Stephan Mueller wrote: > Am Donnerstag, 7. November 2013, 02:03:57 schrieb Nicholas Mc Guire: >> On Wed, 06 Nov 2013, Stephan Mueller wrote: >>> Besides, how on earth shall an attacker even gain knowledge about the >>> state of the CPU or disable CPU mechanisms? Oh, I forgot, your NSA >>> guy. But if he is able to do that, all discussions are moot because >>> he simply disables any noise sources by flipping a bit, reads the >>> memory that is used to hold the state of the RNG or just overwrites >>> the memory locations where data is collected, because the general >>> protection mechanisms offered by the kernel and the underlying >>> hardware are broken. >> >> No need to gain knowledge of the internal CPU state itt would be >> sufficient to be able to put the CPU in a sub-state-space in which >> the distribution is shifted. it may be enough to reduce the truely >> random bits of some key only by a few bits to make it suceptible to >> brute force attacks. > > Note, the proposed RNG contains an unbias operation (the Von-Neumann > unbiaser) which is proven to remove any bias when it is established that > the individual observations are independent. And the way the > observations are generated ensures that they are independent. "Independent" does not mean that your own code avoids reusing data from the previous loop iteration; it means that the _entire_ process that generates the bits is not affected by any memory of the past. The observations are derived from the internal CPU state, which is *not* reset between measurements. Regards, Clemens -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
