Internet DRAFT - draft-huston-rpki-validation
draft-huston-rpki-validation
Network Working Group G. Huston
Internet-Draft G. Michaelson
Intended status: Informational APNIC
Expires: August 13, 2014 February 9, 2014
RPKI Validation Reconsidered
draft-huston-rpki-validation-01.txt
Abstract
This document reviews the certificate validation procedure specified
in RFC6487 and highlights aspects of operational management of
certificates in the RPKI in response to the movement of resources
across registries, and the associated actions of Certification
Authorities to maintain certification of resources during this
movement. The document describes an alternative validation procedure
that reduces the operational impact of certificate management during
resource movement.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on August 13, 2014.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Operational Considerations . . . . . . . . . . . . . . . . . . 4
3. A Specific Resource RPKI Certificate Validation Process . . . 6
3.1. Resource Transfers and Specific Resource Certificate
Validation . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. A Specification of Specific Resource Validation . . . . . 8
4. Local Repository Cache Maintenance . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
This document reviews the certificate validation procedure specified
in [RFC6487] and highlights aspects of operational management of
certificates in the RPKI in response to the movement of resources
across registries, and the associated actions of Certification
Authorities to maintain certification of resources during this
movement. The document describes an alternative validation procedure
that reduces the operational impact of certificate management during
resource movement. The alternative validation procedure also offers
a higher level of robustness in the face of resource inconsistencies
in a putative certificate validation path.
As currently defined in section 7.2 of [RFC6487], validation of PKIX
certificates that conform to the RPKI profile relies on the use of a
path validation process where each certificate in the validation path
is required to meet the certificate validation criteria. This can be
considered to be a recursive validation process where, in the context
of an ordered sequence of certificates, as defined by common Issuer
and Subject Name pairs, a certificate is defined as valid if it
satisfies basic validation criteria relating to the syntactic
correctness, currency of validity dates and similar properties of the
certificate itself, as described in [RFC5280], and also that it
satisfies certain additional criteria with respect to the previous
certificate in the sequence, and that this previous certificate is
itself a valid certificate using the same criteria. This definition
applies recursively to all certificates in the sequence apart from
the initial sequence element, which is required to be a Trust Anchor.
For RPKI certificates, the additional criteria relating to the
previous certificate in this sequence is that the certificate's
number resource set, as defined in [RFC3779], is "encompassed" by the
number resource set contained in the previous certificate.
Because [RFC6487] validation demands that all resources in a
certificate be valid under the parent (and recursively, to the root),
a digitally signed attestation, such as a Route Origin Authorization
(ROA) object [RFC6482], which refers only to a subset of RFC3779-
specified resources from that certificate chain can be concluded to
be invalid, but not by virtue of the relationship between the RFC3779
extensions of the certificates on the putative certificate validation
path and the resources in the ROA, but by other resources described
in these certificates where the "encompassing" relationship of the
resources does not hold. Any such invalidity along the certificate
validation path can cause this outcome, not just at the immediate
parent of the end entity certificate that attests to the key used to
sign the ROA.
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For example, in the certificate sequence:
Certificate 1:
Issuer A, Subject B, Resources 192.0.2.0/24, AS64496-AS64500
Certificate 2:
Issuer B, Subject C, Resources 192.0.2.0/24/24, AS64496-AS64511
Certificate 3:
Issuer C, Subject D, Resources 192.0.2.0/24
Certificate 3 is considered to be an invalid certificate, because the
resources in Certificate 2 are not encompassed by the resources in
Certificate 1, by virtue of certificate 2 holding the resources of
the range AS64501 - AS64511 in this RFC3779 resource extension.
Obviously, these Autonomous Systems numbers are not related to the
IPv4 resources contained in Certificate 3.
2. Operational Considerations
There are two areas of operational concern with the current RPKI
validation definition.
The first is that of the robustness of the operatinal management
procesures in the issuance of certificates. If a subordinate CA
issues a certificate that contains an Internet Number Resource (INR)
collection that is not either exactly equal to, or a strict subset
of, its parent CA, then this issued certificate, and all subordinate
certificates of this issued certificate are invalid. These
certificates are not only defined as invalid when being considered to
validate an INR that is not in the parent CA certificate, but are
defined as invalid for all INRs in the certificate. This creates a
degree of operational fragility in the issuance of certificates, as
all CA's are now required to exercise extreme care in the issuance
and reissuance of certificates that they do not overclaim on the
resources described in the parent CA, as the consequences of an
operational lapse or oversight implies that all the subordinate
certificates from the point of mismatch are invalid. It would be
preferred if the consequences of such an operational lapse were
limited in scope to the specific INRs that formed the mismatch,
rather than including the sntire set of INRs within the scope of
damage from this oversight.
The second operational consideration described here relates to the
situation where a registry withdraws a resource from the current
holder, and the resource to transferred to another registry, to be
registered to a new holder in that registry. The reason why this is
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a consideration in operational deployments of the RPKI lies in the
movement of the "home" registry of number resources during cases of
mergers, acquisitions, business re-alignments, and resource transfers
and the desire to ensure that during this movement all other
resources can continue to be validated.
If the original registry's certification actions are simply to issue
a new certificate for the current holder with a reduced resource set,
and to revoke the original certificate, then there is a distinct
possibility of encountering the situation illustrated by the example
in the previous section. This is a result of an operational process
for certificate issuance by the parent CA being de-coupled from the
certificate operations of child CA.
This de-coupled operation of CAs introduces a risk of unintended
third party damage: since a CA certificate can refer to holdings
which relate to two or more unrelated subordinate certificates, if
this CA certificate becomes invalid due to the reduction in the
resources allocated to this CA relating to one subordinate resource
set, all other subordinate certificates are invalid until the CA
certificate is reissued with a reduced resource set.
In the above example, all subordinate certificates issued by CA C are
invalid until CA B issues a new certificate for CA C with a reduced
resource set.
At the lover levels of the RPKI hierarchy the resource sets affected
by such movements of resources may not encompass significantly large
pools of resources. However, as one ascends through this hierarchy
towards the apex, the larger the resource set that is going to be
affected by a period of invalidity by virtue of such uncoordinated
certificate management actions. In the case of a Regional Internet
Registry (RIR) or National Internet Registry (NIR), the potential
risk arising from uncoordinated certification actions relating to a
transfer of resources is that the entire set of subordinate
certificates that refer to resources administered by the RIR or the
NIR cannot be validated during this period.
Avoiding such situations requires that CA's adhere to a very specific
ordering of certificate issuance. In this framework, the common
registry CA that describes (directly or indirectly) the resources
being shifted from one registry to the other, and also contains in
subordinate certificates (direct or indirect) the certificates for
both registries who are parties to the resource transfer has to
coordinate a specific sequence of actions.
This common registry CA has to first issue a new certificate towards
the "receiving" registry that adds to the RFC3779 extension resource
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set the specific resource being transferred into this receiving
registry. The common registry CA then has to wait until all
registries in the subordinate certificate chain to the receiving
registry have also performed a similar issuance of new certificates,
and in each case a registry must await the issuance of the immediate
superior certificate with the augmented resource set before it, in
turn, can issue its own augmented certificate to its subordinate CA.
This is a "top down" issuance sequence."
It is possible for the common registry to issue a certificate to the
"sending" registry with the reduced resource set at any time, but it
should not revoke the previously issued certificate, nor overwrite
this previously issued certificate in its repository publication
point without specific coordination. Only when the common registry
is assured that the top down certificate issuance process to the
receiving registry CA chain has been completed can the common
registry commence the revocation of the original certificate for the
sending registry, However, it should not so until it is assured that
the immediate subordinate registry CA in the path to the sending
registry has issued a certificate with a reduced resource set, and so
on. This implies that on the sending side the certificate issuance
and revocation is a "bottom up" process.
If this process is not carefully followed, then the risk is that some
or all or the subordinate certificates of this common registry CA
will be unable to be validated until the entire process of
certificate issuance and revocation has been completed. While this
sequenced process is intended to preserve validity of certificates in
the RPKI, it is a complex and operationally cumbersome process.
The underlying consideration here is that the operational
coordination of these certificate issuance and revocation actions to
effect a smooth resource transfer across registries is mandated by
the nature of the certificate validation process described in
[RFC6487].
3. A Specific Resource RPKI Certificate Validation Process
The question considered here is: Is there an alternate definition of
RPKI certificate validity that could remove the requirement for such
careful orchestration of certification actions across the RPKI to
support resource transfers?
The general definition of certificate validity as defined in
[RFC5280] assumes a validation question relating to the relying
party's (RP's) level of trust in a subject's signed material, given
knowledge of a subject's name, the subject's public key, the RP's
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chosen trust anchor(s) and an overall PKI to define the domain of
discourse.
The validation question assumed by the [RFC6487] RPKI certificate
validation process relates to a RP's level of trust in the
combination of some signed material, a certificate that attests to
the public key used to sign this material and the set of all number
resources that have been assigned or allocated to the subject of the
certificate, given knowledge of the certificate, the RP's chosen
trust anchor(s), the RPKI, and the application of the same test
applied to the superior certificate in the RPKI hierarchy, and so on
to a Trust Anchor.
There is a alternative certificate validation procedure that starts
with an attestation containing the subject's signed material and an
explicit enumeration of a set of number resources. The associated
validation question relates to whether a RPKI validation process can
attest to the validity of a subject's signed attestation relating to
a particular set of number resources, rather than a signed
attestation relating to all number resources held by this subject.
We will term this alternate certificate validation process "specific
resource" validation.
If the certificate validation procedure is specifically restricted to
a question of ascertaining the validity of a particular set of number
resources in the context of the RPKI, the RPKI validation procedure
need not be as strict as a recursive "encompassing" condition for the
resources contained in each pair of certificates in the validation
path. It would be sufficient in the context of this "specific
resource" validation procedure to require only that each certificate
in the validation path has a number resource extension that
"encompasses" the specific resources described in the original
validation question. Rather than a validation test for all possible
questions, this is a specific validation question in the context of
specific resources.
This validation question can be informally described as: Given a
certificate and a given resource set, is there an Issuer-Subject
ordered sequence of certificates from a Trust Anchor to the
certificate being validated, where each certificate on this sequence
is well-formed, not revoked by a valid CRL, where the certificate's
lifetimes are valid, and where the RFC3779 resource extension in the
certificate encompass the given resource set?
In the example from Section 1, using a this alternate certificate
validation process, a validation question of certificate 3 and the
resource 10.0.1.0/24, the validation outcome would be positive, in
that certificates 1, 2 and 3 all encompass the specific resource
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10.0.1.0/24, assuming that the certificates are valid in all other
respects.
3.1. Resource Transfers and Specific Resource Certificate Validation
When considering the transfer of resources across registries, and the
associated certification actions, then if the validation process was
one of "specific resource" validation, then there is no requirement
for synchronized orchestration of the process of certificate issuance
and revocation by the CAs involved in this transfer in order to
preserve the validity of resources described in these certificates.
Along the chain of the "sending" registry CA hierarchy each registry
CA can issue a certificate with a reduced resource set that removes
the resource being transferred, and revoke the previously issued
certificate without regard to the specific timing of similar actions
by either it's superior or its subordinate registry CA.
Similarly, in the "receiving" registry hierarchy each CA can issue a
certificate with an augmented resource set that includes the resource
being transferred without particular regard to the timing of similar
actions by the other superior or subordinate registry CAs.
Validation questions relating to the migrating resource made against
certificates on the "sending registry" will return an invalid outcome
as soon as any registry CA in this chain has performed revocation of
the original certificate. Validation questions relating to the
migrating resource made against certificates on the "receiving
registry" will return an valid outcome only when all the registries
in this chain have performed certificate re-issuance and included the
resource in the new certificate.
Critically, at all times validation questions relating to any other
resource using the "specific resource" validation approach will
return the same outcomes throughout this issuance and revocation
process. This "specific resource" validation process engenders a
more robust outcome in RPKI certificate management. Validation
questions relating to resources which are not being transferred from
one registry to another cannot be compromised by any failure to
adhere to a strict process of issuance and revocation relating to the
certification of the resources being transferred.
3.2. A Specification of Specific Resource Validation
The following is a amended specification of certificate validation as
described in [RFC6487] that describes the proposed "specific
resource" certificate validation process.
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Validation of signed resource data using a target resource
certificate and a specific set of number resources consists of
verifying that the digital signature of the signed resource data is
valid, using the public key of the target resource certificate, and
also validating the resource certificate in the context of the RPKI,
using the path validation process. This path validation process
verifies, among other things, that a prospective certification path
(a sequence of n certificates) satisfies the following conditions:
1. for all 'x' in {1, ..., n-1}, the Subject of certificate 'x'
is the Issuer of certificate ('x' + 1);
2. certificate '1' is issued by a trust anchor;
3. certificate 'n' is the certificate to be validated; and
4. for all 'x' in {1, ..., n}, certificate 'x' is valid.
Certificate validation entails verifying that all of the following
conditions hold, in addition to the Certification Path Validation
criteria specified in Section 6 of [RFC5280]:
1. The certificate can be verified using the Issuer's public key
and the signature algorithm
2. The current time lies within the certificate's Validity From
and To values.
3. The certificate contains all fields that MUST be present, as
defined by this specification, and contains values for
selected fields that are defined as allowable values by this
specification.
4. No field, or field value, that this specification defines as
MUST NOT be present is used in the certificate.
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5. The Issuer has not revoked the certificate. A revoked
certificate is identified by the certificate's serial number
being listed on the Issuer's current CRL, as identified by the
CRLDP of the certificate, the CRL is itself valid, and the
public key used to verify the signature on the CRL is the same
public key used to verify the certificate itself.
6. The resource extension data contained in this certificate
"encompasses" the entirety of the resources in the specific
resource set.
7. The Certification Path originates with a certificate issued by
a trust anchor, and there exists a signing chain across the
Certification Path where the Subject of Certificate 'x' in the
Certification Path matches the Issuer in Certificate 'x + 1'
in the Certification Path, and the public key in Certificate
'x' can verify the signature value in Certificate 'x+1'.
A certificate validation algorithm MAY perform these tests in any
chosen order.
4. Local Repository Cache Maintenance
This change in the validation process would have some impact on the
operation of a local cache of validated RPKI certificates. Given
that the validation process requires the specification of a specific
resource set, it would appear that it would not be possible to
validate an RPKI certificate without also specifying a specific
resource set.
However, using a top-down validation process, and an additional local
data structure associated with each locally held validated RPKI
certificate, it is possible to maintain a local cache of validated
certificates, and the set of valid and invalid resources for each
certificate.
The additional data structures are the certificate's validated and
invalidated resource set. These sets are defined as follows:
o If the certificate is used as a Trust Anchor, then the local
validated resource set is copied from the certificate's RFC3779
resource set. There is no invalid resource set.
o Otherwise, the certificate's local validated resource set is
defined as the intersection of this certificate's RFC3779 resource
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set and the parent certificate's local validated resource set.
The certificate's invalid resource set is the difference between
this set and the certificate's RFC3779 resource set.
If the certificate's validated resource set is empty then the
certificate is not valid.
If the invalid resource set is not empty, then any resources that are
contained in this invalid resource set cannot be valid by virtue of
this certificate.
In all operations on the local repository cache, local applications
should use the certificate's local validated resource set in place of
the resources described in the certificate's RFC3779 extension.
The invalid resource set can be used as a diagnostic aide in local
cache management.
5. Security Considerations
The Security Considerations of [RFC6487] apply to the validation
procedure described here.
6. IANA Considerations
No updates to the registries are suggested by this document.
7. Acknowledgements
TBA.
8. References
8.1. Normative References
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779, June 2004.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for
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X.509 PKIX Resource Certificates", RFC 6487,
February 2012.
8.2. Informative References
[RFC6482] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
Origin Authorizations (ROAs)", RFC 6482, February 2012.
Authors' Addresses
Geoff Huston
Asia Pacific Network Information Centre (APNIC)
6 Cordelia St
South Brisbane, QLD 4101
Australia
Phone: +61 7 3858 3100
Email: gih@apnic.net
George Michaelson
Asia Pacific Network Information Centre (APNIC)
6 Cordelia St
South Brisbane, QLD 4101
Australia
Phone: +61 7 3858 3100
Email: ggm@apnic.net
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