Re: switch arc4random to chacha

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On 05/30/14 08:41, Konstantin Belousov wrote:
> On Thu, May 29, 2014 at 09:04:11PM -0400, Ted Unangst wrote:
>> This syncs libc arc4random.c with OpenBSD, mostly to change the 
>> implementation to ChaCha20.
>> 
>> I removed the more complicated seed fetching code and changed it 
>> to just sysctl(). A quick check revealed that the FreeBSD kernel 
>> supports this for at least five years now. It's much simpler to 
>> use code that always works instead of a series of untested 
>> fallbacks that are even less likely to work.
>> 
>> Also removes the addrandom interface as a useless complication. 
>> If the kernel is incapable of properly seeding arc4random, 
>> application code can't do any better.
>> 
>> Unfortunately, I don't have any FreeBSD systems running at the 
>> moment, so I can't make any promises that this will even
>> compile, but it passed the eyeball test.
> 
> Am I right that the patch removes arc4random_stir and 
> arc4random_addrandom symbols ?  If yes, this is done incorrect,
> and it in fact is disallowed, since it breaks ABI.
> 
> The compat shims must be provided, possibly issuing a warning, and 
> default version for the symbols must be removed to prevent linking 
> new consumers.

Actually I have a WIP patchset for this at:

	https://github.com/delphij/freebsd/compare/featurefork;chacha20

It provided compatibility shims for arc4random_stir and
arc4random_addrandom that logs the event for each process once.

Another difference (which I haven't seek for review and would like to
see criticizes) from OpenBSD is that my version have added threading
support.  What it does is that the system will create a maximum of CPU
number's random states and use the states in a LIFO manner, new state
is created on demand when a contention happens and the CPU number
limit haven't been reached.

(I made a further tweak which basically do #define arc4random_stir()
and #define arc4random_addrandom(a,b) in stdlib.h.  This allows
existing applications that insists arc4random_stir() on FreeBSD to
compile -- is there a way to give a compile time warning?)

One thing I haven't done yet is to make the kernel portion of
arc4random() (i.e. kern.arand) to use Chacha20.

Cheers,
- -- 
Xin LI <delphij@delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
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