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.

Library compatibility with Exonum core:

JavaScript light client	Exonum core
0.12.1	0.9.*
0.10.2	0.8.*
0.9.0	0.7.*
0.6.1	0.6.*
0.6.1	0.5.*
0.3.0	0.4.0
0.3.0	0.3.0
0.2.0	0.2.0
0.1.1	0.1.*

Getting started
Data types
Serialization
Hash
Signature
- Sign data
- Verify signature
Transactions
Cryptographic proofs
- Merkle tree proof
- Map proof
Integrity checks
- Verify block
Helpers
Contributing
- Coding standards
- Test coverage
Changelog
License

Getting started

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

The definition of data structures is the main part of each application based on Exonum blockchain.

On the one hand, each transaction must be signed before sending into blockchain. Before the transaction is signed it is converted into byte array under the hood.

On the other hand, 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.

Converting data into a byte array is called serialization. To get the same serialization result on the client and on the service side, there must be a strict serialization rules. This rules are formed by the data structure definition.

Define data type

let type = Exonum.newType({
  fields: [
    { name: 'balance', type: Exonum.Uint32 },
    { name: 'name', type: Exonum.String }
  ]
})

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

Property	Description	Type
fields	List of fields.	`Array`

Field structure:

Field	Description	Type
name	Field name.	`String`
type	Definition of the field type.	Built-in type, array or custom data type defined by the developer.

Built-in types

There are several primitive types are built it into the library. These types must be used when constructing custom data types.

Name	Description	Type
Int8	Number in a range from `-128` to `127`.	`Number`
Int16	Number in a range from `-32768` to `32767`.	`Number`
Int32	Number in a range from `-2147483648` to `2147483647`.	`Number`
Int64	Number in a range from `-9223372036854775808` to `9223372036854775807`.	`Number` or `String`*
Uint8	Number in a range from `0` to `255`.	`Number`
Uint16	Number in a range from `0` to `65535`.	`Number`
Uint32	Number in a range from `0` to `4294967295`.	`Number`
Uint64	Number in a range from `0` to `18446744073709551615`.	`Number` or `String`*
Float32	Floating point number in a range from `-3.40282347e+38f32` to `3.40282347e+38f32`.	`Number` or `String`*
Float64	Floating point number in a range from `-1.7976931348623157e+308f64` to `1.7976931348623157e+308f64`.	`Number` or `String`*
Decimal	Decimal fixed point `79228162514264337593543950336 * 10^-28` to `79228162514264337593543950336`.	`String`*
String	A string of variable length consisting of UTF-8 characters.	`String`
Hash	Hexadecimal string.	`String`
PublicKey	Hexadecimal string.	`String`
Digest	Hexadecimal string.	`String`
Uuid	Hexadecimal string.	`String`
Bool	Value of boolean type.	`Boolean`

*JavaScript limits minimum and maximum integer number. Minimum safe integer in JavaScript is -(2^53-1) which is equal to -9007199254740991. Maximum safe integer in JavaScript is 2^53-1 which is equal to 9007199254740991. For unsafe numbers out of the safe range use String only. To determine either number is safe use built-in JavaScript function Number.isSafeInteger().

Nested data types

Custom data type defined by the developer can be a field of other custom data type.

An example of a nested type:

// Define a nested data type
let date = Exonum.newType({
  fields: [
    { name: 'day', type: Exonum.Uint8 },
    { name: 'month', type: Exonum.Uint8 },
    { name: 'year', type: Exonum.Uint16 }
  ]
})

// Define a data type
let payment = Exonum.newType({
  fields: [
    { name: 'date', type: date },
    { name: 'amount', type: Exonum.Uint64 }
  ]
})

There is no limitation on the depth of nested data types.

Arrays

The array in the light client library corresponds to the vector structure in the Rust language.

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

Property	Description	Type
type	Definition of the field type.	Built-in type, array or custom data type defined by the developer.

An example of an array type field:

// Define an array
let year = Exonum.newArray({
  type: Exonum.Uint16
})

// Define a data type
let type = Exonum.newType({
  fields: [
    { name: 'years', type: year }
  ]
})

An example of an array nested in an array:

// Define an array
let distance = Exonum.newArray({
  type: Exonum.Uint32
})

// Define an array with child elements of an array type
let distances = Exonum.newArray({
  type: distance
})

// Define a data type
let type = Exonum.newType({
  fields: [
    { name: 'measurements', type: distances }
  ]
})

Serialization

Each serializable data type has its (de)serialization rules, which govern how the instances of this type are (de)serialized from/to a binary buffer. Check serialization guide for details.

Signature of serialize function:

type.serialize(data, cutSignature)

Argument	Description	Type
data	Data to serialize.	`Object`
type	Definition of the field type.	Custom data type or transaction.
cutSignature	This flag is relevant only for transaction type. Specifies whether to not include a signature into the resulting byte array. Optional.	`Boolean`

An example of serialization into a byte array:

// Define a data type
let user = Exonum.newType({
  fields: [
    { name: 'firstName', type: Exonum.String },
    { name: 'lastName', type: Exonum.String },
    { name: 'age', type: Exonum.Uint8 },
    { name: 'balance', type: Exonum.Uint32 }
  ]
})

// Data to be serialized
const data = {
  firstName: 'John',
  lastName: 'Doe',
  age: 28,
  balance: 2500
}


// Serialize
let buffer = user.serialize(data) // [21, 0, 0, 0, 4, 0, 0, 0, 25, 0, 0, 0, 3, 0, 0, 0, 28, 196, 9, 0, 0, 74, 111, 104, 110, 68, 111, 101]

The value of the buffer array:

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)

Argument	Description	Type
data	Data to be processed using a hash function.	`Object`
type	Definition of the data type.	Custom data type or transaction.

An example of hash calculation:

// Define a data type
let user = Exonum.newType({
  fields: [
    { name: 'firstName', type: Exonum.String },
    { name: 'lastName', type: Exonum.String },
    { name: 'age', type: Exonum.Uint8 },
    { name: 'balance', type: Exonum.Uint32 }
  ]
})

// Data that has been hashed
const data = {
  firstName: 'John',
  lastName: 'Doe',
  age: 28,
  balance: 2500
}

// Get a hash
let hash = user.hash(data) // 1e53d91704b4b6adcbea13d2f57f41cfbdee8f47225e99bb1ff25d85474185af

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

Exonum.hash(buffer)

Argument	Description	Type
buffer	Byte array.	`Array` or `Uint8Array`.

An example of byte array hash calculation:

const arr = [132, 0, 0, 5, 89, 64, 0, 7]

let hash = Exonum.hash(arr) // 9518aeb60d386ae4b4ecc64e1a464affc052e4c3950c58e32478c0caa9e414db

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)

Argument	Description	Type
secretKey	Secret key as hexadecimal string.	`String`
data	Data to be signed.	`Object`
type	Definition of the data type.	Custom data type or transaction.
buffer	Byte array.	`Array` or `Uint8Array`.

The sign function returns value as hexadecimal String.

An example of data signing:

// Define a data type
let user = Exonum.newType({
  fields: [
    { name: 'firstName', type: Exonum.String },
    { name: 'lastName', type: Exonum.String },
    { name: 'age', type: Exonum.Uint8 },
    { name: 'balance', type: Exonum.Uint32 }
  ]
})

// Data to be signed
const data = {
  firstName: 'John',
  lastName: 'Doe',
  age: 28,
  balance: 2500
}

// 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)

Argument	Description	Type
signature	Signature as hexadecimal string.	`String`
publicKey	Public key as hexadecimal string.	`String`
data	Data that has been signed.	`Object`
type	Definition of the data type.	Custom data type or transaction.

The verifySignature function returns value of Boolean type.

An example of signature verification:

// Define a data type
let user = Exonum.newType({
  fields: [
    { name: 'firstName', type: Exonum.String },
    { name: 'lastName', type: Exonum.String },
    { name: 'age', type: Exonum.Uint8 },
    { name: 'balance', type: Exonum.Uint32 }
  ]
})

// Data that has been signed
const data = {
  firstName: 'John',
  lastName: 'Doe',
  age: 28,
  balance: 2500
}

// Define a signing key pair
const keyPair = {
  publicKey: 'fa7f9ee43aff70c879f80fa7fd15955c18b98c72310b09e7818310325050cf7a',
  secretKey: '978e3321bd6331d56e5f4c2bdb95bf471e95a77a6839e68d4241e7b0932ebe2b' +
  'fa7f9ee43aff70c879f80fa7fd15955c18b98c72310b09e7818310325050cf7a'
}

// Signature obtained upon signing using secret key
const signature = '41884c5270631510357bb37e6bcbc8da61603b4bdb05a2c70fc11d6624792e07' +
 'c99321f8cffac02bbf028398a4118801a2cf1750f5de84cc654f7bf0df71ec00'

// Verify the signature
let result = Exonum.verifySignature(signature, 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:

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

Define transaction

An example of a transaction definition:

let sendFunds = Exonum.newMessage({
  protocol_version: 0,
  service_id: 130,
  message_id: 128,
  fields: [
    { name: 'from', type: Exonum.Hash },
    { name: 'to', type: Exonum.Hash },
    { name: 'amount', type: Exonum.Uint64 }
  ]
})

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

Property	Description	Type
protocol_version	Protocol version.	`Number`
service_id	Service ID.	`Number`
message_id	Message ID.	`Number`
signature	Signature as hexadecimal string. Optional.	`String`
fields	List of fields.	`Array`

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: 'fa7f9ee43aff70c879f80fa7fd15955c18b98c72310b09e7818310325050cf7a',
  to: 'f7ea8fd02cb41cc2cd45fd5adc89ca1bf605b2e31f796a3417ddbcd4a3634647',
  amount: 1000
}

// 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(transactionEndpoint, explorerBasePath, data, signature, sendFunds, timeout, attempts)

sendFunds.send(transactionEndpoint, explorerBasePath, data, signature, timeout, attempts)

Property	Description	Type
transactionEndpoint	API address of transaction handler on a blockchain node.	`String`
explorerBasePath	API address of transaction explorer on a blockchain node.	`String`
data	Data that has been signed.	`Object`
signature	Signature as hexadecimal string.	`String`
type	Definition of the transaction.	Transaction.
timeout	Timeout between attempts to check transaction status. Optional. Default value is `500`.	`Number`
attempts	Number of attempts to check transaction status. Optional. Default value is `10`.	`Number`

The send function returns value of Promise type. 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 handler address
const transactionEndpoint = 'http://127.0.0.1:8200/api/services/cryptocurrency/v1/wallets'

// Define transaction explorer address
const explorerBasePath = 'http://127.0.0.1:8200/api/explorer/v1/transactions?hash='

sendFunds.send(transactionEndpoint, explorerBasePath, data, signature)

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(transactionEndpoint, explorerBasePath, transactions, timeout, attempts)

Property	Description	Type
transactionEndpoint	API address of transaction handler on a blockchain node.	`String`
explorerBasePath	API address of transaction explorer on a blockchain node.	`String`
transactions	List of transactions.	`Array`
timeout	Timeout between attempts to check each transaction status. Optional. Default value is `500`.	`Number`
attempts	Number of attempts to check each transaction status. Optional. Default value is `10`.	`Number`

Transaction structure:

Field	Description	Type
data	Transaction data that has been signed.	`Object`
signature	Signature as hexadecimal string.	`String`
type	Definition of the transaction.	Transaction.

The sendQueue function returns value of Promise type. 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:

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.

Argument	Description	Type
rootHash	The root hash of the Merkle tree as hexadecimal string.	`String`
count	The total number of elements in the Merkle tree.	`Number`
proofNode	The Merkle tree.	`Object`
range	An array of two elements of `Number` type. Represents list of obtained elements: `[startIndex; endIndex)`.	`Array`
type	Definition of the elements type. Optional. The `merkleProof` method expects to find byte arrays or hashes as values in the tree if `type` is not passed.	Custom data type

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.

Argument	Description	Type
json	The JSON presentation of the proof obtained from a full node.	`Object`
KeyType	Data type for keys in the Merkelized map.	Custom or built-in data type
ValueType	Data type for values in the Merkelized map.	Custom data type

The returned object has the following fields:

Field	Description	Type
merkleRoot	Hexadecimal hash of the root of the underlying Merkelized map	`String`
missingKeys	Set of keys which the proof asserts as missing from the map	`Set<KeyType>`
entries	Map of key-value pairs that the are proved to exist in the map	`Map<KeyType, ValueType>`

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.

Returns true if verification is succeeded or false if it is failed.

Argument	Description	Type
data	Structure with block and precommits.	`Object`
validators	An array of validators public keys as a hexadecimal strings.	`Array`

An example of block verification.

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.

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