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Network Working Group                                          J. Snyder
Internet-Draft                                                  Opus One
Expires: April 27, 2012                                    K. O'Donoghue
                                                                    ISOC
                                                                M. Shore
                                                                     TBS
                                                        October 25, 2011


    A Survey of Trust Models and Relationships in Internet Protocols
                  draft-snyder-trust-relationships-00

Abstract

   This document reviews common Internet protocols and discusses how
   each protocol establishes, maintains, and tears down trust
   relationships within the protocol.  This document includes discussion
   of "meta" trust issues, including extra-protocol trust creation,
   management, and destruction.  In cases where specific issues related
   to establishment of trust have been documented, these are discussed
   as well.  By examining both similarities and differences between
   different protocols, this document can help protocol designers and
   maintainers in IETF working groups learn from successful (and un-
   successful) Internet protocols.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 27, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal



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   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Overview and Problem Statement . . . . . . . . . . . . . . . .  3
   4.  DKIM (Domain Keys Identified Mail) . . . . . . . . . . . . . .  4
     4.1.  DKIM Background and Overview . . . . . . . . . . . . . . .  4
     4.2.  Trust Relationships in DKIM  . . . . . . . . . . . . . . .  4
     4.3.  DKIM Diagrams  . . . . . . . . . . . . . . . . . . . . . .  4
   5.  DNSSEC (Domain Name System Security Extensions)  . . . . . . .  4
     5.1.  DNSSEC Background and Overview . . . . . . . . . . . . . .  4
     5.2.  Trust Relationships in DNSSEC  . . . . . . . . . . . . . .  4
     5.3.  DNSSEC Diagrams  . . . . . . . . . . . . . . . . . . . . .  4
   6.  PKI (Public Key Infrastructure)  . . . . . . . . . . . . . . .  4
     6.1.  PKI Background and Overview  . . . . . . . . . . . . . . .  4
     6.2.  Trust Relationships in PKI . . . . . . . . . . . . . . . .  5
       6.2.1.  Basic Model  . . . . . . . . . . . . . . . . . . . . .  5
       6.2.2.  Creating and instantiating trust . . . . . . . . . . .  6
       6.2.3.  Validating Trust . . . . . . . . . . . . . . . . . . .  8
       6.2.4.  Revoking Trust . . . . . . . . . . . . . . . . . . . .  8
     6.3.  PKI Diagrams . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  RPKI (Resource Public Key Infrastructure)  . . . . . . . . . .  9
     7.1.  RPKI Background and Overview . . . . . . . . . . . . . . .  9
     7.2.  Trust Relationships in RPKI  . . . . . . . . . . . . . . .  9
     7.3.  RPKI Diagrams  . . . . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     11.2. Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10









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1.  Introduction

   Many Internet protocols need to establish some type of trust between
   the parties participating in the protocol in order to be effective.
   For example, the Internet Key Establishment (IKE) protocol ([insert]
   [references] [here]) passes through an authentication phase between
   the two IKE peers before it moves to a second phase where
   cryptographic material is established for encrypting and
   authenticating IPsec traffic.  The authentication phase serves to
   establish trust between the two IKE peers.  For example, if the IKE
   peers use pre-shared secrets, then each IKE peer is willing to trust
   the other once they have mutually proven knowledge of a pre-shared
   secret.

   Please note that this document was derived from existing protocols
   and does not attempt to define or re-define the function of any
   Internet protocol.  This document is entirely non-definitive and
   should not be used by implementers as an authoritative source of
   information about protocol behavior or description.

   WHY IS THIS IMPORTANT?

   NEED A BETTER DESCRIPTION OF "TRUST" HERE AND WHAT WE WILL BE LOOKING
   AT EXACTLY.

   The protocols described in the document were chosen for their
   exemplar value.  This document is not meant to be an exhaustive
   description of all protocols and their trust establishment models.


2.  Terminology

   Trust:  This is the definition of Trust.

   Authentication:  This is the definition of Authentication.

   Identification:  This is the definition of Identification.

   Reputation:  This is the definition of Reputation.


3.  Overview and Problem Statement

   In this section, we would provide as much background and other
   related information as we can to help describe some things
   including...

   WHY ARE WE DOING THIS?



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   WHAT IS THE VALUE OF THIS CONTRIBUTION?

   WHAT ARE WE NOT INCLUDING IN THIS DOCUMENT AND WHY?


4.  DKIM (Domain Keys Identified Mail)

4.1.  DKIM Background and Overview

   Protocol Overview

4.2.  Trust Relationships in DKIM

   Trust Models and Relationships in DKIM

4.3.  DKIM Diagrams

   Diagrams go here


5.  DNSSEC (Domain Name System Security Extensions)

5.1.  DNSSEC Background and Overview

   Protocol Overview

5.2.  Trust Relationships in DNSSEC

   Trust Models and Relationships in DNSSEC

5.3.  DNSSEC Diagrams

   Diagrams go here


6.  PKI (Public Key Infrastructure)

6.1.  PKI Background and Overview

   The IETF PKIX working group has specified an X.509v3 profile, and
   that profile and set of associated specifications are colloquially
   referred to as PKIX.  The core specification is RFC 5280.

   Throughout this section we look at how trust is conveyed in PKIX from
   two perspectives:






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   (1)  from the perspective of a relying party -- an entity that
        receives an assertion (credential) and needs to make a decision
        whether or not to trust it, and

   (2)  from the perspective of an end entity -- an entity that needs to
        assert its identity in a way that can be accepted by a relying
        party.

   By way of terminology, the entity which signed a certificate and
   which is vouching for the authenticity of both the certificate and
   the certificate holder is referred to as the issuer.  The entity to
   which the certificate was issued is the subject.

   Trust in PKIX is instantiated through the use of trust anchors.  A
   trust anchor is itself a certificate, but one about which a human has
   made an explicit trust decision.  In this context, subsequent trust
   decisions must successfully chain back to that initial decision --
   that a certification authority is reliable, secure, and honest, and
   that its business practices provide assurance that it will only be
   issuing certificates to entities which are also reliable, secure, and
   honest.

   This document does not yet discuss the Trust Anchor Management
   Protocol. [insert][reference][here] TAMP does not change the
   underlying trust model or the trust lifecycle, although it does
   provide mechanisms for implementing it.

6.2.  Trust Relationships in PKI

6.2.1.  Basic Model

   Perhaps the key assumption around which PKIX is built is that it is
   not necessary for two entities to have an existing relationship in
   order to make a decision whether or not to accept the otherE1/4s
   assertions as 1) correct, and 2) trustworthy.  Rather than
   negotiating in advance of any communication, those decisions are
   mediated through the use of third party agents, and consequently
   whether or not a given entity is trustworthy comes down to the
   question of whether or not the agent (and its agent, and on up the
   chain) can be seen as trustworthy and authoritative, and can make
   reliable assertions about the credentials it has issued.

   A certification authority, which may or may not be a commercial
   entity, issues signed credentials for its customers.  These
   credentials are known as end entity certificates.  Its signature is
   essentially an attestation that the CA has some level of confidence
   that the entity to which the certificate was issued really is who it
   claims to be.  Certificates may be chained from a trust anchor --



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   that is to say, there may be from zero to n certification authorities
   between the trust anchor and the end entity to which the certificate
   has been issued.[insert][reference][here]

   Trust is instantiated by provisioning a root certificate in a local
   cache or in some logically local data store.  This root certificate
   functions as a trust anchor.  If the process of validating an end
   entity certificate does not terminate at a trust anchor, the
   validation fails.

   The data model is essentially hierarchical, and tree-shaped.  While a
   CA may issue multiple (typically many) certificates, a certificate
   may have only one issuer.  At the very top of the trust tree is a
   person or organization who determines which root certificates
   represent a trusted CA (note that this decision and associated
   information are basically determined manually and out-of-band,
   typically requiring human judgment).

   Bidirectional trust may be established between two CAs and their
   subjects through the use of cross-certification.  In this case the
   two CAs issue certificate to each other.  It is still the case,
   however, that a certificate will have one issuer, and that a CA may
   issue multiple (many) certificates.  The decision to cross-certify is
   still out-of-band, and human.  The question of what the trust anchor
   is in this situation is still being debated on the pkix mailing list5
   and is unresolved as of this writing.  (Oct/2011)

   Self-signed certificates merit special mention, because they are so
   commonly deployed.  A self-signed certificate is one in which the
   issuer and the subject are the same.  It is very rarely the case that
   a self-signed certificate is already installed in a root cert cache
   and is functioning as a trust anchor, but it is very common for users
   to accept and install self-signed certificates when they are offered
   by a visited website.

6.2.2.  Creating and instantiating trust

   There are two aspects to creating trust and instantiating it through
   PKIX technologies.  The first aspect relates to the determination
   made by a user or systems administrator (i.e. a relying party) that a
   given certification authority is a reliable source of authority
   regarding the identity of the entities represented in the certificate
   it issues.  The second relates to the determination made by the end
   entity that a given certification authority is a reliable agent --
   that they are who they say they are, that their business practices
   are sound, that the operation of their certificate infrastructure is
   secure, and, perhaps most importantly, that the chain to the trust
   anchor contains only issuers who are also secure, reliable, and



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   trustworthy.  The relying party also needs to have assurances about
   intermediate CAs and certificates in a chain, but this comes into
   play during validation, not during provisioning.

6.2.2.1.  Bootstrapping trust in a relying party

   From an end entity perspective, trust is instantiated, or verified,
   through the presence of trust anchors in a local store.  A decision
   to install or provision a root CA certificate as a trust anchor is an
   out-of-band, human decision and represents a decision to trust that
   the CA represented by that certificate is secure, reliable, and
   authoritative.  It also represents a decision that the intermediate
   CAs underneath the root CA are also secure, reliable, and
   authoritative (this has turned out to be a problem, in practice).

   It is typically the case that web browsers are distributed with a
   cache of root certificates, which have been vetted with varying
   degrees of rigor by the browser developers.  When a user decides to
   use a browser with an existing cache, theyE1/4re implicitly trusting
   the browser developers.  This is not unreasonable -- in theory, the
   browser developer has the resources and expertise to evaluate trust
   anchors for inclusion, and will exclude certificates from unreliable
   CAs.

   In other cases, often in cases where a local CA is issuing
   certificates, a local systems administrator makes the decision to add
   a root CA certificate from a local (or neighboring) CA.

   A special case of bootstrapping trust, and one which poses a security
   problem, is that a user may be offered an unknown certificate, be
   asked by the browser whether or not to accept it, and will not only
   accept the certificate as authentic but also install it locally for
   future use.  In this situation there is an apparent disconnect
   between whatE1/4s happening conceptually in the security transaction
   (the user is being asked whether or not to accept a credential as
   both authentic and trustworthy) and the userE1/4s understanding of
   whatE1/4s going on (the user just wants the connection to complete
   and may not understand the underlying security model).

6.2.2.2.  Bootstrapping trust in an end entity

   In this case, bootstrapping essentially means investigating
   certification authorities, making a decision to acquire a certificate
   from one, and installing that certificate.  Again,this is a human
   decision thatE1/4s instantiated through technical means (the
   provisioning of the certificate).

   Unfortunately there really is no way, as a relying party, to



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   determine the soundness of the end entityE1/4s decision to acquire a
   cert from a particular CA.  It may be that they chose one CA over
   another on the basis of business practices but it may also be the
   case that they chose the least expensive vendor regardless of
   soundness.  When things are working as they should a CA will only
   sell certificates to other very reliable CAs, and on down the chain,
   but there have been several issues with compromised or sloppy
   intermediate CAs in the recent past that call this model into
   question.

6.2.2.3.  A brief digression on EV certs

   The CA/Browser forum has published guidelines for identity
   verification, including specification of specific identity criteria.
   These center around three goals:

   (1)  establish the legal identity of the certificate applicant;

   (2)  establish that the applicant has legal ownership of the entity
        for which the certificate is to be issued (the Subject), and

   (3)  confirm the identity and the authority of the ownerE1/4s agents.

   Certificates issued under these criteria are called Extended
   Validation Certificates.  Browser markers provide visual clues, such
   as color in the address bar, when an EV certificate is present and
   has been validated.  A CA must typically pass an independent audit to
   be accepted by browser vendors as an issuer of EV certs.

6.2.3.  Validating Trust

   In PKIX, trust is chained back to a trust anchor.  Validation
   essentially consists of path validation, with the assumption that
   youE1/4ll trust who your anchor vouches for, and so on up the chain.

   It may also be the case that a non-root certificate - an end-entity
   certificate thatE1/4s not a trust anchor, is explicitly trusted,
   usually through local installation in a browser or other cache.
   Unfortunately itE1/4s often the case that the user is making a
   decision to get a connection to work rather than making an explicit
   trust decision.

6.2.4.  Revoking Trust

   The X.509 lifecycle model typically is based on a long-lived
   credential (months or, more often, years) which may expire without
   being reissued, or may be explicitly revoked.  Explicit revocation
   may be accomplished through a variety of measures:



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   (1)  Manual removal from a browser or other certificate cache,

   (2)  Blacklist checking by the relying party as part of the
        validation process.  This, in turn, may take one of several
        forms:

        (a)  Certificate revocation lists, issued by the certification
             authority which issued the original certificate.  These
             should be created and published on a regular, timely
             schedule and must be checked as part of the certificate
             validation process.

        (b)  A status query at validation time, through the use of the
             Online Certificate Status Protocol

        (c)  Blacklisting by the browser vendor

   The technical means for revoking trust is essentially the same as
   that for revoking a non-trust anchor certificate.  If the trust
   anchor is gone, certificates which chain back to it will fail the
   validation check.

6.3.  PKI Diagrams

   Diagrams go here


7.  RPKI (Resource Public Key Infrastructure)

7.1.  RPKI Background and Overview

   Protocol Overview

7.2.  Trust Relationships in RPKI

   Trust Models and Relationships in RPKI

7.3.  RPKI Diagrams

   Diagrams go here


8.  IANA Considerations

   None.






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9.  Security Considerations

   To be supplied.


10.  Acknowledgements

   Insert list of key collaborators..


11.  References

11.1.  Normative References

11.2.  Informative References


Authors' Addresses

   Joel Snyder
   Opus One, Inc.
   1404 East Lind Road
   Tucson, Arizona  85719
   US

   Phone: +1 520 324 0494
   Email: jms@opus1.com
   URI:   http://www.opus1.com/jms


   Karen O'Donoghue
   The Internet Society
   7167 Goby Lane
   King George, Virginia  22485
   US

   Email: odonoghue@isoc.org
   URI:   http://www.isoc.org


   Melinda Shore
   TBS









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