Service lets you "certify" a document using the Bitcoin blockchain

Re:Service lets you "certify" a document using the Bitcoin b... by skriticos2 on Thursday November 28, 2013 @05:17AM (#6813906)

Collisions are a problem if you want to corrupt data, not if you specifically want a human validate it in a single document.

E.g.:

I claim that I authored the string "foo bar" with hash "1f2ec52b7743687..".

Now you find a collision and go to court arguing:

>> Your honor, but "3HSSHog*8FF9 z!!!!ady94765&$^#" also has the same hash!

I think the court will still assume that "foo bar" is the correct original, not the garbled collision data you produce. And you still can't deny that the original produces the correct hash.

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Re:Service lets you "certify" a document using the Bitcoin b... by beagle3 on Thursday November 28, 2013 @07:08AM (#6814207)

That's not why it would be a problem.

The problem is that I can author "foo bar" and "moo bar" constructed to hash the same, and then assert retroactively which one I meant. While collisions are likely to have random binary garbage in them, it may not matter - I am on phone now, but IIRC I have two PDFs on my desktop that have the same MD5, one of which viewed is an airbus pamphlet, the other being a Boeing one. (created by Dan Kaminski, IIRC)

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Re:Service lets you "certify" a document using the Bitcoin b... by adamryman on Friday November 29, 2013 @11:42AM (#6820018)

Can we see them?

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Re:Service lets you "certify" a document using the Bitcoin b... by beagle3 on Friday November 29, 2013 @03:23PM (#6820877)

I guess they are on a backup or misremembered - but examples are really easy to find on the net if you want them:

http://th.informatik.uni-mannheim.de/people/lucks/HashCollis...

http://www.win.tue.nl/hashclash/ChosenPrefixCollisions/ has a multicollision: 12 PDF files with different content and the same MD5 hash.

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