Network Working Group S. Weiler
Internet-Draft Parsons
Intended status: Standards Track A. Sonalker
Expires: March 25, 2017 TowerSec
R. Austein
Dragon Research Labs
September 21, 2016
A Publication Protocol for the Resource Public Key Infrastructure (RPKI)
draft-ietf-sidr-publication-09
Abstract
This document defines a protocol for publishing Resource Public Key
Infrastructure (RPKI) objects. Even though the RPKI will have many
participants issuing certificates and creating other objects, it is
operationally useful to consolidate the publication of those objects.
This document provides the protocol for doing so.
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 25, 2017.
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
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
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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
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol Specification . . . . . . . . . . . . . . . . . . . 3
2.1. Common XML Message Format . . . . . . . . . . . . . . . . 4
2.2. Publication and Withdrawal . . . . . . . . . . . . . . . 4
2.3. Listing the repository . . . . . . . . . . . . . . . . . 5
2.4. Error handling . . . . . . . . . . . . . . . . . . . . . 6
2.5. Error Codes . . . . . . . . . . . . . . . . . . . . . . . 7
2.6. XML Schema . . . . . . . . . . . . . . . . . . . . . . . 7
3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. <publish/> Query, No Existing Object . . . . . . . . . . 9
3.2. <publish/> Query, Overwriting Existing Object . . . . . . 10
3.3. <withdraw/> Query . . . . . . . . . . . . . . . . . . . . 10
3.4. <success/> Reply . . . . . . . . . . . . . . . . . . . . 10
3.5. <report_error/> With Optional Elements . . . . . . . . . 10
3.6. <report_error/> Without Optional Elements . . . . . . . . 11
3.7. Error Handling With Multi-Element Queries . . . . . . . . 11
3.7.1. Multi-Element Query . . . . . . . . . . . . . . . . . 11
3.7.2. Successful Multi-Element Response . . . . . . . . . . 12
3.7.3. Failure Multi-Element Response, First Error Only . . 12
3.7.4. Failure Multi-Element Response, All Errors . . . . . 13
3.8. <list/> Query . . . . . . . . . . . . . . . . . . . . . . 14
3.9. <list/> Reply . . . . . . . . . . . . . . . . . . . . . . 14
4. Operational Considerations . . . . . . . . . . . . . . . . . 14
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1. Normative References . . . . . . . . . . . . . . . . . . 17
7.2. Informative References . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
This document assumes a working knowledge of the Resource Public Key
Infrastructure (RPKI), which is intended to support improved routing
security on the Internet. [RFC6480]
In order to make participation in the RPKI easier, it is helpful to
have a few consolidated repositories for RPKI objects, thus saving
every participant from the cost of maintaining a new service.
Similarly, relying parties using the RPKI objects will find it faster
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and more reliable to retrieve the necessary set from a smaller number
of repositories.
These consolidated RPKI object repositories will in many cases be
outside the administrative scope of the organization issuing a given
RPKI object. In some cases, outsourcing operation of the repository
will be an explicit goal: some resource holders who strongly wish to
control their own RPKI private keys may lack the resources to operate
a 24x7 repository, or may simply not wish to do so.
The operator of an RPKI publication repository may well be an
Internet registry which issues certificates to its customers, but it
need not be; conceptually, operation of a an RPKI publication
repository is separate from operation of RPKI CA.
This document defines an RPKI publication protocol which allows
publication either within or across organizational boundaries, and
which makes fairly minimal demands on either the CA engine or the
publication service.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
"Publication engine" and "publication server" are used
interchangeably to refer to the server providing the service
described in this document.
"Business Public Key Infrastructure" ("Business PKI" or "BPKI")
refers to a PKI, separate from the RPKI, used to authenticate clients
to the publication engine. We use the term "Business PKI" here
because an Internet registry might already have a PKI for
authenticating its clients and might wish to reuse that PKI for this
protocol. There is, however, no requirement to reuse such a PKI.
2. Protocol Specification
The publication protocol uses XML messages wrapped in signed CMS
messages, carried over HTTP transport.
The publication protocol uses a simple request/response interaction.
The client passes a request to the server, and the server generates a
corresponding response.
A message exchange commences with the client initiating an HTTP POST
with content type of "application/rpki-publication", with the message
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object as the body. The server's response will similarly be the body
of the response with a content type of "application/rpki-
publication".
The content of the POST and the server's response will be a well-
formed Cryptographic Message Syntax (CMS) [RFC5652] object with OID =
1.2.840.113549.1.7.2 as described in Section 3.1 of [RFC6492].
2.1. Common XML Message Format
The XML schema for this protocol is below in Section 2.6. The basic
XML message format looks like this:
<msg
type="query"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<!-- Zero or more PDUs -->
</msg>
<msg
type="reply"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<!-- Zero or more PDUs -->
</msg>
Common attributes:
version: The value of this attribute is the version of this
protocol. This document describes version 4.
type: The possible values of this attribute are "reply" and "query".
A query PDU may be one of three types: <publish/>, <withdraw/>, or
<list/>.
A reply PDU may be one of three types: <success/>, <list/>, or
<report_error/>.
The <publish/> and <withdraw/> PDUs include a tag to facilitate bulk
operation.
2.2. Publication and Withdrawal
The publication protocol uses a common message format to request
publication of any RPKI object. This format was chosen specifically
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to allow this protocol to accommodate new types of RPKI objects
without needing changes to this protocol.
Both the <publish/> and <withdraw/> PDUs have a payload of a tag and
a URI. The <publish/> query also contains the DER object to be
published, encoded in Base64.
Both the <publish/> and <withdraw/> PDUs also have a "hash"
attribute, which carries a hash of an existing object at the
specified repository URI. For <withdraw/> PDUs, the hash is
mandatory, as this operation makes no sense if there is no existing
object to withdraw. For <publish/> PDUs, the hash MUST be present if
the publication operation is overwriting an existing object, and MUST
be omitted if this publication operation is writing to a new URI
where no prior object exists. Presence of an object when no "hash"
attribute is specified is an error, as is absence of the "hash"
attribute or an incorrect hash value when an object is present. Any
such errors MUST be reported using the <report_error/> PDU.
The hash algorithm is SHA-256 [SHS], to simplify comparison of
publication protocol hashes with RPKI manifest hashes.
The intent behind the "hash" attribute is to allow the client and
server to detect any disagreements about the effect that a <publish/>
or <withdraw/> PDU will have on the repository.
Note that every publish and withdraw action requires a new manifest,
thus every publish or withdraw action will involve at least two
objects.
Processing of a query message is handled atomically: either the
entire query succeeds or none of it does. When a query message
contains multiple PDUs, failure of any PDU may require the server to
roll back actions triggered by earlier PDUs.
When a query messages containing <publish/> and/or <withdraw/> PDUs
succeeds, a single <success/> reply is returned.
When a query fails, one or more <report_error/> reply PDUs are
generated. Typically, only one <report_error/> reply is generated,
corresponding to the first query PDU that failed. Servers are
permitted to return multiple <report_error/> PDUs.
2.3. Listing the repository
The <list/> operation allows the client to ask the server for a
complete listing of objects which the server believes the client has
published. This is intended primarily to allow the client to recover
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upon detecting (probably via use of the "hash" attribute, see
Section 2.2) that they have somehow lost synchronization.
The <list/> query consists of a single PDU. A <list/> query must be
the only PDU in a query - it may not be combined with any <publish/>
or <withdraw/> queries.
The <list/> reply consists of zero or more PDUs, one per object
published in this repository by this client, each PDU conveying the
URI and hash of one published object.
2.4. Error handling
Errors are handled at two levels.
Errors that make it impossible to decode a query or encode a response
are handled at the HTTP layer. 4xx and 5xx HTTP response codes
indicate that something bad happened.
In all other cases, errors result in an XML <report_error/> PDU.
Like the rest of this protocol, <report_error/> PDUs are CMS-signed
XML messages and thus can be archived to provide an audit trail.
<report_error/> PDUs only appear in replies, never in queries.
The "tag" attribute of the <report_error/> PDU associated with a
<publish/> or <withdraw/> PDU MUST be set to the same value as the
"tag" attribute in the PDU which generated the error. A client can
use the "tag" attribute to determine which PDU caused processing of
an update to fail.
The error itself is conveyed in the "error_code" attribute. The
value of this attribute is a token indicating the specific error that
occurred.
The body of the <report_error/> element contains two sub-elements:
1. An optional text element <error_text/>, which if present,
contains a text string with debugging information intended for
human consumption.
2. An optional element <failed_pdu/>, which, if present, contains a
verbatim copy of the query PDU whose failure triggered the
<report_error/> PDU. The quoted element must be syntactically
valid.
See Section 3.7 for examples of a multi-element query and responses.
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2.5. Error Codes
These are the defined error codes as well as some discussion of each.
Text similar to these descriptions may be sent in an <error_text/>
element to help explain the error encountered.
xml_error: Encountered an XML problem. Note that some XML errors
may be severe enough to require error reporting at the HTTP layer,
instead. Implementations MAY choose to report any or all XML
errors at the HTTP layer.
permission_failure: Client does not have permission to update this
URI.
bad_cms_signature: Bad CMS signature.
object_already_present: An object is already present at this URI,
yet a "hash" attribute was not specified. A "hash" attribute must
be specified when overwriting or deleting an object. Perhaps
client and server are out of sync?
no_object_present: There is no object present at this URI, yet a
"hash" attribute was specified. Perhaps client and server are out
of sync?
no_object_matching_hash The "hash" attribute supplied does not match
the "hash" attribute of the object at this URI. Perhaps client
and server are out of sync?
consistency_problem: Server detected an update that looks like it
will cause a consistency problem (e.g. an object was deleted, but
the manifest was not updated). Note that a server is not required
to make such checks. Indeed, it may be unwise for a server to do
so. This error code just provides a way for the server to explain
its (in-)action.
other_error: A meteor fell on the server.
2.6. XML Schema
The following is a RelaxNG compact form schema describing the
Publication Protocol.
# $Id: rpki-publication.rnc 3785 2016-09-21 22:21:58Z sra $
# RelaxNG schema for RPKI publication protocol.
default namespace =
"http://www.hactrn.net/uris/rpki/publication-spec/"
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# This is version 4 of the protocol.
version = "4"
# Top level PDU is either a query or a reply.
start |= element msg {
attribute version { version },
attribute type { "query" },
query_elt
}
start |= element msg {
attribute version { version },
attribute type { "reply" },
reply_elt
}
# Tag attributes for bulk operations.
tag = attribute tag { xsd:token { maxLength="1024" } }
# Base64 encoded DER stuff.
base64 = xsd:base64Binary
# Publication URIs.
uri = attribute uri { xsd:anyURI { maxLength="4096" } }
# Digest of an existing object (hexadecimal).
hash = attribute hash { xsd:string { pattern = "[0-9a-fA-F]+" } }
# Error codes.
error |= "xml_error"
error |= "permission_failure"
error |= "bad_cms_signature"
error |= "object_already_present"
error |= "no_object_present"
error |= "no_object_matching_hash"
error |= "consistency_problem"
error |= "other_error"
# <publish/> and <withdraw/> query elements
query_elt |= (
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element publish { tag, uri, hash?, base64 } |
element withdraw { tag, uri, hash }
)*
# <success/> reply
reply_elt |= element success { empty }
# <list/> query and reply
query_elt |= element list { empty }
reply_elt |= element list { uri, hash }*
# <report_error/> reply
reply_elt |= element report_error {
tag?,
attribute error_code { error },
element error_text { xsd:string { maxLength="512000" }}?,
element failed_pdu { query_elt }?
}*
3. Examples
Following are examples of various queries and the corresponding
replies for the RPKI publication protocol.
Note the authors have taken liberties with the Base64, hash, and URI
text in these examples in the interest of making the examples fit
nicely into RFC text format.
3.1. <publish/> Query, No Existing Object
<msg
type="query"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<publish
tag="foo"
uri="rsync://wombat.example/Alice/01a97a70ac477f06.cer">
SGVsbG8sIG15IG5hbWUgaXMgQWxpY2U=
</publish>
</msg>
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3.2. <publish/> Query, Overwriting Existing Object
<msg
type="query"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<publish
hash="01a97a70ac477f06"
tag="foo"
uri="rsync://wombat.example/Alice/01a97a70ac477f06.cer">
SGVsbG8sIG15IG5hbWUgaXMgQWxpY2U=
</publish>
</msg>
3.3. <withdraw/> Query
<msg
type="query"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<withdraw
hash="01a97a70ac477f06"
tag="foo"
uri="rsync://wombat.example/Alice/01a97a70ac477f06.cer"/>
</msg>
3.4. <success/> Reply
<msg
type="reply"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<success/>
</msg>
3.5. <report_error/> With Optional Elements
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<msg
type="reply"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<report_error
error_code="no_object_matching_hash"
tag="foo">
<error_text>
Can't delete an object I don't have
</error_text>
<failed_pdu>
<publish
hash="01a97a70ac477f06"
tag="foo"
uri="rsync://wombat.example/Alice/01a97a70ac477f06.cer">
SGVsbG8sIG15IG5hbWUgaXMgQWxpY2U=
</publish>
</failed_pdu>
</report_error>
</msg>
3.6. <report_error/> Without Optional Elements
<msg
type="reply"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<report_error
error_code="object_already_present"
tag="foo"/>
</msg>
3.7. Error Handling With Multi-Element Queries
3.7.1. Multi-Element Query
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<msg
type="query"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<publish
tag="Alice"
uri="rsync://wombat.example/Alice/01a97a70ac477f06.cer">
SGVsbG8sIG15IG5hbWUgaXMgQWxpY2U=
</publish>
<withdraw
hash="f46a4198efa3070e"
tag="Bob"
uri="rsync://wombat.example/Bob/f46a4198efa3070e.cer"/>
<publish
tag="Carol"
uri="rsync://wombat.example/Carol/32e0544eeb510ec0.cer">
SGVsbG8sIG15IG5hbWUgaXMgQ2Fyb2w=
</publish>
<withdraw
hash="421ee4ac65732d72"
tag="Dave"
uri="rsync://wombat.example/Dave/421ee4ac65732d72.cer"/>
<publish
tag="Eve"
uri="rsync://wombat.example/Eve/9dd859b01e5c2ebd.cer">
SGVsbG8sIG15IG5hbWUgaXMgRXZl
</publish>
</msg>
3.7.2. Successful Multi-Element Response
<msg
type="reply"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<success/>
</msg>
3.7.3. Failure Multi-Element Response, First Error Only
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<msg
type="reply"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<report_error
error_code="no_object_matching_hash"
tag="Dave">
<failed_pdu>
<withdraw
hash="421ee4ac65732d72"
tag="Dave"
uri="rsync://wombat.example/Dave/421ee4ac65732d72.cer"/>
</failed_pdu>
</report_error>
</msg>
3.7.4. Failure Multi-Element Response, All Errors
<msg
type="reply"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<report_error
error_code="no_object_matching_hash"
tag="Dave">
<failed_pdu>
<withdraw
hash="421ee4ac65732d72"
tag="Dave"
uri="rsync://wombat.example/Dave/421ee4ac65732d72.cer"/>
</failed_pdu>
</report_error>
<report_error
error_code="object_already_present"
tag="Eve">
<failed_pdu>
<publish
tag="Eve"
uri="rsync://wombat.example/Eve/9dd859b01e5c2ebd.cer">
SGVsbG8sIG15IG5hbWUgaXMgRXZl
</publish>
</failed_pdu>
</report_error>
</msg>
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3.8. <list/> Query
<msg
type="query"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<list/>
</msg>
3.9. <list/> Reply
<msg
type="reply"
version="4"
xmlns="http://www.hactrn.net/uris/rpki/publication-spec/">
<list
hash="eb719b72f0648cf4"
uri="rsync://wombat.example/Fee/eb719b72f0648cf4.cer"/>
<list
hash="c7c50a68b7aa50bf"
uri="rsync://wombat.example/Fie/c7c50a68b7aa50bf.cer"/>
<list
hash="f222481ded47445d"
uri="rsync://wombat.example/Foe/f222481ded47445d.cer"/>
<list
hash="15b94e08713275bc"
uri="rsync://wombat.example/Fum/15b94e08713275bc.cer"/>
</msg>
4. Operational Considerations
There are two basic options open to the repository operator as to how
the publication tree is laid out. The first option is simple: each
publication client is given its own directory one level below the top
of the rsync module, and there is no overlap between the publication
spaces used by different clients. For example:
rsync://example.org/rpki/Alice/
rsync://example.org/rpki/Bob/
rsync://example.org/rpki/Carol/
This has the advantage of being very easy for the publication
operator to manage, but has the drawback of making it difficult for
relying parties to fetch published objects both safely and as
efficiently as possible.
Given that the mandatory-to-implement retrieval protocol for relying
parties is rsync, a more efficient repository structure would be one
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which minimized the number of rsync fetches required. One such
structure would be one in which the publication directories for
subjects were placed underneath the publication directories of their
issuers: since the normal synchronization tree walk is top-down, this
can significantly reduce the total number of rsync connections
required to synchronize. For example:
rsync://example.org/rpki/Alice/
rsync://example.org/rpki/Alice/Bob/
rsync://example.org/rpki/Alice/Bob/Carol/
Preliminary measurement suggests that, in the case of large numbers
of small publication directories, the time needed to set up and tear
down individual rsync connections becomes significant, and that a
properly optimized tree structure can reduce synchronization time by
an order of magnitude.
The more complex tree structure does require careful attention to the
"base_uri" attribute values when setting up clients. In the example
above, assuming that Alice issues to Bob who in turn issues to Carol,
Alice has ceded control of a portion of her publication space to Bob,
who has in turn ceded a portion of that to Carol, and the "base_uri"
attributes in the <client/> setup messages should reflect this.
The details of how the repository operator determines that Alice has
given Bob permission to nest Bob's publication directory under
Alice's is outside the scope of this protocol.
5. IANA Considerations
IANA is asked to register the application/rpki-publication MIME media
type as follows:
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MIME media type name: application
MIME subtype name: rpki-publication
Required parameters: None
Optional parameters: None
Encoding considerations: binary
Security considerations: Carries an RPKI Publication Protocol
Message, as defined in this document.
Interoperability considerations: None
Published specification: This document
Applications which use this media type: HTTP
Additional information:
Magic number(s): None
File extension(s):
Macintosh File Type Code(s):
Person & email address to contact for further information:
Rob Austein <sra@hactrn.net>
Intended usage: COMMON
Author/Change controller: Rob Austein <sra@hactrn.net>
6. Security Considerations
The RPKI publication protocol and the data it publishes use entirely
separate PKIs for authentication. The published data is
authenticated within the RPKI, and this protocol has nothing to do
with that authentication, nor does it require that the published
objects be valid in the RPKI. The publication protocol uses a
separate Business PKI (BPKI) to authenticate its messages.
Each RPKI publication protocol message is CMS-signed. Because of
that protection at the application layer, this protocol does not
require the use of HTTPS or other transport security mechanisms.
Although the hashes used in the <publish/> and <withdraw/> PDUs are
cryptographic strength, the digest algorithm was selected for
convenience in comparing these hashes with the hashes that appear in
RPKI manifests. The hashes used in the <publish/> and <withdraw/>
PDUs are not particularly security-sensitive, because these PDUs are
protected by the CMS signatures.
Compromise of a publication server, perhaps through mismanagement of
BPKI keys, could lead to a denial-of-service attack on the RPKI. An
attacker gaining access to BPKI keys could use this protocol delete
(withdraw) RPKI objects, leading to routing changes or failures.
Accordingly, as in most PKIs, good key management practices are
important.
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)",
RFC 5652, STD 70, September 2009.
[RFC6492] Huston, G., Loomans, R., Ellacott, B., and R. Austein, "A
Protocol for Provisioning Resource Certificates",
RFC 6492, February 2012.
[SHS] National Institute of Standards and Technology, "Secure
Hash Standard", FIPS PUB 180-4, March 2012,
<http://csrc.nist.gov/publications/fips/fips180-4/
fips-180-4.pdf>.
7.2. Informative References
[RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, February 2012.
Authors' Addresses
Samuel Weiler
Parsons
Email: weiler@tislabs.com
Anuja Sonalker
TowerSec Automotive Cyber Security
Email: asonalker@tower-sec.com
Rob Austein
Dragon Research Labs
Email: sra@hactrn.net
Weiler, et al. Expires March 25, 2017 [Page 17]
