[OTR-dev] Fragmenting proposal

[Paul Wouters]

On Wed, 15 Dec 2004, Ian Goldberg wrote:

> Different IM networks have different maximum lengths that messages can
> be.  Can you guys look over this proposal for message fragmenting, and
> see if there's something I'm missing?  [This will become part of the
> Protocol documentation.]

Since there are no checks on the fragments, doesn't this completely disrupt
the communication you can have if I'm inserting bogus fragments?

>    We could fragment this message into (for example) three pieces:
>
> 	?OTR,1,3,?OTR:AAEKAQAAAICGmmRMlmuq4gY7Ro0GiYAJKWwVZyITNyifFP9VRI
> 	VgyxxGxwVbFjoGMhO9XE0xFisuO6M27DPkX7hCtIXZM2glDszmTklQO5hJPu0g/R
> 	gDZ84q0eeQ5AvexW3Hmp/VHUPTpZfJPep/Ctiqn0oE2y/2yRPyYQjpZCL440sM5i
> 	7B1wAAABTzzL9WbuaxOK8rfrtaw4Lx/iLxeQAAAIAWaGpchsVOV1D6xK5cS5QNAN
> 	elTvyVHreXPSRjU0NFKIHrNDiFwa8lXcIBH/E8MHoQDzw+J2AuU6MuICPT8GMJYB
> 	cSZq0OM7xgmfNlt1viUXxJXbYRpD82ki7QsMA1I7aQo/OqMryKlW5W8UqEjVcCsT
> 	OjEyQphLY,
>
> 	?OTR,2,3,ENG6St9+ivgAAAIBgUjzleG1+VYCXZszTj+x5gNNidVVNKI+MG5elHM
> 	csg2Guef3DBYEsor6YGeqJLAfhk28Tg7tktMQwGN5GXR1ZNkwkoFIOyVRq3lfabf
> 	HtsTp+Hkx5e8OrhTZ1G+ScDeqYbbTtUj631LhXUoyp+7pllVtpyLgqk5z9JYu6Kw
> 	0ZkQAAAAEAAADASZH/uq17EVRo6dBZIL12x9JLx4gpEjgovfNLoORa6E+sMMuG7Z
> 	+zfLQVodXH5shi/dvPzwbVrA/Iw72XHSYtld8lK/FLtjsI5mzancvRAEs1ZDBoBJ
> 	RLW1X54eFHpN/peDi6fBbdXyGahWYyF9MCJxDFCRqAHvEMZbfdyEtkXbFUZM2lJM
> 	2SJJG9zGZ,
>
> 	?OTR,3,3,LCvd2/gF/VOgMlvdus+8TFW0k7cBhAgm/rb+EUeovkWXy2BiVpInXKC
> 	CH+M6EVpUYNG7BPtH44ABwUw6Y5n5sSb6dtout34NGz+dspXMajffkZxFOAcabRw
> 	KIpw==.,

So I am in your WLAN, and send a packet with  ?OTR,2,3,AAAAAAAAAAAA.[...],
Will you ever be able to assemble things when the right packet arrives?
What if I send 25 different ?OTR,2,3 packets?

Then again, I don't want to suggest a pmtu type solution to you either.
I'd probably go for a list of known good values per IM service.

Paul
-- 
    Math is case-sensitive
                             --- Ian Goldberg