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  <front>
    <title abbrev="ECH Deployment Considerations">Encrypted Client Hello Deployment Considerations</title>
    <seriesInfo name="Internet-Draft" value="draft-campling-ech-deployment-considerations-03"/>
    <author initials="A. J." surname="Campling" fullname="Andrew Campling">
      <organization>419 Consulting Limited</organization>
      <address>
        <email>Andrew.Campling@419.Consulting</email>
        <uri>https://www.419.Consulting/</uri>
      </address>
    </author>
    <author initials="P." surname="Vixie" fullname="Paul Vixie">
      <organization>Red Barn</organization>
      <address>
        <email>paul@redbarn.org</email>
        <uri>http://www.redbarn.org/</uri>
      </address>
    </author>
    <author initials="D." surname="Wright" fullname="David Wright">
      <organization>UK Safer Internet Centre</organization>
      <address>
        <email>david.wright@swgfl.org.uk</email>
        <uri>https://saferinternet.org.uk/</uri>
      </address>
    </author>
    <author initials="A." surname="Taddei" fullname="Arnaud Taddei">
      <organization>Broadcom</organization>
      <address>
        <postal>
          <street>1320 Ridder Park Dr</street>
          <city>San Jose</city>
          <region>CA</region>
          <code>95131</code>
          <country>US</country>
        </postal>
        <phone>41795061129</phone>
        <email>Arnaud.Taddei@broadcom.com</email>
        <uri>https://www.linkedin.com/in/arnaudtaddei/</uri>
      </address>
    </author>
    <author initials="S." surname="Edwards" fullname="Simon Edwards">
      <organization>Broadcom</organization>
      <address>
        <postal>
          <street>1320 Ridder Park Dr</street>
          <city>San Jose</city>
          <region>CA</region>
          <code>95131</code>
          <country>US</country>
        </postal>
        <email>Simon.Edwards@broadcom.com</email>
        <uri>https://www.linkedin.com/in/simononsecurity/</uri>
      </address>
    </author>
    <date year="2022" month="November" day="07"/>
    <area>SEC</area>
    <workgroup>secdispatch</workgroup>
    <keyword>ECH</keyword>
    <keyword>Enterprises</keyword>
    <keyword>Operational Security</keyword>
    <abstract>
      <t>This document is intended to inform the community about the impact of the deployment of the proposed
Encrypted Client Hello (ECH) standard that encrypts Server Name
Indication (SNI) and other data.  Data encapsulated by ECH (ie data
included in the encrypted ClientHelloInner) is of legitimate interest
to on-path security actors including those providing inline malware detection, parental
controls, content filtering to prevent access to malware and other risky traffic, mandatory security controls etc.</t>
      <t>The document includes observations on current use cases for SNI data
in a variety of contexts.  It highlights how the use of that data is
important to the operators of both public and private networks and shows how the loss
of access to SNI data will cause difficulties in the provision of a
range of services to end-users, including the potential weakening of cybersecurity defences.
Some mitigations are identified that may be useful for inclusion by those considering the adoption
of support for ECH in their software.</t>
    </abstract>
  </front>
  <middle>
    <section anchor="introduction">
      <name>Introduction</name>
      <t>As noted above, this document includes observations on current use
cases for SNI data in a variety of contexts.  It highlights how the
use of that data is important to the operators of both public and private networks
and shows how the loss of access to SNI data will cause difficulties
in the provision of a range of services to end-users.
Some mitigations are identified that may be useful for inclusion by those considering the adoption of support for ECH in their software.</t>
      <t>The Internet was envisaged as a network of networks, each able to
determine what data to transmit and receive from their peers.
Developments like ECH mark a fundamental change in the architecture
of the Internet, allowing opaque paths to be established from
endpoints to commercial services, some potentially without the
knowledge or permission of the device owners.  This change should not
be undertaken lightly given both the architectural impact on the
Internet and potentially adverse security implications for end users.
Given these implications, it certainly should not be undertaken
without either the knowledge of or consultation with end users, as
outlined in <xref target="RFC8890"/>.</t>
      <t>Whilst it is reasonable to counter that VPNs also establish opaque
paths, a primary difference is that the use of a VPN is a deliberate
act by the user, rather than a choice made by client software,
potentially without either the knowledge and/or consent of the end-
user or device owner.</t>
      <t><xref target="RFC7258"/> discusses the critical need to protect users'
privacy when developing IETF specifications and also recognises that
making networks unmanageable to mitigate pervasive monitoring is not
an acceptable outcome.</t>
      <t><xref target="RFC8404"/> discusses current security and network operations
as well as management practices that may be impacted by the shift to
increased use of encryption to help guide protocol development in
support of manageable and secure networks.  As <xref target="RFC8404"/> notes, "the
implications for enterprises that own the data on their networks or
that have explicit agreements that permit the monitoring of user
traffic are very different from those for service providers who may
be accessing content in a way that violates privacy considerations".</t>
      <t>This document considers the implications of ECH for private network
operators including enterprises and education establishments. The
data encapsulated by ECH is of legitimate interest to on-path
security actors including those providing inline malware detection,
firewalls, parental controls, content filtering to prevent access to malware
and other risky traffic, mandatory security controls (e.g. Data Loss Prevention) etc.</t>
      <t>This document will focus specifically on
the impact of encrypting the SNI data by ECH on public and private networks,
but it should be noted that other elements in the client hello may also be relevant for some
on-path security methods.</t>
    </section>
    <section anchor="encrypted-server-name-indication">
      <name>Encrypted Server Name Indication</name>
      <t><xref target="RFC8744"/> describes the general problem of encrypting the
Server Name Identification (SNI) TLS extension.  The document
includes a brief description of what it characterises as
"unanticipated" usage of SNI information (section 2.1) as well as a
brief (two paragraph) assessment of alternative options in the event
that the SNI data is encrypted (section 2.3).</t>
      <t>The text in <xref target="RFC8744"/> suggests that most of the unanticipated SNI
usage "could also be implemented by monitoring DNS traffic or
controlling DNS usage", although it does then acknowledge the
difficulties posed by encrypted DNS protocols.  It asserts, with
limited evidence, that "most of 'the unanticipated usage' functions
can, however, be realized by other means", although without
considering or quantifying the affordability, operational complexity,
technical capability of affected parties or privacy implications that
might be involved.  It is unclear from the document whether any
stakeholders that may be impacted by the encryption of SNI data have
been consulted; it certainly does not appear to be the case that any such
consultation has taken place.</t>
      <t>The characterisation of "unanticipated usage" of SNI data could be
taken to imply that such usage was not approved and therefore
inappropriate in some manner.  The reality is that the development of
the Internet has many examples of permissionless innovation and so
this "unanticipated usage" of SNI data should not be dismissed as lacking in
either importance or validity.</t>
      <t>This document is intended to address the above limitations of <xref target="RFC8744"/>
by providing more information about the issues posed by the
introduction of ECH due to the loss of visibility of SNI data on
private networks.  To do so it considers the situation within schools,
enterprises and public service providers, building on information previously documented in a
report from a roundtable discussion <xref target="ECH_Roundtable"/> in places.</t>
    </section>
    <section anchor="the-education-sector">
      <name>The Education Sector</name>
      <section anchor="context">
        <name>Context</name>
        <t>Focusing specifically on the education sector, the primary issue
caused by ECH is that it is likely to circumvent the safeguards
applied to protect children through content filtering, whether in the
school or home environments, adding to adverse impacts already
introduced through the use of encrypted DNS protocols such as DNS
over HTTPS <xref target="RFC8484"/>.</t>
        <t>Content filtering that leverages SNI information is used by education
establishments to protect children from exposure to malicious, adult,
extremist and other content that is deemed either age-inappropriate
or unsuitable for other reasons.  Any bypassing of content filtering
by client software on devices will be problematic and may compromise
duties placed on education establishments.  For example: schools in
England and Wales have obligations to provide "appropriate
filtering systems" <xref target="KCSE"/>; schools in the US use Internet
filters and implement other measures to protect children from harmful
online content as a condition for the receipt of certain federal
funding, especially E-rate funds <xref target="CIPA"/>.</t>
      </section>
      <section anchor="why-content-filtering-matters-to-schools">
        <name>Why Content Filtering Matters to Schools</name>
        <t>The impact that ineffective content filtering can have on an
educational institutions should not be underestimated.  For example, a
coroner in the UK in 2021 ruled that a school's failure to prevent a
pupil from accessing harmful material online on its equipment
contributed to her taking her own life <xref target="Coroner"/>.  In this particular
instance, the filtering software installed at the school was either
faulty or incorrectly configured but the case highlights the harmful risks
posed if the filtering is bypassed by client software using ECH.</t>
      </section>
      <section anchor="mitigations">
        <name>Mitigations</name>
        <t>Whilst it may be possible for schools to overcome some of the issues
ECH raises by adopting similar controls to those used by enterprises,
it should be noted that most schools have a very different budget for
IT compared to enterprises and usually have very limited technical
support capabilities.  Therefore, even where technical solutions
exist that may allow them to continue to meet their compliance
obligations, affordability and operational expertise will present
them with significant difficulties.</t>
        <t>Absent funding and technical expertise, schools will need to consider
the best way forward that allows them to remain compliant.  If client
software does not allow ECH to be disabled, any such software that
implements support for ECH may need to be removed from school devices
and replaced, assuming that suitable alternatives are available.
This will have a negative impact on budgets and may be operationally
challenging if institutions have made a significant investment in the
deployment and use of particular applications and technologies.</t>
        <t>There are instances where policies in education establishments allow
for the use of equipment not owned by the institution, including
personal devices and the devices of contractors and site visitors.
These devices are unlikely to be configured to use the institution's
proxy but can nevertheless connect to the school network using a
transparent proxy (see below).  Transparent proxies used for
filtering will typically use SNI data to understand whether a user is
accessing inappropriate data, so encrypting the SNI field will
disrupt the use of these transparent proxies.</t>
        <t>In the event that transparent proxies are no longer effective,
institutions will either have to require more invasive software to be
installed on third party devices before they can be used along with
ensuring they have the capability to comprehend and adequately manage
these technologies or will have to prevent those devices from
operating.  Neither option is desirable.</t>
      </section>
    </section>
    <section anchor="transparent-proxies">
      <name>Transparent Proxies</name>
      <t>A proxy server is a server application that acts as an intermediary
between a client requesting a resource and the server providing that
resource.  Instead of connecting directly, the client directs the
request to the proxy server which evaluates the request before
performing the required network activity.  Proxies are used for
various purposes including load balancing, privacy and security.</t>
      <t>Traditionally, proxies are accessed by configuring a user's
application or network settings, with traffic diverted to the proxy
rather than the target destination.  With "transparent" proxying, the
proxy intercepts packets directed to the destination, making it seem
as though the request is handled by the target destination itself.</t>
      <t>A key advantage of transparent proxies is that they work without
requiring the configuration of user devices or software.  They are
commonly used by organisations to provide content filtering for
devices that they don't own that are connected to their networks.
For example, some education environments use transparent proxies to
implement support for "bring your own device" (BYOD) without needing to load software on third-
party devices.</t>
      <t>Transparent proxies use SNI data to understand whether a user is
accessing inappropriate content without the need to inspect data
beyond the SNI field.  Because of this, encryption of the SNI field,
as is the case with ECH, will disrupt the use of transparent proxies, requiring far more intrusive data inspection to be undertaken instead.</t>
    </section>
    <section anchor="impact-of-ech-on-enterprises-and-organizations">
      <name>Impact of ECH on Enterprises and Organizations</name>
      <section anchor="the-main-requirements">
        <name>The main requirements</name>
        <t>Enterprises and Organizations need to protect themselves for a vast number of reasons, mainly:</t>
        <ul spacing="normal">
          <li>Reduce their Risks. And in particular as part of any Cyber Resilience strategy.</li>
          <li>Protect their Reputation. The term Reputation includes many aspects way beyond the traditional enterprises and organization assets (data, etc.).</li>
          <li>Comply to a growing diverse set of Policies, Regulations, Certifications, Labeling and Guidelines. These requirements are growing in both scope and complexity as they are added to by various bodies in countries and regional authorities around the world.</li>
        </ul>
      </section>
      <section anchor="a-degrading-threat-landscape">
        <name>A degrading threat landscape</name>
        <t>In addition, the general threat landscape which was already very large (see <xref target="I-D.draft-mcfadden-smart-threat-changes"/>), has significantly increased in three ways:</t>
        <ul spacing="normal">
          <li>COVID crisis generally accelerated the overall attack landscape. Indeed as the crisis forced many enterprises and organizations to accelerate their digital transformation, it increased the opportunity for cyber criminals and nation states to launch more attacks, leverage innovations to their advantages, better select their targets, increase their efficiency and increase their rewards, in particular with Ransomware based attacks.</li>
          <li>The Supply Chain is under stress as per the <xref target="SOLARWIND"/> attack</li>
          <li>Nation State attacks are continuing to evolve, for example as noted to those linked to the current Ukraine crisis.</li>
        </ul>
        <t>Attacks are now damaging enterprises and other organizations with ransomware being the number 1 issue by a considerable margin. The attacks are increasing in severity, to the extent that this is now being measured at macroscopic level in some countries:</t>
        <ul spacing="normal">
          <li>EUR1B loss of revenue for French organizations from January to August 2022 <xref target="LOSSINREVENUE"/></li>
          <li>Loss in capitalisation between 1-5% <xref target="LOSSINCAP"/></li>
          <li>Degradation by credit notation agencies <xref target="LOSSINCREDITSCORE"/></li>
        </ul>
        <t>Another implication from the COVID crisis is the acceleration of BYOD
with the current reliance on remote working. This has created two side effects for remote employees, contractors and third parties that need to connect to one or more enterprise
networks on a temporary basis:</t>
        <ul spacing="normal">
          <li>need to use a VPN access to the corporate network, which brings all the benefits (e.g. protected access to corporate network) and risks that VPNs may open (e.g. lateral movement when the end point is compromised),</li>
          <li>need to access a cloud proxy which requires an agent to be installed on the device to steer the traffic to the right place.</li>
        </ul>
        <t>In such circumstances, requiring
software or custom configurations to be installed on those devices
may be problematic (see <xref target="I-D.draft-taddei-smart-cless-introduction"/>.</t>
        <t>This is why network security solutions are required and this is why ECH preventing the access to the SNI makes it impossible for blue teams to defend (see the next sections for details).</t>
        <t>Finally there is a major lack of manpower in cybersecurity with a lack of professionalization which is not compensated anymore by the vocational aspect of cybersecurity so far, so any expansion of technical requirements that ECH would cause will exacerbate the problem.</t>
        <t>All the above conditions are weighing on capabilities to defend, both:</t>
        <ul spacing="normal">
          <li>Directly: a lack of visibility on a key meta data like the SNI will cause significant issues to enterprises and organizations</li>
          <li>Indirectly: should ECH happen and should alternative be provided, managing migrations to any alternative not requiring access to the SNI, in these conditions, is undesirable from a timing, resources, capacities and risks perspectives.</li>
        </ul>
      </section>
      <section anchor="examples-of-regulatory-implications">
        <name>Examples of regulatory implications</name>
        <t>Regulators are accelerating their lawfare capabilities at accelerated pace and new legislations are showing an increased precision on what enterprises can and cannot do. The EU GDPR had ripple effects to Financial Institutions to implement Data Loss Prevention which requires selective decrypt. The recent indication that US regulators are in the process of levying fines of $200m each on a number of institutions because they were unable to track all communications by their employees using WhatsApp or Signal , <xref target="Bloomberg"/>, creates new auditability constraints. It is with growing concern that an ECH enabled ecosystem may clash with future regulatory requirements.</t>
      </section>
      <section anchor="impact-of-ech-deployment-on-network-security-operations">
        <name>Impact of ECH deployment on Network Security Operations</name>
        <section anchor="reminders-on-network-security">
          <name>Reminders on Network Security</name>
          <t>Network Security is a set of security capabilities which is articulated as part of a defense strategy, e.g. Defense In Depth <xref target="NIST-DID"/>, Zero Trust, SASE/SSE, etc. and can trigger and enable other security capabilities such as sandboxing, Data Loss Prevention, Cloud Access Service Broker (CASB), etc. One constituency is a Web Proxy, combining both a TLS proxy and an application level (HTTP) proxy.</t>
          <t>In the same way that <xref target="I-D.draft-ietf-opsec-ns-impact"/> showed the impact of TLS1.3 on operational security, a loss of visibility of the SNI as indicator of compromise (see <xref target="I-D.draft-ietf-opsec-indicators-of-compromise"/>) has two main implications</t>
        </section>
        <section anchor="implications-from-loss-of-meta-data">
          <name>Implications from loss of Meta Data</name>
          <t>The loss of visibility of the SNI, at TLS level, will prevent transparent proxies from applying corporate policies to manage risk and compliancy. Typical examples:</t>
          <ul spacing="normal">
            <li>categories of compromised sites cannot be applied anymore, exposing employees and their organisations to potential cybersecurity risks; alternative approaches to block access to theses sites need to be found</li>
            <li>corporate lists of excluded sites for compliance or policy reasons need alternatives ways to be blocked.</li>
          </ul>
        </section>
        <section anchor="implications-from-loss-of-selective-decrypt">
          <name>Implications from loss of Selective Decrypt</name>
          <t>TLS proxies also have the ability to selectively intercept, avoiding any visibility into or modification of the original application protocol payload - but such selective intercept relies heavily on knowledge of the origin content server hostname, which can be extracted in plaintext from the TLS ClientHello SNI (server name) field.</t>
          <t>This capability allows the application proxy, in particular an HTTPS proxy to engage efficiently specific security controls, e.g. Data Loss Prevention, Sandboxing, etc.</t>
          <t>The loss of SNI visibility will make it more difficult for corporate user flows to be intercepted, with it becoming impossible for BYOD use cases.</t>
          <t>This will create inefficiencies, will require more resources and will increase security risks. It will also be counter productive for privacy as it may require the proxy to decrypt the whole TLS connection.</t>
        </section>
      </section>
    </section>
    <section anchor="specific-implications-for-smbs">
      <name>Specific implications for SMBs</name>
      <t>Small and Medium Business (SMBs) form a particularly vulnerable subset of enterprises and organizations and span from Small Office Home Office (SOHO, sometimes a one person business) to Medium Business with strong variations depending on the country (a 50 employee company is considered the upper range of SMB business in developing countries while it is up to 25'000 in some developed countries).</t>
      <t>Similarly to the above education use case and irrespective of definitions, many SMBs have very limited in-house capabilities to defend themselves, with security often outsourced to Managed Security Service Providers (typically network operators, mid range and small service providers).</t>
    </section>
    <section anchor="public-network-service-providers">
      <name>Public Network Service Providers</name>
      <t>In Public Networks the national, regional and international legislator has to balance between freedom of access to the information on the one hand, and safety of the internet and the protection of other fundamental rights on the other hand.</t>
      <t>There are mainly 2 different approaches:</t>
      <ul spacing="normal">
        <li>First, there are countries which do not have any specific legislation on the issue of blocking, filtering and takedown of illegal internet content: there is no legislative or other regulatory system put in place by the state with a view to defining the conditions and the procedures to be respected by those who engage in the blocking, filtering or takedown of online material. In the absence of a specific or targeted legal framework, several countries rely on an existing "general" legal framework that is not specific to the internet to conduct - what is, generally speaking - limited blocking or takedown of unlawful online material. here the approach has been differentiated in relying on self regulation from the private sector or limited political or legislative intervention to specific areas.</li>
        <li>The other approach has been to set up a legal framework specifically aimed at the regulation of the internet and other digital media, including the blocking, filtering and removal of internet content. Such legislation typically provides for the legal grounds on which blocking or removal may be warranted, the administrative or judicial authority which has competence to take appropriate action and the procedures to be followed.</li>
      </ul>
      <t>In relation to specific areas where the public interest has to be protected more strongly, such as child abuse crimes, terrorism, criminality and national security, many states have a framework for the urgent removal of internet content regarding the above materials without the need of a court order. In such circumstances, administrative authorities, police authorities or public prosecutors are given specific powers to order internet access providers to block access without advance judicial authority. It is common to see such orders requiring action on the part of the internet access provider within 24 hours, and without any notice being given to the content provider or host themselves.</t>
      <t>Particularly in relation to material concerning child abuse and other serious crimes, many countries adopt a "list" system, whereby a central list of blocked URLs or domain names are maintained and updated by the relevant administrative authority. This is notified to the relevant internet access providers, who are required to ensure that blocking is enforced.
Additionally in some states the authorities can request the removal of content that infringes intellectual property, privacy or defamation rights. In this case the removal need to be requested by a court order.</t>
      <t>Generally speaking, the grounds relied on broadly correspond to the interests protected under Article 10(2) of the European Convention of Human Rights (ECHR), namely: the protection of national security, territorial integrity or public safety, the prevention of disorder or crime, the protection of health or morals, the protection of the reputation or rights of others, and the prevention of the disclosure of information received in confidence.
From the methodology we have to distinguish between blocking or takedown of content.</t>
      <ul spacing="normal">
        <li>The blocking, filtering or prevention of access to internet content are generally technical measures intended to restrict access to information or resources typically hosted in another jurisdiction. Such action is normally taken by the internet access provider through hardware or software products that block specific targeted content from being received or displayed on the devices of customers of the internet access provider.</li>
        <li>Takedown or removal of internet content, on the other hand, will instead broadly refer to demands or measures aimed at the website operator (or "host") to remove or delete the offending website content or sub content.</li>
      </ul>
      <t>In these considerations we will refer to blocking only.</t>
      <t>This can be achieved through a number of techniques, including the blocking of the Domain Name System (DNS), the analysis of the SNI field or the Uniform Resource Locator (URL).
Given the increasing adoption of encryption techniques often a mixture of the above techniques is needed.</t>
      <t>In particular for the most serious crimes such as child abuse or national security many countries adopt a "list" methodology, where a central list of blocked Domains or URLs is maintained by the authorities and updated on a regular basis (daily or even hourly) and shared with Public Network Operators that have to enforce the blocking.</t>
      <t>In many jurisdictions there are legal consequences for the Operator not complying with the blocking order.</t>
      <t>Technically the blocking can be implemented using some techniques that have been adapted during time based on the new technologies introduced.</t>
      <t>Historically  depending on the content of the list the technique have been based on DNS or proxy blocking.</t>
      <t>DNS is effective on Domains (the whole domain is blocked), while proxy is effective either on Domain (for encrypted traffic) or URL (for unencrypted traffic).</t>
      <t>Given that nowadays the vast majority of traffic is encrypted, the capability of blocking based on URL is limited to a small portion of traffic and proxy blocking is as effective as that based on the DNS.</t>
      <t>Theoretically DNS blocking would be the preferred option for operators given the more limited investments necessary to implement blocking of the Domains, but given the increased usage of external encrypted DNS services DNS blocking is becoming less effective and operators need to use SNI analysis as well in order to fulfil legal obligations.</t>
      <t>The adoption of ECH will cause additional problems and limit the possibility of implementing operators fulfilling their legal blocking obligations, exposing the population to illegal content related to crimes such as Child Sex Abuse Material (CSAM), malware and other malicious content, and possibly even content deemed to be detrimental to National Security.</t>
    </section>
    <section anchor="threat-detection">
      <name>Threat Detection</name>
      <t><xref target="RFC8404"/> identifies a number of issues arising from increased
encryption of data, some of which apply to ECH.  For example, it
notes that an early trigger for DDoS mitigation involves
distinguishing attacker traffic from legitimate user traffic; this
become more difficult if traffic sources are obscured.</t>
      <t>The various indicators of compromise (IoCs) are documented in <xref target="I-D.draft-ietf-opsec-indicators-of-compromise"/>, which also describes how they
are used effectively in cyber defence. For example, section 4.1.1 of
the document describes the importance of IoCs as part of a defence-
in-depth strategy; in this context, SNI is just one of the range of
indicators that can be used to build up a resilient defence (see
section 3.1 in the same document on IoC types and the 'pyramid of
pain').</t>
      <t>In the same Internet-Draft, section 6.1 expands on the importance of
the defence in depth strategy.  In particular, it explains the role
that domains and IP addresses can play, especially where end-point
defences are compromised or ineffective, or where endpoint security
isn't possible, such as in BYOD, IoT and legacy environments.  SNI
data plays a role here, in particular where DNS data is unavailable
because it has been encrypted; if SNI data is lost too, alongside
DNS, defences are weakened and the attack surface increased.</t>
    </section>
    <section anchor="potential-further-development-of-this-work">
      <name>Potential further development of this work</name>
      <t>This work could consider several potential developments:</t>
      <ul spacing="normal">
        <li>If ECH is enforced what are the solutions to all the above problems and what are the migration paths?</li>
        <li>Elaborate on endpoint security complications as <xref target="I-D.draft-taddei-smart-cless-introduction"/> as well as <xref target="MAGECART"/> <xref target="MITB"/> <xref target="MITB-MITRE"/> <xref target="MALVERTISING"/> showed that in some cases, the only way to detect an attack is through the use of network-based security. The loss of visibility of the SNI data will make it much harder to detect attacks. The endpoints components (operating system, applications, browsers, etc.) cannot be judge and party.</li>
        <li>There are need for further clarifications from the ECH draft, e.g. The link between the Client Facing and the backend servers are not clear enough and need further description. It can't be just 'left to the implementation'</li>
        <li>Will there be any impact to the DNS by adding so many new RRs?</li>
        <li>What happens if Client Facing servers are controlled by malicious actors?</li>
        <li>The Client Facing servers are acting as a new category of middleboxes. In this shift left movement, until the attack surface is minimal and complexities are removed, you have to rely on third parties for inspection. In these conditions, on which basis can they be more trusted than any other middleboxes? Is this creating a concentration problem?</li>
        <li>What prevents a Client Facing server providing security solutions to protect the data path?</li>
        <li>Consolidation considerations - the use of ECH may accelerate the move of content away from standalone servers and on to CDNs, reducing infrastructure resilience.</li>
        <li>Find missing sources to illustrate a number of points, e.g. show how adversaries use digital transformation to accelerate their attacks, how ECH will increase security risks.</li>
        <li>Keep streamlining, clarifying the text e.g. the 2 approaches in the public network service providers section, "Technically the blocking ...".</li>
      </ul>
    </section>
    <section anchor="conclusion">
      <name>Conclusion</name>
      <t>Access to SNI data is sometimes necessary in order for institutions,
including those in the education and finance sectors, to discharge
their compliance obligations.  The introduction of ECH in client
software poses operational challenges that could be overcome on
devices owned by those institutions if policy settings are supported
within the software that allows the ECH functionality to be disabled.</t>
      <t>Third-party devices pose an additional challenge, primarily because
the use of ECH will render transparent proxies inoperable.  The most
likely solution is that institutions will require the installation of
full proxies and certificates on those devices before they are
allowed to be connected to the host networks.  They may alternatively
determine that such an approach is impractical and instead withdraw
the ability for network access by third-party devices.</t>
      <t>An additional option that warrants further consideration is the
development of a standard that allows a network to declare its policy
regarding ECH and other such developments.  Clients would then have
the option to continue in setting up a connection if they are happy
to accept those policies, or to disconnect and try alternative
network options if not.  Such a standard is outside of the scope of
this document but may provide a mechanism that allows the interests
and preferences of client software, end-users and network operators
to be balanced.</t>
    </section>
    <section anchor="security-considerations">
      <name>Security Considerations</name>
      <t>In addition to introducing new operational and financial issues, the
introduction of SNI encryption poses new challenges for threat
detection which this document outlines.  These do not appear to have
been considered within either <xref target="RFC8744"/> or the current ECH Internet-
Draft <xref target="I-D.draft-ietf-tls-esni"/> and should be addressed fully within
the latter's security considerations section.</t>
      <t>This I-D should help improve security in deployments of ECH.</t>
    </section>
    <section anchor="iana-considerations">
      <name>IANA Considerations</name>
      <t>This document has no IANA actions.</t>
    </section>
    <section anchor="acknowledgment">
      <name>Acknowledgment</name>
      <t>In addition to the authors, this document is the product of an
informal group of experts including the following people:</t>
    </section>
  </middle>
  <back>
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <reference anchor="RFC8484" target="https://www.rfc-editor.org/info/rfc8484">
          <front>
            <title>DNS Queries over HTTPS (DoH)</title>
            <author fullname="P. Hoffman" initials="P." surname="Hoffman">
              <organization/>
            </author>
            <author fullname="P. McManus" initials="P." surname="McManus">
              <organization/>
            </author>
            <date month="October" year="2018"/>
            <abstract>
              <t>This document defines a protocol for sending DNS queries and getting DNS responses over HTTPS.  Each DNS query-response pair is mapped into an HTTP exchange.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8484"/>
          <seriesInfo name="DOI" value="10.17487/RFC8484"/>
        </reference>
      </references>
      <references>
        <name>Informative References</name>
        <reference anchor="CIPA" target="https://www.fcc.gov/consumers/guides/childrens-internet-protection-act/">
          <front>
            <title>Children's Internet Protection Act (CIPA)</title>
            <author>
              <organization>FCC</organization>
            </author>
            <date year="2019" month="December" day="30"/>
          </front>
        </reference>
        <reference anchor="Coroner" target="https://www.judiciary.uk/publications/frances-thomas-prevention-of-future-deaths-report/">
          <front>
            <title>Prevention of future deaths report</title>
            <author initials="" surname="Henderson" fullname="Henderson">
              <organization/>
            </author>
            <date year="2021" month="November" day="26"/>
          </front>
        </reference>
        <reference anchor="ECH_Roundtable" target="https://419.consulting/encrypted-client-hello/">
          <front>
            <title>Encrypted Client Hello - Notes from an ECH Roundtable</title>
            <author>
              <organization>419 Consulting</organization>
            </author>
            <date year="2021" month="August" day="18"/>
          </front>
        </reference>
        <reference anchor="KCSE" target="https://419.consulting/encrypted-client-hello/">
          <front>
            <title>Keeping children safe in education 2021</title>
            <author>
              <organization>DfE</organization>
            </author>
            <date year="2021" month="November" day="01"/>
          </front>
        </reference>
        <reference anchor="Bloomberg" target="https://www.bloomberg.com/news/articles/2022-08-16/wall-street-sticker-shock-whatsapp-fines-were-years-in-making">
          <front>
            <title>Wall Street's Record Fines Over WhatsApp Use Were Years in the Making</title>
            <author initials="S." surname="Spezzati" fullname="Stefania Spezzati">
              <organization>Bloomberg</organization>
            </author>
            <author initials="M." surname="Robinson" fullname="Matt Robinson">
              <organization>Bloomberg</organization>
            </author>
            <author initials="L." surname="Beyoud" fullname="Lydia Beyoud">
              <organization>Bloomberg</organization>
            </author>
            <date year="2022" month="August" day="16"/>
          </front>
        </reference>
        <reference anchor="MAGECART" target="https://en.wikipedia.org/wiki/Web_skimming#Magecart">
          <front>
            <title>Magecart</title>
            <author>
              <organization>Wikipedia</organization>
            </author>
            <date year="2022" month="April" day="03"/>
          </front>
        </reference>
        <reference anchor="MALVERTISING" target="https://en.wikipedia.org/wiki/Malvertising">
          <front>
            <title>Malvertising</title>
            <author>
              <organization>Wikipedia</organization>
            </author>
            <date year="2022" month="June" day="02"/>
          </front>
        </reference>
        <reference anchor="MITB" target="https://owasp.org/www-community/attacks/Man-in-the-browser_attack">
          <front>
            <title>Man-in-the-browser attack</title>
            <author>
              <organization>OWASP</organization>
            </author>
            <date>n.d.</date>
          </front>
        </reference>
        <reference anchor="MITB-MITRE" target="https://attack.mitre.org/techniques/T1185/">
          <front>
            <title>Browser Session Hijacking - T1185</title>
            <author>
              <organization>MITRE</organization>
            </author>
            <date year="2022" month="February" day="25"/>
          </front>
        </reference>
        <reference anchor="NIST-DID" target="https://csrc.nist.gov/glossary/term/defense_in_depth#:~:text=Definition(s)%3A,and%20missions%20of%20the%20organization.">
          <front>
            <title>Glossary - defense-in-depth</title>
            <author>
              <organization>NIST</organization>
            </author>
            <date>n.d.</date>
          </front>
        </reference>
        <reference anchor="SOLARWIND" target="https://symantec.broadcom.com/en/solarwinds-sunburst-attacks">
          <front>
            <title>SolarWinds (Sunburst) Attack What You Need to Know</title>
            <author>
              <organization>Symantec, a Division of Broadcom Software Group</organization>
            </author>
            <date year="2020" month="December"/>
          </front>
        </reference>
        <reference anchor="LOSSINCAP" target="https://www.amf-france.org/sites/default/files/2020-02/etude-sur-la-cybercriminalite-boursiere-_-definition-cas-et-perspectives.pdf">
          <front>
            <title>La cybercriminalité boursière – définition, cas et perspectives</title>
            <author initials="A." surname="Neyret" fullname="Alexandre Neyret">
              <organization/>
            </author>
            <author>
              <organization>Autorité des Marchés Financiers</organization>
            </author>
            <date year="2019" month="October" day="10"/>
          </front>
        </reference>
        <reference anchor="LOSSINCREDITSCORE" target="https://www2.deloitte.com/content/dam/Deloitte/global/Documents/Risk/gx-risk-gra-beneath-the-surface.pdf">
          <front>
            <title>Beneath the surface of a cyberattack – A deeper look at business impacts</title>
            <author>
              <organization>Deloitte</organization>
            </author>
            <date year="2016"/>
          </front>
        </reference>
        <reference anchor="LOSSINREVENUE" target="https://anozrway.com/wp-content/uploads/dlm_uploads/2022/09/ANOZR-WAY_Barometre-Ransomware_edition-septembre-2022.pdf">
          <front>
            <title>BAROMÈTRE ANOZR WAY DU RANSOMWARE</title>
            <author>
              <organization>ANOZR WAY</organization>
            </author>
            <date year="2022" month="September" day="04"/>
          </front>
        </reference>
        <reference anchor="RFC8890" target="https://www.rfc-editor.org/info/rfc8890">
          <front>
            <title>The Internet is for End Users</title>
            <author fullname="M. Nottingham" initials="M." surname="Nottingham">
              <organization/>
            </author>
            <date month="August" year="2020"/>
            <abstract>
              <t>This document explains why the IAB believes that, when there is a conflict between the interests of end users of the Internet and other parties, IETF decisions should favor end users. It also explores how the IETF can more effectively achieve this.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8890"/>
          <seriesInfo name="DOI" value="10.17487/RFC8890"/>
        </reference>
        <reference anchor="RFC7258" target="https://www.rfc-editor.org/info/rfc7258">
          <front>
            <title>Pervasive Monitoring Is an Attack</title>
            <author fullname="S. Farrell" initials="S." surname="Farrell">
              <organization/>
            </author>
            <author fullname="H. Tschofenig" initials="H." surname="Tschofenig">
              <organization/>
            </author>
            <date month="May" year="2014"/>
            <abstract>
              <t>Pervasive monitoring is a technical attack that should be mitigated in the design of IETF protocols, where possible.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="188"/>
          <seriesInfo name="RFC" value="7258"/>
          <seriesInfo name="DOI" value="10.17487/RFC7258"/>
        </reference>
        <reference anchor="RFC8404" target="https://www.rfc-editor.org/info/rfc8404">
          <front>
            <title>Effects of Pervasive Encryption on Operators</title>
            <author fullname="K. Moriarty" initials="K." role="editor" surname="Moriarty">
              <organization/>
            </author>
            <author fullname="A. Morton" initials="A." role="editor" surname="Morton">
              <organization/>
            </author>
            <date month="July" year="2018"/>
            <abstract>
              <t>Pervasive monitoring attacks on the privacy of Internet users are of serious concern to both user and operator communities.  RFC 7258 discusses the critical need to protect users' privacy when developing IETF specifications and also recognizes that making networks unmanageable to mitigate pervasive monitoring is not an acceptable outcome: an appropriate balance is needed.  This document discusses current security and network operations as well as management practices that may be impacted by the shift to increased use of encryption to help guide protocol development in support of manageable and secure networks.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8404"/>
          <seriesInfo name="DOI" value="10.17487/RFC8404"/>
        </reference>
        <reference anchor="RFC8744" target="https://www.rfc-editor.org/info/rfc8744">
          <front>
            <title>Issues and Requirements for Server Name Identification (SNI) Encryption in TLS</title>
            <author fullname="C. Huitema" initials="C." surname="Huitema">
              <organization/>
            </author>
            <date month="July" year="2020"/>
            <abstract>
              <t>This document describes the general problem of encrypting the Server Name Identification (SNI) TLS parameter. The proposed solutions hide a hidden service behind a fronting service, only disclosing the SNI of the fronting service to external observers. This document lists known attacks against SNI encryption, discusses the current "HTTP co-tenancy" solution, and presents requirements for future TLS-layer solutions. </t>
              <t>In practice, it may well be that no solution can meet every requirement and that practical solutions will have to make some compromises.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8744"/>
          <seriesInfo name="DOI" value="10.17487/RFC8744"/>
        </reference>
        <reference anchor="I-D.draft-ietf-tls-esni" target="https://www.ietf.org/archive/id/draft-ietf-tls-esni-15.txt">
          <front>
            <title>TLS Encrypted Client Hello</title>
            <author fullname="Eric Rescorla" initials="E." surname="Rescorla">
              <organization>RTFM, Inc.</organization>
            </author>
            <author fullname="Kazuho Oku" initials="K." surname="Oku">
              <organization>Fastly</organization>
            </author>
            <author fullname="Nick Sullivan" initials="N." surname="Sullivan">
              <organization>Cloudflare</organization>
            </author>
            <author fullname="Christopher A. Wood" initials="C. A." surname="Wood">
              <organization>Cloudflare</organization>
            </author>
            <date day="3" month="October" year="2022"/>
            <abstract>
              <t>   This document describes a mechanism in Transport Layer Security (TLS)
   for encrypting a ClientHello message under a server public key.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Source for this draft and an issue tracker can be found at
   https://github.com/tlswg/draft-ietf-tls-esni
   (https://github.com/tlswg/draft-ietf-tls-esni).

              </t>
            </abstract>
          </front>
          <seriesInfo name="Internet-Draft" value="draft-ietf-tls-esni-15"/>
        </reference>
        <reference anchor="I-D.draft-ietf-opsec-indicators-of-compromise" target="https://www.ietf.org/archive/id/draft-ietf-opsec-indicators-of-compromise-02.txt">
          <front>
            <title>Indicators of Compromise (IoCs) and Their Role in Attack Defence</title>
            <author fullname="Kirsty Paine" initials="K." surname="Paine">
              <organization>Splunk Inc.</organization>
            </author>
            <author fullname="Ollie Whitehouse" initials="O." surname="Whitehouse">
              <organization>NCC Group</organization>
            </author>
            <author fullname="James Sellwood" initials="J." surname="Sellwood">
         </author>
            <author fullname="Andrew S" initials="A." surname="S">
              <organization>UK National Cyber Security Centre</organization>
            </author>
            <date day="12" month="September" year="2022"/>
            <abstract>
              <t>   Cyber defenders frequently rely on Indicators of Compromise (IoCs) to
   identify, trace, and block malicious activity in networks or on
   endpoints.  This draft reviews the fundamentals, opportunities,
   operational limitations, and best practices of IoC use.  It
   highlights the need for IoCs to be detectable in implementations of
   Internet protocols, tools, and technologies - both for the IoCs'
   initial discovery and their use in detection - and provides a
   foundation for new approaches to operational challenges in network
   security.

              </t>
            </abstract>
          </front>
          <seriesInfo name="Internet-Draft" value="draft-ietf-opsec-indicators-of-compromise-02"/>
        </reference>
        <reference anchor="I-D.draft-mcfadden-smart-threat-changes" target="https://www.ietf.org/archive/id/draft-mcfadden-smart-threat-changes-04.txt">
          <front>
            <title>BCP72 - A Problem Statement</title>
            <author fullname="Mark McFadden" initials="M." surname="McFadden">
              <organization>internet policy advisors</organization>
            </author>
            <date day="22" month="January" year="2022"/>
            <abstract>
              <t>   RFC3552/BCP72 describes an Internet Threat model that has been used
   in Internet protocol design. More than eighteen years have passed
   since RFC3552 was written and the structure and topology of the
   Internet have changed. With those changes comes a question: has the
   Internet Threat Model changed? Or, is the model described in RFC3552
   still mostly accurate?  This draft attempts to describe a non-
   exhaustive list of changes in the current threat environment. It
   finds that there are both qualitative and quantitative differences
   from the environment described in RFC3552 and is intended as input
   to the IAB program on the Internet threat model started in 2020.

              </t>
            </abstract>
          </front>
          <seriesInfo name="Internet-Draft" value="draft-mcfadden-smart-threat-changes-04"/>
        </reference>
        <reference anchor="I-D.draft-ietf-opsec-ns-impact" target="https://www.ietf.org/archive/id/draft-ietf-opsec-ns-impact-04.txt">
          <front>
            <title>Impact of TLS 1.3 to Operational Network Security Practices</title>
            <author fullname="Nancy Cam-Winget" initials="N." surname="Cam-Winget">
              <organization>Cisco Systems</organization>
            </author>
            <author fullname="Eric Wang" initials="E." surname="Wang">
              <organization>Cisco Systems</organization>
            </author>
            <author fullname="Roman Danyliw" initials="R." surname="Danyliw">
              <organization>Software Engineering Institute</organization>
            </author>
            <author fullname="Roelof DuToit" initials="R." surname="DuToit">
              <organization>Broadcom</organization>
            </author>
            <date day="26" month="January" year="2021"/>
            <abstract>
              <t>   Network-based security solutions are used by enterprises, the public
   sector, internet-service providers, and cloud-service providers to
   both complement and enhance host-based security solutions.  As TLS is
   a widely deployed protocol to secure communication, these network-
   based security solutions must necessarily interact with it.  This
   document describes this interaction for current operational security
   practices and notes the impact of TLS 1.3 on them.

              </t>
            </abstract>
          </front>
          <seriesInfo name="Internet-Draft" value="draft-ietf-opsec-ns-impact-04"/>
        </reference>
        <reference anchor="I-D.draft-taddei-smart-cless-introduction" target="https://www.ietf.org/archive/id/draft-taddei-smart-cless-introduction-03.txt">
          <front>
            <title>Capabilities and Limitations of an Endpoint-only Security Solution</title>
            <author fullname="Arnaud Taddei" initials="A." surname="Taddei">
              <organization>Broadcom</organization>
            </author>
            <author fullname="Candid Wueest" initials="C." surname="Wueest">
              <organization>Acronis</organization>
            </author>
            <author fullname="Kevin A. Roundy" initials="K. A." surname="Roundy">
              <organization>Norton Lifelock</organization>
            </author>
            <author fullname="Dominique Lazanski" initials="D." surname="Lazanski">
              <organization>Last Press Label</organization>
            </author>
            <date day="13" month="July" year="2020"/>
            <abstract>
              <t>   In the context of existing, proposed and newly published protocols,
   this draft RFC is to establish the capabilities and limitations of
   endpoint-only security solutions and explore benefits and
   alternatives to mitigate those limits with the support of real case
   studies.

              </t>
            </abstract>
          </front>
          <seriesInfo name="Internet-Draft" value="draft-taddei-smart-cless-introduction-03"/>
        </reference>
      </references>
    </references>
    <section anchor="contributors" numbered="false" toc="include" removeInRFC="false">
      <name>Contributors</name>
      <contact initials="E." surname="Chien" fullname="Eric Chien">
        <organization>Broadcom</organization>
        <address>
          <email>Eric.Chien@broadcom.com</email>
          <uri>https://www.linkedin.com/in/eric-chien-66b4b258/</uri>
        </address>
      </contact>
      <t>Eric contributed to the analysis of the Man in the Browser attacks.</t>
      <contact initials="G." surname="Scalone" fullname="Gianpaolo Scalone">
        <organization>Vodafone</organization>
        <address>
          <email>gianpaolo-angelo.scalone@vodafone.com</email>
          <uri>https://www.linkedin.com/in/gianpaoloscalone/</uri>
        </address>
      </contact>
      <t>Gianpaolo contributed the research on the Digital Markets Act (DMA) EU law conflict with ECH.</t>
      <contact initials="D." surname="Engberg" fullname="Daniel Engberg">
        <organization>Skandinaviska Enskilda Banken AB (SEB)</organization>
        <address>
          <email>daniel.engberg@seb.se</email>
          <uri>https://www.linkedin.com/in/daniel-engberg-1561aaa/</uri>
        </address>
      </contact>
      <t>Validate the issues for his organization.</t>
      <contact initials="C." surname="Leroy" fullname="Celine Leroy">
        <organization>Eight Advisory</organization>
        <address>
          <email>celine.leroy@8advisory.com</email>
          <uri>https://www.linkedin.com/in/celine-leroy-1a534252/</uri>
        </address>
      </contact>
      <t>Thank you to Celine for her work on cybersecurity financial impacts on enterprises.</t>
      <contact initials="D." surname="Engberg" fullname="Daniel Engberg">
        <organization>Skandinaviska Enskilda Banken AB (SEB)</organization>
        <address>
          <email>daniel.engberg@seb.se</email>
          <uri>https://www.linkedin.com/in/daniel-engberg-1561aaa/</uri>
        </address>
      </contact>
      <t>Validate the issues for his organization.</t>
      <contact initials="G." surname="Tavano" fullname="Gianpiero Tavano">
        <organization>Broadcom</organization>
        <address>
          <email>Gianpiero.Tavano@broadcom.com</email>
          <uri>https://www.linkedin.com/in/gianpiero-tavano-5b975383/</uri>
        </address>
      </contact>
      <t>Review the text, provided feedback and reminded us on the budgetary issues</t>
      <contact initials="R." surname="duToit" fullname="Roelof duToit">
        <organization>Broadcom</organization>
        <address>
          <email>roelof.dutoit@broadcom.com</email>
          <uri>https://www.linkedin.com/in/roelof-du-toit-a66831/</uri>
        </address>
      </contact>
      <t>Roelof contributed many things including research, former I-D, text, the newly setup github, etc.</t>
      <contact initials="D." surname="Lopez" fullname="Diego Lopez">
        <organization>Telefonica</organization>
        <address>
          <email>diego.r.lopez@telefonica.com</email>
          <uri>https://www.linkedin.com/in/dr2lopez/</uri>
        </address>
      </contact>
      <t>Diego contributed in several aspects including MCPs.</t>
      <contact initials="G." surname="Tomic" fullname="Gary Tomic">
        <organization>Broadcom</organization>
        <address>
          <email>gary.tomic@broadcom.com</email>
          <uri>https://www.linkedin.com/in/garytomic/</uri>
        </address>
      </contact>
      <t>Gary contributed many things including research, keep us on scope, critique for when issues where not impacted by ECH as we initially thought.</t>
    </section>
  </back>
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