Ned,
...
I see nothing that cannot be implemented using existing protocols as building
blocks. ...
My point was to say that providing "non-repudiation of message receipt" is
rather tricky and that people use "receipt" carelessly in describing what they
offer as a service. "Strong" receipt requires more than a receipt notification
mechanism, it requires active involvement of a third party or use of an on-line
protocol. I was not implying the use of any building blocks.
...
I hope I've missed something here, but if I haven't I think this pretty much
blows B-CEM out of the water, as least as far as time-critical material and
material available from multiple sources are concerned. ...
What you missed was the existence of the trusted third party (TP) from whom B
can get E anytime.
Regards,
Ali