Friday, September 20, 2013

EC_DRBG backdoor simply proves audit feature

Recent revelations in the national security arena, namely Snowden drops and research into NIST recommended, NSA crafted random number generators finding potential backdoors, have caused the privacy folks to say “see? This is what we have been telling you!” But, I say let’s back up a second and consider the claims by government authorities who insist there is a process in place to prevent widespread abuse. I will attempt to present some information that helps prove this out, that there is an auditable process in place, regardless of how it may be sidestepped, which is another topic for another day.
First, some crypto background on the backdoor in question. Dual_EC_DRBG or Dual Elliptic Curve Deterministic Random Bit Generator is an algorithm designed and published by the NSA, standardized by NIST in Special Publication 800-90.   After the publication, research was performed on the generator by Dan Shumow and Niels Ferguson, apparently crypto guys who are with Microsoft, who discovered that this dual_EC output could be influenced under certain circumstances, rendering such output suspect with regards to key generation, as once the key is determined, it follows that plaintext can be derived more easily than if output of the algorithm was truly and uniformly random.
Backdooring munitions and things is not new, recall stories of CIA intentionally skewing ingredients in The Anarchist Cookbook so that mixing up a kinetic cocktail could be problematic for the budding mixologist, and also recall stories of mass producing a hyper-flammable US flag that burns with an incredible intensity so as to maybe injure the igniting party, or start an unintentional collateral conflagration.
The pre-determined output distortion of dual_EC_DRBG can potentially be plotted and then with a master key, subsequently used to derive contents of the encrypted text and it is this salient point which serves as the basis for this write-up.
Possession of this master key when applied to the distorted output of this algorithm can be used to argue that it serves as part of an audit mechanism, where Snowden claims that the algorithm indeed contains a backdoor.  If the NSA can break all web encryption by emplacement of this particular backdoor, one can also potentially conclude that if NIST says they would not deliberately weaken a cryptographic standard, it is altogether possible that there could be a breakthrough that doesn’t weaken the algorithm, but allows usage of a master key that when applied to this distortion, can decrypt the text.
The audit point comes in when suspicious encrypted text makes its way from analyst to supervisor, and then weighted, and probably forwarded again up the chain, where eventually the master key guy plugs in the master key to reveal the text inside the comms.  So not everyone has the master key.
How then did Snowden abscond with all this data if there is an audit trail? That information is not relevant to this particular write-up, and likely not a part of this audit trail to begin with. These are separate instances of technical control.
So, by tying certain pieces together and looking at some technical details, and understanding the audit and accountability process, I feel it is highly likely that there is a break of this algorithm and that there is a mildly provable case that decryption is meant to be done responsibly.


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