More Displaylink stuff

Alan Cox alan at
Wed Dec 24 11:53:57 PST 2008

> - The key is likely 16 bytes, which are sent as a control transfer. They appear 
> to be random, but the same 16-byte string can appear repeatedly, esp. if the
> device is initialized immediately after bootup. If these 16 bytes are equal, 
> then all bulk transfers are also identical byte-for-byte. Changing a single 
> byte in this transfer causes the device to stop working.

So is this a hash (eg SHA1 or MD5) or crypto - does the same image
generate different patterns as if it is a key ?

> - The bigger data blocks show a surprising regularity: every 4095 bytes, 
> significant portions of the blocks repeat. This can be found by comparing every 
> byte i with the byte at i+offset and increasing a counter if the two bytes are 
> equal. Do this for all offsets from 1 to n. The result is a series
> of maxima at 4095 and multiples thereof.

Might be worth looking to see if the protocol in use is RDP based, that
would be "natural" way to implement a Windows device with a low bandwidth
USB connection for image transmission. 

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