= The Publication Protocol = [[TracNav(doc/RPKI/TOC)]] [[PageOutline]] The publication protocol is really two separate client/server protocols, between different parties. The first is a configuration protocol for an IRBE to use to configure a publication engine, the second is the interface by which authorized clients request publication of specific objects. Much of the architecture of the publication protocol is borrowed from the [[LeftRight|left-right protocol]]: like the left-right protocol, the publication protocol uses CMS-wrapped XML over HTTP with the same eContentType OID and the same HTTP content-type, and the overall style of the XML messages is very similar to the left-right protocol. All operations allow an optional "tag" attribute to allow batching. The publication engine operates a single HTTP server which serves both of these subprotocols. The two subprotocols share a single server port, but use distinct URLs to allow demultiplexing. == Publication control subprotocol == The control subprotocol reuses the message-passing design of the left-right protocol. Configured objects support the "create", "set", "get", "list", and "destroy" actions, or a subset thereof when the full set of actions doesn't make sense. === object === The object allows configuration of data that apply to the entire publication server rather than a particular client. There is exactly one object in the publication server, and it only supports the "set" and "get" actions -- it cannot be created or destroyed. Payload data which can be configured in a object: bpki_crl:: (element) This is the BPKI CRL used by the publication server when signing the CMS wrapper on responses in the publication subprotocol. As the CRL must be updated at regular intervals, it's not practical to restart the publication server when the BPKI CRL needs to be updated. The BPKI model doesn't require use of a BPKI CRL between the IRBE and the publication server, so we can use the publication control subprotocol to update the BPKI CRL. === object === The object represents one client authorized to use the publication server. The object supports the full set of "create", "set", "get", "list", and "destroy" actions. Each client has a "client_handle" attribute, which is used in responses and must be specified in "create", "set", "get", or "destroy" actions. Payload data which can be configured in a object: base_uri:: (attribute) This is the base URI below which this client is allowed to publish data. The publication server may impose additional constraints in the case of a child publishing beneath its parent. bpki_cert:: (element) BPKI CA certificate for this . This is used as part of the certificate chain when validating incoming TLS and CMS messages. If the bpki_glue certificate is in use (below), the bpki_cert certificate should be issued by the bpki_glue certificate; otherwise, the bpki_cert certificate should be issued by the publication engine's bpki_ta certificate. bpki_glue:: (element) Another BPKI CA certificate for this , usually not needed. Certain pathological cross-certification cases require a two-certificate chain due to issuer name conflicts. If used, the bpki_glue certificate should be the issuer of the bpki_cert certificate and should be issued by the publication engine's bpki_ta certificate; if not needed, the bpki_glue certificate should be left unset. == Publication subprotocol == The publication subprotocol is structured somewhat differently from the publication control protocol. Objects in the publication subprotocol represent objects to be published or objects to be withdrawn from publication. Each kind of object supports two actions: "publish" and "withdraw". In each case the XML element representing hte object to be published or withdrawn has a "uri" attribute which contains the publication URI. For "publish" actions, the XML element body contains the DER object to be published, encoded in Base64; for "withdraw" actions, the XML element body is empty. In theory, the detailed access control for each kind of object might be different. In practice, as of this writing, access control for all objects is a simple check that the client's {{{base_uri}}} is a leading substring of the publication URI. Details of why access control might need to become more complicated are discussed in a later section. === object === The object represents an RPKI certificate to be published or withdrawn. === object === The object represents an RPKI CRL to be published or withdrawn. === object === The object represents an RPKI publication manifest to be published or withdrawn. Note that part of the reason for the batching support in the publication protocol is because //every// publication or withdrawal action requires a new manifest, thus every publication or withdrawal action will involve at least two objects. === object === The object represents a ROA to be published or withdrawn. == Error handling == Error in this protocol are handled at two levels. Since all messages in this protocol are conveyed over HTTP connections, basic errors are indicated via the HTTP response code. 4xx and 5xx responses indicate that something bad happened. Errors that make it impossible to decode a query or encode a response are handled in this way. Where possible, errors will result in a message which takes the place of the expected protocol response message. messages are CMS-signed XML messages like the rest of this protocol, and thus can be archived to provide an audit trail. messages only appear in replies, never in queries. The message can appear in both the control and publication subprotocols. The message includes an optional //tag// attribute to assist in matching the error with a particular query when using batching. The error itself is conveyed in the {{{error_code}}} (attribute). The value of this attribute is a token indicating the specific error that occurred. At present this will be the name of a Python exception; the production version of this protocol will nail down the allowed error tokens here, probably in the RelaxNG schema. The body of the element itself is an optional text string; if present, this is debugging information. At present this capabilty is not used, debugging information goes to syslog. == Additional access control considerations == As detailed above, the publication protocol is trivially simple. This glosses over two bits of potential complexity: * In the case where parent and child are sharing a repository, we'd like to nest child under parent, because testing has demonstrated that even on relatively slow hardware the delays involved in setting up separate rsync connections tend to dominate synchronization time for relying parties. * The repository operator might also want to do some checks to assure itself that what it's about to allow the RPKI engine to publish is not dangerous toxic waste. The up-down protocol includes a mechanism by which a parent can suggest a publication URI to each of its children. The children are not required to accept this hint, and the children must make separate arrangements with the repository operator (who might or might not be the same as the entity that hosts the children's RPKI engine operations) to use the suggested publication point, but if everything works out, this allows children to nest cleanly under their parents publication points, which helps reduce synchronization time for relying parties. In this case, one could argue that the publication server is responsible for preventing one of its clients (the child in the above description) from stomping on data published by another of its clients (the parent in the above description). This goes beyond the basic access check and requires the publication server to determine whether the parent has given its consent for the child to publish under the parent. Since the RPKI certificate profile requires the child's publication point to be indicated in an SIA extension in a certificate issued by the parent to the child, the publication engine can infer this permission from the parent's issuance of a certificate to the child. Since, by definition, the parent also uses this publication server, this is an easy check, as the publication server should already have the parent's certificate available by the time it needs to check the child's certificate. The previous paragraph only covers a "publish" action for a {{{}}} object. For "publish" actions on other objects, the publication server would need to trace permission back to the certificate issued by the parent; for "withdraw" actions, the publication server would have to perform the same checks it would perform for a "publish" action, using the current published data before withdrawing it. The latter in turn implies an ordering constraint on "withdraw" actions in order to preserve the data necessary for these access control decisions; as this may prove impractical, the publication server may probably need to make periodic sweeps over its published data looking for orphaned objects, but that's probably a good idea anyway. Note that, in this publication model, any agreement that the repository makes to publish the RPKI engine's output is conditional upon the object to be published passing whatever access control checks the publication server imposes.