Re: scrypt Internet Draft

[Solar Designer <solar@openwall.com>]

On Thu, Nov 01, 2012 at 09:32:23PM +0400, Solar Designer wrote:
> On Tue, Sep 18, 2012 at 05:05:13PM +0200, Simon Josefsson wrote:
> > Sorry, the repository was renamed...  see here instead:
> > 
> > https://www.gitorious.org/scrypt/scrypt-unix-crypt/blobs/master/unix-scrypt.txt
> 
> OK, here's a proposed encoding:
> 
> $7$Nrrrrrpppppsalt$hash
> 
> "N" is one base 64 character for log2(N)
> "rrrrr" is little-endian encoding of r (30 bits)
> "ppppp" is little-endian encoding of p (30 bits)

BTW, the current implementation of scrypt limits r*p to 30 bits, which
matches the above well.  We may use a more compact encoding since at
most one of r or p will fully use the 30 bits at once, but this might
not be worth the added complexity.  Alternatively, for r we may choose
to support powers of two only, which I expect will be sufficient in
practice.  r is there primarily to support longer cache lines, and it
feels unlikely that a future CPU will have cache line length that is not
a power of two.

Alexander