Question - seeding the hw pseudo random number generator

Question - seeding the hw pseudo random number generator

[Krzysztof Kozlowski]

Hi,

I looked at Exynos Pseudo Random Nubmer Generator driver
(drivers/char/hw_random/exynos-rng.c) and noticed that it always seeds
the device with jiffies.  Then I looked at few other drivers and found
that they do not seed themself (or at least I couldn't find this).

I think the hw_random API does not provide generic infrastructure for
seeding.

What is the preferred approach for seeding a PRNG device? Use jiffies or
a fixed value?

Or maybe the interface should be abandoned in favor of crypto API?

Best regards,
Krzysztof

Question - seeding the hw pseudo random number generator

[PrasannaKumar Muralidharan]

> I looked at Exynos Pseudo Random Nubmer Generator driver
> (drivers/char/hw_random/exynos-rng.c) and noticed that it always seeds
> the device with jiffies.  Then I looked at few other drivers and found
> that they do not seed themself (or at least I couldn't find this).

HW random interface is meant for true RNG, not pseudo RNG. Actually
PRNGs should use AF_ALG interface. I think exynos-rng.c should follow
the same.

> I think the hw_random API does not provide generic infrastructure for
> seeding.
>
> What is the preferred approach for seeding a PRNG device? Use jiffies or
> a fixed value?
>
> Or maybe the interface should be abandoned in favor of crypto API?

AF_ALG interface for rng does have seeding support. I think hw_random
does not provide seeding support intentionally as I understand that
True RNG need not require seeding (please correct me if I am wrong).

Regards,
PrasannaKumar

Question - seeding the hw pseudo random number generator

[Herbert Xu]

On Mon, Mar 20, 2017 at 12:19:32PM +0530, PrasannaKumar Muralidharan wrote:
>
> AF_ALG interface for rng does have seeding support. I think hw_random
> does not provide seeding support intentionally as I understand that
> True RNG need not require seeding (please correct me if I am wrong).

Yes.  We should be converting PRNGs in hwrng over to algif_rng.

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Question - seeding the hw pseudo random number generator

[Stephan Müller]

Am Montag, 20. M?rz 2017, 14:28:58 CET schrieb Herbert Xu:

Hi Herbert,

> On Mon, Mar 20, 2017 at 12:19:32PM +0530, PrasannaKumar Muralidharan wrote:
> > AF_ALG interface for rng does have seeding support. I think hw_random
> > does not provide seeding support intentionally as I understand that
> > True RNG need not require seeding (please correct me if I am wrong).
> 
> Yes.  We should be converting PRNGs in hwrng over to algif_rng.

IMHO this not only applies to the PRNGs in drivers/crypto (which should simply 
register with crypto_register_rngs) but also to ~/hacking/sources/linux/arch/
s390/crypto/prng.c which exports a /dev/prandom file.

For the seeding, it may make sense to follow the example given with crypto/
drbg.c using the add_random_ready_callback function.

Ciao
Stephan

Question - seeding the hw pseudo random number generator

[Harald Freudenberger]

On 03/20/2017 02:39 PM, Stephan M?ller wrote:
> Am Montag, 20. M?rz 2017, 14:28:58 CET schrieb Herbert Xu:
>
> Hi Herbert,
>
>> On Mon, Mar 20, 2017 at 12:19:32PM +0530, PrasannaKumar Muralidharan wrote:
>>> AF_ALG interface for rng does have seeding support. I think hw_random
>>> does not provide seeding support intentionally as I understand that
>>> True RNG need not require seeding (please correct me if I am wrong).
>> Yes.  We should be converting PRNGs in hwrng over to algif_rng.
> IMHO this not only applies to the PRNGs in drivers/crypto (which should simply 
> register with crypto_register_rngs) but also to ~/hacking/sources/linux/arch/
> s390/crypto/prng.c which exports a /dev/prandom file.
>
> For the seeding, it may make sense to follow the example given with crypto/
> drbg.c using the add_random_ready_callback function.
>
> Ciao
> Stephan
>

I'll have a look on it. Currently the s390/crypto/prng seeds itself with
an algorithm based on the jitter of the very fine granular hardware
clock of a s390 machine. There were some thoughts and measurements
by an mathematician which let to this algorithm. However, long-term
the s390 platform will provide some kind of true hardware random number
generator and the idea is to use this for seeding the prng.

regards
Harald Freudenberger

Question - seeding the hw pseudo random number generator

[Stephan Müller]

Am Donnerstag, 23. M?rz 2017, 09:03:23 CET schrieb Harald Freudenberger:

Hi Harald,

> I'll have a look on it. Currently the s390/crypto/prng seeds itself with
> an algorithm based on the jitter of the very fine granular hardware
> clock of a s390 machine. There were some thoughts and measurements
> by an mathematician which let to this algorithm.

It takes a page and simply writes 512 times the high-res time stamp using 
get_tod_clock_fast into it. Effectively it uses the same fundamental noise 
source as the jitterentropy. (A couple of months ago I had to perform an 
SP800-90B assessment on exactly that code path. :-) )

> However, long-term
> the s390 platform will provide some kind of true hardware random number
> generator and the idea is to use this for seeding the prng.

The question is just that it provides a device file nobody else provides. And 
the question is whether to consolidate it. If it is a DRNG, the discussion is 
about consolidating it behind AF_ALG. If it is an RNG with its own noise 
source (i.e. it provides entropic data by itself), it should rather be placed 
into drivers/char/hw_random and use the hw-random framework. This framework 
will also ensure that it may seed the /dev/random device kernel-internally.

Ciao
Stephan

Question - seeding the hw pseudo random number generator

[Krzysztof Kozlowski]

On Mon, Mar 20, 2017 at 09:28:58PM +0800, Herbert Xu wrote:
> On Mon, Mar 20, 2017 at 12:19:32PM +0530, PrasannaKumar Muralidharan wrote:
> >
> > AF_ALG interface for rng does have seeding support. I think hw_random
> > does not provide seeding support intentionally as I understand that
> > True RNG need not require seeding (please correct me if I am wrong).
> 
> Yes.  We should be converting PRNGs in hwrng over to algif_rng.

The actual hardware block can be seeded from true RNG (taking data
from thermal noise) so the solutions (if I understand correctly) for
exynos-rng might be:
1. Seed from internal TRNG making it a proper hwrandom device,
2. Convert to AF_ALG and seed with data from user-space through that
   interface.

Thanks for explanation, I'll queue it to my tasks list.

Best regards,
Krzysztof

Question - seeding the hw pseudo random number generator

[Corentin Labbe]

On Mon, Mar 20, 2017 at 09:28:58PM +0800, Herbert Xu wrote:
> On Mon, Mar 20, 2017 at 12:19:32PM +0530, PrasannaKumar Muralidharan wrote:
> >
> > AF_ALG interface for rng does have seeding support. I think hw_random
> > does not provide seeding support intentionally as I understand that
> > True RNG need not require seeding (please correct me if I am wrong).
> 
> Yes.  We should be converting PRNGs in hwrng over to algif_rng.
> 

Problem with this conversion, a huge regression for user space.
Using hwrng is simple as cat /dev/hwrng.
Using algif_rng via AF_ALG is ... unusable for the moment.
Perhaps creating an user space tool (prng-tool which provide a cat /dev/hwrng replacement) is mandatory before any convertion.

Regards

Question - seeding the hw pseudo random number generator

[Herbert Xu]

On Thu, Mar 23, 2017 at 09:23:07AM +0100, Corentin Labbe wrote:
> 
> Problem with this conversion, a huge regression for user space.
> Using hwrng is simple as cat /dev/hwrng.
> Using algif_rng via AF_ALG is ... unusable for the moment.
> Perhaps creating an user space tool (prng-tool which provide a cat /dev/hwrng replacement) is mandatory before any convertion.

Stephan may have a tool to do this.  Stephan?

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Question - seeding the hw pseudo random number generator

[Stephan Müller]

Am Donnerstag, 23. M?rz 2017, 10:44:06 CET schrieb Herbert Xu:

Hi Herbert,

> On Thu, Mar 23, 2017 at 09:23:07AM +0100, Corentin Labbe wrote:
> > Problem with this conversion, a huge regression for user space.
> > Using hwrng is simple as cat /dev/hwrng.
> > Using algif_rng via AF_ALG is ... unusable for the moment.
> > Perhaps creating an user space tool (prng-tool which provide a cat
> > /dev/hwrng replacement) is mandatory before any convertion.
> Stephan may have a tool to do this.  Stephan?

Creating such tool is more or less trivial. It simply requires the invocation 
of kcapi_rng_init, kcapi_rng_seed, kcapi_rng_generate and eventually 
kcapi_rng_destroy from [1]. I can write such a tool if requested.

I see one change we need to add to algif_rng.c: currently the caller must 
provide the specific name of the DRNG to be used. With such a tool, the caller 
does not care about the type of DRNG. Thus, rng_bind should be changed such 
that if name is NULL, it should use crypto_get_default_rng(). This would 
alleviate the caller from selecting "the right" DRNG.

[1] http://www.chronox.de/libkcapi.html

Ciao
Stephan

Question - seeding the hw pseudo random number generator

[Stephan Müller]

Am Donnerstag, 23. M?rz 2017, 10:44:06 CET schrieb Herbert Xu:

Hi Herbert,

> On Thu, Mar 23, 2017 at 09:23:07AM +0100, Corentin Labbe wrote:
> > Problem with this conversion, a huge regression for user space.
> > Using hwrng is simple as cat /dev/hwrng.
> > Using algif_rng via AF_ALG is ... unusable for the moment.
> > Perhaps creating an user space tool (prng-tool which provide a cat
> > /dev/hwrng replacement) is mandatory before any convertion.
> Stephan may have a tool to do this.  Stephan?

Here is a suggestion for such a tool that I could add to libkcapi. Naturally, 
this code is only a demonstrator which lacks some features.

Ciao
Stephan
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Question - seeding the hw pseudo random number generator

[Stephan Müller]

Am Donnerstag, 23. M?rz 2017, 10:44:06 CEST schrieb Herbert Xu:

Hi Herbert,

> On Thu, Mar 23, 2017 at 09:23:07AM +0100, Corentin Labbe wrote:
> > Problem with this conversion, a huge regression for user space.
> > Using hwrng is simple as cat /dev/hwrng.
> > Using algif_rng via AF_ALG is ... unusable for the moment.
> > Perhaps creating an user space tool (prng-tool which provide a cat
> > /dev/hwrng replacement) is mandatory before any convertion.
> Stephan may have a tool to do this.  Stephan?

I added the application kcapi-rng to HEAD of [1]. Create the application with 
the --enable-kcapi-rngapp configure option.

$ kcapi-rng 

Kernel Crypto API Random Number Gatherer

Kernel Crypto API interface library version: libkcapi pre-release 0.13.1
Reported numeric version number 130080

Usage:
        -b --bytes <BYTES>      Number of bytes to generate (required option)
        -h --help       This help information
           --version    Print version
        -v --verbose    Verbose logging, multiple options increase verbosity

Data provided at stdin is used to seed the DRNG

[1] https://github.com/smuellerDD/libkcapi/

Ciao
Stephan