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

[Jerry Van Baren <gerald.vanbaren@smiths-aerospace.com>]

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