Network Working Group                                          S. Weiler
Internet-Draft                                                   Parsons
Intended status: Standards Track                             A. Sonalker
Expires: September 22, 2016 March 25, 2017                                         TowerSec
                                                              R. Austein
                                                    Dragon Research Labs
                                                      September 21, 2016

A Publication Protocol for the Resource Public Key Infrastructure (RPKI)


   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.

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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
   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",
   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
   object as the body.  The server's response will similarly be the body
   of the response with a content type of "application/rpki-

   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:

     <!-- Zero or more PDUs -->

     <!-- Zero or more PDUs -->

   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

   A reply PDU may be one of three types: <success/>, <list/>, or

   The <publish/> and <withdraw/> PDUs include a tag to facilitate bulk

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
   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

   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
   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

   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

   See Section 3.7 for examples of a multi-element query and responses.

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

   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 3595 2016-03-21 21:31:37Z 3785 2016-09-21 22:21:58Z sra $
   # RelaxNG schema for RPKI publication protocol.

   default namespace =

   # 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" },

   start |= element msg {
     attribute version { version },
     attribute type    { "reply" },

   # 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 |= (
     element publish  { tag, uri, hash?, base64 }
   # <withdraw/> query

   query_elt |= |
     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 {
     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


3.2.  <publish/> Query, Overwriting Existing Object


3.3.  <withdraw/> Query


3.4.  <success/> Reply


3.5.  <report_error/> With Optional Elements
         Can't delete an object I don't have

3.6.  <report_error/> Without Optional Elements


3.7.  Error Handling With Multi-Element Queries

3.7.1.  Multi-Element Query

3.7.2.  Successful Multi-Element Response


3.7.3.  Failure Multi-Element Response, First Error Only

3.7.4.  Failure Multi-Element Response, All Errors


3.8.  <list/> Query


3.9.  <list/> Reply


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:


   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
   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:


   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:

      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 <>
      Intended usage:  COMMON
      Author/Change controller: Rob Austein <>

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

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,

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


   Anuja Sonalker
   TowerSec Automotive Cyber Security


   Rob Austein
   Dragon Research Labs