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  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Wed, 5 Mar 2014 17:34:48 -0800
From:	Kees Cook <>
To:	Matt Mackall <>
Cc:	Jason Cooper <>,
	"Theodore Ts'o" <>,
	LKML <>,
	Herbert Xu <>,
	Rusty Russell <>,
	Satoru Takeuchi <>,
	linux-crypto <>,
	Andrew Morton <>
Subject: Re: [PATCH][RESEND 3] hwrng: add randomness to system from rng sources

On Wed, Mar 5, 2014 at 4:52 PM, Matt Mackall <> wrote:
> On Wed, 2014-03-05 at 16:11 -0500, Jason Cooper wrote:
>> > In other words, if there are 4096 bits of "unknownness" in X to start
>> > with, and I can get those same 4096 bits of "unknownness" back by
>> > unmixing X' and Y, then there must still be 4096 bits of "unknownness"
>> > in X'. If X' is 4096 bits long, then we've just proven that
>> > reversibility means the attacker can know nothing about the contents of
>> > X' by his choice of Y.
>> Well, this reinforces my comfortability with loadable modules.  The pool
>> is already initialized by the point at which the driver is loaded.
>> Unfortunately, any of the drivers in hw_random can be built in.  When
>> built in, hwrng_register is going to be called during the kernel
>> initialization process.  In that case, the unknownness in X is not 4096
>> bits, but far less.  Also, the items that may have seeded X (MAC addr,
>> time, etc) are discoverable by a potential attacker.  This is also well
>> before random-seed has been fed in.
> To which I would respond.. so?
> If the pool is in an attacker-knowable state at early boot, adding
> attacker-controlled data does not make the situation any worse. In fact,
> if the attacker has less-than-perfect control of the inputs, mixing more
> things in will make things exponentially harder for the attacker.
> Put another way: mixing can't ever removes unknownness from the pool, it
> can only add more. So the only reason you should ever choose not to mix
> something into the pool is performance.

Excellent. So it sounds like you're okay with my original patch as-is?


Kees Cook
Chrome OS Security
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

Powered by blists - more mailing lists