Skip to content

Latest commit

 

History

History
282 lines (222 loc) · 6.14 KB

frontend.md

File metadata and controls

282 lines (222 loc) · 6.14 KB

Cryptocurrency frontend tutorial

Cryptocurrency demo application is built on Vue.js framework together with Bootstrap.

This tutorial covers the interaction of the client with Exonum blockchain:

Before start

There are two principal types of interaction between the client and the blockchain.

The first case is when the client send some data to blockchain. This data must be signed by the client's secret key before sending. Such a signature can be verified by a blockchain before acceptance. The data, together with its signature and service fields data, is called transaction.

The second case is when the data is signed by the blockchain nodes and the resulting signatures can be verified on the client.

Create a new user

Generate a new key pair:

const keyPair = Exonum.keyPair()

Define transaction:

const TxCreateWallet = Exonum.newMessage({
  network_id: 0,
  protocol_version: 0,
  service_id: 128,
  message_id: 2,
  fields: [
    { name: 'pub_key', type: Exonum.PublicKey },
    { name: 'name', type: Exonum.String }
  ]
})

Prepare transaction data:

const data = {
  pub_key: keyPair.publicKey,
  name: name
}

Sign data:

const signature = TxCreateWallet.sign(keyPair.secretKey, data)

Submit transaction to blockchain:

axios.post('/api/services/cryptocurrency/v1/wallets/transaction', {
  network_id: 0,
  protocol_version: 0,
  service_id: 128,
  message_id: 2,
  signature: signature,
  body: data
})

Add funds

Define transaction:

const TxIssue = Exonum.newMessage({
  network_id: 0,
  protocol_version: 0,
  service_id: 128,
  message_id: 1,
  fields: [
    { name: 'wallet', type: Exonum.PublicKey },
    { name: 'amount', type: Exonum.Uint64 },
    { name: 'seed', type: Exonum.Uint64 }
  ]
})

Prepare transaction data:

const data = {
  wallet: keyPair.publicKey,
  amount: amountToAdd.toString(),
  seed: Exonum.randomUint64()
}

Sign data:

const signature = TxIssue.sign(keyPair.secretKey, data)

Submit transaction to blockchain:

axios.post('/api/services/cryptocurrency/v1/wallets/transaction', {
  network_id: 0,
  protocol_version: 0,
  service_id: 128,
  message_id: 1,
  signature: signature,
  body: data
})

Transfer funds

Define transaction:

const TxTransfer = Exonum.newMessage({
  network_id: 0,
  protocol_version: 0,
  service_id: 128,
  message_id: 0,
  fields: [
    { name: 'from', type: Exonum.PublicKey },
    { name: 'to', type: Exonum.PublicKey },
    { name: 'amount', type: Exonum.Uint64 },
    { name: 'seed', type: Exonum.Uint64 }
  ]
})

Prepare transaction data:

const data = {
  from: keyPair.publicKey,
  to: receiver,
  amount: amountToTransfer,
  seed: Exonum.randomUint64()
}

Sign data:

const signature = TxTransfer.sign(keyPair.secretKey, data)

Submit transaction to blockchain:

axios.post(TX_URL, {
  network_id: 0,
  protocol_version: 0,
  service_id: 128,
  message_id: 0,
  signature: signature,
  body: data
})

Verify proof

Here is how the proof of the user's existence looks:

const data = {
  block_proof: {
    block: {...},
    precommits: [...]
  },
  wallet_proof: {
    to_table: {...},
    to_wallet: {...}
  },
  wallet_history: {
    proof: {...},
    transactions: [...]
  }
}

Verify the block and its precommits:

if (Exonum.verifyBlock(data.block_proof, validators, 0)) {...}

validators is actual list of public keys of validators:

const validators = [
  'a125c020442374014d3cd28f02674a8eb4114e7218c79a1158bdadb0c06b9919',
  ...
]

Extract the value from the Merkle Patricia tree of all tables (data.wallet.mpt_proof). Use state_hash as a root hash of the tree.

const TableKey = Exonum.newType({
  fields: [
    { name: 'service_id', type: Exonum.Uint16 },
    { name: 'table_index', type: Exonum.Uint16 }
  ]
})

const tableKey = TableKey.hash({
  service_id: 0,
  table_index: 0
})

const walletsHash = Exonum.merklePatriciaProof(data.block_proof.block.state_hash, data.wallet_proof.to_table, tableKey)

Extracted value is a root hash of the wallets Merkle Patricia tree (data.wallet.value). Extract wallet from the tree:

const Wallet = Exonum.newType({
  fields: [
    { name: 'pub_key', type: Exonum.PublicKey },
    { name: 'name', type: Exonum.String },
    { name: 'balance', type: Exonum.Uint64 },
    { name: 'history_len', type: Exonum.Uint64 },
    { name: 'history_hash', type: Exonum.Hash }
  ]
})

const wallet = Exonum.merklePatriciaProof(walletsHash, data.wallet_proof.to_wallet, publicKey, Wallet)

Extract transactions meta data from the Merkle tree:

const transactionsMetaData = Exonum.merkleProof(
  wallet.history_hash,
  wallet.history_len,
  data.wallet_history.proof,
  [0, wallet.history_len],
  TransactionMetaData
)

Verify each transaction:

for (let i = 0; i < data.wallet_history.transactions.length; i++) {
  let Transaction = getTransaction(data.wallet_history.transactions[i].message_id)
  const publicKeyOfTransaction = getPublicKeyOfTransaction(data.wallet_history.transactions[i].message_id, data.wallet_history.transactions[i].body)

  Transaction.signature = data.wallet_history.transactions[i].signature

  if (Transaction.hash(data.wallet_history.transactions[i].body) !== transactionsMetaData[i].tx_hash) {
    throw new Error('Invalid transaction hash has been found')
  }

  if (!Transaction.verifySignature(data.wallet_history.transactions[i].signature, publicKeyOfTransaction, data.wallet_history.transactions[i].body)) {
    throw new Error('Invalid transaction signature has been found')
  }
}

getTransaction function returns element of Exonum.newMessage type.