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

Naval, founder of Angel List, has described[1] this and many other excitign usages of Bitcoin, going beyond basic money transfer:

Everyone has a copy of the Bitcoin block chain, so anyone can verify your transactions. You can write software that will crawl the block chain and generate automatic accounting histories for tax and verification purposes. You can engaged in “Trusted Timestamping” – take a cryptographic signature of any document, timestamp it, and put it into the block chain. Anyone can verify that the document existed at a given time. If you sign the document with your private key and another party signs it with theirs, it becomes an undeniable mutually-signed contract. This entirely eliminates notaries and websites like https://www.proofofexistence.com/ are showing the concept. The Namecoin project is building a distributed Domain Name System that allocates and resolve Domain Names without needing ICANN or Verisign, by using the block chain to establish proof-of-ownership.

Really worth a read.

[1] http://startupboy.com/2013/11/07/bitcoin-the-internet-of-mon...

It turns out you can build a surprisingly wide variety of secure application with just a trusted timestamp (or even simpler, a trusted incrementing counter). This paper, published at NSDI 2009, (and won the best paper award) is a pretty good read: http://research.microsoft.com/pubs/78369/trinc_nsdi09.pdf

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.

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.

an application of each once? Btw my crypto is weak, but do answer this. if i apply a hash algorithm on something, it outputs a relatively small number of bytes. Correct me if i am wrong but the strength of the hash lies in the fact that the input space is vastly huge so its difficult to create an input-output mapping for reversing the hash. Now if we use one hash over another, aren't we restricting the input space of the 2nd hash? Wouldn't that make it easier to crack the 2nd hash for this particular usage? And if my above statements are correct then the strength of sch a mechanism only lies in the strength of the first algorithm

Wow, didn't realize that! That's bad news, since the current daily transaction rate (~100k) is within an order of magnitude of the daily limit (~600k = 7 x 3600 x 24).

Fortunately, the doubling time is, from eyeballing the chart below, about 6 months, so that allows ~1-2 years for a fix.

https://blockchain.info/charts/n-transactions?timespan=30day...

> BitCoin can support 7 transactions per second

It doesn't really matter, it's not like they're at all close to that limit. The limit is there to create a market with transaction fees, so it's not just going to be "removed" any time soon.

I'm one of the two developers.

I got the proof server working again so you can play with it.

Try proving data and typing in "testing" (lowercase). It will tell you when we put it in the blockchain. This file should also work: http://s3.amazonaws.com/rapgenius/filepicker%2FvCleswcKTpuRX...

It's a little patchy, but it does work! Payments are fake, and don't do anything! So don't pay! I don't know how much our Bitcoin wallet has left in it. I'll try to remember what we've uploaded so you can try it out.

Bitcoin/crypto code here: https://github.com/wyager/hacktx-proveme

1) AFAIK BitCoin doesn't have comments[1]. When people have stored data in the blockchain in the past, it was by making a series of transactions in order so later those markers could be decoded to represent something else. Some services allow comments to be layered on top of transactions but that doesn't exist in the blockchain.

2) Money is sent and is rendered unspendable[2] afterwards, so I assume the idea is to send the smallest amount possible (although it seems the service takes a fee).

[1] https://en.bitcoin.it/wiki/Block#Block_structure [2] http://www.proofofexistence.com/about

1) Comments are enabled as a service by blockchain.info. For details on how the Genesis Block (and comment by Satoshi) was formed, look at the Bitcoin Wiki[1]

2) Coins are being sent. The Developer page says you must send at least 0.00000001 BTC. Edit: actually 500000 Satoshi.

3) Agree. So does the service. See the Developer Page[2]

[1] https://en.bitcoin.it/wiki/Genesis_block

[2] http://www.proofofexistence.com/developers

> 3)...

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

1) It might be just doing that actually.

2) 500000 satoshis, as it says on http://www.proofofexistence.com/developers

3) If you are tech savvy, the api lets you send a checksum through a curl to their endpoint. http://www.proofofexistence.com/developers

You can put "comments" (raw text) in the transactions. I have done so. Try piping the blockchain database into the unix util `strings` and you will see some. It is a non-standard transaction, and I don't know if they're still allowed.

Hi. Thanks for your questions. I'm the developer behind this. 1 and 2 have been correctly addressed by others. Regarding 3, the documents are NOT uploaded! All hashes are performed client-side via JavaScript. I should make that clearer on the site

It's a way to use the bitcoin blockchain as a non-centralised way to record the fact that you were in possession of a particular file at a particular time, without exposing what that file is, or who you are.

The problem has been around for a long time, especially when dealing with semi-intangibles like Priority for scientific discoveries, or proof of first invention for patents[1]

One solution is to present proof to a trusted but private notary, who can copy or stamp or otherwise indicate that he has seen your documents and so they must have existed at least since the date indicated.

But counterfeiting, forgery, untrustworthy notaries, etc, all make this a less than ideal solution. So we add computers & crypto.

The document in question is condensed down to a single cryptographic hash, which (should[2]) to all intents and purposes be unique for a given document, despite being only a few tens of characters long, regardless of the size of the original input.

This hash then serves as proof[3] that you have the source document, without anyone being able to turn it back into the original document. This is a very one-way process.

Then, you need to find someone to vouch for your hash and indicate when they first saw it. You can do this with lawyers/notaries again as before[4], which partly solves the forgery problem, but not the trust one.

The solution proposed here is to store that hash in the bitcoin block-chain, which is a distributed log of all transactions on the bitcoin network, which has 3 nice properties:

1. It's append-only. Once your hash is encoded in there, it's staying there as long as bitcoin exists[5].

2. It's peer-to-peer/distributed. There's no single controlling organisation you need to trust for answers.

3. It's updated regularly enough that timestamps can be relatively fine-grained.

So you stuff it in there using this tool or whatever, and then X years hence when you need to prove you'd actually created that file in 2013, you should be able to prove that to most people's satisfaction.

This is a loose take on the matter and glosses over whole swathes of other complexities involved, but is probably close enough for [non]government work :)

[1] That is, who discovered/did something first. You may want to be able to claim you did in future, but without making it public at the time, because you might tip your rivals off to the idea before you've fully developed it. See: https://en.wikipedia.org/wiki/Scientific_priority

[2] Breaking (or "colliding") hashes is a whole subfield of cryptography research, and some pretty impressive things have been done there. It's why you probably shouldn't use MD5 for anything nowadays, for example. But again, we'll handwave "Done Properly = unique identifier".

[3] Well, in the same way that a password proves that you're the/a person who knows that password - if you did it right and never told anyone, it should be exclusively you. But if it leaks somehow, others could represent the hash as belonging to something they own. But if they only have the hash and not the original source document, there are relatively easy tests that could distinguish them. That's not very important here though.

[4] https://en.wikipedia.org/wiki/Trusted_timestamping

[5] well, mostly. But it's really hard, and the same capabilities let you defraud the rest of the bitcoin network with double-spending and whatnot, so unless your timestamp priority is super-important, you're probably ok.

    I wrote a haiku
    to run through a hash function
    and send to strangers.

Every time this document is run through a particular function, it returns:

> d15396b27a2b176e6315c9fbbec09e2c2e042e595755902e5ff5eccec1ca634b

If I changed a single character of the document, the function would return an entirely different string.

This means it's very, very difficult to come up with another document that returns the same string when run through this same function.

If I sent my string to a bunch of strangers, they wouldn't know what my haiku is. To find it out, they would have to run through every possible document ever written (and that ever could be written) to hope to return the string.

But if someone decided to say they wrote my haiku, I could prove I wrote it first by showing that the document returns the unique string that I sent off to strangers.

What this service provides is a way of making it easy for strangers to store and date these strings for me, because they're doing it anyway when they're using Bitcoins.

It's like taking a fingerprint of a file and then storing it in a public and distributed database (so it is out of any single parties control). Basically you can prove something existed at a certain time (since if I take a fingerprint of that thing in the future, it will match the record in the distributed database). If the thing changes, so does the fingerprint.

It could be used as a form of "poor mans copyright", where people would send a book manuscript, or whatever, to themselves through registered post and keep the envelope intact so they could use it, if need be, in a court. There could be other uses, you could verify that picture was taken when you said it was etc.

Basically to prove that something existed before a specific date. For instance, grab a random piece of paper on your desk with writings and then try and prove to me that the contents of that paper existed before last year, you can't really do it (easily). Before this, the only (easy) way to achieve this would be to send this document to a third party to store into a database that it did infact exist when sent to the database, but how can you prove that database wasn't manipulated? Another common way to prove something existed before a certain time would be to make a copy and send the copy through the mail to yourself. One you have received this copy from the mail, leave it unopened and now you have proof (through the mail service's date on the stamp) but this isn't too easy, some what of a hassle, and I think you could debate that you could fake it. (Faking the stamp, finding a way to get an opened document through the mail and than replacing the content later, etc.)

What this does is it stores a document's signature into the actual "history" of bitcoins which is public. ANYONE and EVERYONE can access this history of all transactions and by them storing the actual signature of the document into this public "log" you are now able to say that this document DID exist before the specific bitcoin transaction. This removes the hassle of all current methods of proving for existence and now no longer rely on a single third party (which could manipulate it themselves).

Something like this:

Your provider stores when you had which IP address. This is used for instance in file sharing processes. At least in Germany it has turned out that this information is unreliable. So you want to log your IP addresses and you want to have a proof of the logs integrity. You could use this service for the purpose.

However, I don't like that I need to upload something. I'd prefer generating and sending the hash and get it signed.

If some claim to title is omitted from the public record, how exactly would this guard against it?

> Will this have legal weight?

I doubt it. If I have to fax something for it to be a legal document, such an antiquated system will ignore any advances made around it.

There is a developer API that allows you to do this:

    http://www.proofofexistence.com/developers

Maybe calculate the SHA256 on your own box, then upload a document containing only the SHA256?

It uses SHA-256, not SHA-1.

By using SHA-2?

Excuse me?

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.

Yes you could, however, this isn't only about the trustworthiness of your claim. More importantly it's about the trustworthiness of the longevity of the data.

Twitter can remove a single post or turn off their servers and your prove is gone. That's not so easy for a BitCoin transaction. Once it's added to the blockchain it's there for as long as anyone is running a bitcoin node.

But that's kinda centralizing it. What if twitter shuts down? What if twitter's DB is compromised? With bitcoins, it kinda makes all this impossible (cryptographically) and making it super decentralized