On Wed, 2014-03-05 at 16:11 -0500, Jason Cooper wrote: > > In other words, if there are 4096 bits of "unknownness" in X to start > > with, and I can get those same 4096 bits of "unknownness" back by > > unmixing X' and Y, then there must still be 4096 bits of "unknownness" > > in X'. If X' is 4096 bits long, then we've just proven that > > reversibility means the attacker can know nothing about the contents of > > X' by his choice of Y. > > Well, this reinforces my comfortability with loadable modules. The pool > is already initialized by the point at which the driver is loaded. > > Unfortunately, any of the drivers in hw_random can be built in. When > built in, hwrng_register is going to be called during the kernel > initialization process. In that case, the unknownness in X is not 4096 > bits, but far less. Also, the items that may have seeded X (MAC addr, > time, etc) are discoverable by a potential attacker. This is also well > before random-seed has been fed in. To which I would respond.. so? If the pool is in an attacker-knowable state at early boot, adding attacker-controlled data does not make the situation any worse. In fact, if the attacker has less-than-perfect control of the inputs, mixing more things in will make things exponentially harder for the attacker. Put another way: mixing can't ever removes unknownness from the pool, it can only add more. So the only reason you should ever choose not to mix something into the pool is performance. -- Mathematics is the supreme nostalgia of our time. -- 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
