic it
knows about, etc.
The situation is slightly different when the interaction is with
other systems that form a part of the same administrative domain. In
particular, if those other systems employ similar confidential
computing setup, and an encrypted channel is used, then some
additional security can be provided compared to communicating with
other entities in the Internet.
10. Acknowledgments
The authors would like to thank Juhani Kauppi, Jimmy Kjaellman, and
Tero Kauppinen for their work on systems supporting some of the ideas
discussed in this memo, and Dave Thaler, Daniel Migault, Karl
Norrman, and Christian Schaefer for significant feedback on early
version of this draft. The author would also like to thank Marcus
Ihlar, Maria Luisa Mas, Miguel Angel Munos De La Torre Alonso, Jukka
Ylitalo, Bengt Sahlin, Tomas Mecklin, Ben Smeets and many others for
interesting discussions in this problem space.
11. References
11.1. Normative References
[RFC1035] Mockapetris, P.V., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
11.2. Informative References
[AMD] Kaplan, D., Powell, J., and T. Woller, "AMD Memory
Encryption", AMD White Paper , April 2016.
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[Cambridge]
Isaak, J. and M. Hanna, "User Data Privacy: Facebook,
Cambridge Analytica, and Privacy Protection", Computer
51.8 (2018): 56-59, https://ieeexplore.ieee.org/stamp/
stamp.jsp?arnumber=8436400 , 2018.
[CC] Rashid, F.Y., "What Is Confidential Computing?", IEEE
Spectrum, https://spectrum.ieee.org/computing/hardware/
what-is-confidential-computing , May 2020.
[CCC-Deepdive]
Confidential Computing Consortium, ., "A Technical
Analysis of Confidential Computing",
https://confidentialcomputing.io/whitepaper-02-latest ,
January 2021.
[Chautauquan]
"The Chautauquan", Volume 3, Issue 9, p. 543 , June 1883.
[Comparison]
Mofrad, S., Zhang, F., Lu, S., and W. Shi, "A comparison
study of intel SGX and AMD memory encryption technology",
HASP '18, Proceedings of the 7th International Workshop on
Hardware and Architectural Support for Security and
Privacy, Pages 1-8,
https://doi.org/10.1145/3214292.3214301 , June 2018.
[Digging] Hammouchi, H., Cherqi, O., Mezzour, G., Ghogho, M., and M.
El Koutbi, "Digging Deeper into Data Breaches: An
Exploratory Data Analysis of Hacking Breaches Over Time",
Procedia Computer Science, Volume 151, pp. 1004-1009, ISSN
1877-0509, https://doi.org/10.1016/j.procs.2019.04.141,
https://www.sciencedirect.com/science/article/pii/
S1877050919306064 , 2019.
[Efficient]
Suh, G.E., Clarke, D., Gasend, B., van Dijk, M., and S.
Devadas, "Efficient memory integrity verification and
encryption for secure processors", Proceedings. 36th
Annual IEEE/ACM International Symposium on
Microarchitecture, MICRO-36, San Diego, CA, USA, pp.
339-350, doi: 10.1109/MICRO.2003.1253207 , 2003.
[I-D.arkko-arch-infrastructure-centralisation]
Arkko, J., "Centralised Architectures in Internet
Infrastructure", Work in Progress, Internet-Draft, draft-
arkko-arch-infrastructure-centralisation-00, 4 November
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2019, <https://www.ietf.org/archive/id/draft-arkko-arch-
infrastructure-centralisation-00.txt>.
[I-D.arkko-farrell-arch-model-t-redux]
Arkko, J. and S. Farrell, "Internet Threat Model
Evolution: Background and Principles", Work in Progress,
Internet-Draft, draft-arkko-farrell-arch-model-t-redux-01,
22 February 2021, <https://www.ietf.org/archive/id/draft-
arkko-farrell-arch-model-t-redux-01.txt>.
[I-D.iab-dedr-report]
Arkko, J. and T. Hardie, "Report from the IAB Workshop on
Design Expectations vs. Deployment Reality in Protocol
Development", Work in Progress, Internet-Draft, draft-iab-
dedr-report-01, 2 November 2020,
<https://www.ietf.org/archive/id/draft-iab-dedr-report-
01.txt>.
[I-D.ietf-dprive-dnsoquic]
Huitema, C., Mankin, A., and S. Dickinson, "Specification
of DNS over Dedicated QUIC Connections", Work in Progress,
Internet-Draft, draft-ietf-dprive-dnsoquic-02, 22 February
2021, <https://www.ietf.org/archive/id/draft-ietf-dprive-
dnsoquic-02.txt>.
[I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote Attestation Procedures Architecture", Work
in Progress, Internet-Draft, draft-ietf-rats-architecture-
12, 23 April 2021, <https://www.ietf.org/archive/id/draft-
ietf-rats-architecture-12.txt>.
[I-D.ietf-rats-eat]
Mandyam, G., Lundblade, L., Ballesteros, M., and J.
O'Donoghue, "The Entity Attestation Token (EAT)", Work in
Progress, Internet-Draft, draft-ietf-rats-eat-10, 7 June
2021, <https://www.ietf.org/archive/id/draft-ietf-rats-
eat-10.txt>.
[I-D.ietf-tls-esni]
Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS
Encrypted Client Hello", Work in Progress, Internet-Draft,
draft-ietf-tls-esni-11, 14 June 2021,
<https://www.ietf.org/archive/id/draft-ietf-tls-esni-
11.txt>.
[I-D.lazanski-smart-users-internet]
Lazanski, D., "An Internet for Users Again", Work in
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Progress, Internet-Draft, draft-lazanski-smart-users-
internet-00, 8 July 2019,
<https://www.ietf.org/archive/id/draft-lazanski-smart-
users-internet-00.txt>.
[I-D.mandyam-tokbind-attest]
Mandyam, G., Lundblade, L., and J. Azen, "Attested TLS
Token Binding", Work in Progress, Internet-Draft, draft-
mandyam-tokbind-attest-07, 24 January 2019,
<https://www.ietf.org/archive/id/draft-mandyam-tokbind-
attest-07.txt>.
[I-D.reddy-add-server-policy-selection]
Reddy, T., Wing, D., Richardson, M. C., and M. Boucadair,
"DNS Server Selection: DNS Server Information with
Assertion Token", Work in Progress, Internet-Draft, draft-
reddy-add-server-policy-selection-08, 29 March 2021,
<https://www.ietf.org/archive/id/draft-reddy-add-server-
policy-selection-08.txt>.
[I-D.thomson-tmi]
Thomson, M., "Principles for the Involvement of
Intermediaries in Internet Protocols", Work in Progress,
Internet-Draft, draft-thomson-tmi-01, 3 January 2021,
<https://www.ietf.org/archive/id/draft-thomson-tmi-
01.txt>.
[I-D.voit-rats-attestation-results]
Voit, E., Birkholz, H., Hardjono, T., Fossati, T., and V.
Scarlata, "Attestation Results for Secure Interactions",
Work in Progress, Internet-Draft, draft-voit-rats-
attestation-results-01, 10 June 2021,
<https://www.ietf.org/archive/id/draft-voit-rats-
attestation-results-01.txt>.
[Innovative]
Ittai, A., Gueron, S., Johnson, S., and V. Scarlata,
"Innovative Technology for CPU Based Attestation and
Sealing", HASP'2013 , 2013.
[Mem] Henson, M. and S. Taylor, "Memory encryption: a survey of
existing techniques", ACM Computing Surveys volume 46
issue 4 , 2014.
[MozTRR] Mozilla, ., "Security/DOH-resolver-policy",
https://wiki.mozilla.org/Security/DOH-resolver-policy ,
2019.
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[PDoT] Nakatsuka, Y., Paverd, A., and G. Tsudik, "PDoT: Private
DNS-over-TLS with TEE Support", Digit. Threat.: Res.
Pract., Vol. 2, No. 1, Article 3,
https://dl.acm.org/doi/fullHtml/10.1145/3431171 , February
2021.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC7626] Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626,
DOI 10.17487/RFC7626, August 2015,
<https://www.rfc-editor.org/info/rfc7626>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC8324] Klensin, J., "DNS Privacy, Authorization, Special Uses,
Encoding, Characters, Matching, and Root Structure: Time
for Another Look?", RFC 8324, DOI 10.17487/RFC8324,
February 2018, <https://www.rfc-editor.org/info/rfc8324>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
[RFC8558] Hardie, T., Ed., "Transport Protocol Path Signals",
RFC 8558, DOI 10.17487/RFC8558, April 2019,
<https://www.rfc-editor.org/info/rfc8558>.
[RFC8932] Dickinson, S., Overeinder, B., van Rijswijk-Deij, R., and
A. Mankin, "Recommendations for DNS Privacy Service
Operators", BCP 232, RFC 8932, DOI 10.17487/RFC8932,
October 2020, <https://www.rfc-editor.org/info/rfc8932>.
[SGX] Hoekstra, M.E., "Intel(R) SGX for Dummies (Intel(R) SGX
Design Objectives)", Intel,
https://software.intel.com/content/www/us/en/develop/
blogs/protecting-application-secrets-with-intel-sgx.html ,
September 2013.
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[SmartTV] Malkin, N., Bernd, J., Johnson, M., and S. Egelman, "What
Can't Data Be Used For? Privacy Expectations about Smart
TVs in the U.S.", European Workshop on Usable Security
(Euro USEC), https://www.ndss-symposium.org/wp-
content/uploads/2018/06/
eurousec2018_16_Malkin_paper.pdf" , 2018.
[Stallman] Stallman, R., "Can You Trust Your Computer?", GNU.org,
https://www.gnu.org/philosophy/can-you-trust.html , n.d..
[Toys] Chu, G., Apthorpe, N., and N. Feamster, "Security and
Privacy Analyses of Internet of Things Childrens' Toys",
IEEE Internet of Things Journal 6.1 (2019): 978-985,
https://arxiv.org/pdf/1805.02751.pdf , 2019.
[Unread] Obar, J. and A. Oeldorf, "The biggest lie on the
internet{:} Ignoring the privacy policies and terms of
service policies of social networking services",
Information, Communication and Society (2018): 1-20 ,
2018.
[Vastaamo] Redcross Finland, ., "Read this if your personal data was
leaked in the Vastaamo data system break-in",
https://www.redcross.fi/news/20201029/read-if-your-
personal-data-was-leaked-vastaamo-data-system-break ,
October 2020.
Authors' Addresses
Jari Arkko
Ericsson
Email: jari.arkko@ericsson.com
Jiri Novotny
Ericsson
Email: jiri.novotny@ericsson.com
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