Bitcoin Forum

A while ago I've read that only X quantity timestamping can be written into the Bitcoin Blockchain per day (or per block? can't recall).
I would like to know what are the exact limits, as I can't find them anymore after 1h search  :-X

What do you mean by x quantity timestamping? The only place that timestamps are used are in blocks, but even that timestamp doesn't even matter. It is only used for recalculating the difficulty, so there isn't a limit on that.

It may be how you say, but for the sake of clearness I repeat: I've READ that there IS actually a limit on the quantity of information that can be stored per day or per block, can't recall.

However, sorry to contradict you (even though I may be wrong) but each block has a limit size, for what I know, so only a limited quantity of info can be stored in it.

There is a block size limit, if that is what you are talking about. The current limit is 1Mb per block.

Yes. See above. It has nothing to do with timestamps though. The block header has some bytes (IIRC 4 bytes) reserved for a UNIX timestamp.

So if in the next hour 1 million people want to timestamp something in the next hour, they can? No problem would arise?

Timestamp what? What would they be including a timestamp on? The only thing in bitcoin they includes a timestamp are blocks. If a million blocks were attempted to be produced, then after the first 2016 the difficulty would sit through the roof and then blocks would only be made every 10 minutes as it should.

Anything. Photos, PDF, videos.

If there is no limit, can you explain to me why these people are launching this service? https://uproov.com/index.php

Maybe, only 1 MB of information can be stored in a block. The block itself acts as a timestamp for the system. There is one block every 10 minutes on average, so 6 blocks on average. If these 1 million people issue a single transaction together they will probably have no problem to get a place in a block. If every one of the 1 million people wanted to issue a transaction and get a timestamp from a block, they would have to wait longer. How long depends on the size of each transaction. If we assume a typical small transaction size of 225 byte, that all blocks are actually filled by miners, they would need ~255 blocks or 42.5 hours (on average).


"using blockchain technology" does not mean they will use bitcoin. Its possible to make a transaction that is storing any infromation instead of specific bitcoin money moving information though.

Exactly: they are NOT using the Bitcoin blockchain.
So, there must be a reason.

The reasons is: its expensive. Depending on the method you can store 80 bytes per transaction (OP_RETURN) and have to pay the needed fee or you will get a transaction that can never be spend[1].


[1] https://bitcointalk.org/index.php?topic=524877.0

But you could upload only an hash that marks a document: the document could be offline, and you could still match that hash with the document. If the document changes, the hash would prove it's not the same document. This would be a lot cheaper.

or you could use twitter for that, sign it with a PGP key, etc., which would be free. Its certainly possible if that is your question.

But Twitter can close your account, the blockchain can't be closed.

They don't need to publish all the hashes to the blockchain. They can keep them on their systems and push a merkle root from time to time. Whenever someone needs to prove his claim, he shows the document hash and the service gives the fragment that leads to the root. Technically, there are no limits imposed by Bitcoin.

I don't think this system would be very practical or acceptable.

On their site, they say they can "time stamps to the nearest second". They could be using their own blockchain to do that, but don't need to. They only need to send 1 transaction to the bitcoin blockchain containing a hash of their timestamp/file for every authentication they wish to make. I read that users can "see the Blockchain Key independently from our site at Blocktrail.com", so the verification is actually on the bitcoin blockchain. It make sense because it is the most secure blockchain available.

So why should I be using their service and pay also???