As you know in the past few weeks it has emerged that NIST/NSA have been involved in weakening encryption standards over a long period of time so that they can retain the ability to break encryption used by corporations and the general public. We've already seen evidence of that with the Dual_EC_DRBG which has been recently disavowed by NIST after public outcry. That's probably a red herring, I think there's another smoking gun here.
I want to highlight a particular issue in the Advanced Encryption Standard process. The Rijndael algorithm had the option of block sizes of 128, 192 or 256 bits to match the key sizes. When that algorithm was decided as the winner, NIST went away and then defined a "restricted" block size of 128 bits for AES. Apparently that was what the spec called for in the first place.
However that doesn't make sense. If you were concerned about security, why would you have a 256 bit key size, but not have a matching block size? It would appear to be more secure to keep them at the same length. For example, a modern cipher like Threefish which has key sizes of 256, 512 or 1024 bits, also has matching block sizes of 256, 512 or 1024 bits.
Can the overall security of AES with a 256 bit key be reduced from 2256 to 2128 by attacking the lower block size?
Could that be combined that with various other attacks on AES which would reduce the 2128 bit security to even less e.g. 2100 bits?
Now that commercial quantum computers are viable (just one D-Wave Vesuvius is ranked in the top 10 of the TOP500 list), and assuming the NSA have taken advantage of that and constructed a quantum cluster in the basement of Fort Meade/Utah data center, if they employed Grover's algorithm which runs in O(N1/2) time, would that reduce the security of AES to 264 for all key sizes or worse 250 with attacks?
https://en.wikipedia.org/wiki/Advanced_Encryption_Standard https://en.wikipedia.org/wiki/Dual_EC_DRBG#Controversy http://www.gizmag.com/d-wave-quantum-computer-supercomputer-ranking/27476/ https://www.scientificamerican.com/article.cfm?id=google-nasa-snap-up-quantum-computer-dwave-two https://dwave.wordpress.com/2011/12/01/vesuvius-a-closer-look-512-qubit-processor-gallery/ http://www.wired.com/wiredenterprise/2013/06/d-wave-quantum-computer-usc/ http://arstechnica.com/security/2013/09/nsas-pipe-dream-weakening-crypto-will-only-help-the-good-guys/ https://en.wikipedia.org/wiki/Grover%27s_algorithm https://en.wikipedia.org/wiki/Threefish