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Date: Wed, 31 Jul 2013 06:11:51 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: Parallella: bcrypt

Katja,

On Tue, Jul 30, 2013 at 06:40:02PM +0400, Solar Designer wrote:
> Savings may also be possible on Epiphany side by only reading keys
> or/and salt from external memory if the corresponding component has
> changed from the previous call.  To achieve this, maybe you need to use
> a struct like this:
> 
> struct {
> 	char keys_changed;
> 	char salt_changed;
> 	... salt;
> 	... keys;
> }
> 
> and always transfer the portion of it containing the *_changed flags,
> plus as much more data as you need to cover the actually changed
> components.

In fact, since at least one of "salt" or "keys" should change between
crypt_all() calls almost all of the time, and since we prefer to do just
one transfer, we will always be transferring the "salt".  Thus, the
salt_changed flag's only use is to save on reading the salt from
external memory on the Epiphany side if the salt has not changed.  Other
than that, you can always transfer the salt from the host.

Alexander

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