XDC transaction signing with Builder Vault

sequenceDiagram
    autonumber
    actor client1 as XDC client
    participant Blockchain as XDC Blockchain<br> RPC API
    actor client2 as BuilderVault client
    box Builder Vault
      participant TSM1 as MPC Wallet <br>(private key share 1)
      participant TSM2 as MPC Wallet <br>(private key share 2)
      participant TSM3 as MPC Wallet <br>(private key share 3)
    end
    #note over client,TSM2: Create wallet
    opt
      client2 ->> TSM1: create master key
      client2 ->> TSM1: create XDC wallet 
    end

    #note over client,TSM2: Create transations
    client1 ->> Blockchain: get blockchain inputs (gas, nonce, balance) for new tx<br>(sender wallet)
    client1 ->> client1: construct unsigned tx
    client1 ->> client2: request signature (unsigned tx hash)

    client2 ->> TSM1: request share1 signature (unsigned tx hash)
    TSM1 -->> client2: return partial signature
    client2 ->> TSM2: request share2 signature (unsigned tx hash)
    TSM2 -->> client2: return partial signature
    client2 ->> TSM3: request share3 signature (unsigned tx hash)
    TSM3 -->> client2: return partial signature
    client2 ->> client2: combine partial signatures
    client2 -->> client1: return signature
    client1 ->> Blockchain: broadcast signed tx<br>(signed tx)

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Prerequisites

• Go https://go.dev/doc/install
• Register a demo Builder Vault tenant: https://www.blockdaemon.com/wallet/builder-vault
• Download SDK bundle provided in registration email (extract auth certificates)
• Place Builder Vault client.crt & client.key in working directory

Step 1. Create Wallet with Builder Vault and XDC chain path

go run 1-create-xdc-wallet/main.go

• note the new XDC Wallet address and fund it through https://faucet.blocksscan.io
• note the Builder Vault Master Key ID (to be used for future signing)

Step 2. Craft an unsigned transaction with go-ethereum

• set the wallet address created in step 1
• set the destination address to send funds to

go run 2-craft-transaction/main.go

• check the wallet balance is not 0
• note the raw unsigned transaction (to be broadcast once signed)
• note the unsigned transaction hash (to be signed by Builder Vault)

Step 3. Sign transaction with MPC wallet library

• set the Builder Vault Master Key ID to be used for signing (created in step 1)
• set the unsigned transaction hash to be signed by Builder Vault (created in step 2)

go run 3-sign-transaction/main.go

• note the transaction signature

Step 4. Broadcast signed raw transaction with XDC client library

• set the transaction signature hash (created in step 3)
• set the raw unsigned transaction (created in step 2)

go run 4-broadcast-signed-transaction/main.go

• check the transaction hash on a block explorer

XDC Testnet Network details:

• RPC endpoint: https://erpc.apothem.network
• Block explorers: https://explorer.apothem.network https://apothem.blocksscan.io
• Faucets: https://faucet.apothem.network https://faucet.blocksscan.io
• ChainId: 51
• Web wallet: https://wallet.apothem.network https://mnrpc.xinfin.network
• TX decoder: https://rawtxdecode.in/