| Internet Engineering Task Force | P. M. Hallam-Baker |
| Internet-Draft | Comodo Group Inc. |
| Intended status: Standards Track | January 21, 2014 |
| Expires: July 25, 2014 |
OmniBroker Protocol
draft-hallambaker-omnibroker-07
An Omnibroker is an agent chosen and trusted by an Internet user to provide information such as name and certificate status information that are in general trusted even if they are not trustworthy. Rather than acting as a mere conduit for information provided by existing services, an Omnibroker is responsible for curating those sources to protect the user.
The Omnibroker Protocol (OBP) provides an aggregated interface to trusted Internet services including DNS, OCSP and various forms of authentication service. Multiple transport bindings are supported to permit efficient access in virtually every common deployment scenario and ensure access in any deployment scenario in which access is not being purposely denied.
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This Internet-Draft will expire on July 25, 2014.
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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 RFC 2119 [RFC2119].
Today, a network client is required to make queries against multiple information sources to establish a secure connection to a network resource. A DNS query is required to translate network names to Internet addresses. If TLS transport is used, an OSCP query may be required to validate the server certificate. Support for client authentication may require interaction with another service.
Servers require similar support when accepting Internet connections. Even though most networking infrastructure supports some form of network administration, it is left to the network administrator to fill in the gap between server applications and network infrastructure. Making use of such facilities is rarely cost effective except at the very largest installations.
An Omnibroker is a trusted agent that acts as a single point of service for client queries requesting a connection to a named network resource and server advertisements accepting connections to a named network resource.
Omnibroker is implemented as a JSON/REST Web service using Jason Connect (JCX) to establish and manage the long term trust relationship with the Omnibroker provider.
In normal use, an omnibroker client receives service from a single Omnibroker service provider. For performance and reliability reasons, an Omnibroker service provider is expected to provide multiple Omnibroker service instances.
An Omnibroker client acquires the network address information and credentials necessary to access an omnibroker service using the JCX Web Service to establish a connection binding. To ensure reliabilty and the ability to access the service in all circumstances, an Omnibroker connection binding SHOULD specify multiple service instances.
Due to the need for low latency and the need to function in a compromised network environment, three protocol bindings are defined:
The implementation overhead of support for three different protocol bindings is reduced by the choice of a binary encoding for JSON (JSON-B) that is very close in structure to JSON encoding allowing encoders and decoders to support both encodings with minimal additional code.
Regardless of the protocol binding used, all Omnibroker messages are authenticated with protection against replay attack under the cryptographic credentials established in the connection binding service instance.
Directing queries through a single point of contact has performance, relability and security advantages. Directing queries to multiple network information sources degrades performance and may cause a connection request to fail if an information resource is not available. This has led many application providers to limit the information sources they consult. Directing queries through an Omnibroker allows as many information sources to be brought to bear as the broker has local cached data for without loss of performance or reliability.
Making use of additional data sources allows the broker to 'curate' the response. If the broker knows that a Web site always returns a redirect to a TLS secured version of the same site, it can tell a Web Browser to go straight to the secure version. If a Web Server is hosted on a known botnet, the Omnibroker can tell the client that it really does not want to visit that location.
Unlike the traditional DNS configuration, an Ombinbroker client decides which source(s) of trusted information to use rather than relying on whatever happens to be the nearest source to hand.
The traditional DNS approach creates an obvious security risk as DNS is a trusted service and deciding to choose a random DNS service advertised by the local DHCP service is clearly a poor decision process for a trusted service.
Directing service advertisements to a single point of contact has similar benefits. The single point of contact can take responsibility for managing load balancing. Firewall and router configurations can be set automatically. Anti-abuse technologies such as IP address filters and rate limiting devices can be switched in as required.
In simple network configurations such as a residential
IETF culture has traditionally resisted attempts to establish partitions within the open Internet with restricted access to network resources or compromised security. Such 'Walled Gardens' models typically exist for the benefits of those who own the walls rather than those forced to live inside them.
While virtually all residential Internet users reject such controls, most find them acceptable, if not desirable in workplaces and schools.
Omnibroker simplifies the process of establishing such a walled garden but does not make the walls any easier to defend.
From a censorship point of view, the censorship concerns of running an Omnibroker are essentially the same as those of running a DNS service. The party who decides which discovery service to use can determine which content is visible to the users.
Like SCVP [RFC5055] and XKMS [TBS] , Omnibroker permits an Internet client to delegate some or all aspects of PKIX [RFC5280] certificate path chain discovery and validation.
In the normal mode of operation, the Omnibroker service performs only path chain discovery, leaving the client to re-check the PKIX certificate path before relying on it. This gives the Omnibroker the power to veto a client connection to a server that it considers to be unsafe but not the power to tell the client to trust a site of its own choosing.
This ability to veto but not assert trust is appropriate and sufficient for the vast majority of network applications. It allows the broker to make use of additional path validation checks that are not supported in the client such as DANE [RFC6698] or Certificate Transparency [RFC6962].
There are however some workplace environments where the ability to access external network resources with strong encryption is not permissible by enterprise policy or in some cases by law. An intelligence analyst working at the NSA may have a need to access external Web sites that contain important information but must on no account have access to a covert channel that could be used to exfiltrate information. Certain Financial institutions with access to valuable commercial information are required to monitor and record all communications into and out of the company to deter insider trading.
The traditional response to such needs has been to tell the parties affected to look elsewhere for support. As a consequence the techniques used to satisfy such requirements are generally unfriendly to network applications in general and have in some cases put the public Web PKI trust infratructure at risk.
There is an argument to be made that rather than attempting to prohibit such activities entirely, it would be better to provide a principled method of achieving those ends and for mainstream software providers to support it in such a fashion that ensures that network applications configured for that mode of use can be readilly identified as such by end users.
As the preceeding examples demonstrate, a party with control over the Omnibroker service chosen by a user has full control over the network activities of that user. An important corrolary of this fact is that all a user need do to achieve full control over their network activities is to run their own Omnibroker service and connect to that.
For example such an Omnibroker service might be configured to return connection data for permitted domestic Web sites as normal but direct attempts to connect to forbidden foreign news or social media through a privacy network such as TOR.
[For illustrative purposes, all the examples in this section are shown using the Web Services Transport binding. Examples of other transport bindgins are shown in section [TBS].]
[Alice establishes her connection binding to an omnibroker service provider]
The OBP service connection broker answers the query 'what connection parameters should be used to establish the best connection to interract with party X according to protocol Y. Where 'best' is determined by the Omnibroker which MAY take into account parameters specified by the relying party.
The OBP service connection broker supports and extends the traditional DNS resolution service that resolves a DNS name (e.g. www.example.com) to return an IP address (e.g. 10.1.2.3).
When using an Omnibroker as a service connection broker, a client specifies both the DNS name (e.g. www.example.com) and the Internet protocol to be used (e.g. _http._tcp). The returned connection parameters MAY include:
If an attempt to connect with the parameters specified fails, a client MAY report the failure and request a new set of parameters.
Alice uses her Web browser to access the URL http://www.example.com/. The Web browser sends a QueryConnectRequest request to obtain the best connection parameters for the http protocol at www.example.com:
POST /.well-known/OmniQuery/ HTTP/1.1
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Session: Value=GXt4UiDbHMO0q39e1N-0MEKKurfw-yAgIPMJ5IgZmSE;
Id=Jg3BJ086IutOvyLpYAbJZg7CHg2s7MoL81sRM15RUI7Tk0U2Hh9j7UpjdGIj
hcqVodbik_kq1zOK1nXqgBcfSxZRE9wJyTDr3ll6Yf7A_Pk
Host: localhost
Content-Length: 123
Expect: 100-continue
{
"QueryConnectRequest": {
"Identifier": {
"Name": "Example.com",
"Service": "_http",
"Port": 80}}}
The service responds with an ordered list of possible connections. In this case the site is accessible via plain TCP transport or with TLS. Since TLS is the preferred protocol, that connection is listed first.
HTTP/1.1 OK
Content-Length: 335
Date: Tue, 09 Jul 2013 21:38:18 GMT
Server: Microsoft-HTTPAPI/2.0
{
"QueryConnectResponse": {
"Status": 200,
"Connection": [{
"IPAddress": "10.3.2.1",
"IPPort": 443,
"Transport": "TLS",
"TransportPolicy": "TLS=Optional",
"ProtocolPolicy": "Strict"},
{
"IPAddress": "10.3.2.1",
"IPPort": 80,
"ProtocolPolicy": "Strict"}]}}
Each OBP request identifies both the account under which the request is made and the device from which it is made. An OBP broker is thus capable of acting as a peer connection broker service or providing a gateway to such a service.
When using Omnibroker as a peer connection broker, a client specifies the account name and DNS name of the party with which a connection is to be established (e.g. alice@example.com) and the connection protocol to be used (e.g. _xmpp-client._tcp)
The returned connection parameters are similar to those returned in response to a service broker query.
Although the QueryConnectResponse returned the hash of a PKIX certificate considered valid for that connection, the server returns a different certificate which the client verifies using the ValidateRequest query.
POST /.well-known/OmniQuery/ HTTP/1.1
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Session: Value=HzGgeCNwxHcyvrkr-7Y4NvHINT7VVB9zvLEYKGjg6q4;
Id=Jg3BJ086IutOvyLpYAbJZg7CHg2s7MoL81sRM15RUI7Tk0U2Hh9j7UpjdGIj
hcqVodbik_kq1zOK1nXqgBcfSxZRE9wJyTDr3ll6Yf7A_Pk
Host: localhost
Content-Length: 1110
Expect: 100-continue
{
"ValidateRequest": {
"Service": {
"Identifier": [{
"Name": "example.com"}]},
"Credential": [{
"Data":
"MIIC0DCCAbigAwIBAgIQQut6m1F0PodIjIzop_d1uDANBgkqhkiG9w0B
AQUFADARMQ8wDQYDVQQDEwZWb29kb28wHhcNMTMwNjI2MTczOTQyWhcNM
TQwNjI2MDAwMDAwWjARMQ8wDQYDVQQDEwZWb29kb28wggEiMA0GCSqGSI
b3DQEBAQUAA4IBDwAwggEKAoIBAQCdc7Qgx71o6Tq5dFUUhcCn8Nt-2Y9
SGhm3WvsMYIqOIcHq3gjIKN9FWvXzpBbTjz4lCwx-CJT82RBLNDFtsysf
c0G7K_RsNKosYaM-L-DshO6R_314tptn9gnT9tjTPXuiiICQlAP83BuTI
148iEJWL36vbmv5AG6vrtk3T6ah5r2hBXQjt46sLQYweiM-peYIhPTIy9
OYugogfqdzPvaJpDfAukqJBXqMxfscagKPYAGPaICKhobKr11aPam1Tch
k2cBbtuYgSDz6ZGttsKE2omDbcmhbF7gBpRug-E2OH79Q4EVlSSoO9gZ6
AF4Km1A9uK9W_Pg8EPugY3Mgns6lAgMBAAGjJDAiMAsGA1UdDwQEAwIEM
DATBgNVHSUEDDAKBggrBgEFBQcDATANBgkqhkiG9w0BAQUFAAOCAQEACK
9LQNkewOOugaYhs4LfE3xdrRzrcaR0w5cf3wVcgR0ZZo98rDOtu3FAexp
dh6vNaIdU4zAzNJPKKSso3XF2LpQZovKIpUuN9pkZqslqZ0TLXqlyXMbh
eShcqIP1-m6qjZOp95N7jwgxBlEmi_ne-rg1DicXFtAu90LpAZludaQGA
yrj-LC37gzeMo2AG7BAuyFURXJFfxjpGmnueuYfzZIMIQY-lNl6qm_vSM
Iz4uUKqq4lWndahnkJAwI2p5zUM0z3O6OMr_zr8eyrdAL__H4NnG3gVyB
bNoSbvbkxUt_C3oBwFFTupzRMQqJVjzbApyw5H0OzJPJKKkxxhmIYTg"}
]}}
The service validates the certificate according to the Omnibroker service policy.
HTTP/1.1 OK
Content-Length: 45
Date: Tue, 09 Jul 2013 21:38:18 GMT
Server: Microsoft-HTTPAPI/2.0
{
"ValidateResponse": {
"Status": 200}}
The credential validation query provides certificate path validation and status checking.
The service provided by OBP is similar to that provided by OCSP and SCVP. Like SCVP, OBP is an agent selected by the relying party to validate certificates and/or construct trust paths on its behalf.
Service advertisement is the converse of service resolution. An Internet application wishing to accept inbound connections specifies one or more sets of connection parameters for the Omnibroker to register with whatever naming, discovery or other services may be appropriate.
[Examples TBS]
Every query request contains the following common elements:
Every Query Response contains the following common elements:
Specifies an Internet service by means of a DNS address and either a DNS service prefix, an IP port number or both. An Internet peer connection MAY be specified by additionally specifying an account.
Additional information that a service MAY return to support a service connection identification. For example, DNSSEC signatures chains, SAML assertions, DANE records, Certificate Transparency proof chains, etc.
Describes a service connection
Requests a connection context to connect to a specified Internet service or peer.
Specifies the Internet service or peer that a connection is to be established to and the acceptable security policies.
Returns one or more connection contexts in response to a QueryConnectRequest Message.
Advises a broker that one or more Internet services are being offered with particular attributes.
Specifies the connection(s) to be established.
The attributes required depend on the infrastructure(s) that the broker is capable of registering the service with.
Specifies the connection(s)
The Validate query requests validation of credentials presented to establish a connection. For example credentials presented by a server in the process of setting up a TLS session.
Specifies the credentials to be validated and the purpose for which they are to be used.
Reports the status of the credential presented.
To achieve an optimal balance of efficiency and availability, three transport bindings are defined:
Support for the HTTP over TLS binding is REQUIRED.
An OBP message consists of three parts:
Note that although each of the transport bindings defined in this specification entail the use of a JSON encoding for the message data, this is not a necessary requirement for a transport binding.
Protocol schema types are mapped to JSON encoding as follows:
OBP requests and responses are mapped to HTTP POST requests and responses respectively. Java Script Object Notation (JSON) encoding is used to encode requests and responses.
Requests and responses are mapped to HTTP POST transactions. The content of the HTTP message is the message payload. The Content-Type MUST be specified as application/json. The Character set MUST be specified as UTF-8.
The Ticket and Authenticator are specified using the Integrity header as follows:
Session: <base64url (authenticator)> ; ticket=<base64url (ticket)>
[To be generated from spec]
The DNS Tunnel mode of operation makes use of DNS TXT resource record requests and responses to tunnel OBP Query requests. Due to the constraints of this particular mode of operation, use of this transport is in practice limited to supporting transactions that can be expressed within 500 bytes. These include the QueryConnect and ValidateRequest interactions.
Requests are mapped to DNS TXT queries. The request is mapped onto the DNS name portion of the query by encoding the Ticket, Authenticator and JSON encoded Payload using Base32 encoding and appending the result to the service prefix to create a DNS name as follows:
<base32(payload)>.<base32(authenticator)>.<base32(ticket)>.Suffix
The payload MAY be split across multiple DNS labels at any point.
Responses are mapped to DNS TXT records by encoding the Authenticator and JSON encoded Payload using Base64 encoding and cocatenating the result with a periods as a separator as follows:
<base32(payload)>.<base32(authenticator)>
[To be generated from spec]
The UDP transport MAY be used for transactions where the request fits into a single UDP packet and the response can be accomadated in 16 UDP packets. As with the Web Service Binding, Java Script Object Notation (JSON) encoding is used to encode requests and responses.
The request consists of four message segments containing a Header, Ticket, Payload and Authenticator. Each message segment begins with a two byte field that specified the length of the following data segment in network byte order. The Payload is encoded in JSON encoding and the remaining fields as binary data without additional encoding.
The header field for this version of the protocol (1.0) contains two bytes that specify the Major and Minor version number of the transport protocol being 1 and 0 respectively. Future versions of the transport protocol MAY specify additional data fields.
[TBS diagram]
The response consists of a sequence of packets. Each packet consists of a header section and a data section.
The header section consists of a two byte length field followed by two bytes that speciofy the Major and Minor version number of the transport protocol (1 and 0), two bytes that specify the frame number and the total number of frames and two bytes that specify the message identifier.
[TBS diagram]
[Question, should the authenticator be over the whole message or should each packet have its own authenticator?]
[To be generated from spec]
[List of contributors]
[TBS list out all the code points that require an IANA registration]
| [RFC6698] | Hoffman, P. and J. Schlyter, "The DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS) Protocol: TLSA", RFC 6698, August 2012. |
| [RFC6962] | Laurie, B., Langley, A. and E. Kasper, "Certificate Transparency", RFC 6962, June 2013. |