wdiff rfc8211v1.txt rfc8211.txt

Internet Engineering Task Force (IETF) S. Kent
Request for Comments: 8211 BBN Technologies
Category: Informational D. Ma
ISSN: 2070-1721 ZDNS
June 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
http://www.rfc-editor.org/info/rfc8211.

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
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
2. Analysis of RPKI Repository Objects . . . . . . . . . . . . . 3
2.1. CA Certificates . . . . . . . . . . . . . . . . . . . . . 5
2.2. Manifest . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3. Certificate Revocation List . . . . . . . . . . . . . . . 11
2.4. ROA . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.5. Ghostbusters Record . . . . . . . . . . . . . . . . . . . 16
2.6. Router Certificates . . . . . . . . . . . . . . . . . . . 16
3. Analysis of Actions Relative to Scenarios . . . . . . . . . . 18
3.1. Scenario A . . . . . . . . . . . . . . . . . . . . . . . 20
3.2. Scenario B . . . . . . . . . . . . . . . . . . . . . . . 20
3.3. Scenario C . . . . . . . . . . . . . . . . . . . . . . . 20
3.4. Scenario D . . . . . . . . . . . . . . . . . . . . . . . 21
4. Security Considerations . . . . . . . . . . . . . . . . . . . 21
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.1. Normative References . . . . . . . . . . . . . . . . . . 22
6.2. Informative References . . . . . . . . . . . . . . . . . 23
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24

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 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
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 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, 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.

* 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.

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.

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 BGPsec_PATH attributes [RFC8205]
verifiable under these certificates will be
considered invalid.

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.)

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 manifest's EE certificate
expires at the time that the Manifest manifest is scheduled to be replaced, a
delay in publication will cause the Manifest manifest to become invalid, not
merely stale. This very serious outcome should be avoided, e.g., by
making the Manifest 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 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
point but not listed in a valid Manifest. manifest. Thus, the following
actions against a manifest can impact RP processing:

A-2.1 Deletion

A-2.1.1 A Manifest manifest may be deleted from the indicated
publication point. In this circumstance, an RP
may elect to use the previous Manifest 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. 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 manifest may be suppressed.
Suppression of a newer Manifest manifest probably will
cause an RP to rely on a cached Manifest manifest (if
available). The older Manifest 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 manifest may be corrupted. A corrupted Manifest 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, 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).

A-2.4 Modification

A-2.4.1 A Manifest manifest may be modified to remove one or more
objects. Because the modified Manifest 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 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 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 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 manifest may be revoked (by including its EE
certificate on the CRL for the publication point).
A revoked Manifest manifest will be ignored by an RP, which
probably would revert to an older (cached)
Manifest.
manifest. The implications for RPs are equivalent
to A-2.1 with regard to new/changed objects.

A-2.6 Injection

A-2.6.1 A Manifest manifest representing different objects may be
injected into a publication point. The effects
are the same as for a modified Manifest 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.

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).

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.

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.

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.

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.

2.6. Router Certificates

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

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 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 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
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 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.

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.

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
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.

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,
<http://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, <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>.

[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>.

[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>.

[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, <http://www.rfc-editor.org/info/rfc7935>.

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

[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, June 2017.

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,
<http://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,
<http://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,
<http://www.rfc-editor.org/info/rfc2725>.

[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<http://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,
<http://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,
<http://www.rfc-editor.org/info/rfc7682>.

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