Solana DocumentationTokens on SolanaExtensionsConfidential Transfer

Deposit Tokens

How to deposit tokens to confidential pending balance

Before tokens can be transferred confidentially, the public token balance must be converted to a confidential balance. This conversion happens in two stages:

  1. Confidential Pending Balance: Initially, tokens are "deposited" from public balance to a "pending" confidential balance.
  2. Confidential Available Balance: The pending balance is then "applied" to the available balance, making the tokens available for confidential transfers.

This section explains the first stage: depositing public token balance to the confidential pending balance.

The following diagram shows the steps involved in depositing tokens from the public balance to the confidential pending balance:

Deposit Tokens

Required Instruction

To convert a public balance to a confidential pending balance, invoke the ConfidentialTransferInstruction::Deposit instruction. The maximum amount per deposit instruction is limited to 2^48.

The spl_token_client crate provides a confidential_transfer_deposit method that builds and sends a transaction with the Deposit instruction, as demonstrated in the example below.

Example Code

The following example demonstrates how to deposit public token balance to confidential pending balance.

To run the example, start a local validator with the Token Extension Program cloned from mainnet using the following command. You must have the Solana CLI installed to start the local validator.

Terminal
$ 
solana-test-validator --clone-upgradeable-program TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb --url https://api.mainnet-beta.solana.com -r

At the time of writing, the Confidential Transfers isn't enabled on the default local validator. You must clone the mainnet Token Extension Program to run the example code.

use anyhow::{Context, Result};

use solana_client::nonblocking::rpc_client::RpcClient;

use solana_sdk::{

    commitment_config::CommitmentConfig,

    signature::{Keypair, Signer},

    transaction::Transaction,

};

use spl_associated_token_account::{

    get_associated_token_address_with_program_id, instruction::create_associated_token_account,

};

use spl_token_client::{

    client::{ProgramRpcClient, ProgramRpcClientSendTransaction},

    spl_token_2022::{

        extension::{

            confidential_transfer::instruction::{configure_account, PubkeyValidityProofData},

            ExtensionType,

        },

        id as token_2022_program_id,

        instruction::reallocate,

        solana_zk_sdk::encryption::{auth_encryption::*, elgamal::*},

    },

    token::{ExtensionInitializationParams, Token},

};

use spl_token_confidential_transfer_proof_extraction::instruction::{ProofData, ProofLocation};

use std::sync::Arc;



#[tokio::main]

async fn main() -> Result<()> {

    // Create connection to local test validator

    let rpc_client = Arc::new(RpcClient::new_with_commitment(

        String::from("http://localhost:8899"),

        CommitmentConfig::confirmed(),

    ));



    // Load the default Solana CLI keypair to use as the fee payer

    // This will be the wallet paying for the transaction fees

    // Use Arc to prevent multiple clones of the keypair

    let payer = Arc::new(load_keypair()?);

    println!("Using payer: {}", payer.pubkey());



    // Generate a new keypair to use as the address of the token mint

    let mint = Keypair::new();

    println!("Mint keypair generated: {}", mint.pubkey());



    // Set up program client for Token client

    let program_client = ProgramRpcClient::new(rpc_client.clone(), ProgramRpcClientSendTransaction);



    // Number of decimals for the mint

    let decimals = 9;



    // Create a token client for the Token-2022 program

    // This provides high-level methods for token operations

    let token = Token::new(

        Arc::new(program_client),

        &token_2022_program_id(), // Use the Token-2022 program (newer version with extensions)

        &mint.pubkey(),           // Address of the new token mint

        Some(decimals),           // Number of decimal places

        payer.clone(),            // Fee payer for transactions

    );



    // Create extension initialization parameters for the mint

    // The ConfidentialTransferMint extension enables confidential (private) transfers of tokens

    let extension_initialization_params =

        vec![ExtensionInitializationParams::ConfidentialTransferMint {

            authority: Some(payer.pubkey()), // Authority that can modify confidential transfer settings

            auto_approve_new_accounts: true, // Automatically approve new confidential accounts

            auditor_elgamal_pubkey: None,    // Optional auditor ElGamal public key

        }];



    // Create and initialize the mint with the ConfidentialTransferMint extension

    // This sends a transaction to create the new token mint

    let transaction_signature = token

        .create_mint(

            &payer.pubkey(),                 // Mint authority - can mint new tokens

            Some(&payer.pubkey()),           // Freeze authority - can freeze token accounts

            extension_initialization_params, // Add the ConfidentialTransferMint extension

            &[&mint],                        // Mint keypair needed as signer

        )

        .await?;



    // Print results for user verification

    println!("Mint Address: {}", mint.pubkey());

    println!(

        "Mint Creation Transaction Signature: {}",

        transaction_signature

    );



    // ===== Create and configure token account for confidential transfers =====

    println!("\nCreate and configure token account for confidential transfers");



    // Get the associated token account address for the owner

    let token_account_pubkey = get_associated_token_address_with_program_id(

        &payer.pubkey(),          // Token account owner

        &mint.pubkey(),           // Mint

        &token_2022_program_id(), // Token program ID

    );

    println!("Token Account Address: {}", token_account_pubkey);



    // Step 1: Create the associated token account

    let create_associated_token_account_instruction = create_associated_token_account(

        &payer.pubkey(),          // Funding account

        &payer.pubkey(),          // Token account owner

        &mint.pubkey(),           // Mint

        &token_2022_program_id(), // Token program ID

    );



    // Step 2: Reallocate the token account to include space for the ConfidentialTransferAccount extension

    let reallocate_instruction = reallocate(

        &token_2022_program_id(),                      // Token program ID

        &token_account_pubkey,                         // Token account

        &payer.pubkey(),                               // Payer

        &payer.pubkey(),                               // Token account owner

        &[&payer.pubkey()],                            // Signers

        &[ExtensionType::ConfidentialTransferAccount], // Extension to reallocate space for

    )?;



    // Step 3: Generate the ElGamal keypair and AES key for token account

    let elgamal_keypair = ElGamalKeypair::new_from_signer(&payer, &token_account_pubkey.to_bytes())

        .expect("Failed to create ElGamal keypair");

    let aes_key = AeKey::new_from_signer(&payer, &token_account_pubkey.to_bytes())

        .expect("Failed to create AES key");



    // The maximum number of Deposit and Transfer instructions that can

    // credit pending_balance before the ApplyPendingBalance instruction is executed

    let maximum_pending_balance_credit_counter = 65536;



    // Initial token balance is 0

    let decryptable_balance = aes_key.encrypt(0);



    // Generate the proof data client-side

    let proof_data = PubkeyValidityProofData::new(&elgamal_keypair)

        .map_err(|_| anyhow::anyhow!("Failed to generate proof data"))?;



    // Indicate that proof is included in the same transaction

    let proof_location =

        ProofLocation::InstructionOffset(1.try_into()?, ProofData::InstructionData(&proof_data));



    // Step 4: Create instructions to configure the account for confidential transfers

    let configure_account_instructions = configure_account(

        &token_2022_program_id(),               // Program ID

        &token_account_pubkey,                  // Token account

        &mint.pubkey(),                         // Mint

        &decryptable_balance.into(),            // Initial balance

        maximum_pending_balance_credit_counter, // Maximum pending balance credit counter

        &payer.pubkey(),                        // Token Account Owner

        &[],                                    // Additional signers

        proof_location,                         // Proof location

    )?;



    // Combine all instructions

    let mut instructions = vec![

        create_associated_token_account_instruction,

        reallocate_instruction,

    ];

    instructions.extend(configure_account_instructions);



    // Create and send the transaction

    let recent_blockhash = rpc_client.get_latest_blockhash().await?;

    let transaction = Transaction::new_signed_with_payer(

        &instructions,

        Some(&payer.pubkey()),

        &[&*payer],

        recent_blockhash,

    );



    let setup_signature = rpc_client

        .send_and_confirm_transaction(&transaction)

        .await?;

    println!(

        "Create Token Account Transaction Signature: {}",

        setup_signature

    );



    // Mint some tokens to the newly created token account

    // This gives the account some tokens to work with

    let mint_signature = token

        .mint_to(

            &token_account_pubkey,            // Destination account

            &payer.pubkey(),                  // Mint authority

            100 * 10u64.pow(decimals as u32), // Amount (100 tokens with decimal precision)

            &[&payer],                        // Signers

        )

        .await?;



    println!("Mint Tokens Transaction Signature: {}", mint_signature);



    // Deposit the tokens to confidential state

    // This converts regular tokens to confidential tokens

    println!("Deposit tokens to confidential state pending balance");

    let deposit_signature = token

        .confidential_transfer_deposit(

            &token_account_pubkey,            // The token account

            &payer.pubkey(),                  // Authority (owner) of the account

            100 * 10u64.pow(decimals as u32), // Amount to deposit (100 tokens)

            decimals,                         // Decimals of the token

            &[&payer],                        // Signers (owner must sign)

        )

        .await?;



    println!(

        "Confidential Transfer Deposit Signature: {}",

        deposit_signature

    );

    Ok(())

}



// Load the keypair from the default Solana CLI keypair path (~/.config/solana/id.json)

// This enables using the same wallet as the Solana CLI tools

fn load_keypair() -> Result<Keypair> {

    // Get the default keypair path

    let keypair_path = dirs::home_dir()

        .context("Could not find home directory")?

        .join(".config/solana/id.json");



    // Read the keypair file directly into bytes using serde_json

    // The keypair file is a JSON array of bytes

    let file = std::fs::File::open(&keypair_path)?;

    let keypair_bytes: Vec<u8> = serde_json::from_reader(file)?;



    // Create keypair from the loaded bytes

    // This converts the byte array into a keypair

    let keypair = Keypair::from_bytes(&keypair_bytes)?;



    Ok(keypair)

}

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