<p>Just to give a quick update on this, it is no longer necessary to "burn" bitcoins when creating a proof of existence. The <code>OP_RETURN</code> opcode re-enabled in <strong>Bitcoin Core 0.9</strong> can be used to carry 40 bytes of arbitrary data. The coin associated with it will be <strong>added to the transaction fee</strong> and can be claimed by the miner.</p>

<p>Reading the <a href="http://www.proofofexistence.com/about" rel="nofollow">about</a> page it seems <strong>proofofexistence.com</strong> are already using it.</p>

<p><strong>Edit:</strong> According to Nick ODell's inquiry answered by core developer Jeff Garzik, this coin <strong>cannot</strong> be claimed by the miner.</p>

CC BY-SA 3.0
2014-11-01T23:25:12.923Z
Alright, the author of the article has acknowledged this and corrected it. Thanks again Nick, it's really important to get this right.
knaperek
CC BY-SA 3.0
2014-10-23T20:18:20.543Z
`added to the transaction fee` Do you have a citation on that? I haven't heard anything like that.
Nick ODell
CC BY-SA 3.0
2014-10-23T20:32:46.567Z
I know it's not an "authoritative source", but seems pretty legit: ["Interestingly, any value associated with the coin can be claimed as a miner fee."](http://bitzuma.com/posts/op-return-and-the-future-of-bitcoin/)
knaperek
CC BY-SA 3.0
2014-10-24T02:00:47.710Z
I asked #bitcoin-dev, and Jeff Garzik said no. http://pastebin.com/5txuBhGP
Nick ODell
CC BY-SA 3.0
2014-10-24T09:20:17.997Z
Thanks Nick, I've edited my answer. Will ask the author of the cited article for further explanation.
knaperek
CC BY-SA 3.0
2014-10-23T20:00:49.140Z
2014-10-24T09:18:49.213Z
2014-10-24T09:18:49.213Z
knaperek
<p>Well, it's probably not an intended function of the block chain, but I wouldn't call it "unfriendly" because you're not really harming anybody (by reducing the total amount of bitcoins available you're in fact <em>increasing</em> the value of all other bitcoins a little).</p>

<blockquote>
  <p>[...] future versions of the protocol may prevent this type of transaction
  from being accepted into the blockchain?</p>
</blockquote>

<p>No, because it's not possible. The transaction encoding the document hash looks exactly like any other normal pay-to-address transaction. The only difference is the address which is a representation of the document hash instead of a hashed public key, and therefore there is no private key associated with it (that's why it is unspendable). You can't go back from a hash to it's origin though, so you will never know whether it's spendable or not.</p>

CC BY-SA 3.0
2014-01-02T12:38:25.673Z
i think the key point is that there is no way of knowing (from the point of view of the miners including these transactions into a block) that the to-address (document hash) has no private key.
mulllhausen
CC BY-SA 3.0
2014-01-02T10:15:25.540Z
2014-10-24T09:25:44.893Z
2014-10-24T09:25:44.893Z
jnnk
<p><a href="http://www.proofofexistence.com/about" rel="nofollow">http://www.proofofexistence.com/about</a> -- "Use our service to anonymously and securely store an online distributed proof of existence for any document."</p>

<blockquote>
  <p>The document is certified via embedding its SHA256 digest in the bitcoin blockchain. This is done by generating a special bitcoin transaction that encodes/contains the hash via an OP_RETURN script. This is a bitcoin scripting opcode that marks the transaction output as provably unspendable and allows a small amount of data to be inserted, which in our case is the document's hash, plus a marker to identify all of our transactions.</p>
</blockquote>

<p>Naïve question perhaps, but if the bitcoins are lost forever, this seems like an unfriendly use of the bitcoin protocol and the blockchain, and future versions of the protocol may prevent this type of transaction from being accepted into the blockchain?</p>

<blockchain><proof-of-existence>
Does Proof of Existence lose bitcoins?
Simon Woodside
# Does Proof of Existence lose bitcoins?

(Asked by: username_0 on 2014-01-02)

<http://www.proofofexistence.com/about> -- "Use our service to anonymously and securely store an online distributed proof of existence for any document."

> The document is certified via embedding its SHA256 digest in the bitcoin blockchain. This is done by generating a special bitcoin transaction that encodes/contains the hash via an OP\_RETURN script. This is a bitcoin scripting opcode that marks the transaction output as provably unspendable and allows a small amount of data to be inserted, which in our case is the document's hash, plus a marker to identify all of our transactions.

Naïve question perhaps, but if the bitcoins are lost forever, this seems like an unfriendly use of the bitcoin protocol and the blockchain, and future versions of the protocol may prevent this type of transaction from being accepted into the blockchain?

**Tags:** blockchain, proof-of-existence


---

## 2 answers

### Answer by username_3 on 2014-01-02. Score: 4 | Accepted answer

Well, it's probably not an intended function of the block chain, but I wouldn't call it "unfriendly" because you're not really harming anybody (by reducing the total amount of bitcoins available you're in fact *increasing* the value of all other bitcoins a little).

> [...] future versions of the protocol may prevent this type of transaction
> from being accepted into the blockchain?

No, because it's not possible. The transaction encoding the document hash looks exactly like any other normal pay-to-address transaction. The only difference is the address which is a representation of the document hash instead of a hashed public key, and therefore there is no private key associated with it (that's why it is unspendable). You can't go back from a hash to it's origin though, so you will never know whether it's spendable or not.

> **Comments:**
> **username_4**: i think the key point is that there is no way of knowing (from the point of view of the miners including these transactions into a block) that the to-address (document hash) has no private key.  

---

### Answer by username_1 on 2014-10-23. Score: 3

Just to give a quick update on this, it is no longer necessary to "burn" bitcoins when creating a proof of existence. The `OP_RETURN` opcode re-enabled in **Bitcoin Core 0.9** can be used to carry 40 bytes of arbitrary data. The coin associated with it will be **added to the transaction fee** and can be claimed by the miner.

Reading the [about](http://www.proofofexistence.com/about) page it seems **proofofexistence.com** are already using it.

**Edit:** According to username_2 username_2's inquiry answered by core developer Jeff Garzik, this coin **cannot** be claimed by the miner.

> **Comments:**
> **username_2**: `added to the transaction fee` Do you have a citation on that? I haven't heard anything like that.  
> **username_1**: I know it's not an "authoritative source", but seems pretty legit: ["Interestingly, any value associated with the coin can be claimed as a miner fee."](http://bitzuma.com/posts/op-return-and-the-future-of-bitcoin/)  
> **username_2**: I asked #bitcoin-dev, and Jeff Garzik said no. http://pastebin.com/5txuBhGP  
> **username_1**: Thanks username_2, I've edited my answer. Will ask the author of the cited article for further explanation.  
> **username_1**: Alright, the author of the article has acknowledged this and corrected it. Thanks again username_2, it's really important to get this right.  

---

