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:
+XMPP as defined in &rfc3920; does not support direct interaction between endpoints, since it requires a client to authenticate an XML stream with a "home" server and send of all of its outbound XML stanzas through that server (which potentially can route those stanzas through a peer 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:
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 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 opened a direct or mediated connection, they can establish an XML stream over that connection for end-to-end "("e2e") communication. We call this an "e2e stream".
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.
+The mere exchange of stream headers results in an unencrypted and unauthenticated channel between the two entities. The entities SHOULD upgrade the channel to an encrypted stream using the XMPP STARTTLS command defined in &xmppcore; using &rfc4346;, optionally followed by SASL negotiation for mutual authentication (see &rfc4422;).
+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, such as a remote &xep0045; room), or between two remote XMPP services. Therefore, if standard X.509 certificates are used then a party to an e2e XML stream will present either a client certificate or a server certificate as appropriate. If X.509 certificates are used, they MUST at a minimum be generated and validated in accordance with the certificate guidelines guidelines provided in &rfc3920bis;; however, applications of end-to-end XML streams MAY define supplemental guidelines for certificate validation in the context of particular architectures, such as XEP-0174 for link-local streams and XEP-0247 for direct or mediated streams negotiated through XMPP servers.
+To ease the transition from the PGP-based object encryption method specified in &xep0027;, clients using TLS for e2e streams MAY use the OpenPGP TLS extension defined in &rfc5081; (if available).
+Use of other TLS extensions MAY be appropriate as well, including those defined in &rfc4346; and &rfc5054;.
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.
+End-to-end streams SHOULD be encrypted; see the Stream Encryption section of this document.