Jingle RTP Sessions (XEP-0167)  recommends the use of the Secure Real-time Transport Protocol (SRTP) for end-to-end encryption of RTP sessions negotiated using Jingle (XEP-0166) . RFC 5763  provides an approach to establish a Secure Real-time Transport Protocol (SRTP) security context using the Datagram Transport Layer Security (DTLS) protocol. A mechanism of transporting the fingerprint attribute that identifies the key that will be presented during the DTLS handshake in Jingle is defined herein. Inclusion of this information is OPTIONAL in both SIP/SDP and Jingle.
Note that while this specification only describes the use in the context of DTLS-SRTP, the fingerprint transported can be used in other contexts like for example establishing connections using SCTP over DTLS as described in Use of DTLS/SCTP in Jingle ICE-UDP (XEP-0343) .
The SDP format (defined in RFC 4572 ) is shown below.
An example follows.
Additionally, the SDP setup attribute defined in RFC 4145  must be mapped, whose usage for DTLS-SRTP is defined in RFC 5763.
Note that no mapping for the 'holdconn' role is defined herein.
These SDP attributes can be translated into Jingle as a <fingerprint/> element qualified by the 'urn:xmpp:jingle:apps:dtls:0' namespace, as shown below.
An example follows. Note that the whitespace would not appear in actual XML content.
If the Jingle initiator wishes to use DTLS-SRTP, it includes the <fingerprint/> element in its session invitation.
If the receiving party wishes to use DTLS, it also includes the <fingerprint/> element in its session-accept message.
Alternatively, if the receiving party wishes to expedite with ICE and DTLS negotiation without accepting the session, it MAY include the <fingerprint/> element when sending a transport-info message:
If an entity supports establishing a Secure Real-time Transport Protocol security context using the Datagram Transport Layer Security protocol, it MUST advertise that fact in its responses to Service Discovery (XEP-0030)  information ("disco#info") requests by returning a feature of "urn:xmpp:jingle:apps:dtls:0":
In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in Entity Capabilities (XEP-0115) . However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.
Security considerations for DTLS-SRTP itself are provided in RFC 5763.
XMPP stanzas such as Jingle messages and service discovery exchanges are not encrypted or signed. As a result, it is possible for an attacker to intercept these stanzas and modify them, thus convincing one party that the other party does not support DTLS-SRTP and therefore denying the parties an opportunity to use DTLS-SRTP.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
Thanks to Justin Uberti, Peter Saint-Andre and Lance Stout.
This specification defines the following XML namespace:
If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.
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Initial published version approved by the XMPP Council.
Second draft, rewrite no longer based on XEP-0262.
First draft, copied from XEP-0262.