phc-discussions - Re: [PHC] Interest in specification of modular crypt format

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Date: Mon, 07 Sep 2015 12:41:42 +0100
From: Darren J Moffat <Darren.Moffat@...cle.COM>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Interest in specification of modular crypt format

On 09/07/15 11:55, Solar Designer wrote:
> If we continue to build upon the traditional crypt(3) alphabet and
> encoding (like the above specification for scrypt does), then I'd also
> like to include a way to represent the numeric parameters in a more
> compact form: let the little-endian encodings be truncated when the
> values are small.  So e.g. instead of:
>
> $7$C6..../....SodiumChloride$kBGj9fHznVYFQMEn/qDCfrDevf9YDtcDdKvEqHJLV8D
>
> it would be valid to use:
>
> $7$C6$/$SodiumChloride$kBGj9fHznVYFQMEn/qDCfrDevf9YDtcDdKvEqHJLV8D
>
> or if we want to keep the number of '$' characters fixed, then either
> require the '$' delimiters to always be present or maybe introduce '+'
> or '=' for truncation (a character already used in the other base64
> encoding's alphabet, so likely safe to use):
>
> $7$C6+/+SodiumChloride$kBGj9fHznVYFQMEn/qDCfrDevf9YDtcDdKvEqHJLV8D
>
> The savings for classic scrypt are small, but with yescrypt's additional
> parameters they are more significant.

In Solaris crypt(3C) we use this syntax:

If the first character of salt is "$", crypt()  uses  crypt.conf(4)  to
determine  which  shared  module  to load for the encryption algorithm.
The algorithm name crypt() uses to search in crypt.conf is  the  string
between  the  first  and second "$", or between the first "$" and first
"," if a "," comes before the second "$".

Basically ',' is the argument separator so you can end up with things 
like this:

$5,rounds=6000$nlxmTTpz$

So you could have

$7,C6$SodiumChloride$kBGj9fHznVYFQMEn/qDCfrDevf9YDtcDdKvEqHJLV8D

> I think it's desirable for us to arrive at a common approach at encoding
> these things for all PHC-endorsed schemes.  It is less important whether
> this would be part of the specifications for the individual hashing
> schemes or not, although I think that if not right away then it should
> retroactively be added to revisions of those later.

I'd like to be sure that when we add Argon2 support for UNIX user 
password hashes in Solaris that the syntax will be compatible with what 
Linux vendors add.  It is also important that we have a Python 
implementation since parts of OpenStack can be involved in setting the 
password hashes at deployment time.

-- 
Darren J Moffat