On 28-06-18, 17:04, Timur Tabi wrote: > On Thu, Jun 21, 2018 at 6:53 AM, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Jun 21, 2018 at 02:27:10PM +0300, Stanimir Varbanov wrote: > > > So does it generate one bit of output for each bit of hardware- > > generated entropy like /dev/random? Or does it use a hardware- > > generated seed to power a PRNG? > > I have some information to answer this question, although I'm not sure > I can give a strict "yes/no" answer. > > There are a couple relevant documents: > > https://www.qualcomm.com/news/onq/2014/11/07/cryptographic-module-snapdragon-805-fips-140-2-certified > https://csrc.nist.gov/CSRC/media/projects/cryptographic-module-validation-program/documents/security-policies/140sp2944.pdf > > I also got response from a Qualcomm employee: > > "The Qualcomm random number generator used in Snapdragon chips > consists of an entropy source coupled with the HASH-DRBG deterministic > random bit generator from NIST Special Publication 800-90A, using > SHA-256 as the hash function. > > The entropy source is based on sampled ring oscillators. Four ring > oscillators are used to provide high assurance of adequate entropy. > The entropy from the ring oscillators is conditioned using the > 'derivation function' specified by NIST Special Publication 800-90A. > The conditioned entropy is essentially perfect fully entropic data. > It is used both to seed and to periodically reseed the DRGB." > > My understanding is that the PRNG is a real entropy source with some > logic used to normalize the values. To quote: "No RNG uses data > directly from the entropy source; bits in the output are likely > correlated and unlikely to occur with 50% probability. The entropy > post-processing is designed to turn dirty data in clean data." > > Based on the above, it seems to me that the Qualcomm PRNG qualifies as > a real hardware RNG and porting to algif_rng is not the correct path. I think Stan did bring this point earlier that PRNG is compliant to FIPS-140-2. So it can be used by rng clients for various purposes but should not be fed to dev/random as the hw_random does. Herbert, can you please confirm.. -- ~Vinod
