in reply to Authentication of off-line application
Sounds like you need to look at crypto. What you could do everytime the remote site syncs up with the server, the server generates a new key for it, which is then returned to the remote site, and used for the next encryption. The server knows what to expect, since it generated the key. Can you trust the courier in between? Sounds like you may need to do a bit more homework before comitting to this one...
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