Imagine you want to declare your love for someone forever. You could write down your name and the name of your sweetheart on a padlock and affix it to the railings of a bridge, as it happens in Paris, Rome, Florence—even though you’d probably make municipal authorities and art historians very unhappy. Or… you could write a message into the bitcoin blockchain, making it eternal, uncensorable, independent, timestamped, and signed. Sound romantic?
The blockchain is the public registry that tracks all transactions in bitcoin. It’s a decentralized ledger, and over 5,000 copies of it are distributed all around the world, hosted by the nodes of the bitcoin network. The blockchain records who is paying whom; however, it is also possible to slip some extra data (such as text) into these records, the same way you can write down the reasons for a bank wire transfer you are sending.
Unfortunately, the blockchain is a little more complex than a padlock. So here comes Eternitywall.it, a service that lets anyone embed a message in the blockchain, and then visualize it on a digital wall. And you don’t even have to own a bitcoin wallet in order to do it.
Messages must be quite short, not longer than 72 characters. And in order to send a message, a bitcoin transaction needs to be made. Eternitywall offers a free message every hour, otherwise you have to pay a small amount of digital money (0.00015 bitcoins, about 0.06 US dollars at the time of writing) to write into the blockchain and to see the results on the wall. This fee is used to pay the bitcoin network fee required to get a transaction into the blockchain, explains the Eternitywall website. It is the minimum amount of bitcoin needed to make a transaction; there's no fee going to Eternitywall (the site accepts donations, however).
Such messages are anonymous or, to be more precise, they are not directly linked to any identity. If you want to identify the message, you have to pay a little more (0.00016 bitcoin, about
0.07 US dollars) and send it through the Eternitywall app (only for Android so far).
“You can’t sign messages through the website, because we shouldn’t know the private key of your bitcoin wallet. But you can sign messages through our app, since it is client-side and accesses your private key on your smartphone without sharing it with us," Riccardo Casatta, the Italian software engineer who created Eternitywall.it, told Motherboard.
Even if messages are short, the service lets users reply to them, chaining messages together in threads. People can also “like” messages, as in Twitter, or search through them, or share and embed them on social networks.
The result is a public wall full of short messages that will last forever—or at least as long as bitcoin and the blockchain will exist. So far most of the messages are jokes, proverbs, cryptic sentences, and love declarations. Someone is even complaining about spamming the blockchain with these texts. But although having fun is one of the suggested purposes of Eternitywall, the idea behind it is also about experimenting with a censorship-resistant technology. "Even if this site goes down or disappears, your message is guaranteed to persist," Eternitywall says.
“If you live under a dictatorship, you could use it for saying something that your government would remove or block," Casatta said.
Storing metadata, and texts, in the blockchain is not a new idea. It is a feature provided by the bitcoin protocol itself. Bitcoin core developers coded a specific instruction, called OP_RETURN, to add 80 arbitrary bytes in a transaction. There are many projects aimed at writing, retrieving and reading the metadata published into the blockchain through this script.
Eternitywall just makes all this easy and accessible to any user, converting the blockchain into a sort of unchangeable, eternal Twitter. So better think twice before pressing send.