Re: [PATCH] using arc4random for strong randomness matters.

[Stephen Frost]

David, all,

* David CARLIER (devne...@gmail.com) wrote:
> > IIUC, what this code actually does is reseed itself from /dev/urandom
> > every so often and work from a PRNG in between.  That's not a layer that
> > we need, because the code on top is already designed to cope with the
> > foibles of /dev/urandom --- or, to the extent it isn't, that's something
> > we have to fix anyway.  So it seems like having this optionally in place
> > just reduces what we can assume about the randomness properties of
> > pg_strong_random output, which doesn't seem like a good idea.
>
> That I admit these are valid points.

Based on the discussion, it looks like this patch should be marked as
'Rejected', so I've gone ahead and done that.

We can reopen it if that's incorrect for some reason.

Thanks!

Stephen


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Re: [PATCH] using arc4random for strong randomness matters.

[David CARLIER]

> I dunno, it seems like this is opening us to a new set of portability
> hazards (ie, sub-par implementations of arc4random) with not much gain to
> show for it.
>

Hence I reduced to three platforms only.

>
> IIUC, what this code actually does is reseed itself from /dev/urandom
> every so often and work from a PRNG in between.  That's not a layer that
> we need, because the code on top is already designed to cope with the
> foibles of /dev/urandom --- or, to the extent it isn't, that's something
> we have to fix anyway.  So it seems like having this optionally in place
> just reduces what we can assume about the randomness properties of
> pg_strong_random output, which doesn't seem like a good idea.
>
> That I admit these are valid points.
Cheers.


> regards, tom lane
>

Re: [PATCH] using arc4random for strong randomness matters.

[Andres Freund]

On November 22, 2017 8:51:07 AM PST, ilm...@ilmari.org wrote:
>If what is wanted is something more like /dev/urandom, one can call
>getentropy(2) (or on Linux, getrandom(2)) directly, which avoids having
>to open the device file each time.

What does that buy us for our usages?

Andres
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

Re: [PATCH] using arc4random for strong randomness matters.

[Dagfinn Ilmari Mannsåker]

Tom Lane  writes:

> David CARLIER  writes:
>> I m not against as such that depends of the implementation but I ve seen in
>> quick glance it s RC4 ?

arc4random uses ChaCha20 since OpenBSD 5.5 (and libbsd 0.8.0 on Linux).
It uses getentropy(2) to seed itself at regular intervals and at fork().

http://man.openbsd.org/arc4random.3

> More generally, why should we bother with an additional implementation?
> Is this better than /dev/urandom, and if so why?

If what is wanted is something more like /dev/urandom, one can call
getentropy(2) (or on Linux, getrandom(2)) directly, which avoids having
to open the device file each time.

http://man.openbsd.org/getentropy.2
https://manpages.debian.org/stretch/manpages-dev/getrandom.2.en.html

- ilmari
-- 
"The surreality of the universe tends towards a maximum" -- Skud's Law
"Never formulate a law or axiom that you're not prepared to live with
 the consequences of."  -- Skud's Meta-Law

Re: [PATCH] using arc4random for strong randomness matters.

[Andres Freund]

Hi,

Please don't top-quote on postgres mailing lists.


On 2017-11-22 16:16:35 +, David CARLIER wrote:
> > David CARLIER  writes:
> > > I m not against as such that depends of the implementation but I ve seen
> > in
> > > quick glance it s RC4 ?
> >
> > More generally, why should we bother with an additional implementation?
> > Is this better than /dev/urandom, and if so why?

> Basically the call never fails, always generating high quality random data
> (especially the implementations based on Chacha* family, RC4 has
> predictability issues), there is no need of a file descriptor.

I don't really see much benefit in those properties for postgres
specifically. Not needing an fd is nice for cases where you're not
guaranteed to have access to a filesystem, but postgres isn't going to
work in those cases anyway.

Greetings,

Andres Freund

Re: [PATCH] using arc4random for strong randomness matters.

[David CARLIER]

Basically the call never fails, always generating high quality random data
(especially the implementations based on Chacha* family, RC4 has
predictability issues), there is no need of a file descriptor.

On 22 November 2017 at 16:06, Tom Lane  wrote:

> David CARLIER  writes:
> > I m not against as such that depends of the implementation but I ve seen
> in
> > quick glance it s RC4 ?
>
> More generally, why should we bother with an additional implementation?
> Is this better than /dev/urandom, and if so why?
>
> regards, tom lane
>

Re: [PATCH] using arc4random for strong randomness matters.

[Tom Lane]

David CARLIER  writes:
> I m not against as such that depends of the implementation but I ve seen in
> quick glance it s RC4 ?

More generally, why should we bother with an additional implementation?
Is this better than /dev/urandom, and if so why?

regards, tom lane

Re: [PATCH] using arc4random for strong randomness matters.

[David CARLIER]

I m not against as such that depends of the implementation but I ve seen in
quick glance it s RC4 ?

Regards.

On 22 November 2017 at 15:37, David Fetter  wrote:

> On Tue, Nov 21, 2017 at 12:08:46PM +, David CARLIER wrote:
> > Hello,
> >
> > This is my first small personal contribution.
> >
> > Motivation :
> > - Using fail-safe, file descriptor free solution on *BSD and Darwin
> system
> > - Somehow avoiding at the moment FreeBSD as it still uses RC4 (seemingly
> > updated to Chacha20 for FreeBSD 12.0 and eventually backported later on).
> > - For implementation based on Chacha* it is known to be enough fast for
> the
> > purpose.
> > - make check passes.
> >
> > Hope it is good.
> >
> > Thanks in advance.
>
> This is neat.  Apparently, it's useable on Linux with a gizmo called
> libbsd.  Would it be worth it to test for that library on that
> platform?
>
> Best,
> David.
> --
> David Fetter  http://fetter.org/
> Phone: +1 415 235 3778
>
> Remember to vote!
> Consider donating to Postgres: http://www.postgresql.org/about/donate
>

Re: [PATCH] using arc4random for strong randomness matters.

[David Fetter]

On Tue, Nov 21, 2017 at 12:08:46PM +, David CARLIER wrote:
> Hello,
> 
> This is my first small personal contribution.
> 
> Motivation :
> - Using fail-safe, file descriptor free solution on *BSD and Darwin system
> - Somehow avoiding at the moment FreeBSD as it still uses RC4 (seemingly
> updated to Chacha20 for FreeBSD 12.0 and eventually backported later on).
> - For implementation based on Chacha* it is known to be enough fast for the
> purpose.
> - make check passes.
> 
> Hope it is good.
> 
> Thanks in advance.

This is neat.  Apparently, it's useable on Linux with a gizmo called
libbsd.  Would it be worth it to test for that library on that
platform?

Best,
David.
-- 
David Fetter  http://fetter.org/
Phone: +1 415 235 3778

Remember to vote!
Consider donating to Postgres: http://www.postgresql.org/about/donate

[PATCH] using arc4random for strong randomness matters.

[David CARLIER]

Hello,

This is my first small personal contribution.

Motivation :
- Using fail-safe, file descriptor free solution on *BSD and Darwin system
- Somehow avoiding at the moment FreeBSD as it still uses RC4 (seemingly
updated to Chacha20 for FreeBSD 12.0 and eventually backported later on).
- For implementation based on Chacha* it is known to be enough fast for the
purpose.
- make check passes.

Hope it is good.

Thanks in advance.


0001-Using-arc4random-API-for-strong-randomness-if-availa.patch
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