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Date: Wed, 17 Jun 2015 11:10:43 +0200
From: Pierre Schweitzer <pierre@...ctos.org>
To: oss-security@...ts.openwall.com
Subject: Re: PostgreSQL - Predictable cancel key

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OK, got it. Thanks for the extra details!

Cheers,

On 06/16/2015 01:04 PM, Michael Samuel wrote:
> Hi,
> 
> On 16 June 2015 at 20:15, Pierre Schweitzer <pierre@...ctos.org>
> wrote:
> 
>> Well, I've thought about it, but that's still one million seeds
>> and the cancel key you're looking for might have been generated
>> after several random() call. So, that means perhaps 10 millions
>> values to explore? (If we make the hypothesis that for a given
>> initialization, it will only draw 10 PRN)
>> 
> 
> This is CPU, maybe GPU territory. 2^15-2 * 10m =~ 2^38 work
> offline.
> 
> 
>> How relevant would still be your cancel key once you found it?
> 
> 
> In the postmaster mainloop:
> 
> ConnCreate() RandomSalt() -- the md5Salt craziness in the original
> post BackendStartup() MyCancelKey = PostmasterRandom();
> 
> No other calls to random(), srandom() that I can see, and the other
> calls to PostmasterRandom() are generating cancel keys for worker
> procs.
> 
> So if you brute the md5Salt you have a pretty good chance of
> guessing something that was/is/will be a cancel key of another
> session.
> 
> Regards, Michael
> 


- -- 
Pierre Schweitzer <pierre@...ctos.org>
System & Network Administrator
Senior Kernel Developer
ReactOS Deutschland e.V.
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