Re: Zeroization and compiler optimization

From	Beloumi <beloumi@riseup.net>
Newsgroups	comp.lang.java.security
Subject	Re: Zeroization and compiler optimization
Date	2015-06-12 09:34 +0200
Organization	news.netcologne.de
Message-ID	<mle214$4ca$1@newsreader4.netcologne.de> (permalink)
References	<m8br50$a9j$1@newsreader4.netcologne.de> <4knliqvbk6hc$.dlg@kimmeringer.de> <m8gifi$l9e$1@newsreader4.netcologne.de>

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Am 06.01.2015 um 12:55 schrieb Beloumi:
> Am 05.01.2015 um 13:36 schrieb Lothar Kimmeringer:
>> Beloumi wrote:
>>
>>> Sensitive data like keys and passwords should be zeroized immediately
>>> which is usually done by Arrays.fill(...).
>>> A compiler may treat this as dead code and it may be eliminated by an
>>> optimization.
>>> Does anybody knows if this is the case for common Java compilers like
>>> javac, ejc... ?
>>
>> You can try it out by giving the created byte-code to a decompiler.
>> I don't expect that to happen but would be a bit concerned about
>> the Hotspot during runtime. This might throw out that particular
>> part of the code since it's analyzed to be dead.
>>
>>
>> Regards, Lothar
>>
> Thanks for the hint. You're right. The bytecode compiler might not be
> the most problematic point for zeroization. The optimization in Hotspot
> might be “better” than others, but as I know all JIT-compilers can do
> dead code elimination. Is there also a way to figure out if they do?
> Beloumi
> 
For those who are interested... a late update:
I checked javac and eclipse jar compiler by decompiling the code. They
do not eliminate Arrays.fill().
I then checked Hotspot by comparing the time with and without filling
large Arrays. The execution time without these fillings is significantly
shorter, so Hotspot also does not eliminate this code.
I also checked a code which was optimized by ProGuard (Obfuscator) with
this method and the arrays are still filled.
So, false alarm... As I can see redundant code like zeroization is not
eliminated in normal use cases.
Beloumi

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Thread

Zeroization and compiler optimization Beloumi <beloumi@riseup.net> - 2015-01-04 17:52 +0100
  Re: Zeroization and compiler optimization Lothar Kimmeringer <news200709@kimmeringer.de> - 2015-01-05 13:36 +0100
    Re: Zeroization and compiler optimization Beloumi <beloumi@riseup.net> - 2015-01-06 12:55 +0100
      Re: Zeroization and compiler optimization Beloumi <beloumi@riseup.net> - 2015-06-12 09:34 +0200
        Re: Zeroization and compiler optimization Mike Amling <mamling@chaff.us> - 2015-07-06 10:06 -0500
          Re: Zeroization and compiler optimization Beloumi <beloumi@riseup.net> - 2015-07-06 23:24 +0200

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