Can I use the Blockchain to store infinity messages?

[nullius]

It is possible but the real question you need to ask yourself is "wouldn't a blog or a website achieve the same thing?" You could write "messages" in that blog/website and it will remain on the internet for a very long time so that people in the future can read what you wrote.
The difference however is that a blog/website is designed to "store messages" while bitcoin blockchain is not.

I get the impression that the OP wants to store a message that he can prove is unchanged.

Depending on why OP need to prove it's unchanged, website archive service is good enough. An example, Archive.org's Wayback Machine is legit legal evidence, US appeals court judges rule.
For most other cases, archive the website on multiple archive services is good enough. It's not likely multiple operator going to edit same archived website.

I don’t care what some American court (or really, any court) says.  It is not cryptographically secure.

This provides proof of existence in time, at least, albeit not strong proof of authenticity:

How OpenTimestamps 'Carbon Dated' (almost) The Entire Internet With One Bitcoin Transaction

May 25, 2017

[...]

[...description of fake evidence in the Craig Wright scam and how similar scams could work, for the sake of example...]

By consistently timestamping all Internet Archive content, we make attacks like the above easy to detect. The OpenTimestamps proofs we’ve generated are traceable back to the Bitcoin blockchain, a widely witnessed data structure with timestamps that can’t be backdated. Even with a sysadmin’s help, the best the attacker could do is create a modified file that’s very suspiciously missing a timestamp that all other files have.

However, it’s important to note timestamps are not a panacea: they’re just evidence as to when a file existed; by themselves they can’t prove a file is legit. For example, if I had known in 2008 that Satoshi was going to release Bitcoin, I could have generated fake keys and fake Bitcoin papers with 100% real timestamps. While such a scam is much less likely, it’s certainly not impossible¹.

Unfortunately, the link to the database page seems to be 404:
https://opentimestamps.org/internet-archive/

I don’t know if there has been any project to continue timestamping Internet Archive records.  I guess probably not.  There should be.

Other good replies earlier... fell behind here.

[Quickseller]

I get the impression that the OP wants to store a message that he can prove is unchanged. There is nothing stopping an operator of a website from changing content, or back dating a blog post.

That still doesn't justify storing any random messages in bitcoin's blockchain though.

The reason OP_RETURN transactions are valid is to allow people to store data in the blockchain.

A specialized cryptocurrency could be created to store data like this (eg. altcoins such as storej) for this matter.

I think we both know such an altcoin would not give the same authority that the message is unchanged as bitcoin would.

[pooya87]

The reason OP_RETURN transactions are valid is to allow people to store data in the blockchain.

And it is heavily criticized because of what it offers.
The only valid utility I see for OP_Return is when it is used for colored coins, for example Tether where it treats the OP_Return data as a script and by executing that script it can transfer its token from one address to another all built on top of bitcoin. Although that is still parasitic and spammy...

I think we both know such an altcoin would not give the same authority that the message is unchanged as bitcoin would.

Then it proves that this feature is not something people want or care about.

[Quickseller]

The reason OP_RETURN transactions are valid is to allow people to store data in the blockchain.

And it is heavily criticized because of what it offers.
The only valid utility I see for OP_Return is when it is used for colored coins, for example Tether where it treats the OP_Return data as a script and by executing that script it can transfer its token from one address to another all built on top of bitcoin. Although that is still parasitic and spammy...

I don’t think it is appropriate to try to regulate how people should use bitcoin. That really goes against the ethos of why bitcoin was created, at least in my opinion.

If you don’t want people to be able to add arbitrary data in OP_RETURN transactions, you should create a BIP that makes these transactions invalid.

I think we both know such an altcoin would not give the same authority that the message is unchanged as bitcoin would.

Then it proves that this feature is not something people want or care about.

That is obviously not true, people have been including random data in the blockchain for years. I am saying a cryptocurrency whose sole purpose is to store arbitrary messages is not going to have value.

I would also point out that if OP RETURN transactions could not include data, people would start sending minimum output amounts to vanity addresses that send some kind of message. This would both increase the blockchain size and the UTXO set.

[pooya87]

If you don’t want people to be able to add arbitrary data in OP_RETURN transactions, you should create a BIP that makes these transactions invalid.

This was already discussed enough when the OP code was introduced back in the days, there is no need to create a BIP. The majority think it is needed and in fact one of the reasons why it was kept is as you guessed:

I would also point out that if OP RETURN transactions could not include data, people would start sending minimum output amounts to vanity addresses that send some kind of message. This would both increase the blockchain size and the UTXO set.

[plexasm]

if a project like this ever became successful it would quickly become a victim of its own success. there must be a cost for blockspace otherwise you will always be subject to DoS attacks

[Theb]

But what would be the purpose of this blockchain in the first place? This would be good if you are writing educational materials but if we are talking about personal messages I don't think a permanency or even its feature of being public that can be shown to anyone is something that a person would like, that's why the messaging apps we have have its own "private mode" or ways to delete in both ways as these messages are intended to be kept personal. I remembered a while back that someone was worried that a personal message in their transaction was labelled for "child porn" and I can only imagine this kind of thing can be abuse by a lot of people to use in libel or incriminate someone just for the fun of it.

[Timelord2067]

You can embed data into the block-chain via this website:  ^{(Not sure if there are any other websites out there that do so - anyone?)}

https://live.blockcypher.com/btc/embed-data/

You can search embedded data in the block-chain such as this example:

https://blockchair.com/search?q=timelord2067

     

See also this thread: https://bitcointalk.org/index.php?topic=1528808.msg15422712#msg15422712