Now here is a challenge for anyone.. I've been thinking about it for a while, but i have severe problems finding a solution, so I'll just throw it out here.

I have a digital camera that makes a picture. To be sure this picture is not altered from the camera, through the sender system, arriving at the destination, I'd like to make an md5 sub of the picture and print this onto the picture itself as picture data. This can be done on the computer to wich the camera is connected.

Anyone have a good suggestion on how to to this? There is not enough CPU available to brute-force it.

tChr wrote:To be sure this picture is not altered from the camera, through the sender system, arriving at the destination, I'd like to make an md5 sub of the picture and print this onto the picture itself as picture data.

This 'print onto the picture' will alter the picture and its md5!
Why don't you just use pgp or gpg to sign the picture? It gives you an signature file that you just ship with the picture so others can compare it and see if it was changed..
And in case you can use it to encrypt the file too

esteel wrote:

tChr wrote:To be sure this picture is not altered from the camera, through the sender system, arriving at the destination, I'd like to make an md5 sub of the picture and print this onto the picture itself as picture data.

This 'print onto the picture' will alter the picture and its md5!

No shit, sherlock? Thats why its called a "challenge"

You could MD5 the IDAT and then add that as a metadata tag. You would not be altering the IDAT by doing this so the picture would be the same.

tChr wrote:

esteel wrote:

tChr wrote:To be sure this picture is not altered from the camera, through the sender system, arriving at the destination, I'd like to make an md5 sub of the picture and print this onto the picture itself as picture data.

This 'print onto the picture' will alter the picture and its md5!

No shit, sherlock? Thats why its called a "challenge"

If you think about it, the challenge is contradictory.

Assume someone solves it. He gets a picture and can alter the picture to that the MD5 is printed on the picture. This would most probably(!) yield a method to invert MD5 - and thus destroy all faith people have in the "remaining" security of MD5, rendering MD5 useless just about any application of MD5 that you would not use CRC32 at.

And if CRC32 is an option - for THAT brute force should work quite fast (about 2^16 attempts) if using a similar approach to Pollard's Rho method perhaps, but there are other ways to do it... on some torrent site I downloaded a file something_that_should_not_be_names_[DEADFACE].avi which actually had the CRC32 "0xdeadface"

If this is about what I think it is the here is what I do.
Watermark it in photoshop or ship the images in RAW thus allowing you to make sure the image is not altered after you ship it.

This works only if you're talking about what i think you're talking about.

PHREAK wrote:If this is about what I think it is the here is what I do.
Watermark it in photoshop or ship the images in RAW thus allowing you to make sure the image is not altered after you ship it.

First of all.. Automation is required. Second, how do I know wich md5 to use as a watermark?

As far as automation, anything can be automated in photoshop thru actions. Simply batch process the files you need to apply this to (this is something you most likely already know).

If you need more info on how the whole watermark process works, check out this site. http://www.digimarc.com/register/

Again, this only works if you're talking about what I think you're talking about.

But maybe this is not even what you're looking for so if I wasted your time, I appologize.

it its so important it gets transported unalterd why not just use heavy enctypytion?

If the image needs to be viewable while transported; double a normal copy of the encrypted one into the file.

The only way to solve it "realiably" requiers reversing md5,, making md5 useless in the proccess xD. (just like divVerent says)

Ed:
Thats solution is not realiable. ie someone can alter the image and then the info in the metadata.