Light Client for Exonum Blockchain

A JavaScript library to work with Exonum blockchain from browser and Node.js. Used to sign transactions before sending to blockchain and verify blockchain responses using cryptographic proofs. Contains numerous helper functions. Find out more information about the architecture and tasks of light clients in Exonum.

If you are using Exonum in your project and want to be listed on our website & GitHub list — write us a line to exonum@bitfury.com.

Library compatibility with Exonum core:

• Getting started
• Data types
• Hash
• Signature
  • Sign data
  • Verify signature
• Transactions
  • Define transaction
  • Sign transaction
  • Send transaction
  • Send multiple transactions
• Cryptographic proofs
  • Merkle tree proof
  • Map proof
• Integrity checks
  • Verify block
  • Verify table
  • Built-in structures
• Helpers
  • Generate key pair
  • Get random number
  • Converters
    • Hexadecimal to Uint8Array
    • Hexadecimal to String
    • Uint8Array to Hexadecimal
    • Binary String to Uint8Array
    • Binary String to Hexadecimal
    • String to Uint8Array
• Contributing
  • Coding standards
  • Test coverage
• Changelog
• License

Getting started

First of all, you should have installed these tools and libraries:

• C/C++ compiler
• libtool
• automake
• autoconf

On MacOS:

1. Install XCode
2. brew install libtool automake autoconf

On Ubuntu:

sudo apt install gcc libtool automake autoconf

There are several options to include light client library in the application:

The most preferred way is to install Exonum Client as a package from npm registry:

npm install exonum-client

Otherwise you can download the source code from GitHub and compile it before use in browser.

Include in browser:

<script src="node_modules/exonum-client/dist/exonum-client.min.js"></script>

Usage in Node.js:

let Exonum = require('exonum-client')

Data types

Exonum use protobufjs library to serialize structured data into protobuf format.

Each transaction is signed before sending into blockchain. Before the transaction is signed it is converted into byte array under the hood.

The data received from the blockchain should be converted into byte array under the hood before it will be possible to verify proof of its existence using cryptographic algorithm.

Developer can both define data stuctures on the fly or use precompiled stubs with data structures.

To define protobuf structures use protobufjs library.

Example:

let Message = new Type('CustomMessage')
Message.add(new Field('balance', 1, 'uint32'))
Message.add(new Field('name', 2, 'string'))
 
let type = Exonum.newType(Message)

Exonum.newType function requires a single argument of protobuf.Type type with next structure.

Hash

Exonum uses cryptographic hashes of certain data for transactions and proofs.

Different signatures of the hash function are possible:

Exonum.hash(data, type)

type.hash(data)

An example of hash calculation:

// Define a data structure
let Message = new Type('CustomMessage')
Message.add(new Field('balance', 1, 'uint32'))
Message.add(new Field('name', 2, 'string'))
 
// Define a data type
const User = Exonum.newType(Message)
 
// Data that has been hashed
const data = {
  balance: 100,
  name: 'John Doe'
}
 
// Get a hash
let hash = User.hash(data) // 9786347be1ab7e8f3d68a49ef8a995a4decb31103c53565a108170dec4c1c2fa

It is also possible to get a hash from byte array:

Exonum.hash(buffer)

An example of byte array hash calculation:

const arr = [8, 100, 18, 8, 74, 111, 104, 110, 32, 68, 111, 101]
 
let hash = Exonum.hash(arr) // 9786347be1ab7e8f3d68a49ef8a995a4decb31103c53565a108170dec4c1c2fa

Signature

The procedure for signing data using signing key pair and verifying of obtained signature is commonly used in the process of data exchange between the client and the service.

Built-in Exonum.keyPair helper function can be used to generate a new random signing key pair.

Sign data

The signature can be obtained using the secret key of the signing pair.

There are three possible signatures of the sign function:

Exonum.sign(secretKey, data, type)

type.sign(secretKey, data)

Exonum.sign(secretKey, buffer)

The sign function returns value as hexadecimal String.

An example of data signing:

// Define a data structure
let Message = new Type('CustomMessage')
Message.add(new Field('balance', 1, 'uint32'))
Message.add(new Field('name', 2, 'string'))
 
// Define a data type
const User = Exonum.newType(Message)
 
// Data that has been hashed
const data = {
  balance: 100,
  name: 'John Doe'
}
 
// Define a signing key pair
const keyPair = {
  publicKey: 'fa7f9ee43aff70c879f80fa7fd15955c18b98c72310b09e7818310325050cf7a',
  secretKey: '978e3321bd6331d56e5f4c2bdb95bf471e95a77a6839e68d4241e7b0932ebe2b' +
  'fa7f9ee43aff70c879f80fa7fd15955c18b98c72310b09e7818310325050cf7a'
}
 
// Sign the data
let signature = Exonum.sign(keyPair.secretKey, data, User)

Verify signature

The signature can be verified using the author's public key.

There are two possible signatures of the verifySignature function:

Exonum.verifySignature(signature, publicKey, data, type)

type.verifySignature(signature, publicKey, data)

The verifySignature function returns value of Boolean type.

An example of signature verification:

// Define a data structure
let Message = new Type('CustomMessage')
Message.add(new Field('balance', 1, 'uint32'))
Message.add(new Field('name', 2, 'string'))
 
// Define a data type
const User = Exonum.newType(Message)
 
// Data that has been hashed
const data = {
  balance: 100,
  name: 'John Doe'
}
 
// Define a signing key pair
const keyPair = {
  publicKey: 'fa7f9ee43aff70c879f80fa7fd15955c18b98c72310b09e7818310325050cf7a',
  secretKey: '978e3321bd6331d56e5f4c2bdb95bf471e95a77a6839e68d4241e7b0932ebe2b' +
  'fa7f9ee43aff70c879f80fa7fd15955c18b98c72310b09e7818310325050cf7a'
}
 
// Signature obtained upon signing using secret key
const signature = 'a4cf7c457e3f4d54ef0c87900e7c860d2faa17a8dccbaafa573a3a960cda3f66' +
 '27911088138526d9d7e46feba471e6bc7b93262349a5ed18262cbc39c8a47b04'
 
// Verify the signature
let result = Exonum.verifySignature(signature, keyPair.publicKey, data, User) // true

Transactions

Transaction in Exonum is a operation to change the data stored in blockchain. Transaction processing rules is a part of business logic implemented on service side.

Sending data to the blockchain from a light client consist of 3 steps:

1. Describe the fields of transaction using custom data types;
2. Sign data of transaction using signing key pair;
3. Send transaction to the blockchain.

Read more about transactions in Exonum.

Define transaction

An example of a transaction definition:

let Transaction = new Type('CustomMessage')
Transaction.add(new Field('from', 1, 'string'))
Transaction.add(new Field('to', 2, 'string'))
Transaction.add(new Field('amount', 3, 'uint32'))
 
let sendFunds = Exonum.newTransaction({
  author: 'fa7f9ee43aff70c879f80fa7fd15955c18b98c72310b09e7818310325050cf7a',
  chain_id: 0,
  instance_id: 130,
  method_id: 0,
  schema: Transaction
})

Exonum.newTransaction function requires a single argument of Object type with next structure:

Field structure is identical to field structure of custom data type.

Sign transaction

An example of a transaction signing:

// Signing key pair
const keyPair = {
  publicKey: 'fa7f9ee43aff70c879f80fa7fd15955c18b98c72310b09e7818310325050cf7a',
  secretKey: '978e3321bd6331d56e5f4c2bdb95bf471e95a77a6839e68d4241e7b0932ebe2b' +
  'fa7f9ee43aff70c879f80fa7fd15955c18b98c72310b09e7818310325050cf7a'
}
 
// Transaction data to be signed
const data = {
  from: 'John',
  to: 'Adam',
  amount: 50
}
 
// Sign the data
let signature = sendFunds.sign(keyPair.secretKey, data)

Send transaction

To submit transaction to the blockchain send function can be used.

There are two possible signatures of the send function:

Exonum.send(explorerBasePath, type, data, secretKey, attempts, timeout)
 
sendFunds.send(explorerBasePath, data, secretKey, attempts, timeout)

The send function returns value of Promise type with transaction hash as a fulfilled value. Fulfilled state means that transaction is accepted to the block. Fulfilled value contained transaction with its proof.

An example of a transaction sending:

// Define transaction explorer address
const explorerBasePath = 'http://127.0.0.1:8200/api/explorer/v1/transactions'
 
sendFunds.send(explorerBasePath, data, keyPair.secretKey).then(txHash => {})

Send multiple transactions

To submit multiple transactions to the blockchain sendQueue function can be used. Transactions will be stored in the appropriate order. Each transaction from the queue will be sent to the blockchain only after the previous transaction is accepted to the block.

Exonum.sendQueue(explorerBasePath, transactions, secretKey, attempts, timeout)

Transaction structure:

The sendQueue function returns value of Promise type with an array of transaction hashes as a fulfilled value. Fulfilled state means that all transactions are accepted to the block. Fulfilled value contained an array of transactions with its proofs.

Find more examples of operations on transactions:

• Define transaction
• Serialize transaction
• Sign transaction
• Verify signed transaction
• Get a transaction hash
• Send transaction
• Send multiple transactions

Cryptographic proofs

A cryptographic proof is a format in which a Exonum node can provide sensitive data from a blockchain. These proofs are based on Merkle trees and their variants.

Light client library validates the cryptographic proof and can prove the integrity and reliability of the received data.

Read more about design of cryptographic proofs in Exonum.

Merkle tree proof

let elements = Exonum.merkleProof(rootHash, count, tree, range, type)

The merkleProof method is used to validate the Merkle tree and extract a list of data elements.

An example of verifying a Merkle tree.

Map proof

let proof = new Exonum.MapProof(json, KeyType, ValueType)
console.log(proof.entries)

The MapProof class is used to validate proofs for Merkelized maps.

The returned object has the following fields:

An example of using a MapProof.

Integrity checks

Verify block

Exonum.verifyBlock(data, validators)

Each new block in Exonum blockchain is signed by validators. To prove the integrity and reliability of the block, it is necessary to verify their signatures. The signature of each validator are stored in the precommits.

The merkleProof method is used to validate block and its precommits.

The verifyBlock function returns value of Promise type. Fulfilled state means that block is valid.

An example of block verification.

Verify table

Exonum.verifyTable(proof, stateHash, instanceId, tableIndex)

Verify table existence in the root tree.

Returns root hash for the table as hexadecimal String.

Built-in structures

List of built-in Exonum blockchain structures:

List of built-in Exonum consensus structures:

List of built-in Exonum key-value sequence structures:

List of built-in Exonum proofs structures:

List of built-in Exonum runtime structures:

List of built-in Exonum crypto structures:

List of built-in Exonum common structures:

List of built-in Exonum list proof structures:

List of built-in Exonum map proof structures:

Helpers

Generate key pair

const pair = Exonum.keyPair()

{
  publicKey: "...", // 32-byte public key
  secretKey: "..." // 64-byte secret key
}

Exonum.keyPair function generates a new random Ed25519 signing key pair using the TweetNaCl cryptographic library.

Get random number

const rand = Exonum.randomUint64()

Exonum.randomUint64 function generates a new random Uint64 number of cryptographic quality using the TweetNaCl cryptographic library.

Converters

Hexadecimal to Uint8Array

const hex = '674718178bd97d3ac5953d0d8e5649ea373c4d98b3b61befd5699800eaa8513b'
 
Exonum.hexadecimalToUint8Array(hex) // [103, 71, 24, 23, 139, 217, 125, 58, 197, 149, 61, 13, 142, 86, 73, 234, 55, 60, 77, 152, 179, 182, 27, 239, 213, 105, 152, 0, 234, 168, 81, 59]

Hexadecimal to String

const hex = '674718178bd97d3ac5953d0d8e5649ea373c4d98b3b61befd5699800eaa8513b'
 
Exonum.hexadecimalToBinaryString(hex) // '0110011101000111000110000001011110001011110110010111110100111010110001011001010100111101000011011000111001010110010010011110101000110111001111000100110110011000101100111011011000011011111011111101010101101001100110000000000011101010101010000101000100111011'

Uint8Array to Hexadecimal

const arr = new Uint8Array([103, 71, 24, 23, 139, 217, 125, 58, 197, 149, 61, 13, 142, 86, 73, 234, 55, 60, 77, 152, 179, 182, 27, 239, 213, 105, 152, 0, 234, 168, 81, 59])
 
Exonum.uint8ArrayToHexadecimal(arr) // '674718178bd97d3ac5953d0d8e5649ea373c4d98b3b61befd5699800eaa8513b'

Uint8Array to BinaryString

const arr = new Uint8Array([103, 71, 24, 23, 139, 217, 125, 58, 197, 149, 61, 13, 142, 86, 73, 234, 55, 60, 77, 152, 179, 182, 27, 239, 213, 105, 152, 0, 234, 168, 81, 59])
 
Exonum.uint8ArrayToBinaryString(arr) // '0110011101000111000110000001011110001011110110010111110100111010110001011001010100111101000011011000111001010110010010011110101000110111001111000100110110011000101100111011011000011011111011111101010101101001100110000000000011101010101010000101000100111011'

Binary String to Uint8Array

const str = '0110011101000111000110000001011110001011110110010111110100111010110001011001010100111101000011011000111001010110010010011110101000110111001111000100110110011000101100111011011000011011111011111101010101101001100110000000000011101010101010000101000100111011'
 
Exonum.binaryStringToUint8Array(str) // [103, 71, 24, 23, 139, 217, 125, 58, 197, 149, 61, 13, 142, 86, 73, 234, 55, 60, 77, 152, 179, 182, 27, 239, 213, 105, 152, 0, 234, 168, 81, 59]

Binary String to Hexadecimal

const str = '0110011101000111000110000001011110001011110110010111110100111010110001011001010100111101000011011000111001010110010010011110101000110111001111000100110110011000101100111011011000011011111011111101010101101001100110000000000011101010101010000101000100111011'
 
Exonum.binaryStringToHexadecimal(str) // '674718178bd97d3ac5953d0d8e5649ea373c4d98b3b61befd5699800eaa8513b'

String to Uint8Array

const str = 'Hello world'
 
Exonum.stringToUint8Array(str) // [72, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100]

Contributing

The contributing to the Exonum Client is based on the same principles and rules as the contributing to exonum-core.

Coding standards

The coding standards are described in the .eslintrc file.

To help developers define and maintain consistent coding styles between different editors and IDEs we used .editorconfig configuration file.

Test coverage

All functions must include relevant unit tests. This applies to both of adding new features and fixing existed bugs.

Changelog

Detailed changes for each release are documented in the CHANGELOG file.

License

Exonum Client is licensed under the Apache License (Version 2.0). See LICENSE for details.