Make the XOR key an array of bytes as a start to normalise the way the
XOR happens across the board. Given that we're going to be adding
encryption to the packet level and adding more stuff to the packet
header, now is the time to fix this up once and for all.
Crypto context stuff appears to have only ever been supported in
Meterpreter on Windows. The only thing it allowed for is XOR, which is
redundant given that we have packet level XOR in place. Also, it would
appear that MSF didn't have support for it anyway!
With the move torwards packet-level encryption, this is unnecessary so
it needs to go bye bye.
The last issue we had in removing the OpenSSL library from Windows
meterp is making it so that reconnects would behave. With a staged
listener, the first thing that gets sent down the wire is metsrv.dll. As
a result, when a fully staged connect comes in (whether it be from
a stageless payload, from a transport switch or from a sleeping session
waking up), Meterpreter needs to handle the case that the data coming
down the wire is no actually a TLV packet, and hence ignore it.
This "hack" abuses the properties of the XOR key for the packet,
relying on the fact that the XOR key will never contain NULl bytes and
that the first 4 bytes from a staged listener starts with the length of
the metsrv DLL, which is small enough to result in a NULL byte in the
MSB position.
If we see a NULL byte in that position, we assume it's the metsrv header
coming in, and we just ignore it and move on. If the XOR key looks
legit, we assume it's a valid TLV packet.
Dirty, but it's quick and it works!
