Internet DRAFT - draft-tbruijnzeels-sidrops-https-tal
draft-tbruijnzeels-sidrops-https-tal
Network Working Group T. Bruijnzeels
Internet-Draft RIPE NCC
Updates: 7730 (if approved) G. Michaelson
Intended status: Standards Track APNIC
Expires: May 20, 2018 November 16, 2017
Resource Public Key Infrastructure (RPKI) Trust Anchor Locator
draft-tbruijnzeels-sidrops-https-tal-00
Abstract
This document defines a Trust Anchor Locator (TAL) for the Resource
Public Key Infrastructure (RPKI). This document obsoletes RFC 7730
by adding support for HTTPS URIs in a TAL.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 20, 2018.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2. Trust Anchor Locator . . . . . . . . . . . . . . . . . . . . 2
2.1. Trust Anchor Locator Format . . . . . . . . . . . . . . . 2
2.2. TAL and Trust Anchor Certificate Considerations . . . . . 3
2.3. Example . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Relying Party Use . . . . . . . . . . . . . . . . . . . . . . 5
4. HTTPS Considerations . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
This document defines a Trust Anchor Locator (TAL) for the Resource
Public Key Infrastructure (RPKI) [RFC6480]. This format may be used
to distribute trust anchor material using a mix of out-of-band and
online means. Procedures used by Relying Parties (RPs) to verify
RPKI signed objects SHOULD support this format to facilitate
interoperability between creators of trust anchor material and RPs.
This document obsoletes [RFC7730] by adding support for HTTPS URIs in
a TAL.
1.1. Terminology
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [RFC2119].
2. Trust Anchor Locator
2.1. Trust Anchor Locator Format
This document does not propose a new format for trust anchor
material. A trust anchor in the RPKI is represented by a self-signed
X.509 Certification Authority (CA) certificate, a format commonly
used in PKIs and widely supported by RP software. This document
specifies a format for data used to retrieve and verify the
authenticity of a trust anchor in a very simple fashion. That data
is referred to as the TAL.
The motivation for defining the TAL is to enable selected data in the
trust anchor to change, without needing to effect redistribution of
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the trust anchor per se. In the RPKI, certificates contain
extensions that represent Internet Number Resources (INRs) [RFC3779].
The set of INRs associated with an entity acting as a trust anchor is
likely to change over time. Thus, if one were to use the common PKI
convention of distributing a trust anchor to RPs in a secure fashion,
then this procedure would need to be repeated whenever the INR set
for the entity acting as a trust anchor changed. By distributing the
TAL (in a secure fashion), instead of distributing the trust anchor,
this problem is avoided, i.e., the TAL is constant so long as the
trust anchor's public key and its location do not change.
The TAL is analogous to the TrustAnchorInfo data structure specified
in [RFC5914], which is on the Standards Track. That specification
could be used to represent the TAL, if one defined an rsync or HTTPS
URI extension for that data structure. However, the TAL format was
adopted by RPKI implementors prior to the PKIX trust anchor work, and
the RPKI implementer community has elected to utilize the TAL format,
rather than define the requisite extension. The community also
prefers the simplicity of the ASCII encoding of the TAL, versus the
binary (ASN.1) encoding for TrustAnchorInfo.
The TAL is an ordered sequence of:
1. a URI section,
2. a "<CRLF>" or "<LF>" line break,
3. a subjectPublicKeyInfo [RFC5280] in DER format [X.509], encoded
in Base64 (see Section 4 of [RFC4648]). To avoid long lines,
"<CRLF>" or "<LF>" line breaks MAY be inserted into the
Base64-encoded string.
where the URI section is comprised of one of more of the ordered
sequence of:
1.1. an rsync URI [RFC5781], or an HTTPS URI [RFC7230]
1.2. a "<CRLF>" or "<LF>" line break.
2.2. TAL and Trust Anchor Certificate Considerations
Each URI in the TAL MUST reference a single object. It MUST NOT
reference a directory or any other form of collection of objects.
The referenced object MUST be a self-signed CA certificate that
conforms to the RPKI certificate profile [RFC6487]. This certificate
is the trust anchor in certification path discovery [RFC4158] and
validation [RFC5280] [RFC3779].
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The validity interval of this trust anchor SHOULD reflect the
anticipated period of stability of the particular set of INRs that
are associated with the putative trust anchor.
The INR extension(s) of this trust anchor MUST contain a non-empty
set of number resources. It MUST NOT use the "inherit" form of the
INR extension(s). The INR set described in this certificate is the
set of number resources for which the issuing entity is offering
itself as a putative trust anchor in the RPKI [RFC6480].
The public key used to verify the trust anchor MUST be the same as
the subjectPublicKeyInfo in the CA certificate and in the TAL.
The trust anchor MUST contain a stable key. This key MUST NOT change
when the certificate is reissued due to changes in the INR
extension(s), when the certificate is renewed prior to expiration, or
for any reason other than a key change.
Because the public key in the TAL and the trust anchor MUST be
stable, this motivates operation of that CA in an offline mode.
Thus, the entity that issues the trust anchor SHOULD issue a
subordinate CA certificate that contains the same INRs (via the use
of the "inherit" option in the INR extensions of the subordinate
certificate). This allows the entity that issues the trust anchor to
keep the corresponding private key of this certificate offline, while
issuing all relevant child certificates under the immediate
subordinate CA. This measure also allows the Certificate Revocation
List (CRL) issued by that entity to be used to revoke the subordinate
CA certificate in the event of suspected key compromise of this
online operational key pair that is potentially more vulnerable.
The trust anchor MUST be published at a stable URI. When the trust
anchor is reissued for any reason, the replacement CA certificate
MUST be accessible using the same URI.
Because the trust anchor is a self-signed certificate, there is no
corresponding CRL that can be used to revoke it, nor is there a
manifest [RFC6486] that lists this certificate.
If an entity wishes to withdraw a self-signed CA certificate as a
putative trust anchor, for any reason, including key rollover, the
entity MUST remove the object from the location referenced in the
TAL.
Where the TAL contains two or more URIs, then the same self- signed
CA certificate MUST be found at each referenced location. In order
to increase operational resilience, it is RECOMMENDED that the domain
name parts of each of these URIs resolve to distinct IP addresses
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that are used by a diverse set of repository publication points, and
these IP addresses be included in distinct Route Origin
Authorizations (ROAs) objects signed by different CAs.
2.3. Example
rsync://rpki.example.org/rpki/hedgehog/root.cer
<https://rpki.example.org/rpki/hedgehog/root.cer>
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAovWQL2lh6knDx
GUG5hbtCXvvh4AOzjhDkSHlj22gn/1oiM9IeDATIwP44vhQ6L/xvuk7W6
Kfa5ygmqQ+xOZOwTWPcrUbqaQyPNxokuivzyvqVZVDecOEqs78q58mSp9
nbtxmLRW7B67SJCBSzfa5XpVyXYEgYAjkk3fpmefU+AcxtxvvHB5OVPIa
BfPcs80ICMgHQX+fphvute9XLxjfJKJWkhZqZ0v7pZm2uhkcPx1PMGcrG
ee0WSDC3fr3erLueagpiLsFjwwpX6F+Ms8vqz45H+DKmYKvPSstZjCCq9
aJ0qANT9OtnfSDOS+aLRPjZryCNyvvBHxZXqj5YCGKtwIDAQAB
3. Relying Party Use
In order to use the TAL to retrieve and validate a (putative) trust
anchor, an RP SHOULD:
1. Retrieve the object referenced by (one of) the URI(s) contained
in the TAL.
2. Confirm that the retrieved object is a current, self-signed RPKI
CA certificate that conforms to the profile as specified in
[RFC6487].
3. Confirm that the public key in the TAL matches the public key in
the retrieved object.
4. Perform other checks, as deemed appropriate (locally), to ensure
that the RP is willing to accept the entity publishing this self-
signed CA certificate to be a trust anchor. These tests apply to
the validity of attestations made in the context of the RPKI
relating to all resources described in the INR extension of this
certificate.
An RP SHOULD perform these functions for each instance of TAL that it
is holding for this purpose every time the RP performs a
resynchronization across the local repository cache. In any case, an
RP also SHOULD perform these functions prior to the expiration of the
locally cached copy of the retrieved trust anchor referenced by the
TAL.
In the case where a TAL contains multiple URIs, an RP MAY use a
locally defined preference rule to select the URI to retrieve the
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self-signed RPKI CA certificate that is to be used as a trust anchor.
Some examples are:
o Using the order provided in the TAL
o Selecting the URI randomly from the available list
o Creating a prioritized list of URIs based on RP-specific
parameters, such as connection establishment delay
If the connection to the preferred URI fails, or the retrieved CA
certificate public key does not match the TAL public key, the RP
SHOULD retrieve the CA certificate from the next URI, according to
the local preference ranking of URIs.
4. HTTPS Considerations
REMOVE LATER: The following text is inspired by the equivalent
section in [RFC8182], but adapted for this case.
Note that a Man in the Middle (MITM) cannot produce a CA certificate
that would be considered valid according to the process described in
Section 3. However, a MITM can perform withhold or replay attacks
targeting a Relying Party and keep the Relying Party from learning
about an update CA certificate. Because of this, Relying Parties
SHOULD do TLS certificate and host name validation when they fetch a
CA certificate using an HTTPS URI on a TAL.
Relying Party tools SHOULD log any TLS certificate or host name
validation issues found, so that an operator can investigate the
cause. However, such validation issues are often due to
configuration errors or a lack of a common TLS trust anchor. In
these cases, it is better if the Relying Party retrieves the CA
certificate regardless and performs validation on it. Therefore, the
Relying Party MUST continue to retrieve the data in case of errors.
It is RECOMMENDED that Relying Parties and Repository Servers follow
the Best Current Practices outlined in [RFC7525] on the use of HTTP
over TLS (HTTPS) [RFC7230]. Relying Parties SHOULD do TLS
certificate and host name validation using subjectAltName dNSName
identities as described in [RFC6125]. The rules and guidelines
defined in [RFC6125] apply here, with the following considerations:
o Relying Parties and Repository Servers SHOULD support the DNS-ID
identifier type. The DNS-ID identifier type SHOULD be present in
Repository Server certificates.
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o DNS names in Repository Server certificates SHOULD NOT contain the
wildcard character "*".
o A Common Name (CN) field may be present in a Repository Server
certificate's subject name but SHOULD NOT be used for
authentication within the rules described in [RFC6125].
o This protocol does not require the use of SRV-IDs.
o This protocol does not require the use of URI-IDs.
Note, however, that this validation is done on a best-effort basis
and serves to highlight potential issues, but CA certificate
validation in relation to a TAL as described in Section 3 does not
depend on this. Therefore, Relying Parties MAY deviate from the
validation steps listed above.
5. Security Considerations
Compromise of a trust anchor private key permits unauthorized parties
to masquerade as a trust anchor, with potentially severe
consequences. Reliance on an inappropriate or incorrect trust anchor
has similar potentially severe consequences.
This TAL does not directly provide a list of resources covered by the
referenced self-signed CA certificate. Instead, the RP is referred
to the trust anchor itself and the INR extension(s) within this
certificate. This provides necessary operational flexibility, but it
also allows the certificate issuer to claim to be authoritative for
any resource. Relying parties should either have great confidence in
the issuers of such certificates that they are configuring as trust
anchors, or they should issue their own self-signed certificate as a
trust anchor and, in doing so, impose constraints on the subordinate
certificates.
6. Acknowledgements
This approach to trust anchor material was originally described by
Robert Kisteleki.
The authors acknowledge the contributions of Rob Austein and Randy
Bush, who assisted with drafting this document and with helpful
review comments.
The authors acknowledge with work of Roque Gagliano, Terry Manderson,
and Carlos Martinez Cagnazzo in developing the ideas behind the
inclusion of multiple URIs in the TAL.
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779,
DOI 10.17487/RFC3779, June 2004,
<https://www.rfc-editor.org/info/rfc3779>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[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,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC5781] Weiler, S., Ward, D., and R. Housley, "The rsync URI
Scheme", RFC 5781, DOI 10.17487/RFC5781, February 2010,
<https://www.rfc-editor.org/info/rfc5781>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[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>.
[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>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
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[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[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,
<https://www.rfc-editor.org/info/rfc7730>.
[X.509] TU-T Recommendation X.509, "The Directory: Public-key and
attribute certificate frameworks", October 2012.
7.2. Informative References
[RFC4158] Cooper, M., Dzambasow, Y., Hesse, P., Joseph, S., and R.
Nicholas, "Internet X.509 Public Key Infrastructure:
Certification Path Building", RFC 4158,
DOI 10.17487/RFC4158, September 2005,
<https://www.rfc-editor.org/info/rfc4158>.
[RFC5914] Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor
Format", RFC 5914, DOI 10.17487/RFC5914, June 2010,
<https://www.rfc-editor.org/info/rfc5914>.
[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>.
[RFC8182] Bruijnzeels, T., Muravskiy, O., Weber, B., and R. Austein,
"The RPKI Repository Delta Protocol (RRDP)", RFC 8182,
DOI 10.17487/RFC8182, July 2017,
<https://www.rfc-editor.org/info/rfc8182>.
Authors' Addresses
Tim Bruijnzeels
RIPE NCC
Email: tim@ripe.net
George Michaelson
APNIC
Email: ggm@apnic.net
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