lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Mon, 10 Aug 2020 16:48:29 +0200
From:   Willy Tarreau <w@....eu>
To:     David Laight <David.Laight@...lab.com>
Cc:     George Spelvin <lkml@....org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "aksecurity@...il.com" <aksecurity@...il.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "Jason@...c4.com" <Jason@...c4.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "tytso@....edu" <tytso@....edu>,
        "lkml.mplumb@...il.com" <lkml.mplumb@...il.com>,
        "stephen@...workplumber.org" <stephen@...workplumber.org>,
        "fw@...len.de" <fw@...len.de>
Subject: Re: [DRAFT PATCH] random32: make prandom_u32() output unpredictable

On Mon, Aug 10, 2020 at 12:01:11PM +0000, David Laight wrote:
> >  /*
> >   * On 32-bit machines, we use HSipHash, a reduced-width version of SipHash.
> >   * This is weaker, but 32-bit machines are not used for high-traffic
> > @@ -375,6 +377,12 @@ static u32 siprand_u32(struct siprand_state *s)
> >  {
> >  	unsigned long v0 = s->v[0], v1 = s->v[1], v2 = s->v[2], v3 = s->v[3];
> > 
> > +	if (++s->count >= 8) {
> > +		v3 ^= s->noise;
> > +		s->noise += random_get_entropy();
> > +		s->count = 0;
> > +	}
> > +
> 
> Using:
> 	if (s->count-- <= 0) {
> 		...
> 		s->count = 8;
> 	}
> probably generates better code.
> Although you may want to use a 'signed int' instead of 'unsigned long'.

Yeah I know, it's just because I only slightly changed the previous code
there. I had an earlier version that kept the rand state fully padded
when storing intermediate values. That's among the final cleanups I'll
bring if we go down that route.

Thanks!

Willy

Powered by blists - more mailing lists