From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jerry Van Baren <gerald.vanbaren@smiths-aerospace.com>
Date: Wed, 28 Feb 2007 08:51:12 -0500
Subject: [U-Boot-Users] RFC: extended image formats
In-Reply-To: <20070227222912.902CB352B86@atlas.denx.de>
References: <20070227222912.902CB352B86@atlas.denx.de>
Message-ID: <45E588D0.5000305@smiths-aerospace.com>
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To: u-boot@lists.denx.de

Wolfgang Denk wrote:
> Hello,
> 
> I'm trying to figure out what could be done to add (at least in some
> cases) more information to U-Boot images. 
> 
> In this case, the existing CRC32 checksum is not sufficient;
> therequirement is to use some stronger hashes (md5 or sha1) to verify
> the correctness of the kernel and file system images.
> 
> A similar thing happened not so long ago when we discussed how to add
> the OFT blob.
> 
> Here some thoughts:
> 
> * The original 64 byte header is tabu and cannot be changed to provide
>   compatibility to existing versions.
> 
> * A quick & dirty hack could use a multi-file image to add - for
>   example - the SHA1 checksum as separate image in addition to the
>   kernel (and eventually file system) image(s).
> 
>   Add an OFT blob, and the confusion is perfect.
> 
> Seems we need a more structured approach.
> 
> I would like to use this opportunity to collect ideas and suggestions
> for a more generalized  solution  that  is  flexible  and  extensible
> enough to handle not only the current , but also future requirements.
> At least some of them ;-)
> 
> All input welcome...
> 
> Best regards,
> 
> Wolfgang Denk

Two possibilities come to mind for using (abusing) the original 64 byte 
header:

1) If we put an ASCII-hex hash _as_ the name, we could support a 16 byte 
(128 bit) hash.  The name would no longer be pronounceable :-P, but it 
_would_ be unique.  An MD5 hash is typically a 32-character hexadecimal 
number. [Ref: <http://en.wikipedia.org/wiki/MD5>]

2) The name is 32 bytes.  If we trimmed the maximum name length to 28 
bytes, we could use the last 4 bytes as a pointer to a hash.  Bleah, not 
much/any better than the multi-file approach.

gvb