phc-discussions - Re: [PHC] RE: [FORGED] [PHC] Argon2 using memset still

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Date: Mon, 31 Aug 2015 14:53:52 +0200
From: Dmitry Khovratovich <khovratovich@...il.com>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: Re: [PHC] RE: [FORGED] [PHC] Argon2 using memset still

Yes, it almost like that now, but as Samuel Neves pointed out, it seems
there are few compilers (if any) that support memset_s. Visual Studio 2013
does not know about it, for example.

On Mon, Aug 31, 2015 at 1:53 PM, Peter Gutmann <pgut001@...auckland.ac.nz>
wrote:

> Bill Cox <waywardgeek@...il.com> writes:
>
> >g++ has a habit of optimizing calls to memset away.  I doubt that Argon2
> >succeed in it's attempts to clear memory.  I copied this function from
> Blake2:
>
> You could also use environment-specific functions to do this:
>
> #if defined( _MSC_VER ) && VC_GE_2005( _MSC_VER )
>   /* This is just a mapping to RtlSecureZeroMemory() (via WinBase.h) which
>      is implemented as inline code implementing a loop on a pointer
> declared
>          volatile, but unlike the corresponding RtlZeroMemory() there's a
>          contract that this will always zeroise memory even in the face of
>          compiler changes that would otherwise optimise away the access */
>   #define zeroise( memory, size )       SecureZeroMemory( memory, size )
> #elif defined( __STDC_LIB_EXT1__ )
>   /* C11 defines a function memset_s() that guarantees that it won't be
>          optimised away, although this is quite well obfuscated in the
> spec,
>          "the memory indicated by [the memset parameters] may be
> accessible in
>          the future and therefore must contain the values indicated by [the
>          value to set]", hopefully the implementers will know that this
> equates
>          to "the memset_s() call can't be optimised away" */
>   #define zeroise( memory, size )       memset_s( memory, size, 0, size )
> #elif defined( __OpenBSD__ )
>   /* The OpenBSD folks defined their own won't-be-optimised-away bzero()
>          function */
>   #define zeroise( memory, size )       explicit_bzero( memory, size )
> #else
>   #define zeroise( memory, size )       memset( memory, 0, size )
> #endif /* Systems with distinct zeroise functions */
>
> Peter.
>
>


-- 
Best regards,
Dmitry Khovratovich

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