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[HLL] Some ideas on the Harmless Little Protocol
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Some thoughts on HLP:
Here are some things that I think we might want in it:
1. It should be extensible, so there should be some real 'option
negotiation' during protocol setup. Something like A going "I can do
3DES, BLOWFISH and DES; in that order of preference" Then B answering
"Ok, since I can do BLOWFISH, RC5 and DES; let's use BLOWFISH"
2. The ability of the audio compression layer to fall back to a lower
speed. This might be because the modems retrained on a lower speed, or
because something else wants to use the encrypted connection as well.
We were talking about that by using a frame based approach with a
frame-type field in each frame.
3. I don't think we would want a 'reliable' (like TCP) connection
protocol. One lost packet might cause severe delays in the datastream,
which would not be acceptable. Something 'unreliable', like UDP might
be more appropriate.
A conversation might go like this:
Device A Device B
Hi! I'm HLP version 1 Hi! I'm HLP version 2, but I'll step down to
Ok, I know BLOWFISH and DES I know 3DES, BLOWFISH and DES. Let's use
[Key exchange happens]
Allright, we seem to have a 28k8 Ok, I can do that.
link. Let's use the 25kbit codec
Ok, that's it for tonight. Time to relax.
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atrak: Don't tickle me while I'm thinking!