[Beowulf] $1, 279-per-hour, 30, 000-core cluster built on Amazon EC2 cloud

Robert G. Brown rgb at phy.duke.edu
Tue Oct 4 13:39:16 PDT 2011

On Tue, 4 Oct 2011, Chi Chan wrote:

> On Tue, Oct 4, 2011 at 11:58 AM, Rayson Ho <raysonlogin at gmail.com> wrote:
>> BTW, I've heard horror stories related to routing errors with this
>> method - truck drivers delivering wrong tapes or losing tapes
>> (hopefully the data is properly encrypted).
> I just read this on Slashdot today, it is "very hard to encrypt a
> backup tape" (really?):
> http://yro.slashdot.org/story/11/10/04/1815256/saic-loses-data-of-49-million-patients

Not if it is encrypted with a stream cipher -- a stream cipher basically
xors the data with a bitstream generated from a suitable key in a
cryptographic-strength pseudorandom number generator (although there are
variations on this theme).  As a result, it can be quite fast -- as fast
as generating pseudorandom numbers from the generator -- and it produces
a file that is exactly the size of the original message in length.

There are encryption schemes that expend extraordinary amounts of
computational energy in generating the stream, and there are also block
ciphers (which are indeed hard to implement for a streaming tape full of
data, as they usually don't work so well for long messages).  But in the
end no, it isn't that hard to encrypt a backup tape, provided that you
are willing to accept the limitation that the speed of
encrypting/decrypting the stream being written to the tape is basically
limited by the speed of your RNG (which may well be slower than the
speed of most fast networks).


> --Chi

Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu

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