Hi Sandy, Ted, (this is a reply to [3])
I prepared a new release of the CPU Jitter RNG available at [1]. The core of the RNG remains unchanged. However, there are the following changes: - addition of a patch to integrate the RNG into /dev/random as explained in appendix B.3 of [2], although the long-term goal of the RNG is rather the integration into the kernel crypto API when considering the Linux kernel as outlined in appendix B.1 of [2] - ensure that the code is compiled without optimization based on the reasons outlined in section 5.1 of [2] - addition of chapter 5.1 to [2] explaining how the entropy is collected - additional code to execute the CPU Jitter RNG on different OSes (specifically AIX, MacOS and z/OS -- other Unixes are good without additional changes) >On Tue, May 21, 2013 at 3:01 PM, Theodore Ts'o <ty...@mit.edu> wrote: >> I continue to be suspicious about claims that userspace timing >> measurements are measuring anything other than OS behaviour. > >Yes, but they do seem to contain some entropy. See links in the >original post of this thread, the havege stuff and especially the >McGuire et al paper. With the initially shown implementation and documentation I did not really show that sufficient entropy is gathered from the CPU execution jitter -- i.e. that there is unpredictable jitter in the execution time. With a new test I now closed that hole. The newly added test measures the entropy gathered during execution jitter collection, i.e. heart of the RNG in terms of how much statistical entropy it provides. The description of the test is given in section 5.1 of [2]. To ensure that the statistical entropy measurements are indeed showing the information theoretical entropy, section 4.4 of [2] outlines that patterns are not identified in the output of the RNG which would diminish the information theoretical entropy compared to the statistical entropy. That test was then executed on about 200 different systems with the results given in appendix F of [2]. The table stated there supported by the many graphs demonstrates that the CPU Jitter random number generator delivers high-quality entropy on: - a large range of CPUs ranging from embedded systems of MIPS and ARM CPUs, covering desktop systems with AMD and Intel x86 32 bit and 64 bit CPUs up to server CPUs of Intel Itanium, Sparc, POWER and IBM System Z; - a large range of operating systems: Linux (including Android), OpenBSD, FreeBSD, NetBSD, AIX, OpenIndiana (OpenSolaris), AIX, z/OS; - a range of different compilers: GCC, Clang and the z/OS C compiler. The test results show an interesting yet common trend -- i.e. common for the different CPU types: the newer the CPU is, the more CPU execution time jitter is present. [2] appendix F.37 contains entropy measurements on different operating systems on the very same hardware, indicating that the jitter measurements are present regardless of the OS. With the test results, Ted's concerns should be removed. [...] >> For devices like Linux routers, what we desperately need is hardware >> assist; [or] mix >> in additional timing information either at kernel device driver >> level, >> or from systems such as HAVEGE. The concern with HAVEGE is that it is very complex. The implementation is far from being straight forward. >> >> What I'm against is relying only on solutions such as HAVEGE or >> replacing /dev/random with something scheme that only relies on CPU >> timing and ignores interrupt timing. > >My question is how to incorporate some of that into /dev/random. >At one point, timing info was used along with other stuff. Some >of that got deleted later, What is the current state? Should we >add more? Please see the suggestion for an integration with /dev/random given in appendix B.3 of [2]. The source code for the integration is given in patches/linux-3.9-random.patch which is described in patches/README. The patch only utilizes the CPU Jitter RNG when the entropy in the entropy pool falls below the low threshold, i.e. when no entropy from other sources is present. [1] http://www.chronox.de/jent/jitterentropy-20130818.tar.bz2 [2] http://www.chronox.de/jent/doc/CPU-Jitter-NPTRNG.pdf [3] http://www.gossamer-threads.com/lists/linux/kernel/1716565#1716565 Ciao Stephan -- | Cui bono? | -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
