Schneier on Security

Clive Robinson • July 1, 2013 9:50 AM

Folks should remember that in theory the NSA has two contradictory missions,

1, Protect the communications of the USA that effect US National Security.

2, Gain access and understanding on the communications of other nations and nationals (that are assumed to always effect US National Security).

The problem is "National Security" has a definition as broad as required by those formulating US policy, and this has in the past been used to spy on any company that is trying to do business in the same market as US companies irrespective of if the other entities are US or not (note this is not unique to the US the French openly indicated that they did this many years ago, and many other nations have been caught at it in the past).

This "dual role" would make many people and organisations schitso/paranoid and this has certainly appeared to be the case in the past with the NSA.

One trick they grabbed with both hands in the old days of mechanical cipher machines was to have a large key space where some keys were strong and others weak to very weak in some non obvious manner. Because the NSA was responsible for keying material used by the US then they could ensure the use of the strong keys. However anyone capturing the equipment and re-using the design without the required knowledge would end up using a cross section of strong and weak keys on a random basis. Frequently this ment that 20-25% of comms could be broken quickly with these providing usefull information (known plain text etc) to break any of the harder keys.

They refined this idea and it became apparent with clipper that they had moved on to the idea of brittle ciphers where any slight change in the design would weaken security down to around 40bit's equivalent.

With AES they in effect fixed the competition rules such that the code on the NIST site was not only freely downloadable and usable by any one, it was also optomised for speed/efficiency, not security and thus the code that went into nearly all products and code libraries was full of time based side channels etc.

Of more recent times it looks like they are using peoples poor knowledge of random (sequence /) number generators to gain access by way of poorly selected or re-used key material and nonces used in protocols and standards.

We also know from Bob Morris senior [1] who was one of the technical/scientific seniors in the NSA that "known plain text" is still of major interest to the NSA. And as we see with MS Office products, known plain text in very large quantities appear in nearly all user generated files.

There are various other predictors we can use for NSA behaviour, and if people care to read back on this blog various people have pointed out what the likes of the NSA and GCHQ et al have been upto for a number of years.

As has been seen the battle on crypto algorithms is over and the NSA kept winning untill it became clear they could not keep making the equivalent of lies to the politicos. But by then the game had moved on. In that respect nothing realy has changed. However whilst they are still winning the war the tide is turning against them and the technical distance between them and the open / academic community is closing if it has not closed in some areas.

However the NSA whilst not having a monopoly on mathmeticians and people with brains has a number of advantages over the open / academic community. One is funding that whilst not unlimited can certainly be used for what is in effect blue-sky research, whilst the academic community has to find it's funding in an open and accountable way and thus has to keep it's feet closer to the ground.

[1] http://www.ieee-security.org/Cipher/ConfReports/...