Internet DRAFT - draft-ietf-sidr-rpki-tree-validation
draft-ietf-sidr-rpki-tree-validation
SIDR O. Muravskiy
Internet-Draft T. Bruijnzeels
Intended status: Informational RIPE NCC
Expires: September 22, 2016 March 21, 2016
RPKI Certificate Tree Validation by a Relying Party Tool
draft-ietf-sidr-rpki-tree-validation-00
Abstract
This document currently describes the approach to validate the
content of the RPKI certificate tree, as used by the RIPE NCC RPKI
Validator. This approach is independent of a particular object
retrieval mechanism. This allows it to be used with repositories
available over the rsync protocol, the RPKI Repository Delta
Protocol, and repositories that use a mix of both.
This algorithm does not rely on content of repository directories,
but uses the Authority Key Identifier (AKI) field of a manifest and a
certificate revocation list (CRL) objects to discover manifest and
CRL objects issued by a particular Certificate Authority (CA). It
further uses the hashes of manifest entries to discover other objects
issued by the CA.
If the working group finds that algorithm outlined here is useful for
other implementations, we may either update future revisions of this
document to be less specific to the RIPE NCC RPKI Validator
implementation, or we may use this document as a starting point of a
generic validation document and keep this as a detailed description
of the actual RIPE NCC RPKI Validator implementation.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 22, 2016.
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Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Top-down Validation of a Single Trust Anchor Certificate Tree 3
2.1. Fetching the Trust Anchor Certificate Using the Trust
Anchor Locator . . . . . . . . . . . . . . . . . . . . . 4
2.2. Resource Certificate Validation . . . . . . . . . . . . . 4
2.2.1. Finding most recent valid manifest and CRL . . . . . 5
2.2.2. Manifest entries validation . . . . . . . . . . . . . 6
2.3. Object Store Cleanup . . . . . . . . . . . . . . . . . . 6
3. Remote Objects Fetcher . . . . . . . . . . . . . . . . . . . 6
3.1. Fetcher Operations . . . . . . . . . . . . . . . . . . . 7
3.1.1. Fetch repository objects . . . . . . . . . . . . . . 7
3.1.2. Fetch single repository object . . . . . . . . . . . 7
4. Local Object Store . . . . . . . . . . . . . . . . . . . . . 8
4.1. Store Operations . . . . . . . . . . . . . . . . . . . . 8
4.1.1. Store Repository Object . . . . . . . . . . . . . . . 8
4.1.2. Update object's last fetch time . . . . . . . . . . . 8
4.1.3. Get objects by hash . . . . . . . . . . . . . . . . . 8
4.1.4. Get certificate objects by URI . . . . . . . . . . . 8
4.1.5. Get manifest objects by AKI . . . . . . . . . . . . . 8
4.1.6. Delete objects for URI . . . . . . . . . . . . . . . 8
4.1.7. Delete outdated objects . . . . . . . . . . . . . . . 8
4.1.8. Update object's validation time . . . . . . . . . . . 9
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
In order to use information published in RPKI repositories, Relying
Parties (RP) need to retrieve and validate the content of
certificates, CRLs, and other RPKI signed objects. To validate a
particular object, one must ensure that all certificates in the
certificate chain up to the Trust Anchor (TA) are valid. Therefore
the validation of a certificate tree is usually performed top-down,
starting from the TA certificate and descending down the certificate
chain, validating every encountered certificate and its products.
The result of this process is a list of all encountered RPKI objects
with a validity status attached to each of them. These results may
later be used by a Relying Party in taking routing decisions, etc.
Traditionally RPKI data is made available to RPs through the
repositories [RFC6481] accessible over rsync protocol. Relying
parties are advised to keep a local copy of repository data, and
perform regular updates of this copy from the repository (Section 5
of[RFC6481]). The RPKI Repository Delta Protocol
[I-D.ietf-sidr-delta-protocol] introduces another method to fetch
repository data and keep the local copy up to date with the
repository.
This document describes how a Relying Party tool could discover RPKI
objects to download, build certificate path, and validate RPKI
objects, independently from what repository access protocol is used.
To achieve this, it puts downloaded RPKI objects in an object store,
where objects could be found by their URI, hash of their content,
value of the object's AKI field, or combination of these. It also
keeps track of download and validation time for every object, to
perform cleanups of the local copy.
2. Top-down Validation of a Single Trust Anchor Certificate Tree
The validation of a Trust Anchor (TA) certificate tree starts from
its TA certificate. To retrieve the TA certificate, a Trust Anchor
Locator (TAL) object is used, as described in Section 2.1.
If the TA certificate is retrieved, it is validated according to the
Section 7 of [RFC6487] and Section 2.2 of [RFC7730].
Then the TA certificate and all its subordinate objects are validated
as described in Section 2.2.
For all repository objects that were validated during this validation
run, their validation timestamp is updated in an object store (see
Section 4.1.8).
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Outdated objects are removed from the store as described in
Section 2.3. This completes the validation of the TA certificate
tree.
2.1. Fetching the Trust Anchor Certificate Using the Trust Anchor
Locator
The following steps are performed in order to fetch the Trust Anchor
Certificate:
o (Optional) If the Trust Anchor Locator contains a "prefetch.uris"
field, pass the URIs contained there to the fetcher (see
Section 3.1.1). (This field is a non-standard extension to the
TAL format supported by the RIPE NCC Validator. It helps fetching
non-hierarchical rsync repositories more efficiently.)
o Extract the TA certificate URI from the TAL's URI section (see
Section 2.1 of[RFC7730]) and pass to the object fetcher
(Section 3.1.2).
o Retrieve from the object store (see Section 4.1.4) all certificate
objects, for which the URI matches the URI extracted from the TAL
in the previous step, and the public key matches the
subjectPublicKeyInfo field of the TAL (see Section 2.1 of
[RFC7730]).
o If no, or more than one such objects are found, issue an error and
stop validation process. Otherwise, use that object as the Trust
Anchor certificate.
2.2. Resource Certificate Validation
The following steps describe the validation of a single resource
certificate:
o If both the caRepository (Section 4.8.8.1 of [RFC6487]), and the
id-ad-rpkiNotify (Section 3.5 of [I-D.ietf-sidr-delta-protocol])
SIA pointers are present in the given resource certificate, use a
local policy to determine which pointer to use. Extract the URI
from the selected pointer and pass it to the object fetcher (see
Section 3.1.1).
o For a given resource certificate, find its manifest and
certificate revocation list (CRL), using the procedure described
in Section 2.2.1. If no such manifest and CRL could be found,
issue an error and stop processing current certificate.
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o Compare the URI found in the given resource certificate's id-ad-
rpkiManifest field (Section 4.8.8.1 of [RFC6487]) with the URI of
the manifest found in the previous step. If they are different,
issue a warning.
o Perform manifest entries validation as described in Section 2.2.2.
o Validate all resource certificate objects found on the manifest,
using the CRL object found on the manifest, according to Section 7
of [RFC6487].
o Validate all ROA objects found on the manifest, using the CRL
object found on the manifest, according to the Section 4 of
[RFC6482].
o Validate all Ghostbusters Record objects found on the manifest,
using the CRL object found on the manifest, according to the
Section 7 of [RFC6493].
o For every valid resource certificate object found on the manifest,
apply the procedure described in this section (Section 2.2),
recursively, provided that this resource certificate (identified
by its SKI) has not yet been validated during current repository
validation run.
2.2.1. Finding most recent valid manifest and CRL
Fetch from the store (see Section 4.1.5) all objects of type
manifest, whose certificate's AKI field matches the SKI of the
current CA certificate.
Find the manifest object with the highest manifestNumber field
(Section 4.2.1 of [RFC6486]), for which all following conditions are
met:
o There is only one entry in the manifest for which the store
contains exactly one object of type CRL, whose hash matches the
hash of the entry.
o The manifest's certificate AKI equals the above CRL's AKI
o The above CRL is a valid object according to Section 6.3 of
[RFC5280]
o The manifest is a valid object according to Section 4.4 of
[RFC6486], using the CRL found above
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Report an error for every invalid manifest with the number higher
than the number of the valid manifest.
2.2.2. Manifest entries validation
For every entry in the manifest object:
o Construct an entry's URI by appending the entry name to the
current CA's publication point URI.
o Get all objects from the store whose hash attribute equals entry's
hash (see Section 4.1.3).
o If no such objects found, issue an error.
o For every found object, compare its URI with the URI of the
manifest entry. If they do not match, issue a warning.
o If no objects with matching URI found, issue a warning.
o If some objects with non-matching URI found, issue a warning.
2.3. Object Store Cleanup
At the end of the TA tree validation the store cleanup is performed:
o Given all objects that were validated during the current
validation run, remove from the store (Section 4.1.7) all objects
whose URI attribute matches the URI of one of the validated
objects, but the content's hash is different.
o Remove from the store all objects that were last validated more
than 7 days ago.
o Remove from the store all objects that were downloaded more than 2
hours ago and have never been used in a validation process.
The time intervals used in the steps above are a matter of local
policy.
3. Remote Objects Fetcher
The fetcher is responsible for downloading objects from remote
repositories (described in Section 3 of [RFC6481]) using rsync
protocol ([rsync]), or RPKI Repository Delta Protocol (RRDP)
([I-D.ietf-sidr-delta-protocol]).
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3.1. Fetcher Operations
3.1.1. Fetch repository objects
This operation receives one parameter - a URI. For rsync protocol
this URI points to a directory in a remote repository. For RRDP
repository it points to the repository's notification file.
The fetcher performs following steps:
o If the given URI has been downloaded recently (as specified by the
local policy), skip all following steps.
o Download the remote objects using the URI provided (for an rsync
repository use a recursive mode).
o For every new object that is downloaded, try to parse it as an
object of specific RPKI type (certificate, manifest, CRL, ROA,
Ghostbusters record), based on the object's filename extension
(.cer, .mft, .crl, .roa, and .gbr, respectively), and perform
basic RPKI object validation, as specified in [RFC6487] and
[RFC6488].
o For every downloaded valid object, record it in the object store
(Section 4.1.1), and set its last fetch time to the time it was
downloaded (Section 4.1.2).
3.1.2. Fetch single repository object
This operation receives one parameter - a URI that points to an
object in a remote repository.
The fetcher performs following operations:
o If the given URI has been downloaded recently (as specified by the
local policy), skip all following steps.
o Download the remote object using the URI provided.
o Try to parse the downloaded object as an object of a specific RPKI
type (certificate, manifest, CRL, ROA, Ghostbusters record), based
on the object's filename extension (.cer, .mft, .crl, .roa, and
.gbr, respectively), and perform basic RPKI object validation, as
specified in [RFC6487] and [RFC6488].
o If the downloaded object is not valid, issue an error and skip
further steps.
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o Delete objects from the object store (Section 4.1.6) whose URI
matches the URI given.
o Put validated object in the object store (Section 4.1.1), and set
its last fetch time to the time it was downloaded (Section 4.1.2).
4. Local Object Store
4.1. Store Operations
4.1.1. Store Repository Object
Put given object in the store, along with its type, URI, hash, and
AKI, if there is no record with the same hash and URI fields.
4.1.2. Update object's last fetch time
For all objects in the store whose URI matches the given URI, set the
last fetch time attribute to the given timestamp.
4.1.3. Get objects by hash
Retrieve all objects from the store whose hash attribute matches the
given hash.
4.1.4. Get certificate objects by URI
Retrieve from the store all objects of type certificate, whose URI
attribute matches the given URI.
4.1.5. Get manifest objects by AKI
Retrieve from the store all objects of type manifest, whose AKI
attribute matches the given AKI.
4.1.6. Delete objects for URI
For a given URI, delete all objects in the store with matching URI
attribute.
4.1.7. Delete outdated objects
For a given URI and a list of hashes, delete all objects in the store
with matching URI, whose hash attribute is not in the given list of
hashes.
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4.1.8. Update object's validation time
For all objects in the store whose hash attribute matches the given
hash, set the last validation time attribute to the given timestamp.
5. Acknowledgements
This document describes the algorithm as it is implemented by the
software development team at the RIPE NCC. The original idea behind
it was outlined by Tim Bruijnzeels. The authors would also like to
acknowledge contributions by Carlos Martinez, Andy Newton, and Rob
Austein.
6. IANA Considerations
This document has no actions for IANA.
7. Security Considerations
This algorithm uses the content of a manifest object to discover
other objects issued by a particular CA. It verifies that the
manifest is located in the publication point designated in the CA
Certificate. However, if there are other (not enlisted in the
manifest) objects located in that publication point directory, they
will be ignored, even if their content is correct and they are issued
by the same CA as the manifest.
In contrast, objects whose content hash matches the hash listed in
the manifest, but that are not located in the publication directory
listed in their CA certificate, will be used in the validation
process (although a warning will be issued in that case).
The store cleanup procedure described in Section 2.3 tries to
minimise removal and subsequent re-fetch of objects that are
published in some repository but not used in the validation. Once
such objects are removed from the remote repository, they will be
discarded from the local object store after a period of time
specified by a local policy. By generating an excessive amount of
syntactically valid RPKI objects, a man-in-the-middle attack rendered
between a validating tool and a repository could force an
implementation to fetch and store those objects in the object store
before they are being validated and discarded, leading to an out-of-
memory or out-of-disk-space conditions, and, subsequently, a denial
of service.
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8. References
8.1. Normative References
[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, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>.
[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>.
[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>.
[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>.
[RFC7730] Huston, G., Weiler, S., Michaelson, G., and S. Kent,
"Resource Public Key Infrastructure (RPKI) Trust Anchor
Locator", RFC 7730, DOI 10.17487/RFC7730, January 2016,
<http://www.rfc-editor.org/info/rfc7730>.
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8.2. Informative References
[I-D.ietf-sidr-delta-protocol]
Bruijnzeels, T., Muravskiy, O., Weber, B., Austein, R.,
and D. Mandelberg, "RPKI Repository Delta Protocol",
draft-ietf-sidr-delta-protocol-02 (work in progress),
March 2016.
[rsync] "Rsync home page", <https://rsync.samba.org>.
Authors' Addresses
Oleg Muravskiy
RIPE NCC
Email: oleg@ripe.net
Tim Bruijnzeels
RIPE NCC
Email: tim@ripe.net
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