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Dear OTR hackers,
I just implemented reassembly of OTR fragments...
While doing this I stumbled upon (in Protocol-v3):
OTR version 2 messages get fragmented in a similar format, but without
the instance tags fields:
"?OTR,%hu,%hu,%s," , sender_instance, receiver_instance, k , n , piece[k]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I think those arguments should be removed (OTRv2 only uses k, n,
piece[k]).
Furthermore, the protocol description does allow for fragmented
fragments... I'm curious whether there is any use of it? (With my
formal methods background, whenever I write a recursive function
without a (straightforward) termination argument it hurts (tbh, the
termination argument is rather straightforward since fragmentation
prepends and appends some bytes, thus it should all be safe).
I'd explicitly only allow certain messages to be fragmented -- such as
data (query is shorter without fragmentation anyways, ...).
I'm roughly talking about (where arrows indicate fragmentation, using
v2 here for simplicity (and I didn't try to execute this..)):
?OTRv2
-->
?OTR,1,2,?O,
?OTR,2,2,TRv2,
-->
?OTR,1,2,?OTR,1,2,?,
?OTR,2,2,O,,
?OTR,2,2,TRv2,
-->
...
Cheers,
Hannes
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