Web3.js DApp Development – How to Create Offline Accounts and Sign Transactions

blockchainclientsdapp-developmentethereumjsweb3js

I have a question about Ethereum client-side, maybe someone could give a hint…

It's about building a DApp, we need a web client capable of creating offline a private key and a public key, and also send signed transactions to an Ethereum node.

After investigating for a while we came to the conclusion this is possible through the web3.js library (and others like ethereumjs), but it implies using nodejs and browserfy, right? The question is:

Is there any other simpler solution, such as using a simple js file?

Thx in advance!

Best Answer

You are making a wrong assumption. Using Web3.js does not require Browserify or Node.JS. You can drop in web3.js dependency in HTML code like any other JavaScript library. Only building Web3.js distribution requires this build toolchain.

Here is a simple "index.html" application using web3.js.

Related Solutions

[Ethereum] EthereumJS: How to get public key from private key

ethereumjs-wallet can be used to get public key from private key:

> const hdkey = require('ethereumjs-wallet/hdkey')
> const privateKey = hdkey.fromMasterSeed('random')._hdkey._privateKey
> const Wallet = require('ethereumjs-wallet')
> const wallet = Wallet.fromPrivateKey(privateKey)
> wallet.getPublicKeyString()
'0x11f2b30c9479ccaa639962e943ca7cfd3498705258ddb49dfe25bba00a555e48cb35a79f3d084ce26dbac0e6bb887463774817cb80e89b20c0990bc47f9075d5'
> wallet.getPublicKey()
<Buffer 11 f2 b3 0c 94 79 cc aa 63 99 62 e9 43 ca 7c fd 34 98 70 52 58 dd b4 9d fe 25 bb a0 0a 55 5e 48 cb 35 a7 9f 3d 08 4c e2 6d ba c0 e6 bb 88 74 63 77 48 ... >

Another option is to use ethereumjs-util (which is used by ethereumjs-wallet internally):

> const util = require('ethereumjs-util')
> util.privateToPublic(privateKey)
<Buffer 11 f2 b3 0c 94 79 cc aa 63 99 62 e9 43 ca 7c fd 34 98 70 52 58 dd b4 9d fe 25 bb a0 0a 55 5e 48 cb 35 a7 9f 3d 08 4c e2 6d ba c0 e6 bb 88 74 63 77 48 ... >

Yet another option is secp256k1:

> const secp256k1 = require('secp256k1')
> secp256k1.publicKeyCreate(privateKey, false).slice(1)
<Buffer 11 f2 b3 0c 94 79 cc aa 63 99 62 e9 43 ca 7c fd 34 98 70 52 58 dd b4 9d fe 25 bb a0 0a 55 5e 48 cb 35 a7 9f 3d 08 4c e2 6d ba c0 e6 bb 88 74 63 77 48 ... >

slice(1) is to drop type byte which is hardcoded as 04 ethereum.

Parity Node – Safety of Public Hosting

Let me walk you through the options.

I'm assuming you are only requiring the RPC for your users, so either run parity in --public-node mode which disables account storage and transaction signing on your server or disable the wallet with --no-ui.
If you really only want to serve RPC, you can not only disable --no-ui but also the websocket with --no-ws and the dapps server with --no-dapps.
To expose your RPC to the public, you have to set your --jsonrpc-interface to <your public ip> and allow --jsonrpc-hosts all.
And finally, to your initial question: To only expose safe APIs for your users, you can set --jsonrpc-apis safe.

So it looks something like that:

parity --no-ui --no-ws --no-dapps --jsonrpc-interface 133.3.3.37 --jsonrpc-hosts all --jsonrpc-apis safe

Please let me know if this is what you were looking for.

Disclosure: I work for Parity.

Best Answer

Related Solutions

[Ethereum] EthereumJS: How to get public key from private key

Parity Node – Safety of Public Hosting

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