XMPP as defined in &rfc3920; does not support direct interaction between endpoints, since it requires a client to authenticate an XML stream with a server and send of all of its outbound XML stanzas through that server (which potentially may route those stanzas through another server for delivery to the intended recipient). However, in some scenarios it is desirable to establish end-to-end XML streams between two endpoints instead of relying on the standard client-server architecture. These scenarios include:

• Two endpoints cannot access an XMPP server
• Two endpoints want to enforce end-to-end encryption
• Two endpoints want to send a high volume of XMPP traffic but the intermediate servers enforce rate limits

The first scenario is addressed by &xep0174;. The second and third scenarios are addressed by &xep0247;. Both of those technologies result in the establishment of a direct or mediated connection between two endpoints, such as a direct TCP connection, a bytestream through SOCKS5 (&xep0065;) or XMPP itself (&xep0047;), or other future transport methods such as ice-tcp.

Once two endpoints have such a connection, they can establish an XML stream over that connection for end-to-end "("e2e") communication. We call this an "e2e stream".

The initiator and recipient essentially follow the process defined in RFC 3920 to establish XML streams between themselves.

First, the initiator opens an XML stream to the recipient over the negotiated transport.

In accordance with &rfc3921bis;, the initial stream header SHOULD include the 'to' and 'from' attributes. In the case of XEP-0174, these SHOULD be the username@machine-name advertised in the PTR record. In the case of Jingle XML Streams, these SHOULD be the bare JIDs &BAREJID; of the entities as communicated via XMPP.

If the initiator supports stream features and the other stream-related aspects of XMPP 1.0 as specified in RFC 3920, then it SHOULD include the version='1.0' flag as shown in the previous example.

The recipient then responds with a stream header as well:

If both the initiator and recipient included the version='1.0' flag, the recipient SHOULD also send stream features as specified in RFC 3920:

The exchange of stream headers results in an unencrypted and unauthenticated channel between the two entities. See the Security Considerations section of this document regarding methods for authenticating and encrypting the stream.

Once the streams are established, either entity then can send XMPP message, presence, and IQ stanzas, with or without 'to' and 'from' addresses.

To end the stream, either party closes the XML stream:

The other party then closes the stream in the other direction as well:

Both parties then SHOULD close the logical or physical connection between them.

XMPP networks use TLS (&rfc2246;) for channel encryption and SASL (&rfc4422;) for authentication. In the context of e2e XML streams, the parties SHOULD use TLS and SASL EXTERNAL with client certificates, including clientCert requests during the TLS negotiation for the purpose of mutual authentication.

End-to-end XML streams can be negotiated between two XMPP clients, between an XMPP client and a remote XMPP service (i.e., a service with which a client does not have a direct XML stream), or between two remote XMPP services. Therefore, a party to an e2e XML stream will present either a client certificate or a server certificate as appropriate. Such certificates MUST be generated and validated in accordance with the certificate guidelines guidelines provided in &rfc3920bis;.

A future version of this specification may provide additional guidelines regarding certificate validation in the context of end-to-end encryption.

This document requires no interaction with &IANA;.

This document requires no interaction with the ®ISTRAR;.