Re: SHA-2 and other hashes

["Norman Gray" <gray@nxg.name>]

Ulrich, hello.

On 3 Jun 2019, at 13:50, Ulrich Windl wrote:

> ie, pretty much what I expected ‑‑ but in glibc's crypt(3), the 
> $5$ and
> > $6$ hashes are the result of an unspecified number of rounds of such
> > hashing (the $1$/MD5 glibc hash does appear to be compatible with
> > OpenLDAP {SMD5}, though).  (Quite possibly everyone else in the world
> > already knew this, but I didn't!)
>
>
> Hi!
>
> First the number of rounds is NOT unspecified: It
> s explicitly specified, it's optional, and (I think) it defaults to 
> one.

Good point -- the number of rounds is indeed exposed.

If I'm correctly reading crypt/sha256-crypt.c in 
<https://ftp.gnu.org/gnu/glibc/>, then the default number of rounds is 
5000 and, as you say, the number of rounds can be indicated in a 
param=value clause in the passwd string (as gestured towards in 
<https://github.com/P-H-C/phc-string-format/blob/master/phc-sf-spec.md>).

But I may have been unclear: by 'unspecified' I meant 'not described in 
a formal specification' (as far as I can see), so that I would not be 
comfortable trying to reimplement the glibc password-hashing process 
based on documentation alone.

Best wishes,

Norman


--
Norman Gray  :  https://nxg.me.uk