[U-Boot-Users] RFC: extended image formats

[U-Boot-Users] RFC: extended image formats

[Wolfgang Denk]

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

-- 
DENX Software Engineering GmbH, HRB 165235 Munich, CEO: Wolfgang Denk
Office:  Kirchenstr. 5,       D-82194 Groebenzell,            Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Don't have a battle of wits with an unarmed opponent.

[U-Boot-Users] RFC: extended image formats

[Jerry Van Baren]

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

[U-Boot-Users] RFC: extended image formats

[Txema Lopez]

Jerry Van Baren wrote:

>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
>  
>
What about an image tail?. The last 2 longs of the name could be changed by:
u32 tail_magic_number; /* A magic number to detect an image with a tail */
u32 tail_offset; /* Offset to the tail from the image header */

The tail structure will add the new information for the next versions of 
U-Boot.



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[U-Boot-Users] RFC: extended image formats

[Josh Boyer]

On 2/27/07, Wolfgang Denk <wd@denx.de> 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.

Just curious, but why isn't CRC32 sufficient exactly?

josh

[U-Boot-Users] RFC: extended image formats

[Jerry Van Baren]

Josh Boyer wrote:
> On 2/27/07, Wolfgang Denk <wd@denx.de> 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.
> 
> Just curious, but why isn't CRC32 sufficient exactly?
> 
> josh

CRC32 is pretty weak with respect to:
* Multibit errors:
   * It will detect all single bit errors - good
   * It will detect all two bit errors up to a block size that
       is dependent on the CRC length & polynomial (2KBytes for
       CRC-32 IIRC, but I may recall incorrectly - much less than
       a u-boot image size in any case) - bad
   * It detects some multibit errors but not all of them - bad
* Cryptography: it is trivial (cryptographically speaking) to "fix
     up" the CRC after changing something in the block it is
     covering - very bad.

Ref:
   <http://en.wikipedia.org/wiki/List_of_checksum_algorithms>
   <http://en.wikipedia.org/wiki/Cyclic_redundancy_check>

HTH,
gvb