michel.d.loweverizon.com
Date: Mon Jan 12 2004 - 13:15:41 CST

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Stuart,
It would seem like a cool idea but I can think of a couple of drawbacks.
I'm not a kernel
hacker or anything but it seems to me that unless your security app is an
actual part of
the operating system kernel (easy if Linux, tough if Windows), every time
your operating
system does a context switch your crypto key stored in a register would get
dumped into
RAM along with all the other pertinent info (gen'l purpose registers, stack
pointer, etc.).
So your key would wind up back in storage anyway. Presumably other user
processes
can't "see" your data but if we're assuming the system is compromised I
think you would
have to also assume the intruder has super user/administrator/root
authority and therefore
CAN see your private storage areas. If you patch the OS you would also
have to know
which floating point registers are REALLY used by your kernel and which
ones are just
"reserved for future use" and therefore available for you to reserve and
manipulate in
your kernel patch.

Just my two cents,
Mike

_________________
Michel D. Lowe

                                                                                                                                       
                      lsi
                      <stuartcyberdeli To: secprogsecurityfocus.com
                      x.net> cc:
                                               Subject: storing crypto key in CPU registers
                      01/11/2004 10:57
                      AM
                      Please respond to
                      stuart
                                                                                                                                       
                                                                                                                                       

Just a thought:

Whilst reading some compiler documentation the point was made that
"The Intel x86 chips offer eight 32-bit registers, while the x87
numeric coprocessor sports another eight 80-bit floating point
registers.".

Some of these registers are used internally. But maybe at least one
of them is available to store up to 80 bits of crypto key, in a
location that is not coredumped or swapfiled?

Multiple registers could be combined to store a larger keysize.

Previous discussion has commented that storing a key for programmatic
access is unavoidably insecure. While storing keys in registers on
the CPU itself does not rectify the problem, it might potentially
reduce the number of avenues of attack available.

Stuart
--
Stuart Udall
stuart at cyberdelix dot net - http://www.cyberdelix.net/
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