On Fri, Dec 27, 2019 at 11:29:22AM +0100, Stephan Mueller wrote: > > My definition of TRNG is identical to the German AIS 31 and I guess identical > to your definition of a TRNG. > > A TRNG will produce an amount of random data that is equal to the amount of > "fresh" entropy that was provided by the noise source. I.e. it should be > identical to the blocking_pool behavior. This begs the question of determining: (a) how much "fresh entropy" you can actually get from a noise source, (b) at what rate the "fresh entropy" is arriving, and (c) what assurance(s) you have that the noise source is actually working correctly. You can't make those assurances from software alone; it needs to be an aspect of holistic design of the hardware's design; the supply chain, and the software. So if we are going to claime that we have something like GRND_TRUERANDOM or /dev/trandom, or whatever, it needs to work on IOT devices running ARM, RISC-V, MIPS, PowerPC, x86. Some of these architectures have no instruction reordering and are stupid simple; some of these hardware platforms may have no high-resolution clock or cryptographic instructions. In addition, if you use a hardware device which is USB attached, how does the kernel know that it really is the device that you think it is? The only way you know that a ChaosKey is a ChaosKey is by its USB vendor and product id --- which can be easily forged by an attacker, either in the supply chain or delivery path, or who walks up to the laptop, yanks out the ChaosKey and replaces it with a "PutinKey" or a "NSAKey". So creating somethinig which shows up as "true random number generator" as a generic Linux concept seems to me to be fraught endeavor, and I'm not at all convince people need it. > - add a new GRND_TRUERANDOM flag to getrandom(2) which allows access to the > TRNG. Andy did not like it because he mentioned that it may be misused since > the syscall is unprivileged. Even if we could solve the "how the hell can the kernel guarantee that the noise source is legitimate" problem in a general way that works across all of the architectures, we still have the problem that everyone thinks they need "the good stuff". Suppose the system call was privileged and "true randomness" could only be accessed as root. What would happen? Application programmers would give instructions requiring that their application be installed as root to be more secure, "because that way you can get access the _really_ good random numbers". So let's take a step back and ask the question: "Exactly what _value_ do you want to provide by creating some kind of true random interface?" What does this enable? What applications does this really help? As I thought while watching the latest Star Wars movie: Why? Why? Whywhywhy? - Ted
