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Date: Fri, 10 Aug 2012 19:09:55 +0400
From: Alexander Cherepanov <cherepan@...me.ru>
To: john-dev@...ts.openwall.com
Subject: Re: mscash2 / hmac-md5 ambiguity

On 09.08.2012 03:30, magnum wrote:
> On 2012-08-08 23:27, Alexander Cherepanov wrote:
>> On 2012-07-27 09:58, Frank Dittrich wrote:
>>> On 07/27/2012 06:58 AM, Frank Dittrich wrote:
>>>> On 07/27/2012 12:57 AM, Alexander Cherepanov wrote:
>>>>> One solution is to add to hmac-md5 hashes some prefix like
>>>>> $HMAC-MD5$ or
>>>>> {HMAC-MD5}. BTW why there is none now?
>>>>
>>>> Because for hmac-md5 *any* input is valid, you don't know if a hash is
>>>> prefixed, of if "{HMAC-MD5}" just happens to be the begin of an
>>>> unprefixed string, so you'd have to convert it to "{HMAC-MD5}{HMAC-MD5}"
>>
>> If we always require some prefix in this format then there is no
>> problem. When
>> the prefix is present then we accept this hash and strip the prefix before
>> actual processing. When there are no such prefix we simply reject this hash
>> (for this format).
>
> I believe we currently never really require format tags.

What do you mean? Prefix '$1$' is required, '$PHPS$' is required,
'{SHA}' is required, '{SSHA}' is required.

 > If you put a
> dynamic_0 tag on a 32-character hex string, it will be recognized as a
> raw-md5 with no --format given. If you do not use the tag, you can load
> the bare hash using --format=raw-md5. I really like it this way so I
> think I disagree with the above idea.

The difference here is that you don't have a string for hmac-md5, you have
two strings. So you need to combine them into one string. At this step you
decide inn which order to concatenate strings and which separator to use.
Adding some prefix doesn't change much.

> However, I did not write the hmac-md5 format (I did optimize it a while
> ago). When I wrote the hmac-sha1 I just mimiced the md5 one. If we have
> concensus on some new input format (like putting the salt last) I have
> no objections. I haven't seen this format ITW in any form btw.
-- 
Alexander Cherepanov

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