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I have an idea for a dApp using Ethereum that would require user registration and a login system. Once logged in, the user will trigger transactions and smart contract part will come in. However, I am confused if I should I be storing the user details in a central database or in the blockchain? From what I've studied so far it seems using the blockchain as a replacement for database isn't the right way to think about it and data storage can also get very expensive.

I'm quite new to dApp/Ethereum so a lot of these concepts are still muddy to me, so any help would be appreciated.

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I've answered a similar but different question that may have a bearing on your project - https://stackoverflow.com/questions/42520069/handling-user-profiles-in-ethereum-dapps/42543219#42543219

It obviously depends on the goals and requirements of your project


One of the beauties of using a platform like Ethereum is that you can build a ZERO click login. If we establish that the user's web3.eth.accounts[0] is proof that the user controls the private key of that account's address, then you will always know that the user is valid.

User Signup

  • Users have Ethereum accounts.
  • On sign up user data is collected in an HTML form
  • User submits the form
  • Store the data in the database along with the Eth address

User Validation

  • User visits the website
  • web3js gets the active Ethereum account
  • AJAX passes the eth address to the database
  • If we recognise the address log the individual in

Thank you for your response. Pardon my lack of knowledge but how would an user have Ethereum account?

It's ok, we all begin (and kind of perpetually remain) as learners, asking is the best way to fill in the gaps in your knowledge.

A user would have an Ethereum account by creating one with something like MetaMask, or Parity, or Mist.

Also, when you mention storing user credentials in a database do you mean a normal relational database?

Yes. There are many cases where storing data on the Ethereum network makes sense, and other cases where it doesn't. From the sound of your question it seems like your data is personal information about the user, which would probably be best stored in a traditional relational database.

Lastly, for web3js to access this active Ethereum account would the user need MetaMask installed? Because AFAIK it allows the use of web3js. Again, apologies if these come off as rudimentary queries.

Well it depends on the browser the user is using, if they are using Chrome then MetaMask or Parity extensions will be required. You can also develop your own interface if you like.

Browsers like Mist have web3js built in. Parity although not a browser in the sense your users are familiar with can also be used like a browser with native web3js.

But the main principle is that the user has a means to securely store their private key on their machine. Secondarily the user has a means to conveniently transact on the Ethereum network.


However, I still have trouble understanding why a user would need an Ethereum account to simply run the dApp. From a traditional sense, all a user should need is register/login to starting using the application.

Because on the blockchain all authority comes from the user and their signed transactions. And user transactions can only be signed by the user's private key. There is no point in an application being a dApp if everything is centralised.

In the case of dApp are we to assume that a normal user of the app should have MetaMask and use it to create their Ethereum account?

No it doesn't have to be MetaMask, it can be something else that does the same thing for the user. But like I said above, if you are building a dApp then the user needs to be able to manage their own keys. Otherwise even if you have functionality happening on the blockchain, what ever it is that you've built it isn't decentralised.

A question you need to ask yourself. "Am I building something using the blockchain for the sake of building something on the blockchain? Or does my application depend on the fundamental properties of a programmable blockchain?"

  • Thank you for your response. Pardon my lack of knowledge but how would an user have Ethereum account? Also, when you mention storing user credentials in a database do you mean a normal relational database? Lastly, for web3js to access this active Ethereum account would the user need MetaMask installed? Because AFAIK it allows the use of web3js. Again, apologies if these come off as rudimentary queries. – ZeroDarkThirty Mar 16 '17 at 12:57
  • I've updated my answer to reply to your answers. – Samuel Hawksby-Robinson Mar 16 '17 at 13:17
  • Okay, now it's starting to get a bit more clear. From what I've gathered, one type of user data is the one that involves personal information, which will be stored in a relational database. This data can later be used for user authentication during login. However, I still have trouble understanding why a user would need an Ethereum account to simply run the dApp. From a traditional sense, all a user should need is register/login to starting using the application. In the case of dApp are we to assume that a normal user of the app should have MetaMask and use it to create their Ethereum account? – ZeroDarkThirty Mar 16 '17 at 13:28
  • I've updated my answer again. – Samuel Hawksby-Robinson Mar 16 '17 at 15:18
  • Hey Samuel, I've done some more study on my own since your last updated. From what I understand so far the user will create an Ethereum account using MetaMask and register via an HTML form - all those data will be stored in the database (including the Ethereum account public key). Next when they try to login, the system will check the active account in the browser (in MetaMask) against the existing accounts in the database. But my question is - if its a private app intended to be used for people with permission - what's stopping anyone from creating an account via MetaMask and registering? – ZeroDarkThirty Apr 3 '17 at 14:51

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