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Comment by taway2012 | Hacker News Reader

taway2012

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 uploaded is a non-starter for anybody savvy enough to be using this service. Users should be able to directly specify the checksum.

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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

5460 satoshis is the current default minimum that Bitcoin itself allows (other transactions are valid, but won't be forwarded, thus you need to hand it over to a miner yourself for inclusion in a block).

> 3)...

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

This would be better if the site was served over HTTPS. At the moment anyone could MITM the Javascript to steal the file's contents.

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

2) Those 500000 satoshis are sent to the proofofexistence people and they keep them. In the actual proof transaction only 1 satoshi is sent to each of the proof addresses.

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

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