Transfer Tokens
How to confidentially transfer tokens from one token account to another
To confidentially transfer tokens from one token account to another, both the
sender and recipient must have token accounts configured with the
ConfidentialTransferAccount
state and approved for confidential transfers.
The sender's token account must also have an available confidential balance to
transfer from.
To transfer tokens confidentially:
-
Create three proofs client side:
Equality Proof (CiphertextCommitmentEqualityProofData): Verifies that the new available balance ciphertext after the transfer matches its corresponding Pedersen commitment, ensuring the source account's new available balance is correctly computed as
new_balance = current_balance - transfer_amount
.Ciphertext Validity Proof (BatchedGroupedCiphertext3HandlesValidityProofData): Verifies that the transfer amount ciphertexts are properly generated for all three parties (source, destination, and auditor), ensuring the transfer amount is correctly encrypted under each party's public key.
Range Proof (BatchedRangeProofU128Data): Verifies that the new available balance and transfer amount (split into low/high bits) are all non-negative and within a specified range.
-
For each proof:
- Invoke the ZK ElGamal proof program to verify the proof data.
- Store the proof-specific metadata in a proof "context state" account to use in other instructions.
-
Invoke the ConfidentialTransferInstruction::Transfer instruction, providing the proof context state accounts.
-
Close the proof context state accounts to recover the SOL used to create them.
The following diagram shows the steps involved in transferring tokens from a sender's token account to a recipient's token account.
Required Instructions
To confidentially transfer tokens from one token account to another, you must:
- Generate an equality proof, ciphertext validity proof, and range proof client-side
- Invoke the Zk ElGamal proof program to verify the proofs and initialize the "context state" accounts
- Invoke the ConfidentialTransferInstruction::Transfer instruction providing the three proof accounts.
- Close the three proof accounts to recover rent.
The spl_token_client
crate provides the following methods:
confidential_transfer_create_context_state_account
method that creates a proof account.confidential_transfer_transfer
method that invokes theTransfer
instruction.confidential_transfer_close_context_state_account
method that closes a proof account.
Example Code
The following example demonstrates how to confidentially transfer tokens between token accounts.
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.
$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::{account_info::{TransferAccountInfo, WithdrawAccountInfo},instruction::{configure_account, PubkeyValidityProofData},ConfidentialTransferAccount,},BaseStateWithExtensions, 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 spl_token_confidential_transfer_proof_generation::withdraw::WithdrawProofData;use std::sync::Arc;#[tokio::main]async fn main() -> Result<()> {// Create connection to local test validatorlet 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 keypairlet sender = Arc::new(load_keypair()?);println!("Sender: {}", sender.pubkey());// Generate a new keypair to use as the address of the token mintlet mint = Keypair::new();println!("Mint keypair generated: {}", mint.pubkey());// Set up program client for Token clientlet program_client = ProgramRpcClient::new(rpc_client.clone(), ProgramRpcClientSendTransaction);// Number of decimals for the mintlet decimals = 9;// Create a token client for the Token-2022 program// This provides high-level methods for token operationslet 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 mintSome(decimals), // Number of decimal placessender.clone(), // Fee payer for transactions);// Create extension initialization parameters for the mint// The ConfidentialTransferMint extension enables confidential (private) transfers of tokenslet extension_initialization_params =vec![ExtensionInitializationParams::ConfidentialTransferMint {authority: Some(sender.pubkey()), // Authority that can modify confidential transfer settingsauto_approve_new_accounts: true, // Automatically approve new confidential accountsauditor_elgamal_pubkey: None, // None if no auditor}];// Create and initialize the mint with the ConfidentialTransferMint extension// This sends a transaction to create the new token mintlet transaction_signature = token.create_mint(&sender.pubkey(), // Mint authority - can mint new tokensSome(&sender.pubkey()), // Freeze authority - can freeze token accountsextension_initialization_params, // Add the ConfidentialTransferMint extension&[&mint], // Mint keypair needed as signer).await?;println!("Mint Address: {}", mint.pubkey());println!("Create Mint Transaction Signature: {}",transaction_signature);// ===== Create and configure token account for confidential transfers =====println!("\nCreate and Configure Sender Token Account");// Get the associated token account address for the ownerlet sender_token_account_pubkey = get_associated_token_address_with_program_id(&sender.pubkey(), // Token account owner&mint.pubkey(), // Mint&token_2022_program_id(), // Token program ID);println!("Sender Token Account Address: {}", sender_token_account_pubkey);// Step 1: Create the associated token accountlet create_associated_token_account_instruction = create_associated_token_account(&sender.pubkey(), // Funding account&sender.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 extensionlet reallocate_instruction = reallocate(&token_2022_program_id(), // Token program ID&sender_token_account_pubkey, // Token account&sender.pubkey(), // Payer&sender.pubkey(), // Token account owner&[&sender.pubkey()], // Signers&[ExtensionType::ConfidentialTransferAccount], // Extension to reallocate space for)?;// Step 3: Generate the ElGamal keypair and AES key for token accountlet sender_elgamal_keypair = ElGamalKeypair::new_from_signer(&sender, &sender_token_account_pubkey.to_bytes()).expect("Failed to create ElGamal keypair");let sender_aes_key = AeKey::new_from_signer(&sender, &sender_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 must be executedlet maximum_pending_balance_credit_counter = 65536;// Initial token balance is 0let sender_decryptable_balance = sender_aes_key.encrypt(0);// Generate the proof data client-sidelet proof_data = PubkeyValidityProofData::new(&sender_elgamal_keypair).map_err(|_| anyhow::anyhow!("Failed to generate proof data"))?;// Indicate that proof is included in the same transactionlet proof_location =ProofLocation::InstructionOffset(1.try_into()?, ProofData::InstructionData(&proof_data));// Step 4: Create instructions to configure the account for confidential transferslet configure_account_instructions = configure_account(&token_2022_program_id(), // Program ID&sender_token_account_pubkey, // Token account&mint.pubkey(), // Mint&sender_decryptable_balance.into(), // Initial balancemaximum_pending_balance_credit_counter, // Maximum pending balance credit counter&sender.pubkey(), // Token Account Owner&[], // Additional signersproof_location, // Proof location)?;// Combine all instructionslet mut instructions = vec![create_associated_token_account_instruction,reallocate_instruction,];instructions.extend(configure_account_instructions);// Create and send the transactionlet recent_blockhash = rpc_client.get_latest_blockhash().await?;let transaction = Transaction::new_signed_with_payer(&instructions,Some(&sender.pubkey()),&[&sender],recent_blockhash,);let transaction_signature = rpc_client.send_and_confirm_transaction(&transaction).await?;println!("Create Sender Token Account Transaction Signature: {}",transaction_signature);// Mint some tokens to the newly created token account// This gives the account some tokens to work withlet mint_signature = token.mint_to(&sender_token_account_pubkey, // Destination account&sender.pubkey(), // Mint authority100 * 10u64.pow(decimals as u32), // Amount (100 tokens)&[&sender], // Signers).await?;println!("Mint Tokens to Sender Token Account Transaction Signature: {}", mint_signature);// Deposit the tokens to confidential state// This converts public tokens balance to confidential pending balanceprintln!("Deposit tokens to confidential state pending balance");let deposit_signature = token.confidential_transfer_deposit(&sender_token_account_pubkey, // The token account&sender.pubkey(), // Authority (owner) of the account100 * 10u64.pow(decimals as u32), // Amount to deposit (100 tokens)decimals, // Decimals of the token&[&sender], // Signers (owner must sign)).await?;println!("Confidential Transfer Deposit Signature: {}",deposit_signature);// Apply the pending balance to available balanceprintln!("Apply pending balance to available balance");let apply_signature = token.confidential_transfer_apply_pending_balance(&sender_token_account_pubkey, // The token account&sender.pubkey(), // Authority (owner) of the accountNone, // Optional ApplyPendingBalanceAccountInfo, generated if not providedsender_elgamal_keypair.secret(), // ElGamal secret k ey for decryption&sender_aes_key, // AES key for encryption of balance and transfer amounts&[&sender], // Signers (owner must sign)).await?;println!("Apply Pending Balance Signature: {}", apply_signature);// ===== Withdraw half of the tokens from confidential available balance =====println!("\nWithdraw tokens from confidential available balance to public balance");// Calculate the withdraw amount (half of the deposited amount)let withdraw_amount = 50 * 10u64.pow(decimals as u32); // Half of the 100 tokens deposited// Get the token account data to access the confidential transfer extensionlet token_account = token.get_account_info(&sender_token_account_pubkey).await?;// Unpack the ConfidentialTransferAccount extension portion of the token account datalet extension_data = token_account.get_extension::<ConfidentialTransferAccount>()?;// Confidential Transfer extension information needed to construct a `Withdraw` instructionlet withdraw_account_info = WithdrawAccountInfo::new(extension_data);// Create keypairs for the proof accountslet equality_proof_context_state_keypair = Keypair::new();let equality_proof_context_state_pubkey = equality_proof_context_state_keypair.pubkey();let range_proof_context_state_keypair = Keypair::new();let range_proof_context_state_pubkey = range_proof_context_state_keypair.pubkey();// Create a withdraw proof datalet WithdrawProofData {equality_proof_data,range_proof_data,} = withdraw_account_info.generate_proof_data(withdraw_amount, // Amount to withdraw from confidential available balance&sender_elgamal_keypair, // ElGamal keypair for encryption&sender_aes_key, // AES key for encryption)?;// Generate the equality proof accountprintln!("Creating equality proof context state account...");let equality_proof_signature = token.confidential_transfer_create_context_state_account(&equality_proof_context_state_pubkey, // Public key of the new equality proof context state account&sender.pubkey(), // Authority that can close the context state account&equality_proof_data, // Proof data for the equality proof verificationfalse, // False: combine account creation and proof verification in one transaction&[&equality_proof_context_state_keypair], // Signer for the new account).await?;println!("Equality Proof Context State Account Signature: {}",equality_proof_signature);// Generate the range proof accountprintln!("Creating range proof context state account...");let range_proof_signature = token.confidential_transfer_create_context_state_account(&range_proof_context_state_pubkey, // Public key of the new range proof context state account&sender.pubkey(), // Authority that can close the context state account&range_proof_data, // Proof data for the range proof verificationtrue, // True: split account creation and proof verification into separate transactions (for large proofs)&[&range_proof_context_state_keypair], // Signer for the new account).await?;println!("Range Proof Context State Account Signature: {}",range_proof_signature);// Perform the withdrawalprintln!("Executing withdrawal transaction...");let withdraw_signature = token.confidential_transfer_withdraw(&sender_token_account_pubkey, // Token account to withdraw from&sender.pubkey(), // Owner of the token accountSome(&spl_token_client::token::ProofAccount::ContextAccount(equality_proof_context_state_pubkey, // Reference to the equality proof account)),Some(&spl_token_client::token::ProofAccount::ContextAccount(range_proof_context_state_pubkey, // Reference to the range proof account)),withdraw_amount, // Amount to withdraw from confidential available balancedecimals, // Decimal precision of the tokenSome(withdraw_account_info), // Data from confidential transfer extension for proof verification&sender_elgamal_keypair, // ElGamal keypair for encryption&sender_aes_key, // AES key for encryption&[&sender], // Owner must sign the transaction).await?;println!("Withdraw Transaction Signature: {}", withdraw_signature);// Close the context state accounts to recover rentprintln!("Closing equality proof context state account...");let close_equality_signature = token.confidential_transfer_close_context_state_account(&equality_proof_context_state_pubkey, // Equality proof context state account to close&sender_token_account_pubkey, // Account that will receive the lamports&sender.pubkey(), // Authority allowed to close the account&[&sender], // Authority must sign).await?;println!("Close Equality Proof Account Signature: {}",close_equality_signature);println!("Closing range proof context state account...");let close_range_signature = token.confidential_transfer_close_context_state_account(&range_proof_context_state_pubkey, // Range proof context state account to close&sender_token_account_pubkey, // Account that will receive the lamports&sender.pubkey(), // Authority allowed to close the account&[&sender], // Authority must sign).await?;println!("Close Range Proof Account Signature: {}",close_range_signature);// ===== Create a recipient token account for confidential transfers =====println!("\nCreate Recipient Token Account");// Create a new keypair to use as the recipient account ownerlet recipient = Keypair::new();println!("Recipient: {}", recipient.pubkey());// Fund the recipient account with SOL for transaction feeslet fund_signature = rpc_client.send_and_confirm_transaction(&Transaction::new_signed_with_payer(&[solana_sdk::system_instruction::transfer(&sender.pubkey(),&recipient.pubkey(),1_000_000_000, // 1 SOL)],Some(&sender.pubkey()),&[&sender],rpc_client.get_latest_blockhash().await?,)).await?;println!("Fund Recipient Signature: {}", fund_signature);// Get the associated token account address for the recipient ownerlet recipient_token_account_pubkey = get_associated_token_address_with_program_id(&recipient.pubkey(), // Token account owner&mint.pubkey(), // Same mint as before&token_2022_program_id(), // Token program ID);println!("Recipient Token Account Address: {}",recipient_token_account_pubkey);// Step 1: Create the associated token accountlet create_associated_token_account_instruction = create_associated_token_account(&recipient.pubkey(), // Funding account&recipient.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 extensionlet reallocate_instruction = reallocate(&token_2022_program_id(), // Token program ID&recipient_token_account_pubkey, // Token account&recipient.pubkey(), // Payer&recipient.pubkey(), // Token account owner&[&recipient.pubkey()], // Signers&[ExtensionType::ConfidentialTransferAccount], // Extension to reallocate space for)?;// Step 3: Generate the ElGamal keypair and AES key for recipient token accountlet recipient_elgamal_keypair =ElGamalKeypair::new_from_signer(&recipient, &recipient_token_account_pubkey.to_bytes()).expect("Failed to create ElGamal keypair");let recipient_aes_key =AeKey::new_from_signer(&recipient, &recipient_token_account_pubkey.to_bytes()).expect("Failed to create AES key");// Maximum pending balance credit counter, same as beforelet maximum_pending_balance_credit_counter = 65536;// Initial token balance is 0let decryptable_balance = recipient_aes_key.encrypt(0);// Generate the proof data client-sidelet proof_data = PubkeyValidityProofData::new(&recipient_elgamal_keypair).map_err(|_| anyhow::anyhow!("Failed to generate proof data"))?;// Indicate that proof is included in the same transactionlet proof_location =ProofLocation::InstructionOffset(1.try_into()?, ProofData::InstructionData(&proof_data));// Step 4: Create instructions to configure the account for confidential transferslet configure_account_instructions = configure_account(&token_2022_program_id(), // Program ID&recipient_token_account_pubkey, // Token account&mint.pubkey(), // Mint&decryptable_balance.into(), // Initial balancemaximum_pending_balance_credit_counter, // Maximum pending balance credit counter&recipient.pubkey(), // Token Account Owner&[], // Additional signersproof_location, // Proof location)?;// Combine all instructionslet mut instructions = vec![create_associated_token_account_instruction,reallocate_instruction,];instructions.extend(configure_account_instructions);// Create and send the transactionlet recent_blockhash = rpc_client.get_latest_blockhash().await?;let transaction = Transaction::new_signed_with_payer(&instructions,Some(&recipient.pubkey()),&[&recipient],recent_blockhash,);let transaction_signature = rpc_client.send_and_confirm_transaction(&transaction).await?;println!("Create Recipient Token Account Transaction Signature: {}",transaction_signature);// ===== Perform a confidential transfer from sender account to recipient account =====println!("\nPerform Confidential Transfer");let transfer_amount = 25 * 10u64.pow(decimals as u32); // Transfer 25 tokens// Get the token account data to access the confidential transfer extension statelet token_account = token.get_account_info(&sender_token_account_pubkey).await?;let extension_data = token_account.get_extension::<ConfidentialTransferAccount>()?;// Create TransferAccountInfo from the extension datalet transfer_account_info = TransferAccountInfo::new(extension_data);// Generate the proof data for the transferlet transfer_proof_data = transfer_account_info.generate_split_transfer_proof_data(transfer_amount,&sender_elgamal_keypair,&sender_aes_key,recipient_elgamal_keypair.pubkey(),None, // auditor ElGamal public key (none if no auditor))?;// Create proof context accountslet equality_proof_context_state_keypair = Keypair::new();let equality_proof_context_state_pubkey = equality_proof_context_state_keypair.pubkey();let ciphertext_validity_proof_context_state_keypair = Keypair::new();let ciphertext_validity_proof_context_state_pubkey =ciphertext_validity_proof_context_state_keypair.pubkey();let range_proof_context_state_keypair = Keypair::new();let range_proof_context_state_pubkey = range_proof_context_state_keypair.pubkey();// Create context state account for equality proofprintln!("Creating equality proof context state account for transfer...");let equality_proof_signature = token.confidential_transfer_create_context_state_account(&equality_proof_context_state_pubkey, // Public key of the new equality proof context state account&sender.pubkey(), // Authority that can close the context state account&transfer_proof_data.equality_proof_data, // Proof data for the equality proof verificationfalse, // False: combine account creation and proof verification in one transaction&[&equality_proof_context_state_keypair], // Signer for the new account).await?;println!("Transfer Equality Proof Account Signature: {}",equality_proof_signature);// Create context state account for ciphertext validity proofprintln!("Creating ciphertext validity proof context state account...");let ciphertext_proof_signature = token.confidential_transfer_create_context_state_account(&ciphertext_validity_proof_context_state_pubkey, // Public key of the new ciphertext validity proof context state account&sender.pubkey(), // Authority that can close the context state account&transfer_proof_data.ciphertext_validity_proof_data_with_ciphertext.proof_data, // Proof data for the ciphertext validity proof verificationfalse, // False: combine account creation and proof verification in one transaction&[&ciphertext_validity_proof_context_state_keypair], // Signer for the new account).await?;println!("Ciphertext Validity Proof Account Signature: {}",ciphertext_proof_signature);// Create context state account for range proofprintln!("Creating range proof context state account...");let range_proof_signature = token.confidential_transfer_create_context_state_account(&range_proof_context_state_pubkey, // Public key of the new range proof context state account&sender.pubkey(), // Authority that can close the context state account&transfer_proof_data.range_proof_data, // Proof data for the range proof verificationtrue, // True: split account creation and proof verification into separate transactions (for large proofs)&[&range_proof_context_state_keypair], // Signer for the new account).await?;println!("Range Proof Account Signature: {}", range_proof_signature);// Execute the confidential transferprintln!("Executing confidential transfer transaction...");// Create a ProofAccountWithCiphertext for the ciphertext validity prooflet ciphertext_validity_proof_account_with_ciphertext =spl_token_client::token::ProofAccountWithCiphertext {proof_account: spl_token_client::token::ProofAccount::ContextAccount(ciphertext_validity_proof_context_state_pubkey,),ciphertext_lo: transfer_proof_data.ciphertext_validity_proof_data_with_ciphertext.ciphertext_lo,ciphertext_hi: transfer_proof_data.ciphertext_validity_proof_data_with_ciphertext.ciphertext_hi,};let transfer_signature = token.confidential_transfer_transfer(&sender_token_account_pubkey, // Source account&recipient_token_account_pubkey, // Destination account&sender.pubkey(), // Authority (owner) of source accountSome(&spl_token_client::token::ProofAccount::ContextAccount(equality_proof_context_state_pubkey, // Reference to the equality proof account)),Some(&ciphertext_validity_proof_account_with_ciphertext),Some(&spl_token_client::token::ProofAccount::ContextAccount(range_proof_context_state_pubkey, // Reference to the range proof account)),transfer_amount, // Amount to transferNone, // Custom data for verification (optional)&sender_elgamal_keypair, // ElGamal keypair for source account&sender_aes_key, // AES key for source accountrecipient_elgamal_keypair.pubkey(), // ElGamal public key of destination accountNone, // Auditor ElGamal public key (none if no auditor)&[&sender], // Signers).await?;println!("Confidential Transfer Signature: {}", transfer_signature);// Apply pending balance on the recipient account to make transferred funds availableprintln!("Applying pending balance on recipient account...");let apply_signature = token.confidential_transfer_apply_pending_balance(&recipient_token_account_pubkey, // The token account&recipient.pubkey(), // Authority (owner) of the accountNone, // Optional new decryptable available balancerecipient_elgamal_keypair.secret(), // ElGamal secret key for encryption&recipient_aes_key, // AES key for encryption&[&recipient], // Signers (owner must sign)).await?;println!("Recipient Account Apply Pending Balance Signature: {}",apply_signature);// Close the context state accounts to recover rentprintln!("Closing equality proof context state account...");let close_equality_signature = token.confidential_transfer_close_context_state_account(&equality_proof_context_state_pubkey, // Equality proof context state account to close&sender_token_account_pubkey, // Account that will receive the lamports&sender.pubkey(), // Authority allowed to close the account&[&sender], // Authority must sign).await?;println!("Close Transfer Equality Proof Account Signature: {}",close_equality_signature);println!("Closing ciphertext validity proof context state account...");let close_ciphertext_signature = token.confidential_transfer_close_context_state_account(&ciphertext_validity_proof_context_state_pubkey, // Ciphertext validity proof context state account to close&sender_token_account_pubkey, // Account that will receive the lamports&sender.pubkey(), // Authority allowed to close the account&[&sender], // Authority must sign).await?;println!("Close Ciphertext Validity Proof Account Signature: {}",close_ciphertext_signature);println!("Closing range proof context state account...");let close_range_signature = token.confidential_transfer_close_context_state_account(&range_proof_context_state_pubkey, // Range proof context state account to close&sender_token_account_pubkey, // Account that will receive the lamports&sender.pubkey(), // Authority allowed to close the account&[&sender], // Authority must sign).await?;println!("Close Range Proof Account Signature: {}",close_range_signature);println!("\nConfidential transfer completed successfully!");println!("Sender Token Account: {}", sender_token_account_pubkey);println!("Recipient Token Account: {}",recipient_token_account_pubkey);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 toolsfn load_keypair() -> Result<Keypair> {// Get the default keypair pathlet 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 byteslet 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 keypairlet keypair = Keypair::from_bytes(&keypair_bytes)?;Ok(keypair)}
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