SIDR                                                             S. Kent
Internet-Draft                                                       BBN
Intended status: Informational                                     D. Ma
Expires: April 15, 2016                                             ZDNS
                                                        October 13, 2015


Adverse Actions by a Certification Authority (CA) or Repository Manager
            in the Resource Public Key Infrastructure (RPKI)
                   draft-kent-sidr-adverse-actions-01

Abstract

   This document analyzes actions by or against a CA or independent
   repository manager in the RPKI that can adversely affect the Internet
   Number Resources (INRs) associated with that CA or its subordinate
   CAs.  The analysis is based on examination of the data items in the
   RPKI repository, as controlled by a CA (or independent repository
   manager) and fetched by Relying Parties (RPs).  The analysis is
   performed from the perspective of an affected INR holder.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on April 15, 2016.

Copyright Notice

   Copyright (c) 2015 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
   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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Analysis of RPKI Repository Objects . . . . . . . . . . . . .   3
     2.1.  ROA . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Manifest  . . . . . . . . . . . . . . . . . . . . . . . .   7
     2.3.  Ghostbusters Record . . . . . . . . . . . . . . . . . . .   9
     2.4.  Certificate Revocation List . . . . . . . . . . . . . . .  10
     2.5.  CA Certificates . . . . . . . . . . . . . . . . . . . . .  12
     2.6.  Router Certificates . . . . . . . . . . . . . . . . . . .  15
   3.  Analysis of Actions Relative to Scenarios . . . . . . . . . .  16
     3.1.  Scenario A  . . . . . . . . . . . . . . . . . . . . . . .  17
     3.2.  Scenario B  . . . . . . . . . . . . . . . . . . . . . . .  18
     3.3.  Scenario C  . . . . . . . . . . . . . . . . . . . . . . .  18
     3.4.  Scenario D  . . . . . . . . . . . . . . . . . . . . . . .  19
   4.  Detection and Remediation . . . . . . . . . . . . . . . . . .  19
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  21
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   Both Suspenders [I-D.kent-sidr-suspenders] and RPKI Validation
   Reconsidered [I-D.ietf-sidr-rpki-validation-reconsidered] address
   mistakes by Resource Public Key Infrastructure (RPKI) [RFC6480]
   Certification Authorities (CAs) (with respect to subordinate CAs).
   However, mistakes are not the only way that adverse changes to RPKI
   data can arise.  A CA or repository operator might be subject to an
   attack [RFC7132].  For a CA, if an attack allows an adversary to use
   the private keys of that CA to sign RPKI objects, then the effect is
   analogous to the CA making mistakes.  There is also the possibility
   that a CA or repository operator may be subject to legal measures
   that compel them to generate "bogus" signed objects or remove
   legitimate repository data.  In many cases, such actions may be hard
   to distinguish from non-malicious mistakes, other than with respect
   to the time required to remedy the adverse action.  Thus this
   document examines the implications of adverse actions with respect to
   Internet Number Resources (INRs) irrespective of the cause of the



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   actions.  The document proposes mitigation strategies that take into
   account the nature of adverse actions, e.g., distinguishing malicious
   vs. erroneous actions.

   This document analyzes the various types of actions by a CA (or
   independent repository manager) that can adversely affect the
   Internet Number Resources (INRs) associated with that CA, as well as
   the INRs of subordinate CAs.  The analysis is based on examination of
   the data items in the RPKI repository, as controlled by a CA (or
   independent repository manager) and fetched by Relying Parties (RPs).
   The analysis is done from the perspective of an affected INR holder.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Analysis of RPKI Repository Objects

   This section enumerates the RPKI repository system objects and
   examines how changes to them affect Route Origination Authorizations
   (ROAs) and router certificate validation.  Identifiers are assigned
   to errors for reference by later sections of this document.

   The RPKI repository [RFC6481] contains a number of (digitally signed)
   objects that are fetched and processed by RPs.  Until the deployment
   of BGPsec [I-D.ietf-sidr-bgpsec-overview], the principal goal of the
   RPKI is to enable an RP to validate ROAs [RFC6482].  A ROA binds
   address space to an Autonomous System Number (ASN).  A ROA can be
   used to verify BGP announcements with respect to route origin
   [RFC6483].  The most important objects in the RPKI for origin
   validation are ROAs; all of the other RPKI objects exist to enable
   the validation of ROAs in a fashion consistent with the INR
   allocation system.  Thus errors that result in changes to a ROA, or
   to RPKI objects needed to validate a ROA, can cause RPs to reach
   different (from what was intended) conclusions about the validity of
   the bindings expressed in a ROA.

   When BGPsec is deployed, router certificates
   [I-D.ietf-sidr-bgpsec-pki-profiles] will be added to repository
   publication points.  These are End-Entity (EE) certificates used to
   verify signatures applied to BGP update data, to enable path
   validation [I-D.ietf-sidr-bgpsec-protocol].  Router certificates are
   as important to path validation as ROAs are to origin validation.

   The objects contained in the RPKI repository are of two types:
   conventional PKI objects (certificates and Certificate Revocation



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   Lists (CRLs)) and RPKI-specific signed objects.  The latter make use
   of a common encapsulation format [RFC6488] based on the Cryptographic
   Message Syntax (CMS) [RFC5652].  A syntax error in this common format
   will cause an RP to reject the object as invalid.  In turn, this may
   cause a ROA at a publication point to be considered invalid.

   Adverse actions take several forms:



      *  Deletion (D) is defined as removing an object from a
         publication point, without the permission of the INR holder.

      *  Suppression (S) is defined as not deleting an object, or not
         publishing an object, as intended by an INR holder.  This
         action also includes retaining a prior version of an object in
         a publication point when a newer version is available for
         publication.

      *  Corruption (C) is defined as modification of a signed object in
         a fashion not requiring access to the private key used to sign
         the object.  Thus a corrupted object will not carry a valid
         signature.  Implicitly, the corrupted object replaces the
         legitimate version.

      *  Modification (M) is defined as publishing a syntactically
         valid, verifiable version of an object that differs from the
         (existing) version authorized by the INR holder.  Implicitly,
         the legitimate version of the affected object is deleted and
         replaced by the modified object.

      *  Revocation (R) is defined as revoking a certificate (EE or CA)
         by placing its serial number on the appropriate CRL, without
         authorization of the INR holder.

      *  Injection (I) is defined as introducing an instance of a signed
         object into a publication point (without authorization of the
         INR holder).  It assumes that the signature on the object will
         be viewed as valid by RPs.

   The first three of these actions (deletion, suppression, and
   corruption) can be effected by any entity that manages the
   publication point of the affected INR holder.  Also, an entity with
   the ability to act as a man-in-the-middle between an RP and a
   repository can effect these actions with respect to the RP in
   question.





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   The latter three actions (modification, revocation, and injection)
   nominally require access to the private key of the INR holder.

   All six of these actions also can be effected by a parent CA.  A
   parent CA could reissue the INR holder's CA certificate, but with a
   different public key, matching a private key to which the parent CA
   has access.  The CA could generate new signed objects using the
   private key associated with the reissued certificate, and publish
   these objects at a location of its choosing.

   Most of these actions may be performed independently or in
   combination with one another.  For example, a ROA may be revoked and
   deleted or revoked and replaced with a modified ROA.  Where
   appropriate, the analysis of adverse actions will distinguish which
   of these individual actions, or combinations thereof, yield different
   outcomes for RPs.  Recall that the focus of the analysis is the
   impact on ROAs and router certificates, with respect to RP
   processing.

   The following sections examine how the actions enumerated above
   affect objects in the RPKI repository system.  Each action is
   addressed in order (Deletion, Suppression, Corruption, Modification,
   Revocation, and Injection) for each object, making it easy to see how
   every action has been considered with regard to each object.  (For
   the GhostBusters record we condensed the discussion of the actions
   because the impact is the same in each case.)

2.1.  ROA

   In addition to the generic RPKI object syntax checks, ROA validation
   requires that the signature on the ROA can be validated using the
   public key from the EE certificate embedded in the ROA [RFC6482].  It
   also requires that the EE certificate be validated consistently with
   the procedures described in [RFC6482] and [RFC6487].  Adverse actions
   against a ROA can cause the following errors:



      A-1.1  A ROA may be deleted from the indicated publication point.
             The result is to void the binding between the prefix(es)
             and the AS number in the ROA.  An RP that previously viewed
             this binding as authentic will now not have any evidence
             about its validity.  For origin validation, this means that
             a legitimate route will be treated as NotFound (if there
             are no other ROAs for the same prefix) or Invalid (if there
             is another ROA for the same prefix, but with a different AS
             number).




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      A-1.2  Suppression

             A-1.2.1  Publication of a newer ROA may be suppressed.  If
                      the INR holder intended to change the binding
                      between the prefix(es) and the AS number in the
                      ROA, this change will not be effected.  As a
                      result, RPs may continue to believe an old prefix/
                      ASN binding that is no longer what the INR holder
                      intended.

             A-1.2.2  If an INR holder intends to issue and publish two
                      (or more) new ROAs for the same address space, one
                      (or more) of the new ROAs may be suppressed while
                      the other is published.  In this case, RPs will
                      de-preference the suppressed prefix/ASN binding.
                      Suppression of the new ROA might cause traffic to
                      flow to an ASN other than the one(s) intended by
                      the INR holder.

             A-1.2.3  If an INR holder intends to delete all ROAs for
                      the same address space, some of them may be
                      retained while the others are deleted.  Preventing
                      the deletion of some ROAs can cause traffic to
                      continue to be delivered to the ASNs that were
                      advertised by these ROAs.  Deletion of all ROAs is
                      consistent with a transfer of address space to a
                      different INR holder, in a phased fashion.  Thus
                      this sort of attack could interfere with the
                      successful transfer of the affected address space
                      (until such time as the prefixes are removed from
                      the previous INR holder's CA certificate).

      A-1.3  A ROA may be corrupted.  A corrupted ROA will be ignored by
             an RP, so the effect is essentially the same as for A-1.1
             and 1.5.  A possible difference is that an RP may be
             alerted to the fact that the ROA was corrupted, which might
             attract attention to the attack.

      A-1.4  A ROA may be modified so that the Autonomous System Number
             (ASN) or one or more of the address blocks in a ROA is
             different from the values the INR holder intended for this
             ROA.  (This action assumes that the modified ROA's ASN and
             address ranges are authorized for use by the INR holder.)
             This attack will cause RPs to de-preference the legitimate
             prefix/ASN binding intended by the INR holder.






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      A-1.5  A ROA may be revoked (by placing its EE certificate on the
             CRL for the publication point).  This has the same effect
             as A-1.1.

      A-1.6  A ROA expressing different bindings than those published by
             the INR holder may be injected into a publication point.
             This action could authorize an additional ASN to advertise
             the specified prefix, allowing that ASN to originate routes
             for the prefix, thus enabling route origin spoofing.  The
             injected ROA might express a different prefix for an ASN
             already authorized to originate a route, e.g., a longer
             prefix, which could enable that ASN to override other
             advertisements using shorter prefixes.

2.2.  Manifest

   Each repository publication point contains a manifest [RFC6486].  The
   RPKI incorporates manifests to enable RPs to detect suppression and/
   or substitution of (more recent) publication point objects, as the
   result of a mistake or attack.  A manifest enumerates (by filename)
   all of the other signed objects at the publication point.  The
   manifest also contains a hash of each enumerated file, to enable an
   RP to determine if the named file content matches what the INR holder
   identified in the manifest.

   A manifest is an RPKI signed object, so it is validated as per
   [RFC6488].  If a manifest is modified in a way that causes any of
   these checks to fail, the manifest will be considered invalid.
   Suppression of a manifest itself (indicated by a stale manifest) also
   can cause an RP to not detect suppression of other signed objects at
   the publication point.  (Note that if a Manifest's EE certificate
   expires at the time that the Manifest is scheduled to be replaced, a
   delay in publication will cause the Manifest to become invalid, not
   merely stale.  This very serious outcome should be avoided, e.g., by
   making the Manifest EE certificate's notAfter value the same as that
   of the CA certificate under which it was issued).  If a signed object
   at a publication point can be validated (using the rules applicable
   for that object type), then an RP MAY accept that object, even if
   there is no matching entry for it on the manifest.  However, it
   appears that most RP software ignores publication point data that
   fails to match Manifest entries (at the time this document was
   written).

   Corruption, suppression, modification, or deletion of a manifest
   might not affect RP processing of other publication point objects, as
   specified in [RFC6486].  However, as noted above, many RP
   implementations ignore objects that are present at a publication




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   point but not listed in a valid Manifest.  Thus the following actions
   against a manifest can impact RP processing:



      A-2.1  A Manifest may be deleted from the indicated publication
             point.  In this circumstance an RP may elect to use the
             previous Manifest that it has, and may ignore any new/
             changed objects at the publication point.  The implications
             of this action are equivalent to suppression of publication
             of the objects that are not recognized by RPs because the
             new objects are not present in the old Manifest.  For
             example, a new ROA could be ignored (A-1.2).  A newly
             issued CA certificate might be ignored (A-5.1).  A
             subordinate CA certificate that was revoked might still be
             viewed as valid by RPs (A-4.1).  A new or changed router
             certificate might be ignored (A-6.2) as would a revised
             Ghostbusters record (A-3.1).

      A-2.2  Publication of a newer Manifest may be suppressed.
             Suppression of a newer Manifest probably will cause an RP
             to rely on a previous (cached) Manifest.  The older
             Manifest would not enumerate newly added objects, and thus
             those objects might be ignored by an RP, equivalent to
             deletion of those objects (A-1.1, A-3.1, A-4.1, A-5.1,
             A-6.1).

      A-2.3  A Manifest may be corrupted.  A corrupted Manifest will be
             rejected by RPs.  This may cause RPs to rely on a previous
             manifest, with the same impact as A-2.2.  If an RP does not
             revert to using a cached Manifest, the impact of this
             action is very severe, i.e., all publication point objects
             will be viewed as invalid, including subordinate tree
             objects.  This is equivalent to revoking or deleting an
             entire subtree (see A-4.4.2).

      A-2.4  Modification

             A-2.4.1  A Manifest may be modified to remove one or more
                      objects.  Because the modified Manifest is viewed
                      as valid by RPs, any objects that were removed may
                      be ignored by RPs.  This is equivalent to deleting
                      these objects from the repository.  The impact of
                      this action will vary, depending on which objects
                      are (effectively) removed.  However, the impact is
                      equivalent to deletion of the object in question,
                      (A-1.1, A-3.1, A-4.1, A-5.1, A-6.1).




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             A-2.4.2  A Manifest may be modified to add one or more
                      objects.  If an added object has a valid signature
                      (and is non-expired), it will be accepted by RPs
                      and processed accordingly.  If the added object
                      was previously deleted by the INR holder, this
                      action is equivalent to suppressing deletion of
                      that object.  If the object is newly created, or
                      modified, it is equivalent to a modification or
                      injection action for the type of object in
                      question, and thus is discussed in the relevant
                      section for those actions for the object type.

             A-2.4.3  A Manifest may be modified to list an incorrect
                      hash for one or more objects.  An object with an
                      incorrect hash may be ignored by an RP.  Thus the
                      effect may be equivalent to corrupting the object
                      in question, although the error reported by RP
                      software would differ from that reported for a
                      corrupted object.  (The Manifest specifications do
                      not require an RP to ignore an object that has a
                      valid signature and that is not revoked or
                      expired, but for which the hash doesn't match the
                      object.  However, an RP may elect to do so.)

      A-2.5  A Manifest may be revoked (by including its EE certificate
             on the CRL for the publication point).  A revoked Manifest
             will be ignored by an RP, which probably would revert to an
             older (cached) Manifest.  The implications for RPs are
             equivalent to A-2.1, with regard to new/changed objects.

      A-2.6  A Manifest representing different objects may be injected
             into a publication point.  The effects are the same as for
             a modified Manifest (see above).  The impact will depend on
             the type of the affected object(s), and thus is discussed
             in the relevant section(s) for each object type.

2.3.  Ghostbusters Record

   The Ghostbusters record [RFC6493] is a signed object that MAY be
   included at a publication point, at the discretion of the INR holder
   or publication point operator.  The record is validated according to
   [RFC6488].  Additionally, the syntax of the record is verified based
   on the vCard profile from Section 5 of [RFC6493].  Errors in this
   record do not affect RP processing.  However, if an RP encounters a
   problem with objects at a publication point, the RP may use
   information from the record to contact the publication point
   operator.




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   Adverse actions against a Ghostbusters record can cause the following
   error:



      A-3.1  Deletion, suppression, corruption, or revocation of a
             Ghostbusters record could prevent an RP from contacting the
             appropriate entity when a problem is detected by the RP.
             Modification or injection of a Ghostbusters record could
             cause an RP to contact the wrong entity, thus delaying
             remediation of a detected anomaly.  All of these actions
             are viewed as equivalent from an RP processing perspective;
             they do not alter RP validation of ROAs or router
             certificates.  However, these actions can interfere with
             remediation of a problem when detected by an RP.

2.4.  Certificate Revocation List

   Each publication point contains a CRL that enumerates revoked (not
   yet expired) certificates issued by the CA associated with the
   publication point [RFC6481].

   Adverse actions against a CRL can cause the following errors:



      A-4.1  Deletion

             A-4.1.1  If a CRL is deleted, RPs will continue to use an
                      older, previously fetched Certificate Revocation
                      List.  As a result, they will not be informed of
                      any changes in revocation status of subordinate CA
                      or router certificates or the EE certificates of
                      signed objects, e.g., ROAs.  This action is
                      equivalent to corruption of a CRL, since a
                      corrupted CRL will not be accepted by an RP.

             A-4.1.2  Deletion of a CRL could cause an RP to continue to
                      accept a ROA that no longer expresses the intent
                      of an INR holder.  As a result, an announcement
                      for the affected prefixes would be viewed as
                      Valid, instead of NotFound or Invalid.  In this
                      case, the effect is analogous to A-1.2.

             A-4.1.3  If a router certificate were revoked, and the CRL
                      were deleted, RPs would not be aware of the
                      revocation.  They might continue to accept the
                      old, revoked, router certificate.  If the



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                      certificate had been revoked due to a compromise
                      of the router's private key, RPs would be
                      vulnerable to accepting routes signed by an
                      unauthorized entity.

             A-4.1.4  If a subordinate CA certificate were revoked on
                      the deleted CRL, the revocation would not take
                      effect.  This could interfere with a transfer of
                      address space from the subordinate CA, adversely
                      affecting routing to the new holder of the space.

      A-4.2  If publication of the most recent CRL is suppressed, an RP
             will not be informed of the most recent revocation status
             of subordinate CA or router certificates or the EE
             certificates of signed objects.  If an EE certificate has
             been revoked and the associated signed object is still
             present in the publication point, an RP might mistakenly
             treat that object as valid.  (This would happen if the
             object is still in the manifest or the RP is configured to
             process valid objects that are not on the manifest.)  This
             type of action is of special concern if the affected object
             is a ROA, a router certificate, or a subordinate CA
             certificate.  The effects here are equivalent to CRL
             deletion (A-4.1), but suppression of a new CRL may not even
             be reported as an error, i.e., if the suppressed CRL were
             issued before the NextUpdate time (of the previous CRL).

      A-4.3  If a CRL is corrupted, an RP will reject it.  If a prior
             CRL has not yet exceeded its NextUpdate time, an RP will
             continue to use the prior CRL.  Even if the prior CRL has
             passed the NextUpdate time, an RP may choose to continue to
             rely on the prior CRL.  The effects are essentially
             equivalent to suppression or deletion of a CRL (A-4.1,
             A-4.2)

      A-4.4  Modification

             A-4.4.1  If a CRL is modified to erroneously list a signed
                      object's EE certificate as revoked, the
                      corresponding object will be treated as invalid by
                      RPs, even if it is present in a publication point.
                      If this object is a ROA, the (legitimate) binding
                      expressed by the ROA will be ignored by an RP (see
                      A-1.5).  If a CRL is modified to erroneously list
                      a router certificate as revoked, a path signature
                      associated with that certificate will be treated
                      as Not Valid by RPs (see A-6.5).




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             A-4.4.2  If a CRL is modified to erroneously list a CA
                      certificate as revoked, that CA and all
                      subordinate signed objects will be treated as
                      invalid by RPs.  Depending on the location of the
                      affected CA in the hierarchy, these effects could
                      be very substantial, causing routes that should be
                      Valid to be treated as NotFound.

             A-4.4.3  If a CRL is modified to omit a revoked EE, router,
                      or CA certificate, RPs likely will continue to
                      accept the revoked, signed object as valid.  This
                      contravenes the intent of the INR holder.  If an
                      RP continues to accept a revoked ROA, it may make
                      routing decisions on now-invalid data.  This could
                      cause valid routes to be de-preferenced and
                      invalid routes to continue to be accepted.

      A-4.5  A CRL cannot be revoked, per se, but it will fail
             validation if the CA certificate under which it was issued
             is revoked.  See A-5.5 for a discussion of that action.

      A-4.6  Insertion of a bogus CRL can have the same effects as
             listed above for a modified CRL, depending on the form of
             the inserted CRL.

2.5.  CA Certificates

   Every INR holder is represented by one or more CA certificates.  An
   INR holder has multiple CA certificates if it holds resources
   acquired from different sources.  Also, every INR holder has more
   than one CA certificate during key rollover [RFC6489] and algorithm
   rollover [RFC6916].

   If a publication point is not a leaf in the RPKI hierarchy, then the
   publication point will contain one or more CA certificates, each
   representing a subordinate CA.  Each subordinate CA certificate
   contains a pointer (SIA) to the publication point where the signed
   objects associated with that CA can be found [RFC6487].

   A CA certificate is a complex data structure and thus errors in that
   structure may have different implications for RPs depending on the
   specific data that is in error.

   Adverse actions against a CA certificate can cause the following
   errors:






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      A-5.1  Deletion of a CA certificate would cause an RP to not be
             able to locate signed objects generated by that CA, except
             those that have been cached by the RP.  Thus an RP would be
             unaware of changed or new (issued after the cached data)
             INR bindings asserted in subordinate ROAs, and the RP would
             be unable to validate new or changed router certificates.
             If the missed objects were intended to replace ROAs or
             router certificates prior to expiration, then when those
             objects expire, RPs may cease to view them as valid.  As a
             result, valid routes may be viewed as NotFound or Invalid.

      A-5.2  If publication of a CA certificate is suppressed, the
             impact depends on what changes appeared in the suppressed
             certificate.  If the SIA value changed, the effect would be
             the same as in A-5.1 or 5.4.2.  If the 3779 extensions in
             the suppressed certificate changed, the impact would be the
             same as in 5.4.1.  If the AIA extension changed in the
             suppressed certificate, the impact would be the same as in
             5.4.3.

      A-5.3  Corruption of a CA certificate will cause it to be rejected
             by RPs.  In turn, this may cause subordinate signed objects
             to become invalid.  An RP that has cached the subtree under
             the affected CA certificate may continue to view it as
             valid, until objects expire.  But changed or new objects
             might not be retrieved, depending on details of the design
             of the RP software.  Thus this action may be equivalent to
             suppressing changes to the affected subtree.

      A-5.4  Modification

             A-5.4.1  If a CA certificate is modified, but still
                      conforms to the RPKI certificate profile
                      [RFC6485], it will be accepted by RPs.  If an
                      [RFC3779] extension in this certificate is changed
                      to exclude INRs that were previously present, then
                      subordinate signed objects will become invalid if
                      they rely on the excised INRs.  If these objects
                      are CA certificates, their subordinate signed
                      objects will be treated as invalid.  If the
                      objects are ROAs, the binding expressed by the
                      affected ROAs will be ignored by RPs.  If the
                      objects are router certificates, BGPsec_Path
                      attributes [I-D.ietf-sidr-bgpsec-protocol]
                      verifiable under these certificates will be
                      considered invalid.





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             A-5.4.2  If the SIA extension of a CA certificate is
                      modified to refer to another publication point,
                      this will cause an RP to look at another location
                      for subordinate objects.  This could cause RPs to
                      not acquire the objects that the INR holder
                      intended to be retrieved - manifests, ROAs, router
                      certificates, Ghostbuster records, or any
                      subordinate CA certificates associated with that
                      CA.  If the objects at this new location contain
                      invalid signatures or appear to be corrupted, they
                      may be rejected.  In this case, cached versions of
                      the objects may be viewed as valid by an RP, until
                      they expire.  If the objects at the new location
                      have valid signatures and pass path validation
                      checks, they will replace the cached objects,
                      effectively replacing the INR holder's objects.

             A-5.4.3  If the AIA extension in a CA certificate is
                      modified, it would point to a different CA
                      certificate, not the parent CA certificate.  This
                      extension is used only for path discovery, not
                      path validation.  Path discovery in the RPKI is
                      usually performed on a top-down basis, starting
                      with TAs and recursively descending the RPKI
                      hierarchy.  Thus there may be no impact on the
                      ability of clients to acquire and validate
                      certificates if the AIA is modified.

             A-5.4.4  If the Subject Public Key Info (and Subject Key
                      Identifier extension) in a CA certificate is
                      modified to contain a public key corresponding to
                      a private key held by the parent, the parent could
                      sign objects as children of the affected CA
                      certificate.  With this capability, the parent
                      could replace the INR holder, issuing new signed
                      objects that would be accepted by RPs (as long as
                      they do not violate the path validation criteria).
                      This would enable the parent to effect
                      modification, revocation, and injection actions
                      against all of the objects under the affected CA
                      certificate, including subordinate CA
                      certificates.

      A-5.5  If a CA certificate is revoked an RP will treat as invalid
             all subordinate signed objects, both immediate and
             trasitively.  The effects are essentially the same as
             described in A-4.4.2.




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      A-5.6  If a CA certificate is injected the impact will depend on
             the data contained in the injected certificate.  Changes
             will generally be equivalent to modification actions as
             described in A-5.4.

2.6.  Router Certificates

   Router certificates are used by RPs to verify signatures on
   BGPsec_Path attributes carried in Update messages.

   Each AS is free to determine the granularity at which router
   certificates are managed [I-D.ietf-sidr-bgpsec-pki-profiles].  Each
   participating AS is represented by one or more router certificates.
   During key or algorithm rollover, multiple router certificates will
   be present in a publication point, even if the AS is normally
   represented by just one such certificate.

   Adverse actions against router certificates can cause the following
   errors:



      A-6.1  Deletion of a router certificate would cause an RP to not
             be able to verify signatures applied to BGPsec_Path
             attributes on behalf of the AS in question.  In turn, this
             would cause the route to be treated with lower preference
             than competing routes that have valid BGPsec_Path attribute
             signatures.  (However, if another router certificate for
             the affected AS is valid and contains the same AS number
             and public key, and is in use by that AS, there would be no
             effect on routing.  This scenario will arise if a router
             certificate is renewed, i.e., issued with a new validity
             interval.)

      A-6.2  Suppression of a router certificate could have the same
             impact as deletion of a certificate of this type, i.e., if
             no router certificate was available, BGPsec attributes that
             should be verified using the certificate would fail
             validation.  If an older certificate existed, and had not
             expired, it would be used by RPs.  If the older certificate
             contained a different ASN, the impact would be the same as
             in A-6.4.

      A-6.3  Corruption of a router certificate will result in the
             certificate being rejected by RPs.  Absent a valid router
             certificate, BGPsec_Path attributes associated with that
             certificate will be unverifiable.  In turn, this would
             cause the route to be treated with lower preference than



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             competing routes that have valid BGPsec_Path attribute
             signatures.

      A-6.4  If a router certificate is modified to represent a
             different ASN, but it still passes syntax checks, then this
             action could cause signatures on BGPsec_Path attributes to
             be associated with the wrong AS.  This could cause signed
             routes to be inconsistent with the intent of the INR
             holder, e.g., traffic might be routed via a different AS
             than intended.

      A-6.5  If a router certificate were revoked, BGPsec_Path
             attributes verifiable using that certificate would not
             longer be considered valid.  The impact would be the same
             as for a deleted certificate, as described in A-6.1

      A-6.6  Insertion of a router certificate could authorize
             additional routers to sign BGPsec traffic for the targeted
             ASN, and thus undermine fundamental BGPsec security
             guarantees.

3.  Analysis of Actions Relative to Scenarios

   This section examines the types of problems that can arise in four
   scenarios described below.  We consider mistakes, (successful)
   attacks against a CA or a publication point, and situations in which
   a CA or publication point manager is compelled to take action by a
   law enforcement authority.

   We explore the following four scenarios:



      A.  An INR holder operates its own CA and manages its own
          repository publication point.

      B.  An INR holder operates its own CA, but outsources management
          of its repository publication point to its parent or another
          entity.

      C.  An INR holder outsources management of its CA to its parent,
          but manages its own repository publication point.

      D.  An INR holder outsources management of its CA and its
          publication point to its parent.

   Note that these scenarios focus on the affected INR holder as the
   party directly affected by an adverse action.  The most serious cases



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   arise when the INR holder appears as a high-tier CA in the RPKI
   hierarchy; in such situations subordinate INR holders may be affected
   as a result of an action.  A mistake by or an attack against a "leaf"
   has more limited impact because all of the affected INRs belong to
   the INR holder itself.

   In Scenario A, actions by the INR holder can adversely affect all of
   its resources and, transitively, resources of any subordinate CAs.
   (If the CA is a "leaf" in the RPKI, then it has no subordinate CAs
   and the damage is limited to its own INRs.)

   In Scenario B, actions by the (outsourced) repository operator also
   can adversely affect the resources of the INR holder, and those of
   any subordinates CAs.  (If the CA is a "leaf" in the RPKI, then it
   has no subordinate CAs and the damage is limited, as in Scenario A.)
   The range of adverse effects here includes those in Scenario A, and
   adds a new potential source of adverse actions, i.e., the outsourced
   repository operator.

   In Scenario C, all signed objects associated with the INR holder are
   generated by the parent CA but are self-hosted.  (We expect this
   scenario to be rare, because an INR holder that elects to outsource
   CA operation seems unlikely to manage its own repository publication
   point.)  Because that CA has the private key used to sign them, it
   can generate alternative signed objects---ones not authorized by the
   INR holder.  However, erroneous objects created by the parent CA will
   not be published by the INR holder IF the holder checks them first.
   Because the parent CA is acting on behalf of the INR holder, mistakes
   by or attacks against that entity are equivalent to ones effected by
   the INR holder in Scenario A.

   The INR holder is most vulnerable in Scenario D.  Actions by the
   parent CA, acting on behalf of the INR holder, can adversely affect
   all signed objects associated with that INR holder, including any
   subordinate CA certificates.  These actions will presumably translate
   directly into publication point changes, because the parent CA is
   managing the publication point for the INR holder.  The range of
   adverse effects here includes those in Scenarios A, B, and C.

3.1.  Scenario A

   In this scenario, the INR holder acts as its own CA and it manages
   its own publication point.  Actions by the INR holder can adversely
   affect all of its resources and, transitively, resources of any
   subordinate CAs.  (If the CA is a "leaf" in the RPKI, then it has no
   subordinate CAs and the damage is limited to its own INRs.)  Mistakes
   by the INR holder can cause any of the actions noted in Section 2.  A
   successful attack against this CA can effect all of the modification,



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   revocation, or injection actions noted in that section.  (We assume
   that objects generated by the CA are automatically published).  An
   attack against the publication point can effect all of the deletion,
   suppression, or corruption actions noted in that section.

3.2.  Scenario B

   In this scenario, the INR holder acts as its own CA and but it
   delegates management of it own publication point to a third party.
   Mistakes by the INR holder can cause any of the modification,
   revocation, or injection actions described in Section 2.  Actions by
   the repository operator can adversely affect the resources of the INR
   holder, and those of any subordinate CAs.  (If the CA is a "leaf" in
   the RPKI, then it has no subordinate CAs and the damage is limited,
   as in Scenario A.)  The range of adverse effects here includes those
   in Scenario A, and adds a new potential source of adverse actions,
   i.e., the third party repository operator.  A successful attack
   against the CA can effect all of the modification, revocation, or
   injection actions noted in that section (assuming that objects
   generated by the CA are automatically published).  Here, actions by
   the publication point manager (or attacks against that entity) can
   effect all of the deletion, suppression, or corruption actions noted
   in Section 2.

3.3.  Scenario C

   In this scenario, the INR holder outsources management of its CA to
   its parent, but manages its own repository publication point.  All
   signed objects associated with the INR holder are generated by the
   parent CA but are self-hosted.  (We expect this scenario to be rare,
   because an INR holder that elects to outsource CA operation seems
   unlikely to manage its own repository publication point.)  Because
   that CA has the private key used to sign them, it can generate
   alternative signed objects -- ones not authorized by the INR holder.
   However, erroneous objects created by the parent CA will not be
   published by the INR holder IF the holder checks them first.  Because
   the parent CA is acting on behalf of the INR holder, mistakes by or
   attacks against that entity are equivalent to ones effected by the
   INR holder in Scenario A.  Mistakes by the INR holder, acted upon by
   the parent CA, can cause any of the actions noted in Section 2.
   Actions unilaterally undertaken by the parent CA also can have the
   same effect, unless the INR holder checks the signed objects before
   publishing them.  A successful attack against the parent CA can
   effect all of the modification, revocation, or injection actions
   noted in Section 2, unless the INR holder checks the signed objects
   before publishing them.  An attack against the INR holder (in its
   role as repository operator) can effect all of the deletion,
   suppression, or corruption actions noted in Section 2 (because the



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   INR holder is managing its publication point), unless the INR holder
   checks the signed objects before publishing them.  (An attack against
   the INR holder implies that the path it uses to direct the parent CA
   to issue and publish objects has been compromised.)

3.4.  Scenario D

   In this scenario an INR holder outsources management of both its CA
   and its publication point to its parent.  The INR holder is most
   vulnerable in this scenario.  Actions by the parent CA, acting on
   behalf of the INR holder, can adversely affect all signed objects
   associated with that INR holder, including any subordinate CA
   certificates.  These actions will presumably translate directly into
   publication point changes, because the parent CA is managing the
   publication point for the INR holder.  The range of adverse effects
   here includes those in Scenarios A, B, and C.  Mistakes by the INR
   holder, acted upon by the parent CA, can cause any of the actions
   noted in Section 2.  Actions unilaterally undertaken by the parent CA
   also can have the same effect.  A successful attack against the
   parent CA can effect all of the modification, revocation, or
   injection actions noted in Section 2.  An attack against the parent
   CA can also effect all of the deletion, suppression, or corruption
   actions noted in Section 2 (because the parent CA is managing the INR
   holder's publication point).

4.  Detection and Remediation

   To detect problems, each INR holder SHOULD check the signed objects
   available in its publication point on a regular basis.  This document
   RECOMMENDS that each INR holder perform such checks as a side-effect
   of acquiring RPKI data for local processing, e.g., 3-4 times a day.
   Third parties also can perform checks on behalf of RPs, to detect
   adverse actions.  This is consistent with the outsourcing options
   noted in the use cases in Section 1.  In either situation, detection
   of adverse actions requires that the cognizant party have available a
   reference set of RPKI data for the INR holder.  The reference set
   includes all signed objects in the publication point(s) of the INR
   holder plus the CA certificate for each publication point.

   If an adverse action is the result of a mistake by, or an attack
   against, a superior CA or a repository manager, the INR holder SHOULD
   contact the relevant entity as soon as possible.  It is expected that
   a mistake by these entities normally will be corrected and new
   objects published within 24-72 hours.  An attack against a superior
   CA or repository manager also should be remedied by the affected
   parties, but the time to repair the damage may be longer, because of
   the additional activities that may accompany responding to an attack,




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   e.g., assessing the extent of the attack, identifying and remediating
   the vulnerabilities that allowed the attack, etc.

   In both of these situations, the harmful effects of adverse actions
   can be mitigated if RPs delay acting on changes that might be
   attributable to adverse actions.  This observation motivates the
   introduction of hysteresis into the RPKI validation process, at least
   with respect to changes that are indicative of an adverse action.
   The idea is that an RP would continue to accept as valid objects that
   were previously valid (based on local cache history), and ignore
   recent changes, for some interval.

   Sometimes an INR holder may wish to make a change that might be
   viewed as an adverse action, without encountering such a delay.  To
   accommodate this situation, the RPKI can be extended to allow an INR
   holder to provide independent confirmation of such changes.  A
   mechanism of this sort could prevent mistakes by a superior CA or
   repository manager from having an immediate, adverse effect.  If the
   independent confirmation is not completely dependent on the RPKI
   repository and CA system, it can be immune to mistakes by or attacks
   against superior CAs and repository managers, and mistakes by or
   attacks against third-party CAs and repository managers.

   The effects of an attack on an INR holder itself may not be countered
   by a mechanism of this sort; an adversary who can attack a CA and/or
   repository management function of an INR holder may be able to attack
   the independent confirmation mechanism at the same time.  The use of
   a separate mechanism does create the potential for additional
   safeguards against such attacks.  However, the extent to which this
   potential is achieved will depend on how an INR holder implements and
   manages this mechanism.

   If a superior CA or repository manager is compelled to engage in an
   adverse action against an INR holder, e.g., by a law enforcement
   agency, use of an independent confirmation mechanism also may be able
   to counter such an action.  In this situation, the actions are not
   likely to be reversed quickly, unlike a mistake or attack.  This
   situation might argue for a longer period of delay.  An INR holder
   and a subordinate INR holder may disagree about an action that
   invalidates the holdings of the subordinate.  The addition of
   hysteresis and an independent confirmation mechanism to the RPKI
   ought not to deprive an INR holder of the legitimate ability to take
   such actions.  This argues for a time limit on the hysteresis and
   confirmation mechanism, consistent with the business practices of
   RPKI CAs.  This time limit should be long enough to allow affected
   entities to remedy mistakes and recover from attacks.  It also should
   be short enough to not impede the resolution of legitimate actions by
   an INR holder relative to subordinate INR holders.



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5.  Security Considerations

   This informational document describes a threat model for the RPKI,
   focusing on mistakes by or attacks against CAs and independent
   repository managers.  It is intended to support the design of future
   RPKI security mechanisms that seek to address the concerns associated
   with such actions.

6.  IANA Considerations

   This document has no actions for IANA.

7.  Acknowledgements

   The authors thank Richard Hansen and David Mandelberg for their
   review feedback and editorial assistance.

8.  References

8.1.  Normative References

   [I-D.ietf-sidr-bgpsec-overview]
              Lepinski, M., "An Overview of BGPsec", draft-ietf-sidr-
              bgpsec-overview-07 (work in progress), June 2015.

   [I-D.ietf-sidr-bgpsec-pki-profiles]
              Reynolds, M. and S. Kent, "A Profile for BGPsec Router
              Certificates, Certificate Revocation Lists, and
              Certification Requests", draft-ietf-sidr-bgpsec-pki-
              profiles-11 (work in progress), August 2015.

   [I-D.ietf-sidr-bgpsec-protocol]
              Lepinski, M., "BGPsec Protocol Specification", draft-ietf-
              sidr-bgpsec-protocol-13 (work in progress), July 2015.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3779]  Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
              Addresses and AS Identifiers", RFC 3779,
              DOI 10.17487/RFC3779, June 2004,
              <http://www.rfc-editor.org/info/rfc3779>.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <http://www.rfc-editor.org/info/rfc5652>.



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   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <http://www.rfc-editor.org/info/rfc6480>.

   [RFC6481]  Huston, G., Loomans, R., and G. Michaelson, "A Profile for
              Resource Certificate Repository Structure", RFC 6481,
              DOI 10.17487/RFC6481, February 2012,
              <http://www.rfc-editor.org/info/rfc6481>.

   [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
              Origin Authorizations (ROAs)", RFC 6482,
              DOI 10.17487/RFC6482, February 2012,
              <http://www.rfc-editor.org/info/rfc6482>.

   [RFC6483]  Huston, G. and G. Michaelson, "Validation of Route
              Origination Using the Resource Certificate Public Key
              Infrastructure (PKI) and Route Origin Authorizations
              (ROAs)", RFC 6483, DOI 10.17487/RFC6483, February 2012,
              <http://www.rfc-editor.org/info/rfc6483>.

   [RFC6485]  Huston, G., "The Profile for Algorithms and Key Sizes for
              Use in the Resource Public Key Infrastructure (RPKI)",
              RFC 6485, DOI 10.17487/RFC6485, February 2012,
              <http://www.rfc-editor.org/info/rfc6485>.

   [RFC6486]  Austein, R., Huston, G., Kent, S., and M. Lepinski,
              "Manifests for the Resource Public Key Infrastructure
              (RPKI)", RFC 6486, DOI 10.17487/RFC6486, February 2012,
              <http://www.rfc-editor.org/info/rfc6486>.

   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487,
              DOI 10.17487/RFC6487, February 2012,
              <http://www.rfc-editor.org/info/rfc6487>.

   [RFC6488]  Lepinski, M., Chi, A., and S. Kent, "Signed Object
              Template for the Resource Public Key Infrastructure
              (RPKI)", RFC 6488, DOI 10.17487/RFC6488, February 2012,
              <http://www.rfc-editor.org/info/rfc6488>.

   [RFC6489]  Huston, G., Michaelson, G., and S. Kent, "Certification
              Authority (CA) Key Rollover in the Resource Public Key
              Infrastructure (RPKI)", BCP 174, RFC 6489,
              DOI 10.17487/RFC6489, February 2012,
              <http://www.rfc-editor.org/info/rfc6489>.






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   [RFC6493]  Bush, R., "The Resource Public Key Infrastructure (RPKI)
              Ghostbusters Record", RFC 6493, DOI 10.17487/RFC6493,
              February 2012, <http://www.rfc-editor.org/info/rfc6493>.

   [RFC6916]  Gagliano, R., Kent, S., and S. Turner, "Algorithm Agility
              Procedure for the Resource Public Key Infrastructure
              (RPKI)", BCP 182, RFC 6916, DOI 10.17487/RFC6916, April
              2013, <http://www.rfc-editor.org/info/rfc6916>.

   [RFC7132]  Kent, S. and A. Chi, "Threat Model for BGP Path Security",
              RFC 7132, DOI 10.17487/RFC7132, February 2014,
              <http://www.rfc-editor.org/info/rfc7132>.

8.2.  Informative References

   [I-D.ietf-sidr-rpki-validation-reconsidered]
              Huston, G., Michaelson, G., Martinez, C., Bruijnzeels, T.,
              Newton, A., and A. Aina, "RPKI Validation Reconsidered",
              draft-ietf-sidr-rpki-validation-reconsidered-02 (work in
              progress), October 2015.

   [I-D.kent-sidr-suspenders]
              Kent, S. and D. Mandelberg, "Suspenders: A Fail-safe
              Mechanism for the RPKI", draft-kent-sidr-suspenders-03
              (work in progress), April 2015.

Authors' Addresses

   Stephen Kent
   BBN Technologies
   10 Moulton St
   Cambridge, MA  02138-1119
   USA

   EMail: kent@bbn.com


   Di Ma
   ZDNS
   4 South 4th St.
   Zhongguancun
   Haidian, Beijing  100190
   China

   EMail: madi@zdns.cn






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