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Date: Wed, 24 Jul 2013 19:56:32 +0100 (BST)
From: hakre <>
To: "" <>,
  Solar Designer <>
Subject: Re: NUL bytes in Unix crypt SALT string using SHA-256 and SHA-512

----- Ursprüngliche Message -----
> Von: Solar Designer <>
> An:; hakre <>
> CC: 
> Gesendet: 1:15 Mittwoch, 24.Juli 2013
> Betreff: Re: [crypt-dev] NUL bytes in Unix crypt SALT string using SHA-256 and SHA-512
> Hi hakre,
> I'm afraid your question is mostly off-topic for this mailing list.
> On this mailing list, we're not very interested in fine details of the
> existing password hashing methods - rather, we're interested in moving
> forward.

Thanks for the nice reminder. Moving forward is good :D

> So the only relevant aspect close to your question is: "should
> future password hashing methods allow arbitrary salts, or would C
> strings be OK?"  This new question has been sort of answered in the PHC
> call for submissions - - "A salt
> of 16 bytes", "const void *salt, size_t saltlen" - thus, NULs may 
> be
> embedded in the salt.  However, if/when a crypt(3) interface is created
> on top of a PHC submission, it will have the "no embedded NULs"
> restriction for its salt strings (at the crypt(3) interface level at
> least) due to how crypt(3) is defined.

That makes perfect sense, thanks a lot for the feedback.

> As to your actual off-topic question, see below:
> On Tue, Jul 23, 2013 at 05:25:14PM +0100, hakre wrote:
>>  I've got a clarification question regarding the (up-to 16 characters 
> used) SALT string for Unix crypt using SHA-256 and SHA-512.
>>  Is it acceptable by the definition of the algorithm to provide 16 NUL 
> bytes? In the meaning that those 16 chars are used as SALT?
> The reference implementation uses C strings, so if it is considered part
> of the definition then you technically can't have embedded NULs.
> Alexander

Thanks again even this was off-topic.

Have a good time


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