CBDC Chaincode

Disclaimer

This chaincode is provided solely for educational and prototyping purposes. - It must not be used in live financial environments without thorough auditing, testing, and tailoring for legal, regulatory, and security requirements. - CBDC systems involve complex central banking policies, cryptographic controls, compliance audits, and jurisdictional regulations that this simplified implementation does not cover. - Any real-world deployment of such a contract must go through a complete security audit, formal verification, and regulatory alignment in the context of the target financial system.

package main
 
import (
	"encoding/json"
	"fmt"
	"regexp"
	"strconv"
	"strings"
	"time"
 
	"github.com/hyperledger/fabric-contract-api-go/contractapi"
)
 
// Regex pattern for account ID validation
var idPattern = regexp.MustCompile(`^[a-zA-Z0-9_.-]{4,64}$`)
 
const (
	RoleCentralBank     = "centralbank"
	RoleRetailBank      = "retailbank"
	RoleAuditor         = "auditor"
	RetailTransferCap   = 100000
	MultisigThreshold   = 500000
)
 
// CBDCContract defines the chaincode structure
type CBDCContract struct {
	contractapi.Contract
}
 
// Account represents a CBDC wallet
type Account struct {
	Owner      string            `json:"owner"`
	Balance    uint64            `json:"balance"`
	CreatedAt  string            `json:"createdAt"`
	LastActive string            `json:"lastActive"`
	Frozen     bool              `json:"frozen"`
	Tags       map[string]string `json:"tags"`
	History    []TransactionLog  `json:"history"`
}
 
// TransactionLog stores audit trails for an account
type TransactionLog struct {
	Action       string `json:"action"`
	Amount       uint64 `json:"amount,omitempty"`
	Counterparty string `json:"counterparty,omitempty"`
	Timestamp    string `json:"timestamp"`
	Initiator    string `json:"initiator"`
}
 
// Role mapping from MSP ID
func getRoleFromMSP(msp string) string {
	switch strings.ToLower(msp) {
	case "centralbankmsp":
		return RoleCentralBank
	case "retailbankmsp":
		return RoleRetailBank
	case "auditormsp":
		return RoleAuditor
	default:
		return ""
	}
}
 
// Role-based access control
func (c *CBDCContract) hasRole(ctx contractapi.TransactionContextInterface, allowedRoles ...string) bool {
	mspID, err := ctx.GetClientIdentity().GetMSPID()
	if err != nil {
		return false
	}
	role := getRoleFromMSP(mspID)
	for _, r := range allowedRoles {
		if r == role {
			return true
		}
	}
	return false
}
 
// Enforce transfer caps for retail banks
func (c *CBDCContract) enforceTransactionCap(ctx contractapi.TransactionContextInterface, amount uint64) error {
	mspID, err := ctx.GetClientIdentity().GetMSPID()
	if err != nil {
		return fmt.Errorf("unable to determine MSPID")
	}
	role := getRoleFromMSP(mspID)
	if role == RoleRetailBank && amount > RetailTransferCap {
		return fmt.Errorf("transfer amount exceeds retail bank cap of %d", RetailTransferCap)
	}
	return nil
}
 
// If multisig approval is needed
func (c *CBDCContract) multisigApprovalRequired(amount uint64) bool {
	return amount > MultisigThreshold
}
 
// Stub for future multisig enforcement
func (c *CBDCContract) verifyMultisigApproval(ctx contractapi.TransactionContextInterface, txID string) error {
	return nil // To be implemented
}
 
// Account ID validation
func validateID(id string) error {
	if !idPattern.MatchString(id) {
		return fmt.Errorf("invalid account ID format")
	}
	return nil
}
 
// Create or load account, and persist if new
func (c *CBDCContract) getOrCreateAccount(ctx contractapi.TransactionContextInterface, id string) (*Account, error) {
	a, err := c.getAccount(ctx, id)
	if err == nil {
		return a, nil
	}
	ts, _ := ctx.GetStub().GetTxTimestamp()
	timestamp := time.Unix(ts.Seconds, int64(ts.Nanos)).Format(time.RFC3339)
	newAccount := &Account{
		Owner:      id,
		Balance:    0,
		CreatedAt:  timestamp,
		LastActive: timestamp,
		Frozen:     false,
		Tags:       make(map[string]string),
		History:    []TransactionLog{},
	}
	if err := c.saveAccount(ctx, id, newAccount); err != nil {
		return nil, err
	}
	return newAccount, nil
}
 
// Load existing account from state
func (c *CBDCContract) getAccount(ctx contractapi.TransactionContextInterface, id string) (*Account, error) {
	data, err := ctx.GetStub().GetState(id)
	if err != nil {
		return nil, err
	}
	if data == nil {
		return nil, fmt.Errorf("account not found")
	}
	var acc Account
	if err := json.Unmarshal(data, &acc); err != nil {
		return nil, err
	}
	return &acc, nil
}
 
// Persist account to world state
func (c *CBDCContract) saveAccount(ctx contractapi.TransactionContextInterface, id string, acc *Account) error {
	data, err := json.Marshal(acc)
	if err != nil {
		return err
	}
	return ctx.GetStub().PutState(id, data)
}
 
// Get client identity
func (c *CBDCContract) GetInvoker(ctx contractapi.TransactionContextInterface) (string, error) {
	id, err := ctx.GetClientIdentity().GetID()
	if err != nil || id == "" {
		return "", fmt.Errorf("unable to retrieve or validate invoker ID")
	}
	return id, nil
}
 
// Central bank can issue tokens
func (c *CBDCContract) IssueTokens(ctx contractapi.TransactionContextInterface, recipient string, amount uint64) error {
	if !c.hasRole(ctx, RoleCentralBank) {
		return fmt.Errorf("only central bank can issue tokens")
	}
	if err := validateID(recipient); err != nil {
		return err
	}
	if amount == 0 {
		return fmt.Errorf("amount must be greater than zero")
	}
	invoker, err := c.GetInvoker(ctx)
	if err != nil {
		return err
	}
	account, err := c.getOrCreateAccount(ctx, recipient)
	if err != nil {
		return err
	}
	if account.Frozen {
		return fmt.Errorf("account is frozen")
	}
	ts, _ := ctx.GetStub().GetTxTimestamp()
	timestamp := time.Unix(ts.Seconds, int64(ts.Nanos)).Format(time.RFC3339)
	account.Balance += amount
	account.LastActive = timestamp
	account.History = append(account.History, TransactionLog{"ISSUE", amount, recipient, timestamp, invoker})
	if err := c.saveAccount(ctx, recipient, account); err != nil {
		return err
	}
	return ctx.GetStub().SetEvent("TokensIssued", []byte(fmt.Sprintf("%s:%d", recipient, amount)))
}
 
// Central bank can burn tokens
func (c *CBDCContract) BurnTokens(ctx contractapi.TransactionContextInterface, account string, amount uint64) error {
	if !c.hasRole(ctx, RoleCentralBank) {
		return fmt.Errorf("only central bank can burn tokens")
	}
	if err := validateID(account); err != nil {
		return err
	}
	if amount == 0 {
		return fmt.Errorf("amount must be greater than zero")
	}
	invoker, err := c.GetInvoker(ctx)
	if err != nil {
		return err
	}
	a, err := c.getAccount(ctx, account)
	if err != nil {
		return err
	}
	if a.Frozen {
		return fmt.Errorf("account is frozen")
	}
	if a.Balance < amount {
		return fmt.Errorf("insufficient balance")
	}
	ts, _ := ctx.GetStub().GetTxTimestamp()
	timestamp := time.Unix(ts.Seconds, int64(ts.Nanos)).Format(time.RFC3339)
	a.Balance -= amount
	a.LastActive = timestamp
	a.History = append(a.History, TransactionLog{"BURN", amount, "", timestamp, invoker})
	if err := c.saveAccount(ctx, account, a); err != nil {
		return err
	}
	return ctx.GetStub().SetEvent("TokensBurned", []byte(fmt.Sprintf("%s:%d", account, amount)))
}
 
// Freeze an account
func (c *CBDCContract) FreezeAccount(ctx contractapi.TransactionContextInterface, account string) error {
	if !c.hasRole(ctx, RoleCentralBank) {
		return fmt.Errorf("only central bank can freeze accounts")
	}
	a, err := c.getAccount(ctx, account)
	if err != nil {
		return err
	}
	a.Frozen = true
	return c.saveAccount(ctx, account, a)
}
 
// Unfreeze an account
func (c *CBDCContract) UnfreezeAccount(ctx contractapi.TransactionContextInterface, account string) error {
	if !c.hasRole(ctx, RoleCentralBank) {
		return fmt.Errorf("only central bank can unfreeze accounts")
	}
	a, err := c.getAccount(ctx, account)
	if err != nil {
		return err
	}
	a.Frozen = false
	return c.saveAccount(ctx, account, a)
}
 
// Get account balance with no access control (can be restricted further)
func (c *CBDCContract) GetBalance(ctx contractapi.TransactionContextInterface, account string) (uint64, error) {
	a, err := c.getAccount(ctx, account)
	if err != nil {
		return 0, err
	}
	return a.Balance, nil
}
 
// Get transaction history
func (c *CBDCContract) GetHistory(ctx contractapi.TransactionContextInterface, account string) ([]TransactionLog, error) {
	a, err := c.getAccount(ctx, account)
	if err != nil {
		return nil, err
	}
	return a.History, nil
}
 
// Get account tags
func (c *CBDCContract) GetTags(ctx contractapi.TransactionContextInterface, account string) (map[string]string, error) {
	a, err := c.getAccount(ctx, account)
	if err != nil {
		return nil, err
	}
	return a.Tags, nil
}
 
// Admin can tag accounts
func (c *CBDCContract) AdminAddTag(ctx contractapi.TransactionContextInterface, account, key, value string) error {
	if !c.hasRole(ctx, RoleCentralBank) {
		return fmt.Errorf("only central bank can tag accounts")
	}
	if len(key) > 32 || len(value) > 64 {
		return fmt.Errorf("tag key/value too long")
	}
	a, err := c.getAccount(ctx, account)
	if err != nil {
		return err
	}
	a.Tags[key] = value
	return c.saveAccount(ctx, account, a)
}
 
// Chaincode entry point
func main() {
	chaincode, err := contractapi.NewChaincode(new(CBDCContract))
	if err != nil {
		panic(fmt.Sprintf("Error creating CBDC chaincode: %v", err))
	}
	if err := chaincode.Start(); err != nil {
		panic(fmt.Sprintf("Error starting CBDC chaincode: %v", err))
	}
}

This CBDC (Central Bank Digital Currency) chaincode is written for Hyperledger Fabric and is intended strictly for educational and prototyping purposes. It is not production-ready and must not be deployed in a live financial system without substantial auditing, rigorous testing, and tailoring to specific regulatory and operational requirements. Real-world CBDC implementations are complex, involving monetary policy, central banking rules, and advanced security mechanisms, none of which are fully captured in this simplified contract. The contract does not include protections against replay attacks, does not implement cryptographic signature verification, lacks privacy guarantees, and omits enforcement for multisignature approvals or advanced compliance policies.

Conceptually, this chaincode simulates a basic CBDC management system deployed on a permissioned Hyperledger Fabric network. It provides core features that a central bank might need to issue and manage digital fiat currency. These features include the ability to issue or burn currency, freeze or unfreeze accounts, set metadata tags on accounts, enforce role-based access, and maintain an account-level audit trail. Additionally, it includes a mechanism to apply transaction limits for retail banks. The contract uses Go and the Fabric Contract API and relies on standard transaction context interfaces to interact with the ledger state.

The system recognizes three roles based on the MSP ID of the organization invoking a transaction. The central bank has full administrative control, allowing it to issue and burn tokens, freeze or unfreeze accounts, and add tags. Retail banks are permitted to interact with the system under certain constraints, such as a transfer cap. Auditors are not yet integrated but are envisioned as read-only participants. These roles are determined by mapping the MSP ID to predefined role labels, and permissions are enforced using a utility method that checks if the invoker’s role is among those allowed for a specific operation.

Data in the system is centered around the concept of an account. Each account includes an owner ID, token balance, creation and last active timestamps, a frozen flag, a tag map for metadata, and a list of transaction logs that serve as the audit trail. When an account is created, it is initialized with default values, and every transaction affecting the account updates its state and appends a corresponding entry to its history. Account state is stored in the ledger as a serialized JSON object.

The chaincode allows the central bank to issue tokens to any valid account. Before issuing, it checks that the recipient ID is properly formatted, that the amount is positive, and that the target account is not frozen. It then updates the account balance, sets the last active timestamp, and logs the issuance event. The burning of tokens follows a similar logic but deducts from the account balance and ensures that the balance is sufficient to cover the burn request. Both actions emit chaincode events for external observability.

Accounts can be frozen or unfrozen by the central bank. When an account is frozen, it becomes ineligible for token issuance or burning. This provides a simple control mechanism for suspending suspicious or non-compliant actors in the system. In addition to these lifecycle operations, the chaincode supports tagging, allowing the central bank to attach short metadata entries to accounts. This could be used for tagging accounts as KYC-verified, associating them with a branch ID, or any other administrative classification.

Several querying functions are exposed, including the ability to read an account’s balance, view its transaction history, or retrieve its metadata tags. Currently, these functions are unrestricted, meaning that any network participant can query any account’s data. In a real-world deployment, this would need to be restricted to protect financial privacy and enforce access policies, potentially using Fabric’s private data collections or attribute-based access control.

The chaincode also introduces a concept of transaction caps for retail banks. A configurable threshold ensures that retail banks cannot process high-value operations beyond a specified amount. However, these caps do not apply to the central bank, which retains full authority over token issuance and burning. Additionally, there is a placeholder mechanism for enforcing multisignature approvals on high-value transactions. While the code identifies when such an approval would be required, it does not currently implement any logic to validate multiple approvals or signatures. This remains a stub for future enhancement.

This chaincode implements a simplified CBDC (Central Bank Digital Currency) logic using the Hyperledger Fabric framework. It demonstrates the key responsibilities of a central bank in managing digital token issuance and enforcement controls.

Key Functionalities

Role-based access via MSP ID mapping (Central Bank, Retail Bank, Auditor)
Token issuance and burning (by Central Bank only)
Account freezing and unfreezing
Transfer caps for Retail Banks
Metadata tagging for accounts
Transaction history logging
Event emission for observability
Uses contractapi in Go for implementation

Roles

Roles are inferred from MSP IDs:

const (
    RoleCentralBank = "centralbank"
    RoleRetailBank  = "retailbank"
    RoleAuditor     = "auditor"
)
 
Role resolution is done using:
 
func getRoleFromMSP(msp string) string {
    switch strings.ToLower(msp) {
    case "centralbankmsp":
        return RoleCentralBank
    case "retailbankmsp":
        return RoleRetailBank
    case "auditormsp":
        return RoleAuditor
    default:
        return ""
    }
}

Account Structure

type Account struct {
    Owner      string
    Balance    uint64
    CreatedAt  string
    LastActive string
    Frozen     bool
    Tags       map[string]string
    History    []TransactionLog
}

Each account maintains metadata, balance, timestamps, and a full transaction log.

Transaction Logging

Audit logs are captured using:

type TransactionLog struct {
    Action       string
    Amount       uint64
    Counterparty string
    Timestamp    string
    Initiator    string
}

Token Issuance (Central Bank Only)

func (c *CBDCContract) IssueTokens(ctx contractapi.TransactionContextInterface, recipient string, amount uint64) error

Only accessible by centralbank role
Fails if recipient is frozen
Updates balance and appends to history
Emits TokensIssued event

Token Burning (Central Bank Only)

func (c *CBDCContract) BurnTokens(ctx contractapi.TransactionContextInterface, account string, amount uint64) error

Deducts from account
Fails if frozen or underfunded
Emits TokensBurned event

Account Freezing

func (c *CBDCContract) FreezeAccount(ctx contractapi.TransactionContextInterface, account string) error
func (c *CBDCContract) UnfreezeAccount(ctx contractapi.TransactionContextInterface, account string) error

Only the central bank may freeze/unfreeze accounts
Prevents future operations on frozen accounts

Metadata Tagging

func (c *CBDCContract) AdminAddTag(ctx contractapi.TransactionContextInterface, account, key, value string) error

Adds key-value metadata (e.g., "kyc": "verified")
Length restrictions: key ≤ 32, value ≤ 64

Account Queries

func (c *CBDCContract) GetBalance(ctx, account string) (uint64, error)
func (c *CBDCContract) GetHistory(ctx, account string) ([]TransactionLog, error)
func (c *CBDCContract) GetTags(ctx, account string) (map[string]string, error)

Currently unrestricted
Should be secured using role-based visibility or private data

Transfer Cap for Retail Banks

Retail banks are restricted from performing operations above a defined threshold:

const RetailTransferCap = 100000

Enforced via:

func (c *CBDCContract) enforceTransactionCap(ctx contractapi.TransactionContextInterface, amount uint64) error

CBDC Chaincode

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