- Encrypted Key Transport
Encrypted Key Transport or EKT is an extension to SRTP that fits within the SRTP framework and reduces the amount of signaling control that is needed in an SRTP session. EKT securely distributes the SRTP master key and other information for each SRTP source, using SRTCP to transport that information. With this method, SRTP entities are free to choose SSRC values as they see fit, and to start up new SRTP sources with new SRTP master keys within a session without coordinating with other entities via signaling or other external means. This fact allows to reinstate the RTP collision detection and repair mechanism, which is nullified by the current SRTP specification because of the need to control SSRC values closely. An SRTP endpoint using EKT can generate new keys whenever an existing SRTP master key has been overused, or start up a new SRTP source to replace an old SRTP source that has reached the packet-count limit.
EKT also solves the problem in which the burst loss of the N initial SRTP packets can confuse an SRTP receiver, when the initial RTP sequence number is greater than or equal to 2^16 - N. These features simplify many architectures that implement SRTP.
EKT provides a way for an SRTP session participant, either sender or receiver, to securely transport its SRTP master key and current SRTP rollover counter to the other participants in the session. This data, possibly in conjunction with additional data provided by an external signaling protocol, furnishes the information needed by the receiver to instantiate an SRTP/SRTCP receiver context.
EKT does not control the manner in which the SSRC and master key are generated; it is concerned only with their secure transport. Those values may be generated on demand by the SRTP endpoint, or may be dictated by an external mechanism such as a signaling agent or a secure group controller.
EKT is not intended to replace external key establishment mechanisms such as SDP Security Descriptions
SDES orMikey (RFC3830). Instead, it is used in conjunction with those methods, and it relieves them of the burden of tightly coordinating every SRTP source among every SRTP participant.Reference: http://tools.ietf.org/html/draft-mcgrew-srtp-ekt-03
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