Network Working Group                                        B. Trammell
Internet-Draft                                                    Google
Intended status: Informational                          October 17, 2019
Expires: April 19, 2020

                   Optional Security Is Not An Option


   This document explores the common properties of optional security
   protocols and extensions, and notes that due to the base-rate fallacy
   and general issues with coordinated deployment of protocols under
   uncertain incentives, optional security protocols have proven
   difficult to deploy in practice.  This document defines the problem,
   examines efforts to add optional security for routing, naming, and
   end-to-end transport, and extracts guidelines for future efforts to
   deploy optional security protocols based on successes and failures to

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem statement . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Case studies  . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Routing security: BGPSEC and RPKI . . . . . . . . . . . .   4
     3.2.  DNSSEC  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  HTTP over TLS . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Discussion and Recommendations  . . . . . . . . . . . . . . .   7
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Many of the protocols that make up the Internet architecture were
   designed and first implemented in an envrionment of mutual trust
   among network engineers, operators, and users, on computers that were
   incapable of using cryptographic protection of confidentiality,
   integrity, and authenticity for those protocols, in a legal
   environment where the distribution of cryptographic technology was
   largely restricted by licensing and/or prohibited by law.  The result
   has been a protocol stack where security properties have been added
   to core protocols using those protocols' extension mechanisms.

   As extension mechanisms are by design optional features of a
   protocol, this has led to a situation where security is optional up
   and down the protocol stack.  Protocols with optional security have
   proven to be difficult to deploy.  This document describes and
   examines this problem, and provides guidance for future evolution of
   the protocol, based on current work in network measurement and usable
   security research.

2.  Problem statement

   Consider an optional security extension with the following

   1.  The extension is optional: a given connection or operation will
       succeed without the extension, albeit without the security
       properties the extension guarantees.

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   2.  The extension has a true positive probability P: the probability
       that it will cause any given operation to fail, thereby
       successfully preventing an attack that would have otherwise
       succeeded had the extension not been enabled.  This probability
       is a function of the extension's effectiveness as well as the
       probability that said operation will be an instance of the attack
       the extension prevents.

   3.  The extension has a false positive probability Q: the probability
       it will cause any given operation to fail due to some condition
       other than an attack, e.g. due to a misconfiguration.

   Moving from no deployment of an optional security extension to full
   deployment is a protocol transition as described in [RFC8170].  We
   posit that the implicit transition plans for these protocols have
   generally suffered from an underestimation of the disincentive (as in
   section 5.2 of [RFC8170]) linked to the relationship between P and Q
   for any given protocol.

   Specifically, if Q is much greater than P, then any user of an
   optional security extension will face an overwhelming incentive to
   disable that extension, as the cost of dealing with spuriously
   failing operations overwhelms the cost of dealing with relatively
   rare successful attacks.  This incentive becomes stronger when the
   cause of the false positive is someone else's problem; i.e. not a
   misconfiguration the user can possibly fix.  This situation can arise
   when poor design, documentation, or tool support elevates the
   incidence of misconfiguration (high Q), in an environment where the
   attack models addressed by the extension are naturally rare (low P).

   This is not a novel observation; a similar phenomenon following from
   the base-rate fallacy has been studied in the literature on
   operational security, where the false positive and true positive
   rates for intrusion detection systems have a similar effect on the
   applicability of these systems.  Axelsson showed [Axelsson99] that
   the false positive rate must be held extremely low, on the order of 1
   in 100,000, for the probability of an intrusion given an alarm to be
   worth the effort of further investigation.

   Indeed, the situation is even worse than this.  Experience with
   operational security monitoring indicates that when Q is high enough,
   even true positives P may be treated as "in the way".

3.  Case studies

   Here we examine four optional security extensions, BGPSEC [RFC8205],
   RPKI [RFC6810], DNSSEC [RFC4033], and the addition of TLS to HTTP/1.1

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   [RFC2818], to see how the relationship of P and Q has affected their

   We choose these examples as all four represent optional security, and
   that perfect deployment of the associated extensions - securing the
   routing control plane, the Internet naming system, and end-to-end
   transport (at least for the Web platform) - would represent
   completely "securing" the Internet architecture at layers 3 and 4.

3.1.  Routing security: BGPSEC and RPKI

   The Border Gateway Protocol [RFC4271] (BGP) is used to propagate
   interdomain routing information in the Internet.  Its original design
   has no integrity protection at all, either on a hop-by-hop or on an
   end-to-end basis.  In the meantime, the TCP Authentication Option
   [RFC5925] (and MD5 authentication [RFC2385], which it replaces) have
   been deployed to add hop-by-hop integrity protection.

   End-to-end protection of the integrity of BGP announcements is
   protected by two complementary approaches.  Route announcements in
   BGP updates protected by BGPSEC [RFC8205] have the property that the
   every Autonomous System (AS) on the path of ASes listed in the UPDATE
   message has explicitly authorized the advertisement of the route to
   the subsequent AS in the path.  RPKI [RFC6810] protects prefixes,
   granting the right to advertise a prefix (i.e., be the first AS in
   the AS path) to a specific AS.  RPKI serves as a trust root for
   BGPSEC, as well.

   These approaches are not yet universally deployed.  BGP route origin
   authentication approaches provide little benefit to individual
   deployers until it is almost universally deployed [Lychev13].  RPKI
   route origin validation is similarly deployed in about 15% of the
   Internet core; two thirds of these networks only assign lower
   preference to non-validating announcements.  This indicates
   significant caution with respect to RPKI mistakes [Gilad17].

   There are indications that this caution may be abating.  At the RIPE
   78 meeting in May 2019, Job Snijders reported that networks are
   beginning to validate route origins, especially on peering sessions
   [Snijders19].  Concerted effort to improve tooling for RPKI signing
   and validation have reduced Q.  Deployment is acclerating, which
   Snijders attributes in part to fear of missing out: as individual
   networks deploy validation and find that the risk to availability is
   lower than feared, and their operators realize that the added
   security of rejecting RPKI invalid announcements can be used as a
   competetive advantage.  The actions of smaller networks can drive to
   decisions by larger ones: Snijders relates a story in which the
   current "snowball effect" began with a single small operator in the

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   Netherlands announcing that they were rejecting invalids, and that
   nothing bad had happened.  This uptake appears to continue: RIPE NCC
   reported at the following RIPE 79 meeting in October 2019
   [Trenaman19] that the RPKI is growing to be a fundamental part of the
   Internet infrastructure, and that they are increasing budget and
   investing in technical infrastructure and process improvements to
   better support RPKI.  This investment and attention should have the
   effect of reducing Q.

3.2.  DNSSEC

   The Domain Name System (DNS) [RFC1035] provides a distributed
   protocol for the mapping of Internet domain names to information
   about those names.  As originally specified, an answer to a DNS query
   was considered authoritative if it came from an authoritative server,
   which does not allow for authentication of information in the DNS.
   DNS Security [RFC4033] remedies this through an extension, allowing
   DNS resource records to be signed using keys linked to zones, also
   distributed via DNS.  A name can be authenticated if every level of
   the DNS hierarchy from the root up to the zone containing the name is

   The root zone of the DNS has been signed since 2010.  As of 2016, 89%
   of TLD zones were also signed.  However, the deployment status of
   DNSSEC for second-level domains (SLDs) varies wildly from region to
   region and is generally poor: only about 1% of .com, .net. and .org
   SLDs were properly signed [DNSSEC-DEPLOYMENT].  Chung et al found
   recently that second-level domain adoption was linked incentives for
   deployment: TLDs which provided direct financial incentives to SLDs
   for having correctly signed DNS zones tend to have much higher
   deployment, though these incentives must be carefully designed to
   ensure that they measure correct deployment, as opposed to more
   easily-gamed indirect metrics [Chung17].

   However, the base-rate effect tends to reduce the use of DNSSEC
   validating resolvers, which remains below 15% of Internet clients

   DNSSEC deployment is hindered by other obstacles, as well.  Since the
   organic growth of DNS software predates even TCP/IP, even EDNS, the
   foundational extension upon which DNSSEC is built are not universally
   deployed, which inflates Q.  The recent DNS Flag Day effort (see aims to remedy this by purposely breaking
   backward interoperability with servers that are not EDNS-capable, by
   coordinating action among DNS software developers and vendors.

   In addition, for the Web platform at least, DNSSEC is not percieved
   as having essential utility, given the deployment of TLS and the

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   assurances provided by the Web PKI (on which, see Section 3.3).  A
   connection intercepted due to a poisoned DNS cache would fail to
   authenticate unless the attacker also obtained a valid certificate
   from the name, rendering DNS interception less useful, in effect,
   reducing P.

3.3.  HTTP over TLS

   Security was added to the Web via HTTPS, running HTTP over TLS over
   TCP, in the 1990s [RFC2818].  Deployment of HTTPS crossed 50% of web
   traffic in 2017.

   Base-rate effects didn't hinder the deployment of HTTPS per se;
   however, until recently, warnings about less-safe HTTPS
   configurations (e.g. self-signed certificates, obsolete versions of
   SSL/TLS, old ciphersuites, etc.) were less forceful due to the
   prevalence of these configurations.  As with DNS Flag Day, making
   changes to browser user interfaces that inform the user of low-
   security configurations is facilitated by coordination among browser
   developers [ChromeHTTPS].  If one browser moves alone to start
   displaying warnings or refusing to connect to sites with less-safe or
   unsafe configurations, then users will tend to percieve the safer
   browser as more broken, as websites that used to work don't anymore:
   i.e., non-coordinated action can lead to the false perception that an
   increase in P is an increase in Q.  This coordination continues up
   the Web stack within the W3C [SecureContexts].

   The Automated Certificate Management Environment [ACME] has further
   accelerated the deployment of HTTPS on the server side, by
   drastically reducing the effort required to properly manage server
   certificates, reducing Q by making configuration easier than
   misconfiguration.  Let's Encrypt leverages ACME to make it possible
   to offer certificates at scale for no cost with automated validation,
   issuing 90 million active certificates protecting 150 million domain
   names in December 2018 [LetsEncrypt2019].

   Deployment of HTTPS accelerated in the wake of the Snowden
   revelations.  Here, the perception of the utility of HTTPS has
   changed.  Increasing confidentiality of Web traffic for openly-
   available content was widely seen as not worth the cost and effort
   prior to these revelations.  However, as it became clear that the
   attacker model laid out in [RFC7624] was a realistic one, content
   providers and browser vendors put the effort in to increase
   implementation and deployment.

   The ubiquitous deployment of HTTPS is not yet complete; however, all
   indications are that it will represent a rare eventual success story
   in the ubiquitous deployment of an optional security extention.  What

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   can we learn from this success?  We note that each endpoint deciding
   to use HTTPS saw an immediate benefit, which is an indicator of good
   chances of success for incremental deployment [RFC8170].  However,
   the acceleration of deployment since 2013 is the result of the
   coordinated effort of actors throughout the Web application and
   operations stack, unified around a particular event which acted as a
   call to arms.  While there are downsides to market consolidation, the
   relative consolidation of the browser market has made coordinated
   action to change user interfaces possible, as well as making it
   possible to launch a new certificate authority (by adding its issuer
   to the trusted roots of a relatively small number of browsers) from
   nothing in a short period of time.

4.  Discussion and Recommendations

   It has been necessary for all new protocol work in the IETF to
   consider security since 2003 [RFC3552], and the Internet Architecture
   Board recommended that all new protocol work provide confidentiality
   by default in 2014 [IAB-CONFIDENTIALITY]; new protocols should
   therefore already not rely on optional extensions to provide security
   guarantees for their own operations or for their users.

   In many cases in the running Internet, the ship has sailed: it is not
   at this point realistic to replace protocols relying on optional
   features for security with new, secure protocols.  While these full
   replacements would be less susceptible to base-rate effects, they
   have the same misaligned incentives to deploy as the extensions the
   architecture presently relies on.

   The base rate fallacy is essential to this situation, so the P/Q
   problem is difficult to sidestep.  However, an examination of our
   case studies does suggest incremental steps toward improving the
   current situation:

   o  When natural incentives are not enough to overcome base-rate
      effects, external incentives (such as financial incentives) have
      been shown to be effective to motivate single deployment
      decisions.  This essentially provides utility in the form of cash,
      offseting the negative cost of high Q.

   o  While "flag days" are difficult to arrange in the current
      Internet, coordinated action among multiple actors in a market
      (e.g.  DNS resolvers or web browsers) can reduce the risk that
      temporary breakage due to the deployment of new security protocols
      is perceived as an error, at least reducing the false perception
      of Q.

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   o  Efforts to automate configuration of security protocols, and to
      improve tooling for managing secure operations, can reduce the
      incidence of misconfiguration Q, and have had a positive impact on

   Coordinated action has demonstrated success in the case of HTTPS, so
   examining the outcome (or failure) of DNS Flag Day will provide more
   information about the likelihood of future such actions to move
   deployment of optional security features forward.  It is difficult to
   see how insights on coordinated action in DNS and HTTPS can be
   applied to routing security, however, given the number of actors who
   would need to coordinate to make present routing security approaches
   widely useful.  We note, however, that the MANRS effort
   ( provides an umbrella activity under which any
   future coordination might take place.

   We note that the cost of a deployment decision (at least for DNSSEC)
   could readily be extracted from the literature [Chung17].
   Extrapolation from this work of a model for determining the total
   cost of full deployment of DNSSEC (or, indeed, of comprehensive
   routing security) is left as future work.

5.  Acknowledgments

   Many thanks to Peter Hessler, Geoff Huston, and Roland van Rijswijk-
   Deij for conversations leading to the problem statement presented in
   this document.  Thanks to Martin Thomson for his feedback on the
   document itself, which has greatly improved subsequent versions.  The
   title shamelessly riffs off that of Berkeley tech report about IP
   options written by Rodrigo Fonseca et al., via a paper at IMC 2017 by
   Brian Goodchild et al.

   This work is partially supported by the European Commission under
   Horizon 2020 grant agreement no. 688421 Measurement and Architecture
   for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat
   for Education, Research, and Innovation under contract no. 15.0268.
   This support does not imply endorsement.

6.  Informative References

   [ACME]     Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
              Kasten, "Automatic Certificate Management Environment
              (ACME)", draft-ietf-acme-acme-18 (work in progress),
              December 2018.

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              Axelsson, S., "The Base-Rate Fallacy and its Implications
              for the Difficulty of Intrusion Detection (in ACM CCS
              1999)", 1999, <

              Schechter, E., "["A milestone for Chrome security -
              marking HTTP as \"not secure\" (Google blog post)", nil]",
              July 2018, <

   [Chung17]  Chung, T., van Rijswijk-Deij, R., Choffnes, D., Levin, D.,
              Maggs, B., Mislove, A., and C. Wilson, "Understanding the
              Role of Registrars in DNSSEC Deployment", November 2017,

              Internet Society, ., "State of DNSSEC Deployment 2016",
              December 2016,

   [Gilad17]  Gilad, Y., Cohen, A., Herzberg, A., Schapira, M., and H.
              Schulman, "Are We There Yet? On RPKI's Deployment and
              Security (in NDSS 2017)", November 2017,

              Internet Architecture Board, ., "IAB Statement on Internet
              Confidentiality", November 2014,

              Aas, J., "Looking Forward to 2019 (Let's Encrypt blog
              post)", December 2018,

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              Lychev, R., Goldberg, S., and M. Schapira, "BGP Security
              in Partial Deployment - Is the Squeeze Worth the Juice?
              (in SIGCOMM 2013)", 2013,

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <>.

   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
              Signature Option", RFC 2385, DOI 10.17487/RFC2385, August
              1998, <>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              DOI 10.17487/RFC3552, July 2003,

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <>.

   [RFC6810]  Bush, R. and R. Austein, "The Resource Public Key
              Infrastructure (RPKI) to Router Protocol", RFC 6810,
              DOI 10.17487/RFC6810, January 2013,

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   [RFC7624]  Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
              Trammell, B., Huitema, C., and D. Borkmann,
              "Confidentiality in the Face of Pervasive Surveillance: A
              Threat Model and Problem Statement", RFC 7624,
              DOI 10.17487/RFC7624, August 2015,

   [RFC8170]  Thaler, D., Ed., "Planning for Protocol Adoption and
              Subsequent Transitions", RFC 8170, DOI 10.17487/RFC8170,
              May 2017, <>.

   [RFC8205]  Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
              Specification", RFC 8205, DOI 10.17487/RFC8205, September
              2017, <>.

              van Kesteren, A., "Secure Contexts Everywhere", January
              2018, <

              Snijders, J., "Routing Security Update Q2 2019 (RIPE 78
              presentation)", May 2019, <

              Trenaman, N., "RPKI Resilience - How Trustworthy is our
              Trust Anchor?", October 2019, <

Author's Address

   Brian Trammell
   Gustav-Gull-Platz 1
   8004 Zurich


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