C# Transaction – How to Sign a Transaction Using C#

c#json-rpcnethereum

I want to create a signed transaction using C#, which will later be used by Nethereum via JSON-RPC to call eth_sendRawTransaction.

I have the raw transaction and the private key, now how do I sign the data with the key?

Best Answer

To expand the other response, to provide offline transaction signing in Nethereum you can do the following:

First, you will need your private key, and sender address. You can retrieve the sender address from your private key using Nethereum.Core.Signing.Crypto.EthECKey.GetPublicAddress(privateKey); if you only have the private key.

var privateKey = "0xb5b1870957d373ef0eeffecc6e4812c0fd08f554b37b233526acc331bf1544f7"; var senderAddress = "0x12890d2cce102216644c59daE5baed380d84830c";

Now using web3 first you will need to retrieve the total number of transactions of your sender address.

var web3 = new Web3(); var txCount = await web3.Eth.Transactions.GetTransactionCount.SendRequestAsync(senderAddress);

The txCount will be used as the nonce to sign the transaction.

Now using web3 again, you can build an encoded transaction as following:

var encoded = web3.OfflineTransactionSigning.SignTransaction(privateKey, receiveAddress, 10, txCount.Value);

If you need to include the data and gas there are overloads for it.

You can verify an encoded transaction: Assert.True(web3.OfflineTransactionSigning.VerifyTransaction(encoded));

Or get the sender address from an encoded transaction:

web3.OfflineTransactionSigning.GetSenderAddress(encoded);

To send the encoded transaction you will "SendRawTransaction"

var txId = await web3.Eth.Transactions.SendRawTransaction.SendRequestAsync("0x" + encoded);

You can see this example on the unit test

Or a "real" implementation on the Game sample

Related Solutions

Ethereum Transactions – Creating and Signing Offline Raw Transactions

ethereumjs-tx is a library with this example:

npm install ethereumjs-tx

const Tx = require('ethereumjs-tx').Transaction
var privateKey = new Buffer('e331b6d69882b4cb4ea581d88e0b604039a3de5967688d3dcffdd2270c0fd109', 'hex')

var rawTx = {
  nonce: '0x00',
  gasPrice: '0x09184e72a000', 
  gasLimit: '0x2710',
  to: '0x0000000000000000000000000000000000000000', 
  value: '0x00', 
  data: '0x7f7465737432000000000000000000000000000000000000000000000000000000600057'
}

var tx = new Tx(rawTx)
tx.sign(privateKey)

var serializedTx = tx.serialize()
console.log(serializedTx.toString('hex'))

[Ethereum] How to sign transaction for calling sendRawTransaction JSON RPC method

You might find this answer helpful: How to transfer ether from one account to another using EthereumJ

It gives an example of using the EthereumJ java library to create a transaction and sign it with a private key. It uses the Transaction sign() method. The example goes on to submit the transaction via the library, but for your case you could serialize it and submit it to the sendRawTransaction RPC call.

Something like:

Transaction tx = new Transaction( ... );
tx.sign(senderKey);
String hex =  Hex.toHexString(tx.getEncoded())

See the example here: https://github.com/ethereum/ethereumj/blob/develop/ethereumj-core/src/main/java/org/ethereum/samples/SendTransaction.java

Best Answer

Related Solutions

Ethereum Transactions – Creating and Signing Offline Raw Transactions

[Ethereum] How to sign transaction for calling sendRawTransaction JSON RPC method

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