Finally, as was indicated in the slides, keying for SRTP
store-and-forward only requires that existing key management
protocols
are extended to allow also carrying information about CID,
CCI and SSS.
For the e2e keying in the answering machine use case, the sender must
hold a shared key or certificate with the responder. This
situation is
thus exactly as when you send an encrypted email.
But we lack a mechanism to acquire such a shared key or
certificate on the Internet for SIP (or email, for that matter),
correct? I am told that MIKEY-RSA has some mechanism to acquire
such information but I haven't seen it described anywhere -- it
certainly isn't in an IETF document that I am aware of.
-d
When you refer to MIKEY-RSA having some mechanism to acquire such
information (shared key / certificate) I believe you refer to
MIKEY-RSA-R. In MIKEY-RSA-R the initiator attaches his certificate in
the first message and the responder uses it to return the key to be
used. This works well when there is an on-line connection between the
two but wouldn't work for SRTP Store-and-Forward applications. Here
we must rely on either predistributed keys or certificates or that keys
or certificates can be acquired from an online third party. As I said
before this situation is exactly as for secure email. And secure email
is used!