Cross-Chain Transfer Protocol (CCTP) on Solana

Introduction

Cross-Chain Transfer Protocol (CCTP) is a permissionless on-chain utility that facilitates USDC transfers securely between blockchains networks via native burning and minting. Circle created it to improve capital efficiency and minimize trust requirements when using USDC across blockchain networks. CCTP enables developers to build multi-chain applications that provide secure, 1:1 transfers of USDC across blockchains for their users.

Developer Documentation

To learn more about how to integrate with CCTP, please see our developer documentation here.

Deployments

Devnet
MessageTransmitter	CCTPmbSD7gX1bxKPAmg77w8oFzNFpaQiQUWD43TKaecd
TokenMessengerMinter	CCTPiPYPc6AsJuwueEnWgSgucamXDZwBd53dQ11YiKX3

Mainnet
MessageTransmitter	CCTPmbSD7gX1bxKPAmg77w8oFzNFpaQiQUWD43TKaecd
TokenMessengerMinter	CCTPiPYPc6AsJuwueEnWgSgucamXDZwBd53dQ11YiKX3

Program Verification

Mainnet on-chain progams can be verified with the following steps:

# Checkout deployed commit
git checkout 4e8f1d7bd4c95c3e1f4cb8ba2118897b7163c7c4
# Build a verifiable build 
anchor build --verifiable
# Verify MessageTransmitter
anchor verify --program-name message_transmitter --provider.cluster mainnet --skip-build CCTPmbSD7gX1bxKPAmg77w8oFzNFpaQiQUWD43TKaecd
# Verify TokenMessengerMinter
anchor verify --program-name token_messenger_minter --provider.cluster mainnet --skip-build CCTPiPYPc6AsJuwueEnWgSgucamXDZwBd53dQ11YiKX3

Contract Design

Solana offers a different smart contract model to traditional EVM-based blockchains. In traditional EVM-based chains, contract code/logic and state are combined into a single contract deployed on-chain. With Solana, a smart contract is read-only or stateless and contains just program logic. This creates a logical separation of state (accounts) and contract logic (programs). This model allows for a single generic Solana program to operate across various accounts without requiring additional deployments. This is the crucial difference between Solana and EVM-based smart contracts.

CCTP protocol on EVM chains consists of three contracts:

MessageTransmitter: Generic message passing. Sends all messages on the source chain, and receives all messages on the destination chain.
TokenMessenger: Entrypoint for cross-chain token transfer. Routes messages to burn a token on source chain, and mint it on destination chain.
TokenMinter: Responsible for minting and burning tokens. Contains chain-specific settings used by minters and burners.

On Solana, the CCTP protocol implementation is split into two programs: MessageTransmitter and TokenMessengerMinter. Where TokenMessengerMinter encapsulates the functionality of both TokenMessenger and TokenMinter contracts. To ensure alignment with EVM contracts' logic and state and to facilitate future upgrades and maintenance, the code and state of Solana programs reflect the EVM counterparts as closely as possible.

Solana CCTP programs are written in Rust and leverage the Anchor framework that makes it easier and more efficient for developers to create, deploy, and manage smart contracts on the Solana blockchain. Along with the program, an IDL (Interface Description Language) can be generated and deployed on-chain making it much easier for developers to interact with the CCTP program. See Deployment guide for more details.

Each CCTP program instruction emits one or more events upon execution. Depending on the purpose of instruction, events are emitted via Anchor's CPI events functionality or by creating new stand-alone accounts where such events are stored. Stand-alone account addresses are randomly generated on a client and passed to the program. The program initializes the account, writes the event, and sets itself as the owner. Replace instructions don't update previously created event accounts but create new ones. This is done to make it easier for the client to generate a replace instruction because it doesn't need to look up the original account address. At this time, only MessageSent events are emitted via stand-alone accounts.

Backend services can observe new account-based events by introspecting instructions and extracting event account addresses. Once the event has been processed, the account could be deleted and rent SOL reclaimed with reclaimEventAccount instruction. Rent SOL can only be returned to the original rent payer.

MessageTransmitter Module

Instructions

initialize

Initialize MessageTransmitter. This operation needs to be performed prior to using any other instructions. During the initialization, authorities are set to the upgrade authority.

Parameter	Type	Description
localDomain	u32	Solana domain id
attester	[u8; 20]	Attester to enable
maxMessageBodySize	u64	Maximum size of message body, in bytes
version	u32	Message Format version

transferOwnership

Change the authority of MessageTransmitter.

Parameter	Type	Description
newOwner	Pubkey	New authority

acceptOwnership

Serves as a safety net after the authority has been changed. If an address has been inputted incorrectly, the former authority can rectify this by invoking the transferOwnership instruction once more.

Parameter	Type	Description
N/A

updatePauser

Change the pauser of MessageTransmitter.

Parameter	Type	Description
newPauser	Pubkey	New pauser

updateAttesterManager

Change the AttesterManager of MessageTransmitter.

Parameter	Type	Description
newAttesterManager	Pubkey	New authority

receiveMessage

Receive a message. Messages with a given nonce can only be broadcast successfully once for a pair of domains. The message body of a valid message is passed to the specified recipient for further processing.

Parameter	Type	Description
message	Vec<u8>	Message bytes
attestation	Vec<u8>	Signed attestation of message

sendMessage

Send a message to the destination domain and recipient. Emits a MessageSent event which will be attested by Circle’s attestation service.

Parameter	Type	Description
destinationDomain	u32	Destination domain identifier
recipient	Pubkey	Address to handle message body on destination domain
messageBody	Vec<u8>	Application-specific message to be handled by recipient

sendMessageWithCaller

Send a message to the destination domain and recipient, for a specified destinationCaller on the destination domain. Emits a MessageSent event which will be attested by Circle’s attestation service.

Parameter	Type	Description
destinationDomain	u32	Destination domain identifier
recipient	Pubkey	Address to handle message body on destination domain
messageBody	Vec<u8>	Application-specific message to be handled by recipient
destinationCaller	Pubkey	Caller on the destination domain

replaceMessage

Replace a message with a new message body and/or destination caller.

Parameter	Type	Description
originalMessage	Vec<u8>	Original message to replace
originalAttestation	Vec<u8>	Attestation of originalMessage
newMessageBody	Vec<u8>	New message body of replaced message
newDestinationCaller	Pubkey	The new destination caller, which may be the same as the original destination caller

setSignatureThreshold

Set the threshold of signatures required to attest to a message.

Parameter	Type	Description
newSignatureThreshold	u32	New signature threshold

enableAttester

Enable an attester.

Parameter	Type	Description
newAttester	[u8; 20]	Attester to enable

disableAttester

Disable an attester.

Parameter	Type	Description
attester	[u8; 20]	Attester to disable

setMaxMessageBodySize

Set the max message body size.

Parameter	Type	Description
newMaxMessageBodySize	u64	New signature threshold

pause

Pause MessageTransmitter.

Parameter	Type	Description
None

unpause

Resume MessageTransmitter.

Parameter	Type	Description
None

reclaimEventAccount

Deletes the event account and reclaims rent SOL to the original rent payer. This instruction requires a valid attestation to be executed.

Parameter	Type	Description
attestation	Vec<u8>	Attestation of the message

getNoncePDA

View-only helper instruction to look-up usedNonces account for receiveMessage and isNonceUsed instructions.

Parameter	Type	Description
nonce	u64	Message nonce
sourceDomain	u32	Domain identifier

isNonceUsed

View-only helper instruction that returns true if the nonce is already used, i.e. the message is received on the destination chain.

Parameter	Type	Description
nonce	u64	Message nonce

State

MessageTransmitter

Stores MessageTransmitter configuration and next available nonce.

Field	Type	Description
owner	Pubkey	Main authority of the program
pendingOwner	Pubkey	New authority that needs to be accepted
attesterManager	Pubkey	Attester Manager of the program
pauser	Pubkey	Pause / unpause authority
paused	bool	Specifies whether MessageTransmitter is paused
localDomain	u32	Solana domain id
version	u32	Message Format version
signatureThreshold	u32	Threshold of signatures required to attest to a message
enabledAttesters	Vec<Pubkey>	Enabled attesters (message signers)
maxMessageBodySize	u64	Maximum size of message body, in bytes
nextAvailableNonce	u64	Next available nonce from this source domain

UsedNonces

On-chain account that stores used nonces.

Field	Type	Description
remoteDomain	u32	Remote domain id
firstNonce	u64	First nonce in the usedNonces array
usedNonces	[bool; 500]	Flags indicating if the nonce is used

Events

OwnershipTransferStarted

Field	Type	Description
previousOwner	Pubkey	Previous owner
newOwner	Pubkey	New owner

OwnershipTransferred

Field	Type	Description
previousOwner	Pubkey	Previous owner
newOwner	Pubkey	New owner

PauserChanged

Field	Type	Description
newAddress	Pubkey	New pauser

AttesterManagerUpdated

Field	Type	Description
previousAttesterManager	Pubkey	Previous AttesterManager
newAttesterManager	Pubkey	New AttesterManager

MessageSent

Emitted when a new message is dispatched.

Field	Type	Description
rent_payer	Pubkey	Account rent payer
message	Vec<u8>	Raw bytes of message

MessageReceived

Emitted when a new message is received.

Field	Type	Description
caller	Pubkey	Authorized caller of receiveMessage() on destination domain
sourceDomain	u32	The source domain this message originated from
nonce	u64	Unique message nonce
sender	Pubkey	The sender of this message
messageBody	Vec<u8>	Raw bytes of message

SignatureThresholdUpdated

Emitted when threshold number of attestations (m in m/n multisig) is updated.

Field	Type	Description
oldSignatureThreshold	u32	Old signature threshold
newSignatureThreshold	u32	New signature threshold

AttesterEnabled

Emitted when an attester is enabled.

Field	Type	Description
attester	[u8; 20]	Newly enabled attester

AttesterDisabled

Emitted when an attester is disabled.

Field	Type	Description
attester	[u8; 20]	Newly disabled attester

MaxMessageBodySizeUpdated

Emitted when max message body size is updated.

Field	Type	Description
newMaxMessageBodySize	u64	New maximum message body size, in bytes

Pause

Emitted when MessageTransmitter is paused.

Field	Type	Description
None

Unpause

Emitted when MessageTransmitter is resumed.

Field	Type	Description
None

TokenMessenger Module

Instructions

initialize

Initialize TokenMessenger. This operation needs to be performed prior to using any other instructions. During the initialization, authorities are set to the upgrade authority.

Parameter	Type	Description
tokenController	Pubkey	Token controller address
messageTransmitter	Pubkey	Local Message Transmitter
messageBodyVersion	u32	Version of message body format

transferOwnership

Change the authority of TokenMessenger.

Parameter	Type	Description
newOwner	Pubkey	New authority

acceptOwnership

Serves as a safety net after the authority has been changed. If an address has been inputted incorrectly, the former authority can rectify this by invoking the transferOwnership instruction once more.

Parameter	Type	Description
N/A

depositForBurn

Deposit and burn tokens from sender to be minted on destination domain. Minted tokens will be transferred to mintRecipient.

Parameter	Type	Description
amount	u64	Amount of tokens to deposit and burn
destinationDomain	u32	Destination domain identifier
mintRecipient	Pubkey	Address of mint recipient on destination domain

depositForBurnWithCaller

Deposit and burn tokens from sender to be minted on destination domain. Minted tokens will be transferred to mintRecipient.

Parameter	Type	Description
amount	u64	Amount of tokens to deposit and burn
destinationDomain	u32	Destination domain identifier
mintRecipient	Pubkey	Address of mint recipient on destination domain
destinationCaller	Pubkey	Caller on the destination domain

replaceDepositForBurn

Replace a BurnMessage to change the mint recipient and/or destination caller. Allows the sender of a previous BurnMessage (created by depositForBurn) to send a new BurnMessage to replace the original. The new BurnMessage will reuse the amount and burn token of the original, without requiring a new deposit.

This is useful in cases where the user specified an incorrect address and has no way to safely mint the previously burned tokens.

Parameter	Type	Description
originalMessage	Vec<u8>	Original message to replace
originalAttestation	Vec<u8>	Attestation of originalMessage
newMintRecipient	Pubkey	Address of mint recipient on destination domain
newDestinationCaller	Pubkey	Caller on the destination domain

handleReceiveMessage

Handle an incoming message received by the local MessageTransmitter, and take the appropriate action. For a burn message, mint the associated token to the requested recipient on the local domain.

Parameter	Type	Description
remoteDomain	u32	The domain where the message originated from
sender	Pubkey	The sender of the message (remote TokenMessenger)
messageBody	Vec<u8>	The message body bytes

addRemoteTokenMessenger

Add the TokenMessenger for a remote domain.

Parameter	Type	Description
domain	u32	Domain of remote TokenMessenger
tokenMessenger	Pubkey	Address of remote TokenMessenger

removeRemoteTokenMessenger

Remove the TokenMessenger for a remote domain.

Parameter	Type	Description
N/A

State

TokenMessenger

Stores TokenMessenger configuration.

Field	Type	Description
owner	Pubkey	Main authority of the program
pendingOwner	Pubkey	New authority that needs to be accepted
localMessageTransmitter	Pubkey	Local Message Transmitter responsible for sending and receiving messages to/from remote domains
messageBodyVersion	u32	Version of message body format

RemoteTokenMessenger

Stores information about TokenMessenger on remote domain.

Field	Type	Description
domain	u32	Domain of remote TokenMessenger
tokenMessenger	Pubkey	Valid TokenMessenger on remote domain

Events

OwnershipTransferStarted

Field	Type	Description
previousOwner	Pubkey	Previous owner
newOwner	Pubkey	New owner

OwnershipTransferred

Field	Type	Description
previousOwner	Pubkey	Previous owner
newOwner	Pubkey	New owner

DepositForBurn

Emitted when a DepositForBurn message is sent.

Field	Type	Description
nonce	u64	Unique nonce reserved by message
burnToken	Pubkey	Mint address of token burnt on Solana
amount	u64	Deposit amount
depositor	Pubkey	Address where deposit is transferred from
mintRecipient	Pubkey	Address receiving minted tokens on destination domain
destinationDomain	u32	Destination domain
destinationTokenMessenger	Pubkey	Address of TokenMessenger on destination domain
destinationCaller	Pubkey	Authorized caller of receiveMessage() on destination domain

MintAndWithdraw

Emitted when tokens are minted.

Field	Type	Description
mintRecipient	Pubkey	Recipient address of minted tokens
amount	u64	Amount of minted tokens
mintToken	Pubkey	Mint address of minted token

RemoteTokenMessengerAdded

Emitted when a remote TokenMessenger is added.

Field	Type	Description
domain	u32	Domain of remote TokenMessenger
tokenMessenger	Pubkey	Address of remote TokenMessenger

RemoteTokenMessengerRemoved

Emitted when a remote TokenMessenger is removed.

Field	Type	Description
domain	u32	Domain of remote TokenMessenger
tokenMessenger	Pubkey	Address of remote TokenMessenger

TokenMinter Module

Instructions

setTokenController

Change the token controller address.

Parameter	Type	Description
newTokenController	Pubkey	New token controller

updatePauser

Change the pauser address.

Parameter	Type	Description
newPauser	Pubkey	New pauser

setMaxBurnAmountPerMessage

Set the maximum burn amount per message.

Parameter	Type	Description
burnLimitPerMessage	u64	Maximum burn amount per message

addLocalToken

Add a new local token.

Parameter	Type	Description
N/A

removeLocalToken

Remove local token.

Parameter	Type	Description
N/A

linkTokenPair

Link supported pair of local and remote tokens.

Parameter	Type	Description
remoteDomain	u32	Remote domain
remoteToken	Pubkey	Remote token address
localToken	Pubkey	Local token address

unlinkTokenPair

Unlink a pair of local and remote tokens.

Parameter	Type	Description
N/A

pause

Pause TokenMinter.

Parameter	Type	Description
None

unpause

Resume TokenMinter.

Parameter	Type	Description
None

burnTokenCustody

Burn tokens in the custody. If the specified amount is greater than the current balance, then the entire balance is burned, i.e., no error is returned in such case.

Parameter	Type	Description
amount	u64	Amount of tokens to burn

State

TokenMinter

Stores TokenMinter configuration and records stats.

Field	Type	Description
tokenController	Pubkey	Authority to manage token address mappings, and per-message burn limits
pauser	Pubkey	Pause / unpause authority
paused	bool	Specifies whether the TokenMinter is paused

TokenPair

Supported mintable tokens on remote domains, mapped to their corresponding local token.

Field	Type	Description
remoteDomain	u32	Remote domain
remoteToken	Pubkey	Remote token address
localToken	Pubkey	Local token mint address

LocalToken

Supported tokens on the local domain.

Field	Type	Description
custody	Pubkey	Custody token account
mint	Pubkey	Token mint address
burnLimitPerMessage	u64	Maximum burn amount per message
messagesSent	u64	Total number of messages sent
messagesReceived	u64	Total number of messages received
amountSent	u64	Amount of tokens sent (burned)
amountReceived	u64	Amount of tokens received (minted)

Events

SetTokenController

Field	Type	Description
tokenController	Pubkey	New token controller

PauserChanged

Field	Type	Description
newAddress	Pubkey	New pauser

Mint

Emitted when a mint request is processed.

Field	Type	Description
amount	u64	Minted amount

Burn

Emitted when a burn request is processed.

Field	Type	Description
amount	u64	Burned amount

SetBurnLimitPerMessage

Emitted when a burn limit per message is set.

Field	Type	Description
token	Pubkey	Token mint address
burnLimitPerMessage	u64	New burn limit per message

LocalTokenAdded

Emitted when a new local token is added.

Field	Type	Description
custody	Pubkey	Custody token account
mint	Pubkey	Token mint address

LocalTokenRemoved

Emitted when a local token is removed.

Field	Type	Description
custody	Pubkey	Custody token account
mint	Pubkey	Token mint address

TokenPairLinked

Emitted when a token pair is linked.

Field	Type	Description
localToken	Pubkey	Local token mint address
remoteDomain	u32	Remote domain
remoteToken	Pubkey	Remote token address

TokenPairUnlinked

Emitted when a token pair is linked.

Field	Type	Description
localToken	Pubkey	Local token mint address
remoteDomain	u32	Remote domain
remoteToken	Pubkey	Remote token address

Pause

Emitted when TokenMinter is paused.

Field	Type	Description
None

Unpause

Emitted when TokenMinter is resumed.

Field	Type	Description
None

Permissions

The following table shows the permissions for calling each instruction:

module	instruction	permissionless	pauser	attester manager	token controller	owner	upgrade authority	program (e.g. TokenMessenger)	MessageTransmitter
MessageTransmitter	initialize						x
MessageTransmitter	transferOwnership					x
MessageTransmitter	acceptOwnership					x
MessageTransmitter	updatePauser					x
MessageTransmitter	updateAttesterManager					x
MessageTransmitter	receiveMessage	x
MessageTransmitter	sendMessage							x
MessageTransmitter	sendMessageWithCaller							x
MessageTransmitter	replaceMessage							x
MessageTransmitter	setSignatureThreshold			x
MessageTransmitter	enableAttester			x
MessageTransmitter	disableAttester			x
MessageTransmitter	setMaxMessageBodySize					x
MessageTransmitter	pause		x
MessageTransmitter	unpause		x
TokenMessenger	initialize						x
TokenMessenger	transferOwnership					x
TokenMessenger	acceptOwnership					x
TokenMessenger	depositForBurn	x
TokenMessenger	depositForBurnWithCaller	x
TokenMessenger	replaceDepositForBurn	x
TokenMessenger	handleReceiveMessage								x
TokenMessenger	addRemoteTokenMessenger					x
TokenMessenger	removeRemoteTokenMessenger					x
TokenMinter	setTokenController					x
TokenMinter	updatePauser					x
TokenMinter	setMaxBurnAmountPerMessage				x
TokenMinter	addLocalToken				x
TokenMinter	removeLocalToken				x
TokenMinter	linkTokenPair				x
TokenMinter	unlinkTokenPair				x
TokenMinter	pause		x
TokenMinter	unpause		x

Deployment guide

Setup Environment

Clone the repository from https://github.com/circlefin/solana-cctp-contracts.
Install the latest Solana tools from https://docs.solana.com/cli/install-solana-cli-tools. If you already have Solana tools, run solana-install update to get the latest compatible version.
Install the latest Rust stable from https://rustup.rs/. If you already have Rust, run rustup update to get the latest version.
Install the latest Anchor framework from https://www.anchor-lang.com/docs/installation. If you already have Anchor, run avm update to get the latest version.

Rustfmt is used to format the code. It requires nightly features to be activated:

Install nightly rust toolchain. https://rust-lang.github.io/rustup/installation/index.html#installing-nightly
Execute git config core.hooksPath .githooks to activate pre-commit hooks.

[Optional] Vscode setup

Install rust-analyzer extension
If formatting doesn't work, make sure that rust-analyzer.rustfmt.extraArgs is set to +nightly

Build

First, generate new keys for the program addresses with solana-keygen new -o <PROG_ID_JSON>. Then, replace the existing program IDs with the newly generated addresses in Anchor.toml, programs/message-transmitter/src/lib.rs, and programs/token-messenger-minter/src/lib.rs.

Also, ensure the path to your wallet in Anchor.toml is correct. Alternatively, when running Anchor deploy or test commands, you can specify your wallet with --provider.wallet argument. The wallet's pubkey will be set as an upgrade authority upon initial deployment of the program. It is strongly recommended to use multisig upgrade authority when deploying to the mainnet.

To build the program run anchor build command from the root solana-cctp-contracts directory:

cd solana-cctp-contracts
anchor build

Cargo Dependencies

To ensure with certainty that packages are not changed unexpectedly as well as to enable reproducible, verifiable builds, all Cargo dependencies are vendored locally in the vendor directory and enabled via the .cargo/config.toml file.

Test

Unit tests are executed with the cargo test command:

cargo test -- --nocapture

Integration tests can be started as follows:

npm install
anchor test -- --features test

By default, integration tests are executed on a local validator, so it won't cost you any SOL.

Deploy

To deploy the program to the devnet and upload the IDL use the following commands:

anchor deploy --provider.cluster devnet --program-name message_transmitter --program-keypair <PROG_ID_JSON>
anchor deploy --provider.cluster devnet --program-name token_messenger_minter --program-keypair <PROG_ID_JSON>
anchor idl init --provider.cluster devnet --filepath ./target/idl/message_transmitter.json <PROGRAM ID>
anchor idl init --provider.cluster devnet --filepath ./target/idl/token_messenger_minter.json <PROGRAM ID>

Initialize

Before the first use of the CCTP programs they must be initialized with the MessageTransmitter#initialize and TokenMessenger#initialize instructions.

License: LICENSE

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README.md

README.md

Cross-Chain Transfer Protocol (CCTP) on Solana

Contents

Introduction

Developer Documentation

Deployments

Program Verification

Contract Design

MessageTransmitter Module

Instructions

State

Events

TokenMessenger Module

Instructions

State

Events

TokenMinter Module

Instructions

State

Events

Permissions

Deployment guide

Setup Environment

[Optional] Vscode setup

Build

Cargo Dependencies

Test

Deploy

Initialize

Files

README.md

Latest commit

History

README.md

File metadata and controls

Cross-Chain Transfer Protocol (CCTP) on Solana

Contents

Introduction

Developer Documentation

Deployments

Program Verification

Contract Design

MessageTransmitter Module

Instructions

State

Events

TokenMessenger Module

Instructions

State

Events

TokenMinter Module

Instructions

State

Events

Permissions

Deployment guide

Setup Environment

[Optional] Vscode setup

Build

Cargo Dependencies

Test

Deploy

Initialize