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Date: Wed, 06 May 2015 23:10:41 +0200
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To: Albert Casademont <albertcasademont@gmail.com>
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Subject: Re: [PHP-DEV] password_hash() best practices
From: cmbecker69@gmx.de (Christoph Becker)

Albert Casademont wrote:

> The iteration count is very different because in bcrypt it's not an
> iteration count number at all, it's a "cost". And it's kinda exponential: a
> hash with a cost of 11 is twice as hard to compute than that of a 10. At
> our company we are using a cost of 11 right now, which means a hash is
> computed in around 100ms in a Core i7

A cost of N means 2**N rounds (i.e. iteration counts).  Therefore a cost
of 10 means 1024 rounds.  However, the complexity of the underlying
primitive should affect what is to be considered a reasonable iteration
count.  For instance, CRYPT_BLOWFISH has a minimum of 16 rounds, while
CRYPT_SHA256 has a minimum of 1000.

-- 
Christoph M. Becker