docs: add statement on our refusal to insert backdoors

docs/backdoors.txt

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+Statement on Backdoors
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+October 5, 2010
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+The New York Times has recently reported that the current U.S. administration is proposing a bill that would apparently, if passed, require communication systems to facilitate government wiretapping and access to encrypted data:
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+ http://www.nytimes.com/2010/09/27/us/27wiretap.html (login required; username/password pairs available at  http://www.bugmenot.com/view/nytimes.com).
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+Commentary by the  Electronic Frontier Foundation (https://www.eff.org/deeplinks/2010/09/government-seeks ),  Peter Suderman / Reason (http://reason.com/blog/2010/09/27/obama-administration-frustrate ),  Julian Sanchez / Cato Institute (http://www.cato-at-liberty.org/designing-an-insecure-internet/ ).
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+The core Tahoe developers promise never to change Tahoe-LAFS to facilitate government access to data stored or transmitted by it. Even if it were desirable to facilitate such access—which it is not—we believe it would not be technically feasible to do so without severely compromising Tahoe-LAFS' security against other attackers. There have been many examples in which backdoors intended for use by government have introduced vulnerabilities exploitable by other parties (a notable example being the Greek cellphone eavesdropping scandal in 2004/5). RFCs  1984 and  2804 elaborate on the security case against such backdoors.
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+Note that since Tahoe-LAFS is open-source software, forks by people other than the current core developers are possible. In that event, we would try to persuade any such forks to adopt a similar policy.
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+The following Tahoe-LAFS developers agree with this statement:
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+David-Sarah Hopwood
+Zooko Wilcox-O'Hearn
+Brian Warner
+Kevan Carstensen
+Frédéric Marti
+Jack Lloyd
+François Deppierraz
+Yu Xue
+Marc Tooley