Canon's Image Data Verification Kit DVK-E2 ?

Hadmut Danisch hadmut at danisch.de
Thu Jan 29 02:36:59 EST 2004


Hi,

Canon provides a so called Data Verification Kit
which allegedly allows to detect whether a digital 
image has been tampered with since it has been taken
with a digital camera.

I found the announcement at
http://www.dpreview.com/news/0401/04012903canondvke2.asp 

They say:

  How it works

  The kit consists of a dedicated SM (secure mobile) card
  reader/writer and verification software. When the appropriate
  function (Personal Function 31) on the EOS-1D Mark II or EOS-1Ds is
  activated, a code based on the image contents is generated and
  appended to the image. When the image is viewed, the data
  verification software determines the code for the image and compares
  it with the attached code. If the image contents have been
  manipulated in any way, the codes will not match and the image
  cannot be verified as the original. 

So some kind of hash code or digital signature is generated. 

Does anybody know details about this? I never heard that there
are digital mass market cameras which could generate digital
signatures.  But if the signature is generated inside the SM card
only, why should the PC where the image was modified be unable to
write the modified image the same way as a digital camera writes
an unmodified one? (And, btw., how do they detect that the
picture was taken at a real scene and is not a repro of a
modified and printed picture?)

I guess the secure mobile card generates some signature and they
presume that the attacker would not have access to the memory card. 
This would start to protect the image not from the moment it 
had been taken, but from the moment when it was copied from the 
card to other media. And it would require to trust the
photographer.

Is there a technical description of those secure mobile cards 
available? I didn't find any details, just marketing blabla.


regards
Hadmut

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