Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

proofofexistence.com

Post reply on HN
Print view View original

41–50 of 86 posts

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

#41

Post by AsymetricCom »

diminish wrote: post #21
machrider wrote: post #17

This idea is generally called "trusted timestamping": http://en.wikipedia.org/wiki/Trusted_timestamping One example would be to take a photo of a rental car showing damage at the time you rented it and be able to prove it was taken at that time. Then the rental company cannot later claim you caused the damage. This is a pretty clever use of the blockchain as a publicly-visible and authenticated timestamp. This way, t…

I was developing a similar online notary. My idea is to timestamp open code, docs etc create a prior case database against patent trolls and goliaths.

Now I just have to trust their hashing algorithm..

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

#42

Post by onnoonno »

nwh wrote: post #32
gnerd wrote: post #29

Earlier quoted context omitted.

> The limit is there to create a market with transaction fees, so it's not just going to be "removed" any time soon. The limit is actually there to limit the size of a block. It has nothing to do with transaction fees. Click the link I posted: https://en.bitcoin.it/wiki/Scalability#Current_bottlenecks It used to be 250K and then this year was raised to 1M so it probably will get lifted again. That is the goal of the…

> The limit is actually there to limit the size of a block. It has nothing to do with transaction fees. Again, the limit is there to create a market with transaction fees. People jostle for space in the block and a market develops around how much people are willing to pay to get into the next block. It's based on the assumption that miners pick the transactions with the highest fees to include in their blocks, which…

No. That is redefining the purpose of this limit. It was meant only as a anti-spam measure and now people like you claim it is necessary. There is a _natural_ limit to the minimum transaction fee which is determined by the orphan cost (including transactions means slower block propagation means higher chance of a found block being orphaned by another, concurrent block). Bitcoin needs to eventually scale to survive and that means removing the block size limit and optimizing the protocol for lowest possible orphan cost.

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

#44

Post by tghw »

delinka wrote: post #40
richardlblair wrote: post #38

So, if I could automate this, could I use this to prove in court that logs were created, and not tampered with? Just trying to think of practical uses of this cool project, and it's the first thing that came to mind.

Yes. Or that a contract was not created before a certain date. Or, as another poster suggested, that a photo of a damaged rental car was taken before you took possession of the car.

Or that a contract was not created before a certain date.

I think you have that one backwards. You can demonstrate a contract did exist at a certain date. There is no proof of non-existence before that date.

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

#45

Post by jd007 »

This is definitely a cool idea, but there could be potential issues if it is to be relied upon for long periods of time. If at any point in the future the hash algorithm used (SHA256 right now it seems) is found to be vulnerable then it could invalidate all past certifications. You don't really even need a full collision attack, a chosen prefix collision attack is enough to completely destroy the system's validity. MD5 is already vulnerable to chosen prefix attacks, maybe in 5 or 10 years SHA256 will be too...

Perhaps using a combination of different hash algorithms that we know are secure today to certify a file together would be a potential solution to the problem. It's not perfect, but at least this way all the algorithms used need to be compromised for the certification to break.

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

#46

Post by fragsworth »

onnoonno wrote: post #42
nwh wrote: post #32

Earlier quoted context omitted.

> The limit is actually there to limit the size of a block. It has nothing to do with transaction fees. Again, the limit is there to create a market with transaction fees. People jostle for space in the block and a market develops around how much people are willing to pay to get into the next block. It's based on the assumption that miners pick the transactions with the highest fees to include in their blocks, which…

No. That is redefining the purpose of this limit. It was meant only as a anti-spam measure and now people like you claim it is necessary. There is a _natural_ limit to the minimum transaction fee which is determined by the orphan cost (including transactions means slower block propagation means higher chance of a found block being orphaned by another, concurrent block). Bitcoin needs to eventually scale to survive an…

It's limited so that the blockchain grows at a linear rate instead of an exponential rate.

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

#47

Post by jcoder »

taway2012 wrote: post #28

Couple questions. 1) AFAIK, bitcoin has "comments" within transactions. Why not embed the checksum as a comment in a transaction between wallets you control? 2) In the approach described here, no coins are being sent with the transaction (right?). Are blockchain participants really accepting NOP transactions involving 0 BTC transfers. Maybe I missed something. 3) As others pointed out, requiring the whole file to be…

> 3)...

"Your document will not be uploaded. The cryptographic digest is calculated client-side."

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

#48

Post by onnoonno »

fragsworth wrote: post #46
onnoonno wrote: post #42

Earlier quoted context omitted.

No. That is redefining the purpose of this limit. It was meant only as a anti-spam measure and now people like you claim it is necessary. There is a _natural_ limit to the minimum transaction fee which is determined by the orphan cost (including transactions means slower block propagation means higher chance of a found block being orphaned by another, concurrent block). Bitcoin needs to eventually scale to survive an…

It's limited so that the blockchain grows at a linear rate instead of an exponential rate.

Huh? If Bitcoin is really successful and eventually used by everyone on the planet and people use it with about constant rate, the blockchain will grow linearly. Until then bitcoin will grow presumably S-shaped which means that there will be a phase of exponential growth that we are in now. If it is crippled by people insisting on 7txn/s for "economic reasons", its transaction rate will probably peak and then decay.

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

#49

Post by GhotiFish »

tghw wrote: post #44
delinka wrote: post #40

Earlier quoted context omitted.

Yes. Or that a contract was not created before a certain date. Or, as another poster suggested, that a photo of a damaged rental car was taken before you took possession of the car.

Or that a contract was not created before a certain date. I think you have that one backwards. You can demonstrate a contract did exist at a certain date. There is no proof of non-existence before that date.

you're right, it can be used to prove that a contract with both signatures existed before a date, not after. So if Alice makes an agreement with Bob, Alice can't turn around and say that the contract was only ratified after Alice failed to meet certain obligations.

Then again, digital signatures come with a timestamp, Alice could lie about that timestamp, but it would be obvious to Bob that she did.

Fun to think about.

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

#50

Post by twakefield »

I wonder if these concepts could be used to change the way land records are maintained and eliminate the need for title insurance [1] in the U.S. I am no expert but the current system doesn't seemed to have changed much in the past century or so. This results in a lucrative business (title insurance) that effectively insures against book keeping mistakes.

[1] http://en.wikipedia.org/wiki/Title_insurance

Post reply on HN