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Javascript/Typescript

Aleo SDK

Tools for Building Zero Knowledge Web Apps​

The Aleo SDK is a collection of JavaScript libraries for building zero knowledge web applications in both the browser and node.js.

Overview​

Aleo provides the ability to run programs in zero knowledge. The Aleo SDK provides the tools to use these programs within the browser and all other levels of the web stack to build privacy preserving applications.

The Aleo SDK provides the following functionality (Click to see examples):

  1. Aleo account management
  2. Web-based program execution and deployment
  3. Aleo credit transfers
  4. Management of program state and data
  5. Communication with the Aleo network

Table of Contents​

Installation​

NPM​

To install the Aleo SDK from NPM run:

npm install @aleohq/sdk or yarn add @aleohq/sdk.

Build from source​

To build the project from source, go to this project's root and execute:

npm install && npm run build

Usage​

Zero Knowledge Web App Examples​

Create Leo App​

A set of fully functional examples of zero knowledge web apps can be found in create-leo-app. Create-aleo-app provides several web-app templates in common web frameworks such as React that can be used as a starting point for building zero knowledge web apps.

Developers can get started immediately with create-react-app by running: npm create aleo-app@latest

Provable Tools​

Additionally, the SDK powers provable.tools - a React app that provides a graphical interface for most of the functionality provided by the SDK and can be used as a reference for usage of the SDK. Source code for provable.tools can be found in the SDK repo here

1. Create an Aleo Account​

The first step in operating a zero knowledge web application is creating a cryptographic identity for a user. In the context of Aleo, this process starts by generating a private key. From this private key, several keys that enable a user to interact with Aleo programs can be derived.

These keys include:

Private Key​

The key used to represent an identity of an individual user. This key is used to authorize zero knowledge program execution.

View Key​

This key is derived from the private key and can be used to identify all records and transaction data that belongs to an individual user.

Compute Key​

A key that can be used to trustlessly run applications and generate transactions on a user's behalf.

Address​

A public address that can be used to trustlessly identify a user in order for that user to receive official Aleo credits or unique data defined by other zero-knowledge Aleo programs.

All of these keys can be created using the account object:

import { Account } from '@aleohq/sdk';

const account = new Account();

// Individual keys can then be accessed through the following methods
const privateKey = account.privateKey();
const viewKey = account.viewKey();
const address = account.address();

Please note that all keys are considered sensitive information and should be stored securely.

2. Execute Aleo Programs​

2.1 Aleo Programs​

Aleo programs provide the ability for users to make any input or output of a program private and prove that the program was run correctly. Keeping program inputs and outputs private allows developers to build privacy into their applications.

Zero-Knowledge programs are written in one of two languages:

  1. Leo: A high level, developer friendly language for developing zero knowledge programs.
  2. Aleo Instructions: A low level language that provides developers fine grained control over the execution flow of zero knowledge programs. Leo programs are compiled into Aleo Instructions under the hood.

Documentation for both languages can be found at developer.aleo.org.

Hello world in the Leo Language​

// A simple program adding two numbers together
program helloworld.aleo {
  transition hello(public a: u32, b: u32) -> u32 {
      let c: u32 = a + b;
      return c;
  }
}

Hello world in Aleo instructions​

program helloworld.aleo;

// The leo code above compiles to the following Aleo instructions
function hello:
    input r0 as u32.public;
    input r1 as u32.private;
    add r0 r1 into r2;
    output r2 as u32.private;

2.2 Program Execution Model​

The SDK provides the ability to execute Aleo Instructions programs %100 client-side within the browser.

The ProgramManager object encapsulates the functionality for executing programs and making zero knowledge proofs about them. Under the hood it uses cryptographic code compiled from snarkVM into WebAssembly. JavaScript bindings to this WebAssembly code allows execution of programs in zero knowledge fully within the browser without requiring any external communication with the internet. Users interested in lower level details on how this is achieved can visit the aleo-wasm crate.

The basic execution flow of a program is as follows:

  1. A web app is loaded with an instance of the ProgramManager object
  2. An Aleo program in Aleo Instructions format is loaded into the ProgramManager as a wasm object
  3. The web app provides a user input form for the program
  4. The user submits the inputs and the zero knowledge execution is performed client-side within WebAssembly
  5. The result is returned to the user
  6. (Optional) A fully encrypted zero knowledge transcript of the execution is optionally sent to the Aleo network

A diagrammatic representation of the program execution flow is shown below.

graph LR
    p1[Leo Program]
    p2[Aleo Instructions]
 
    subgraph Browser Web-App
        subgraph ProgramManager
            subgraph Aleo-Wasm-Module
                in-memory-program
            end
        end
    end

    p1-->p2--load program--oin-memory-program-.ZK result.->user
    user-.user input.->in-memory-program
    in-memory-program-."ZK result (Optional)".->Aleo-Network

2.3 WebAssembly Initialization​

❗WebAssembly must be initialized before calling any SDK functions. The current Aleo SDK manages the wasm initialization. Therefore, the workers must be defined properly.

Aleo programs are made zero knowledge through the usage of ZkSnarks. The Rust code behind Aleo programs and the ZkSnarks that make them zero knowledge are hosted in the snarkVM Repository. The Aleo SDK compiles this code to WebAssembly and creates JavaScript bindings, enabling Aleo programs to run directly in the browser.

Before any logic within the SDK is run within the browser however, the WebAssembly module the SDK contains must be initialized before any SDK functions can be executed. This is done simply by calling the initializeWasm function at a point in your code before any other SDK functions are called:

import { Account, initializeWasm } from '@aleohq/sdk';

// Assuming top-level await is enabled. This can also be initialized within a promise.
await initializeWasm();

/// Create a new Aleo account
const account = new Account();

An example of how to initialize WebAssembly in a React app is shown in Section 2.8

2.4 Local Program Execution​

A simple example of running the hello world program within the web browser is shown below:

import { Account, Program } from '@aleohq/sdk';

/// Create the source for the "hello world" program
const program = "program helloworld.aleo;\n\nfunction hello:\n    input r0 as u32.public;\n    input r1 as u32.private;\n    add r0 r1 into r2;\n    output r2 as u32.private;\n";
const programManager = new ProgramManager();

/// Create a temporary account for the execution of the program
const account = new Account();
programManager.setAccount(account);

/// Get the response and ensure that the program executed correctly
const executionResponse = await programManager.executeOffline(program, "hello", ["5u32", "5u32"]);
const result = executionResponse.getOutputs();
assert(result === ["10u32"]);

2.5 Program execution on the Aleo Network​

The SDK also provides the ability to execute programs and record an encrypted transcript of the execution on the Aleo network that anyone can trustlessly verify.

This process can be thought of being executed in three steps:

  1. A program is run locally
  2. A proof that the program was executed correctly and that the outputs follow from the inputs is generated
  3. A transcript of the proof is generated client-side containing encrypted proof data (see Section 4) and any public outputs or state the user of the program wishes to reveal
  4. The proof transcript is posted to the Aleo network and verified by the Aleo validator nodes in a trustless manner
  5. If the proof is valid, it is stored and anyone can later verify the proof and read the outputs the author of the program has chosen to make public. Private inputs will remain encrypted, but the author of the proof can also choose to retrieve this encrypted state at any point and decrypt it locally for their own use.

This process of posting the execution to the Aleo Network serves as a globally trustless and verifiable record of program execution. It also provides a global record of any state changes made to either records or data stored on the Aleo network.

A simple example of running the hello world program on the Aleo network is shown below:

import { Account, AleoNetworkClient, NetworkRecordProvider, ProgramManager, KeySearchParams} from '@aleohq/sdk';

// Create a key provider that will be used to find public proving & verifying keys for Aleo programs
const keyProvider = new AleoKeyProvider();
keyProvider.useCache = true;

// Define an account which will execute the transaction on-chain
const account = new Account({ privateKey: private_key });
const privateKeyObject = PrivateKey.from_string(private_key);

// Create a record provider that will be used to find records and transaction data for Aleo programs
const networkClient = new AleoNetworkClient("https://api.explorer.aleo.org/v1");
const recordProvider = new NetworkRecordProvider(account, networkClient);

// Initialize a program manager to talk to the Aleo network with the configured key and record providers
const programName = "hello_hello.aleo";
const programManager = new ProgramManager("https://api.explorer.aleo.org/v1", keyProvider, recordProvider);
programManager.setHost("https://api.explorer.aleo.org/v1")
programManager.setAccount(account);

// For example: "cacheKey": "hello_hello:hello"
const cacheKey = `${programId}:${aleoFunction}`;
const keySearchParams = new AleoKeyProviderParams({ "cacheKey": cacheKey });

// Execute the program function
const executionResponse = await programManager.execute(
        programId,
        aleoFunction,
        fee,
        false,
        inputs,
        undefined,
        keyParams,
        undefined,
        undefined,
        undefined,
        privateKeyObject
    );

const transaction = await programManager.networkClient.getTransaction(executionResponse);

A reader of the above example may notice the RecordProvider and KeyProvider classes that were not present in the local execution example. The KeyProvider class helps users of the SDK find Proving Keys for programs. Proving Keys allow zero knowledge proofs that the programs were executed correctly to be created. The RecordProvider class helps find Records which are private data associated with programs that can be changed and updated throughout time. These two concepts are explained in more detail below.

2.6 Program Proving Keys & Program Records​

Executing Aleo programs in zero knowledge requires two additional pieces of information.

  1. Function Proving & Verifying Keys: Proving and Verifying keys are cryptographic keys that are generated when a program function is executed. These keys are public and unique for each function in a program. The proving key allows any party to execute the program and generate a proof that the program was executed correctly. The verifying keys allow any party to verify that the proof was generated correctly and the execution is correct. These keys are required to create the zero knowledge property of program execution.
  2. Program Records: Records are private state generated by a program belonging to a unique private keyholder. Records are generated by a program's functions and can be changed and updated by when a user runs various functions of the program. These records are private by default and are used to manage updatable private state. One of the most clear usages of records is to the credits record in the credits.aleo. Credits records are one of two official ways of representing Aleo credits on the Aleo Network and are used to pay all transaction fees on the network. More information on Records can be found in the Records section below.

For this reason, all programs will need proving and verifying keys to operate and many functions in Aleo programs will require records as inputs. To simplify the process of managing keys and records, the Aleo SDK provides two abstractions for managing these concepts:

  1. KeyProvider: When programs execute, by default, they will synthesize the proving and verifying keys needed to make a zero knowledge proof. However, these keys are large and expensive to generate. For this reason, applications may want to store these keys and re-use them for future execution. The KeyProvider interface provides the ability for users of the SDK to provide their own key storage and retrieval mechanism. The SDK provides a default implementation of the KeyProvider interface via the AleoKeyProvider class.
  2. RecordProvider: When programs execute, they will often need to find records that belong to a user. The RecordProvider interface allows users of the SDK to implement their own record storage and retrieval mechanism. The SDK provides a default implementation of the RecordProvider interface via the NetworkRecordProvider class which searches the Aleo network for records uniquely belonging to a user.

The ProgramManager class is capable of taking a KeyProvider and RecordProvider as arguments and will use them to find the correct keys and records for a program execution.

2.7 Deploy a new Program to the Aleo Network​

The Aleo Network contains a public registry of programs that can be executed by anyone. Any user can add an Aleo program to the network (as long as it doesn't already currently exist) by paying a deployment fee in Aleo credits. The SDK provides a simple interface for deploying programs to the Aleo network using the program manager.

import { Account, AleoNetworkClient, NetworkRecordProvider, ProgramManager, KeySearchParams} from '@aleohq/sdk';

// Create a key provider that will be used to find public proving & verifying keys for Aleo programs
const keyProvider = new AleoKeyProvider();
keyProvider.useCache = true;

// Create a record provider that will be used to find records and transaction data for Aleo programs
const networkClient = new AleoNetworkClient("https://api.explorer.aleo.org/v1");
const recordProvider = new NetworkRecordProvider(account, networkClient);

// Initialize a program manager to talk to the Aleo network with the configured key and record providers
const programManager = new ProgramManager("https://api.explorer.aleo.org/v1", keyProvider, recordProvider);

// Define an Aleo program to deploy
const program = "program hello_hello.aleo;\n\nfunction hello:\n    input r0 as u32.public;\n    input r1 as u32.private;\n    add r0 r1 into r2;\n    output r2 as u32.private;\n";

// Define a fee to pay to deploy the program
const fee = 1.8; // 1.8 Aleo credits

// Deploy the program to the Aleo network
const tx_id = await programManager.deploy(program, fee);

// Verify the transaction was successful
const transaction = await programManager.networkClient.getTransaction(tx_id);

2.8 React Example​

The above concepts can be tied together in a concrete example of a React web app. This example can be installed in one step by running:

npm create aleo-app@latest

Wasm Initialization​

The WASM module can be initialized within the browser. A common way of achieving this within a React App is using a React UseEffect hook.

aleo-wasm-hook.js

import { useEffect, useState } from "react";
import * as sdk from "@aleohq/sdk";

await sdk.initializeWasm();
export const useAleoWASM = () => {
    const [aleoInstance, setAleoInstance] = useState(null);

    useEffect(() => {
        if (aleoInstance === null) {
            setAleoInstance(sdk);
        }
    }, []); // eslint-disable-line react-hooks/exhaustive-deps
    return aleoInstance;
};

Once a hook for the WASM initialization is created, it can be used anywhere within the app.

Program Execution​

Program execution is a computationally expensive process. For this reason, it is recommended to execute programs in webworkers.

We will have 2 main components for workers:

  • worker.js
  • AleoWorker.js (Manager for worker file)
Example Web Worker Usage

A worker file that performs the execution can be created as follows: worker.js

import {
  Account,
  ProgramManager,
  PrivateKey,
  initThreadPool,
  AleoKeyProvider,
  AleoNetworkClient,
  NetworkRecordProvider,
} from "@aleohq/sdk";
import { expose, proxy } from "comlink";

await initThreadPool();

async function localProgramExecution(program, aleoFunction, inputs) {
  const programManager = new ProgramManager();

  // Create a temporary account for the execution of the program
  const account = new Account();
  programManager.setAccount(account);

  const executionResponse = await programManager.run(
    program,
    aleoFunction,
    inputs,
    false,
  );
  return executionResponse.getOutputs();
}

async function getPrivateKey() {
  const key = new PrivateKey();
  return proxy(key);
}

async function deployProgram(program) {
  const keyProvider = new AleoKeyProvider();
  keyProvider.useCache(true);

  // Create a record provider that will be used to find records and transaction data for Aleo programs
  const networkClient = new AleoNetworkClient("https://api.explorer.aleo.org/v1");

  // Use existing account with funds
  const account = new Account({
    privateKey: "user1PrivateKey",
  });

  const recordProvider = new NetworkRecordProvider(account, networkClient);

  // Initialize a program manager to talk to the Aleo network with the configured key and record providers
  const programManager = new ProgramManager(
    "https://api.explorer.aleo.org/v1",
    keyProvider,
    recordProvider,
  );

  programManager.setAccount(account);

  // Define a fee to pay to deploy the program
  const fee = 1.9; // 1.9 Aleo credits

  // Deploy the program to the Aleo network
  const tx_id = await programManager.deploy(program, fee);

  return tx_id;
}

const workerMethods = { localProgramExecution, getPrivateKey, deployProgram };
expose(workerMethods);

AleoWorker.js

import { wrap } from "comlink";

let singletonWorker = null;

const AleoWorker = () => {
    if (!singletonWorker) {
        const worker = new Worker(new URL("worker", import.meta.url), {
            type: "module",
        });

        worker.onerror = function(event) {
            console.error("Error in worker: " + event?.message);
        };

        singletonWorker = wrap(worker);
    }
    return singletonWorker;
};

export { AleoWorker };

Using both WebWorkers and SDK initialization in React, a single-page app can be created by importing AleoWorker.js, which executes Aleo zero-knowledge programs.

Example App.jsx Implementing Zero Knowledge Program Execution

App.jsx

import { useState } from "react";
import reactLogo from "./assets/react.svg";
import aleoLogo from "./assets/aleo.svg";
import "./App.css";
import helloworld_program from "../helloworld/build/main.aleo?raw";
import { AleoWorker } from "./workers/AleoWorker";

const aleoWorker = AleoWorker();
function App() {
  const [count, setCount] = useState(0);
  const [account, setAccount] = useState(null);
  const [executing, setExecuting] = useState(false);
  const [deploying, setDeploying] = useState(false);

  const generateAccount = async () => {
    const key = await aleoWorker.getPrivateKey();
    setAccount(await key.to_string());
  };

  async function execute() {
    setExecuting(true);
    const result = await aleoWorker.localProgramExecution(
      helloworld_program,
      "main",
      ["5u32", "5u32"],
    );
    setExecuting(false);

    alert(JSON.stringify(result));
  }

  async function deploy() {
    setDeploying(true);
    try {
      const result = await aleoWorker.deployProgram(helloworld_program);
      console.log("Transaction:")
      console.log("https://api.explorer.aleo.org/v1/transaction?id=" + result)
      alert("Transaction ID: " + result);
    } catch (e) {
      console.log(e)
      alert("Error with deployment, please check console for details");
    }
    setDeploying(false);
  }

  return (
    <>
      <div>
        <a href="https://aleo.org" target="_blank" rel="noopener noreferrer">
          <img src={aleoLogo} className="logo" alt="Aleo logo" />
        </a>
        <a href="https://react.dev" target="_blank" rel="noopener noreferrer">
          <img src={reactLogo} className="logo react" alt="React logo" />
        </a>
      </div>
      <h1>Aleo + React</h1>
      <div className="card">
        <button onClick={() => setCount((count) => count + 1)}>
          count is {count}
        </button>
        <p>
          <button onClick={generateAccount}>
            {account
              ? `Account is ${JSON.stringify(account)}`
              : `Click to generate account`}
          </button>
        </p>
        <p>
          <button disabled={executing} onClick={execute}>
            {executing
              ? `Executing...check console for details...`
              : `Execute helloworld.aleo`}
          </button>
        </p>
        <p>
          Edit <code>src/App.jsx</code> and save to test HMR
        </p>
      </div>

      {/* Advanced Section */}
      <div className="card">
        <h2>Advanced Actions</h2>
        <p>
          Deployment on Aleo requires certain prerequisites like seeding your
          wallet with credits and retrieving a fee record. Check README for more
          details.
        </p>
        <p>
          <button disabled={deploying} onClick={deploy}>
            {deploying
              ? `Deploying...check console for details...`
              : `Deploy helloworld.aleo`}
          </button>
        </p>
      </div>
      <p className="read-the-docs">
        Click on the Aleo and React logos to learn more
      </p>
    </>
  );
}

export default App;

Integrating Aleo Programs Into Your App​

If you are starting with a simple framework template rather than with Aleo templates, handling files with a .aleo extension in a web application requires specific configurations because these files are not natively recognized by most web development environments. The .aleo extension typically belongs to Aleo zero-knowledge programs, which are special scripts or codes used within the Aleo platform to ensure privacy and security through cryptographic proofs.

To integrate these files into a web application, such as a React app, you need to define how they should be treated during the build process.

Configuration File

Adding configuration rules in your build system (like Vite, Webpack, or Next.js) is necessary to tell the build tool how to process these files. Using something like raw-loader in this configuration ensures that .aleo files are loaded as plain text. This step is essential because it converts the content of .aleo files into a usable format that your web application can execute or display.

module:{
  rules:[
          {
        test: /\.aleo$/i,
        use: 'raw-loader',
      },
  ]
}
Handling .aleo Types in TypeScript
If you are using TypeScript, you need to inform the TypeScript compiler about the type of content these files contain by declaring a module for *.aleo files:

config.d.ts

declare module '*.aleo' {
   const content: string;
   export default content;
 }

Make sure that you included custom types in your tsconfig file.

A full example of this implementation can be found here

3. Aleo Credit Transfers​

3.1 Aleo Credits​

The official token of operation of the Aleo Network are Aleo credits. Aleo credits are used to pay all fees for program execution on the Aleo network.

Aleo credits are defined in the credits.aleo program. This program is deployed to the Aleo Network and defines data structures representing Aleo credits and the functions used to manage them.

There are two ways to hold Aleo credits.

1 - Private balances via credits.aleo records​

The first method is owning a credits record which enables a participant in the Aleo network to hold a private balance of Aleo credits.

record credits:
    owner as address.private;
    microcredits as u64.private;

A user's total private credits balance will consist of all unspent credits records owned by the user with a nonzero microcredits value.

2 - Public balances via credits.aleo account mapping​

The second is by holding a balance in the account mapping in the credits.aleo program on the Aleo Network.

mapping account:
    key owner as address.public;
    value microcredits as u64.public;

The total public credits balance of a user is the value of account mapping at the user's address. Users can hold both private and public balances simultaneously.

More information about records and mappings and how they related to private and public balances are explained in the Managing Program Data and Private State section.

3.2 Transfer Aleo Credits​

The ProgramManager allows transfers of aleo credits via the transfer method. This function executes the credits.aleo program under the hood.

There are four transfer functions available.

1. transfer_private​

Takes a credits record of owned by the sender, subtracts an amount from it, and adds that amount to a new record owned by the receiver. This function is %100 private and does not affect the account mapping.

graph LR
    user1--record1 \n owner: user1address \n balance: 10000u64-->t1[transfer_private]
    user1--amount: 4000u64-->t1
    t1-.record2 \n owner: user1address \n amount: 6000u64.->user1
    t1--record3  \n owner: user2address \n balance: 4000u64-->user2

2. transfer_private_to_public​

Takes a credits record of owned by the sender, subtracts an amount from it, and adds that amount to the account mapping of the receiver. This function is %50 private and %50 public. It consumes a record as a private input and generates a public balance in the account mapping entry belonging to the receiver.

graph LR
    subgraph credits.aleo
        m1[account mapping \n key: user3address \n value: 3000u64]
    end
    user1--record3 \n owner: user2address \n balance: 4000u64-->t1[transfer_private_to_public]
    t1-.record4 \n owner: user2address \n amount: 1000u64.->user1
    t1--amount 3000u64-->m1

3. transfer_public​

Subtracts an amount of credits stored in the account mapping of the credits.aleo program, and adds that amount to the account mapping of the receiver. This function is 100% public and does not consume or generate any records.

graph LR
    subgraph credits.aleo account mappings - state 2
        m3[account mapping \n key: user4address \n value: 3000u64]
        m4[account mapping \n key: user3address \n value: 0u64]
    end
    
    subgraph credits.aleo account mappings - state 1
        m2[account mapping \n key: user3address \n value: 3000u64]--transfer_public \n recipient: user4address \n amount: 3000u64-->m3
        m1[account mapping \n key: user4address \n value: N/A]
    end

4. transfer_public_to_private​

Subtracts an amount credits stored in the account mapping of the credits.aleo program and adds that amount to a new private record owned by the receiver. This function is %50 private and %50 public. It publicly consumes a balance in the account mapping entry belonging to the sender and generates a private record as a private output.

graph LR
    subgraph credits.aleo account mappings - state 2
        m2[account mapping \n key: user5address \n value: 0u64]
    end
    
    subgraph credits.aleo account mappings - state 1
        m1[account mapping \n key: user5address \n value: 3000u64]
    end

    m1--recipient: user6address \n amount: 3000u64-->transfer_public_to_private
    transfer_public_to_private--record5 \n owner: user6address \n amount: 3000u64-->user6

All four of these functions can be used to transfer credits between users via the transfer function in the ProgramManager by specifying the transfer type as the third argument.

import { Account, ProgramManager, AleoKeyProvider, NetworkRecordProvider, AleoNetworkClient } from '@aleo/sdk';

// Create a new NetworkClient, KeyProvider, and RecordProvider
const account = Account.from_string({privateKey: "user1PrivateKey"});
const networkClient = new AleoNetworkClient("https://api.explorer.aleo.org/v1");
const keyProvider = new AleoKeyProvider();
const recordProvider = new NetworkRecordProvider(account, networkClient);

// Initialize a program manager with the key provider to automatically fetch keys for executions
const USER_1_ADDRESS = "user1Address";
const programManager = new ProgramManager("https://api.explorer.aleo.org/v1", keyProvider, recordProvider);
programManager.setAccount(account);

// Send a private transfer to yourself
const tx_id = await programManager.transfer(1, USER_1_ADDRESS, "transfer_private", 0.2);

// Update or initialize a public balance in your own account mapping
const tx_id_2 = await programManager.transfer(1, USER_1_ADDRESS, "transfer_private_to_public", 0.2);

// Check the value of your public balance
let public_balance = programManager.networkClient.getMappingValue("credits.aleo", USER_1_ADDRESS);
assert(public_balance === 0.2*1_000_000);

/// Send public transfer to another user
const USER_2_ADDRESS = "user2Address";
const tx_id_3 = await programManager.transfer(1, USER_2_ADDRESS, "transfer_public", 0.1);

// Check the value of the public balance and assert that it has been updated
public_balance = programManager.networkClient.getMappingValue("credits.aleo", USER_1_ADDRESS);
const user2_public_balance = programManager.networkClient.getMappingValue("credits.aleo", USER_1_ADDRESS);
assert(public_balance === 0.1*1_000_000);
assert(user2_public_balance === 0.1*1_000_000);

/// Create a private record from a public balance
const tx_id_4 = await programManager.transfer(1, USER_1_ADDRESS, "transfer_public_to_private", 0.1);

// Check the value of the public balance and assert that it has been updated
public_balance = programManager.networkClient.getMappingValue("credits.aleo", USER_1_ADDRESS);
assert(public_balance === 0);

3.2 Checking Public Balances​

As shown above, a public balance of any address can be checked with getMappingValue function of the NetworkClient.

const networkClient = new AleoNetworkClient("https://api.explorer.aleo.org/v1");
const USER_1_ADDRESS = "user1Address";
const public_balance = networkClient.getMappingValue("credits.aleo", USER_1_ADDRESS);

4. Managing Program Data and Private State​

4.1 Private State Data: Records​

Records in are analogous to concept of UTXOs. When a record is created by a program, it can then be consumed later by the same program as an input to a function. Once a record is used as input, it is considered consumed and cannot be used again. In many cases a new record will be created from the output of the function. Records are private by default and are associated with a single Aleo program and a single private key representing a user.

4.2 Record Usage Example: Private Value Transfers​

A straightforward example of a usage of records in a program can be demonstrated by explaining the process of private value transfers of official Aleo credits on the Aleo network.

Aleo credits are the official token in which all on-chain execution and deployment fees are paid. Credits can be public or private. Private credits are represented by the credits record in the credits.aleo program.

record credits:
    owner as address.private;
    microcredits as u64.private;

Credits records contain an owner field representing the address which owns the record and a microcredits field representing the amount of microcredits in the record. 1 credit is equal to 1,000,000 microcredits.

An example of an Aleo function that both takes a record as input and outputs a record is the transfer_private function of the credits.aleo program. This function takes a private credits record as input and outputs two new private credits records as output (one that sends the credits to the recipient and one that sends the remaining credits to the sender).

The source code for the transfer_private is:

function transfer_private:
    input r0 as credits.record;
    input r1 as address.private;
    input r2 as u64.private;
    sub r0.microcredits r2 into r3;
    cast r1 r2 into r4 as credits.record;
    cast r0.owner r3 into r5 as credits.record;
    output r4 as credits.record;
    output r5 as credits.record;

The transfer_private function can be graphically represented by the graph below. In the graph the first record "Record 1" is consumed and can never be used again. From the data in Record 1, two more records are created. One containing the intended amount for the recipient which is now owned by the recipient and another containing the remaining credits which is sent back to the sender.

graph LR
    User1[Sender Address]
    i1[Input 1: Credits Record 1]-->p1
    i2[Input 2: Recipient Address]-->p1
    p1[Credits.aleo:transfer_private]
    p1--Credits Record 2-->User1
    p1--Credits Record 3-->R1[Recipient Address]

This chain of ownership is tracked by the Aleo Blockchain when users choose to submit their transactions to the Aleo Network. This allows other users who receive records to receive the updated data and verify that this data was provably generated by the intended program.

What this process allows is a private chain of state to be created between multiple users. In the context of value transfers, a chain of state might look like the following:

graph LR
    user1--record1-->t1[transfer_private]
    t1-.record2.->user1
    t1--record3-->user2
    user2--record3-->t2[transfer_private]
    t2--record5-->user3
    t2-.record4.->user2

The above state chain would be executed in the following way using the SDK:

Step 1 - User 1 sends a private value transfer to User 2​

// USER 1
import { Account, ProgramManager, AleoKeyProvider, NetworkRecordProvider, AleoNetworkClient } from '@aleo/sdk';

// Create a new NetworkClient, KeyProvider, and RecordProvider
const account = Account.from_string({privateKey: "user1PrivateKey"});
const networkClient = new AleoNetworkClient("https://api.explorer.aleo.org/v1");
const keyProvider = new AleoKeyProvider();
const recordProvider = new NetworkRecordProvider(account, networkClient);

// Initialize a program manager with the key provider to automatically fetch keys for executions
const USER_2_ADDRESS = "user2Address";
const programManager = new ProgramManager("https://api.explorer.aleo.org/v1", keyProvider, recordProvider);
programManager.setAccount(account);

/// Send private transfer to user 2
const tx_id = await programManager.transfer(1, USER_2_ADDRESS, "transfer_private", 0.2);

Step 2 - User 2 receives the transaction ID and fetches the credits record they received from user 1 from the network. They then send it to user 3​

// USER 2
import { Account, ProgramManager, AleoKeyProvider, NetworkRecordProvider, AleoNetworkClient } from '@aleo/sdk';

// Create a new NetworkClient, KeyProvider, and RecordProvider
const account = Account.from_string({privateKey: "user2PrivateKey"});
const networkClient = new AleoNetworkClient("https://api.explorer.aleo.org/v1");
const keyProvider = new AleoKeyProvider();
const recordProvider_User2 = new NetworkRecordProvider(account, networkClient);

// Initialize a program manager with the key provider to automatically fetch keys for executions
const programManager = new ProgramManager("https://api.explorer.aleo.org/v1", keyProvider, recordProvider);
programManager.setAccount(account);

// Fetch the transaction from the network that user 1 sent
const transaction = await programManager.networkClient.getTransaction(tx_id);
const record = <string>transaction.execution.transitions[0].outputs[0].value;

// Decrypt the record with the user's view key
const recordCiphertext = <RecordCiphertext>RecordCiphertext.fromString(record);
const recordPlaintext = <RecordPlaintext>recordCiphertext.decrypt(account.viewKey());

// Send a transfer to user 3 using the record found above
const USER_3_ADDRESS = "user3Address";
const tx_id = await programManager.transfer(1, USER_3_ADDRESS, "transfer_private", 0.2, undefined, recordPlaintext);

When an execution such as transfer_private consumes or generates a record is posted on the network and encrypted transcript of the execution is posted, containing an encrypted version of the record output and a transaction ID.

Because the records are encrypted when they're posted on the network, they do not reveal any information about the party who executed the program, nor the contents of the record. The only information that is revealed is the program ID, function name, encrypted function inputs, and the transaction ID of the program execution. No user except for the recipient of the record can see the contents of the record.

Below you can see what the exact data which is posted to the Aleo Network when transfer_private is run. Note that the record, the amount transferred, and both the sender & recipient addresses are all encrypted.

transfer_private Execution Transcript
  "transactions": [
    {
      "status": "accepted",
      "type": "execute",
      "index": 0,
      "transaction": {
        "type": "execute",
        "id": "at1s7dxunms8xhdzgaxrwf0yvq2dqgxtf4a3j8g878rhfr0zwhap5gqywsw8y",
        "execution": {
          "transitions": [
            {
              "id": "as1thy8fvkz0rkls5wnmfq5udrcvvzurq7mqk8pkhjf63htqjf9mugqp0mfhd",
              "program": "credits.aleo",
              "function": "transfer_private",
              "inputs": [
                {
                  "type": "record",
                  "id": "1406044754369042876058586523429806531093330762697573675195902502647806778955field",
                  "tag": "242626059121157295593694555515381893342956813170338731374395259242800138642field"
                },
                {
                  "type": "private",
                  "id": "1533599744296862879610225011439684001995294756698105572984689232395187168232field",
                  "value": "ciphertext1qgqgpu7m8p0rwjahwffyvm4g4n6903d6ufqty74z4504w4rn356hgp9jvpuvx8suu0pukr3sl7n8x65dz35nu4jdy4lgcguxldygufrfpyqd6xr5"
                },
                {
                  "type": "private",
                  "id": "4081557229261486898857101724786348855190759711760925564309233047223407640812field",
                  "value": "ciphertext1qyqxd9wue0qh8hs6dgevn7zleedfkzf7pft8ecked2xq3pw54pgqzyqr69sgx"
                }
              ],
              "outputs": [
                {
                  "type": "record",
                  "id": "1388064668770056715587596299070268626507043043686185311840561493640415146425field",
                  "checksum": "5376939704883651492329501631722578074516322228314928758786996843926470523116field",
                  "value": "record1qyqsq4r7mcd3ystjvjqda0v2a6dxnyzg9mk2daqjh0wwh359h396k7c9qyxx66trwfhkxun9v35hguerqqpqzqzshsw8dphxlzn5frh8pknsm5zlvhhee79xnhfesu68nkw75dt2qgrye03xqm4zf5xg5n6nscmmzh7ztgptlrzxq95syrzeaqaqu3vpzqf03s6"
                },
                {
                  "type": "record",
                  "id": "4635504195534945632234501197115926012056789160185660629718795843347495373207field",
                  "checksum": "3428805926164481449334365355155755448945974546383155334133384781819684465685field",
                  "value": "record1qyqsp2vsvvfulmk0q0tmxq7p9pffhfhha9h9pxsftujh57kkjuahx9s0qyxx66trwfhkxun9v35hguerqqpqzq8etfmzt2elj37hkf9fen2m2qes8564sr8k970zyud5eqmq7ztzq5r3095mkfdzqzz7yp6qfavqsl3t22t6dvgauqqt2xqk98zwmtusq5ck7fm"
                }
              ],
              "tpk": "5283803395323806407328334221689294196419052177553228331323093330938016699852group",
              "tcm": "4398026033398688325681745841147300822741685834906186660771751747897598751646field"
            }
          ],

Record Decryption​

If a user receives a private record from a program execution, they can use the SDK to decrypt encrypted records with their view keys and view their contents. Only records that are owned by the user can be decrypted. Decryption of records that are not owned by the user will fail.

Record decryption and ownership verification can be done in the SDK using the following code:

import { Account, RecordCiphertext, RecordPlaintext } from '@aleo/sdk';

// Create an account from an existing private key
const account = Account.from_string({privateKey: "existingPrivateKey"});

// Record value received as a string from program output or found on the Aleo network
const record = "record1qyqsq4r7mcd3ystjvjqda0v2a6dxnyzg9mk2daqjh0wwh359h396k7c9qyxx66trwfhkxun9v35hguerqqpqzqzshsw8dphxlzn5frh8pknsm5zlvhhee79xnhfesu68nkw75dt2qgrye03xqm4zf5xg5n6nscmmzh7ztgptlrzxq95syrzeaqaqu3vpzqf03s6";

const recordCiphertext = RecordCiphertext.fromString(record);

// Check ownership of the record. If the account is the owner, decrypt the record
if (RecordCiphertext.is_owner(account.viewKey())) {
   // Decrypt the record with the account's view key
   const recordPlaintext = recordCiphertext.decrypt(account.viewKey());

   // View the record data
   console.log(recordPlaintext.toString());
}

4.3 Public State Data: Mappings​

Mappings are simple key value stores defined in a program. They are represented by a key and a value each of a specified type. They are stored directly within the Aleo blockchain and can be publicly read by any participant in the Aleo network.

An example of a mapping usage is account mapping in the credits.aleo program.

mapping account:
    key owner as address.public;
    value microcredits as u64.public;

The account mapping is used to store public credits balances on the Aleo network. It takes a public address as a key and a public u64 value representing the number of microcredits owned by the address.

Mappings within programs are identified by the mapping identifier. Any program where this keyword appears contains an on-chain mapping. An example of a program that uses a mapping is shown below:

program player_mapping_example.aleo

// The mapping identifier representing a score
mapping score:
    key player as address.public;
    value score as u64.public;
    
// The update score function    
function update_score:
    input r0 as address.public;
    input r1 as u64.public;

// The finalize code block will be executed by Aleo network nodes.
// When it runs it will update the value of the mapping.
finalize update_score:
    input r0 as address.public;
    input r1 as u64.public;
    get.or_use score[r0] 0u64 into r2;
    add r1 r2 into r3;
    set r3 into account[r0];

Note that the above function has a finalize identifier. This identifier is used to identify a portion of a function's code that should be executed by nodes on the Aleo network. Program mappings are updated exclusively by code run by nodes on the Aleo Network written in finalize blocks.

4.4 Reading Mappings​

Any state within a program mapping is public and can be read by any participant in the Aleo network. The NetworkClient class provides the getMapping method to read the public mappings within a program and the getMappingValue method to read the value of a specific key within a mapping.

import {  AleoNetworkClient } from '@aleo/sdk';

const networkClient = new AleoNetworkClient("https://api.explorer.aleo.org/v1");
const creditsMappings = networkClient.getMappings("credits.aleo");
assert(creditsMappings === ["account"]);

const publicCredits = networkClient.getMapping("credits.aleo", "[a valid aleo account with zero balance]");
assert(publicCredits === "0u64");

4.5 Initializing & Updating Mappings​

Updating mappings is done by executing a program function on the Aleo network which has a finalize block that updates the program's mapping. For instance the transfer_public function in the credits.aleo program updates the account mapping (and thus a user's balance) when called.

// The public interface called by users
function transfer_public:
    input r0 as address.public;
    input r1 as u64.public;
    finalize self.signer r0 r1;

// The finalize block run by nodes on the Aleo network which update a user's public balance
finalize transfer_public:
    input r0 as address.public;
    input r1 as address.public;
    input r2 as u64.public;
    get.or_use account[r0] 0u64 into r3;
    sub r3 r2 into r4;
    set r4 into account[r0];
    get.or_use account[r1] 0u64 into r5;
    add r5 r2 into r6;
    set r6 into account[r1];

From the perspective of the caller of the API, this is as simple as executing a normal Aleo function. Given the inputs to a function with a finalize scope that updates a mapping are valid, the mapping will either be intialized or updated by the Aleo network. All the user of the SDK must do is ensure that the inputs to the function are valid.

If function inputs are Invalid, the Network will return an error, but the fee paid for the transaction will still be consumed. So it is important to ensure that the inputs to a function are valid before executing it.

A simple example of a mapping update can be shown by simply executing the 'transfer_public` as shown below.

import { Account, ProgramManager, AleoKeyProvider, NetworkRecordProvider, AleoNetworkClient } from '@aleo/sdk';

// Create a new NetworkClient, KeyProvider, and RecordProvider
const account = Account.from_string({privateKey: "user1PrivateKey"});
const networkClient = new AleoNetworkClient("https://api.explorer.aleo.org/v1");
const keyProvider = new AleoKeyProvider();
const recordProvider = new NetworkRecordProvider(account, networkClient);

// Initialize a program manager with the key provider to automatically fetch keys for executions
const RECIPIENT_ADDRESS = "user1Address";
const programManager = new ProgramManager("https://api.explorer.aleo.org/v1", keyProvider, recordProvider);
programManager.setAccount(account);

// Update or initialize a public balance
const tx_id = await programManager.transfer(1, RECIPIENT_ADDRESS, "transfer_private_to_public", 0.2);

5. Communicating with the Aleo Network​

Communication with the Aleo network is done through the AleoNetworkClient class. This class provides methods to query data from Aleo network nodes and submit transactions to the Aleo network.

A full list of methods provided by the AleoNetworkClient class and usage examples can be found in the Network Client API documentation.

Further Documentation​

API documentation for this package, the Leo Language, and Aleo instructions can be found on the Aleo Developer Hub.

To view the API documentation for this package locally, open docs/index.html. To regenerate the documentation, run npx jsdoc --configure jsdoc.json --verbose