





Internet Engineering Task Force (IETF)                           S. Kent
Request for Comments: 8211                              BBN Technologies
Category: Informational                                            D. Ma
ISSN: 2070-1721                                                     ZDNS
                                                          September 2017


Adverse Actions by a Certification Authority (CA) or Repository Manager
            in the Resource Public Key Infrastructure (RPKI)

Abstract

   This document analyzes actions by or against a Certification
   Authority (CA) or an 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 done from the
   perspective of an affected INR holder.  The analysis is based on
   examination of the data items in the RPKI repository, as controlled
   by a CA (or an independent repository manager) and fetched by Relying
   Parties (RPs).  The analysis does not purport to be comprehensive; it
   does represent an orderly way to analyze a number of ways that errors
   by or attacks against a CA or repository manager can affect the RPKI
   and routing decisions based on RPKI data.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It has been approved for publication by the Internet
   Engineering Steering Group (IESG).  Not all documents approved by the
   IESG are a candidate for any level of Internet Standard; see
   Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8211.













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Copyright Notice

   Copyright (c) 2017 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
   (https://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.  Analysis of RPKI Repository Objects . . . . . . . . . . . . .   4
     2.1.  CA Certificates . . . . . . . . . . . . . . . . . . . . .   6
     2.2.  Manifest  . . . . . . . . . . . . . . . . . . . . . . . .   9
     2.3.  Certificate Revocation List . . . . . . . . . . . . . . .  12
     2.4.  ROA . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
     2.5.  Ghostbusters Record . . . . . . . . . . . . . . . . . . .  17
     2.6.  Router Certificates . . . . . . . . . . . . . . . . . . .  18
   3.  Analysis of Actions Relative to Scenarios . . . . . . . . . .  19
     3.1.  Scenario A  . . . . . . . . . . . . . . . . . . . . . . .  21
     3.2.  Scenario B  . . . . . . . . . . . . . . . . . . . . . . .  21
     3.3.  Scenario C  . . . . . . . . . . . . . . . . . . . . . . .  21
     3.4.  Scenario D  . . . . . . . . . . . . . . . . . . . . . . .  22
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  22
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  23
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  25
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26














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1.  Introduction

   In the context of this document, any change to the Resource Public
   Key Infrastructure (RPKI) [RFC6480] that diminishes the set of
   Internet Number Resources (INRs) associated with an INR holder, and
   that is contrary to the holder's wishes, is termed "adverse".  This
   analysis is done from the perspective of an affected INR holder.  An
   action that results in an adverse charge (as defined above) may be
   the result of an attack on a CA [RFC7132], an error by a CA, or an
   error by or an attack on a repository operator.  Note that the CA
   that allocated the affected INRs may be acting in accordance with
   established policy; thus, the change may be contractually justified
   even though viewed as adverse by the INR holder.  This document
   examines the implications of adverse actions within the RPKI with
   respect to INRs, irrespective of the cause of the actions.

   Additionally, when a Route Origin Authorization (ROA) or router
   certificate is created that "competes" with an existing ROA or router
   certificate (respectively), the creation of the new ROA or router
   certificate may be adverse.  (A newer ROA competes with an older ROA
   if the newer ROA points to a different Autonomous System Number
   (ASN), contains the same or a more specific prefix, and is issued by
   a different CA.  A newer router certificate competes with an older
   router certificate if the newer one contains the same ASN, contains a
   different public key, and is issued by a different CA.)  Note that
   transferring resources or changing of upstream providers may yield
   competing ROAs and/or router certificates under some circumstances.
   Thus, not all instances of competition are adverse actions.

   As noted above, adverse changes to RPKI data may arise due to several
   types of causes.  A CA may make a mistake in managing the RPKI
   objects it signs, or it may be subject to an attack.  If an attack
   allows an adversary to use the private key 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 make adverse changes to
   RPKI data.  In many cases, such actions may be hard to distinguish
   from mistakes or attacks, other than with respect to the time
   required to remedy the adverse action.  (Presumably, the CA will take
   remedial action when a mistake or an attack is detected, so the
   effects are similar in these cases.  If a CA has been legally
   compelled to effect an adverse change, remediation will likely not be
   swift.)

   This document analyzes the various types of actions by a CA (or an
   independent repository operator) that can adversely affect the 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



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   repository, as controlled by a CA (or an independent repository
   operator) and fetched by RPs.

2.  Analysis of RPKI Repository Objects

   This section enumerates the RPKI repository system objects and
   examines how changes to them affect Route Origin Authorizations
   (ROAs) and router certificate validation.  Identifiers are assigned
   to errors for reference by later sections of this document.  Note
   that not all adverse actions may be encompassed by this taxonomy.

   The RPKI repository [RFC6481] contains a number of (digitally signed)
   objects that are fetched and processed by RPs.  Until the deployment
   of BGPsec [RFC8205], the principal goal of the RPKI is to enable an
   RP to validate ROAs [RFC6482].  A ROA binds address space to an 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 [RFC8209] will be added
   to repository publication points.  These are end entity (EE)
   certificates used to verify signatures applied to BGP update data and
   to enable path validation [RFC8205].  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
   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, e.g., a ROA or manifest, as
   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.



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      *  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.

   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 between
   individual actions, or combinations thereof, that 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.





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   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
   each action has been considered with regard to each object.  (For the
   Ghostbusters Record [RFC6493], we condensed the discussion of the
   actions because the impact is the same in each case.)

2.1.  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 Subject Information Access (SIA) pointer to the
   publication point where the signed objects associated with that CA
   can be found [RFC6487].

   A CA certificate is a complex data structure; 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:

      A-1.1  Deletion

             A-1.1.1  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.







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      A-1.2  Suppression

             A-1.2.1  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-1.1 or
                      A-1.4.3.  If the [RFC3779] extensions in the
                      suppressed certificate changed, the impact would
                      be the same as in A-1.4.1.  If the Authority
                      Information Access (AIA) extension changed in the
                      suppressed certificate, the impact would be the
                      same as in A-1.4.4.  Suppression of a renewed/
                      re-issued certificate may cause an old certificate
                      to expire and thus be rejected by RPs.

      A-1.3  Corruption

             A-1.3.1  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-1.4  Modification

             A-1.4.1  If a CA certificate is modified but still conforms
                      to the RPKI certificate profile [RFC7935], 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 [RFC8205]
                      verifiable under these certificates will be
                      considered invalid.







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             A-1.4.2  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-1.4.3  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 trust anchors (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-1.4.4  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.  (Note that key rollover also yields
                      a new CA certificate.  However, the new
                      certificate will coexist with the old one for a
                      while, which may help distinguish this legitimate
                      activity from an adverse action.)





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      A-1.5  Revocation

             A-1.5.1  If a CA certificate is revoked, an RP will treat
                      as invalid all subordinate signed objects, both
                      immediate and transitive.  The effects are
                      essentially the same as described in A-3.4.2.

      A-1.6  Injection

             A-1.6.1  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-1.4.

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) can
   also 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





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   implementations ignore objects that are present at a publication
   point but not listed in a valid manifest.  Thus, the following
   actions against a manifest can impact RP processing:

      A-2.1  Deletion

             A-2.1.1  A manifest may be deleted from the indicated
                      publication point.  In this circumstance, an RP
                      may elect to use the previous manifest (if
                      available) 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-1.1).  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-4.1).

      A-2.2  Suppression

             A-2.2.1  Publication of a newer manifest may be suppressed.
                      Suppression of a newer manifest probably will
                      cause an RP to rely on a cached manifest (if
                      available).  The older manifest would not
                      enumerate newly added objects; thus, those objects
                      might be ignored by an RP, which is equivalent to
                      deletion of those objects (A-1.1, A-3.1, A-4.1,
                      A-5.1, and A-6.1).

      A-2.3  Corruption

             A-2.3.1  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
                      probably be viewed as invalid, including
                      subordinate tree objects.  This is equivalent to
                      revoking or deleting an entire subtree (see
                      A-4.4.2).






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      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, and A-6.1).

             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 not 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 is thus 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  Revocation

             A-2.5.1  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.







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      A-2.6  Injection

             A-2.6.1  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 is thus discussed in the
                      relevant section(s) for each object type.

2.3.  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-3.1  Deletion

             A-3.1.1  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-3.1.2  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-5.2.

             A-3.1.3  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
                      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.








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             A-3.1.4  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-3.2  Suppression

             A-3.2.1  If publication of the most recent CRL is
                      suppressed, an RP will not be informed of the most
                      recent revocation status of a 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 if 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-3.1), 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-3.3  Corruption

             A-3.3.1  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-3.1 and
                      A-3.2).













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      A-3.4  Modification

             A-3.4.1  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-5.5).  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).

             A-3.4.2  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-3.4.3  If a CRL is modified to omit a revoked EE, router,
                      or CA certificate, RPs will likely 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-3.5  Revocation

             A-3.5.1  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-1.5 for a discussion
                      of that action.

      A-3.6  Injection

             A-3.6.1  Insertion of a bogus CRL can have the same effects
                      as listed above for a modified CRL, depending on
                      how the inserted CRL differs from the correct CRL.









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2.4.  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-4.1  Deletion

             A-4.1.1  A ROA may be deleted from the indicated
                      publication point.  The result is to void the
                      binding between the prefix(es) and the Autonomous
                      System (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).

      A-4.2  Suppression

             A-4.2.1  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-4.2.2  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.










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             A-4.2.3  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-4.3  Corruption

             A-4.3.1  A ROA may be corrupted.  A corrupted ROA will be
                      ignored by an RP, so the effect is essentially the
                      same as for A-4.1 and A-4.5.  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-4.4  Modification

             A-4.4.1  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.

      A-4.5  Revocation

             A-4.5.1  A ROA may be revoked (by placing its EE
                      certificate on the CRL for the publication point).
                      This has the same effect as A-4.1.












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      A-4.6  Injection

             A-4.6.1  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.  In
                      this case, the injected ROA is considered to be in
                      competition with any existing authorized ROAs for
                      the specified prefix.

             A-4.6.2  An 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.  If there are other ROAs that
                      authorize different ASNs to advertise routes to
                      the injected ROA's prefix, then the injected ROA
                      is in competition with these ROAs.

2.5.  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.

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

      A-5.1  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.





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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 [RFC8209].  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

             A-6.1.1  Deletion of a router certificate would cause an RP
                      to be unable 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 it
                      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

             A-6.2.1  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
                      has 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.









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      A-6.3  Corruption

             A-6.3.1  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 competing
                      routes that have valid BGPsec_PATH attribute
                      signatures.

      A-6.4  Modification

             A-6.4.1  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  Revocation

             A-6.5.1  If a router certificate were revoked, BGPsec_PATH
                      attributes verifiable using that certificate would
                      no longer be considered valid.  The impact would
                      be the same as for a deleted certificate, as
                      described in A-6.1.

      A-6.6  Injection

             A-6.6.1  Insertion of a router certificate could authorize
                      additional routers to sign BGPsec traffic for the
                      targeted ASN, and thus undermine fundamental
                      BGPsec security guarantees.  If there are
                      existing, authorized router certificates for the
                      same ASN, then the injected router certificate is
                      in competition with these existing certificates.

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.




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   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
   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 can
   also 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.




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   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,
   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 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



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   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
   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.  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 provide a basis for the
   design of future RPKI security mechanisms that seek to address the
   concerns associated with such actions.



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   The analysis in this document identifies a number of circumstances in
   which attacks or errors can have significant impacts on routing.  One
   ought not interpret this as a condemnation of the RPKI.  It is only
   an attempt to document the implications of a wide range of attacks
   and errors in the context of the RPKI.  The primary alternative
   mechanism for disseminating routing information is Internet Routing
   Registry (IRR) technology [RFC2650] [RFC2725], which uses the Routing
   Policy Specification Language (RPSL) [RFC2622].  IRR technology
   exhibits its own set of security problems, which are discussed in
   [RFC7682].

5.  IANA Considerations

   This document does not require any IANA actions.

6.  References

6.1.  Normative References

   [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,
              <https://www.rfc-editor.org/info/rfc3779>.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <https://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,
              <https://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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc6483>.

   [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,
              <https://www.rfc-editor.org/info/rfc6486>.



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   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487,
              DOI 10.17487/RFC6487, February 2012,
              <https://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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc6489>.

   [RFC6493]  Bush, R., "The Resource Public Key Infrastructure (RPKI)
              Ghostbusters Record", RFC 6493, DOI 10.17487/RFC6493,
              February 2012, <https://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, <https://www.rfc-editor.org/info/rfc6916>.

   [RFC7935]  Huston, G. and G. Michaelson, Ed., "The Profile for
              Algorithms and Key Sizes for Use in the Resource Public
              Key Infrastructure", RFC 7935, DOI 10.17487/RFC7935,
              August 2016, <https://www.rfc-editor.org/info/rfc7935>.

   [RFC8205]  Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
              Specification", RFC 8205, DOI 10.17487/RFC8205, September
              2017, <https://www.rfc-editor.org/info/rfc8205>.

   [RFC8209]  Reynolds, M., Turner, S., and S. Kent, "A Profile for
              BGPsec Router Certificates, Certificate Revocation Lists,
              and Certification Requests", RFC 8209,
              DOI 10.17487/RFC8209, September 2017,
              <https://www.rfc-editor.org/info/rfc8209>.












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6.2.  Informative References

   [RFC2622]  Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D.,
              Meyer, D., Bates, T., Karrenberg, D., and M. Terpstra,
              "Routing Policy Specification Language (RPSL)", RFC 2622,
              DOI 10.17487/RFC2622, June 1999,
              <https://www.rfc-editor.org/info/rfc2622>.

   [RFC2650]  Meyer, D., Schmitz, J., Orange, C., Prior, M., and C.
              Alaettinoglu, "Using RPSL in Practice", RFC 2650,
              DOI 10.17487/RFC2650, August 1999,
              <https://www.rfc-editor.org/info/rfc2650>.

   [RFC2725]  Villamizar, C., Alaettinoglu, C., Meyer, D., and S.
              Murphy, "Routing Policy System Security", RFC 2725,
              DOI 10.17487/RFC2725, December 1999,
              <https://www.rfc-editor.org/info/rfc2725>.

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

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

   [RFC7682]  McPherson, D., Amante, S., Osterweil, E., Blunk, L., and
              D. Mitchell, "Considerations for Internet Routing
              Registries (IRRs) and Routing Policy Configuration",
              RFC 7682, DOI 10.17487/RFC7682, December 2015,
              <https://www.rfc-editor.org/info/rfc7682>.




















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Acknowledgements

   The authors thank Richard Hansen and David Mandelberg for their
   extensive review, feedback, and editorial assistance.  Thanks also go
   to Daiming Li for her editorial assistance.

Authors' Addresses

   Stephen Kent
   BBN Technologies
   10 Moulton St
   Cambridge, MA  02138-1119
   United States of America

   Email: kent@alum.mit.edu


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

   Email: madi@zdns.cn



























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