Carbon Credit Token (CCT) Smart Contract

A comprehensive smart contract for managing carbon credits on the Stacks blockchain, enabling transparent tracking, trading, and retirement of carbon offset credits.

Overview

The Carbon Credit Token (CCT) contract implements a fungible token standard specifically designed for carbon credits. It provides functionality for minting verified carbon credits, transferring them between parties, and permanently retiring them to claim carbon offsets.

Features

Core Token Functionality

• ERC-20 Compatible: Standard token operations (transfer, approve, allowance)
• Minting: Create new carbon credits with detailed metadata
• Retirement: Permanently burn credits to claim carbon offsets
• Batch Operations: Efficient batch transfers

Carbon Credit Specific Features

• Project Tracking: Each credit is linked to a specific carbon offset project
• Vintage Year: Credits include the year the carbon reduction occurred
• Methodology: Tracks the carbon accounting methodology used
• Verification: Only authorized verifiers can mint new credits
• Retirement Tracking: Permanent record of retired credits per user

Security & Administration

• Access Control: Owner and verifier authorization system
• Contract Pausing: Emergency pause functionality
• Input Validation: Comprehensive validation of all inputs
• Error Handling: Detailed error codes for debugging

Contract Details

• Token Name: Carbon Credit Token
• Token Symbol: CCT
• Decimals: 6
• Blockchain: Stacks

Key Functions

Token Operations

;; Transfer tokens
(transfer (amount uint) (sender principal) (recipient principal) (memo (optional (buff 34))))

;; Approve spending allowance
(approve (spender principal) (amount uint))

;; Transfer from approved allowance
(transfer-from (amount uint) (sender principal) (recipient principal))

Carbon Credit Management

;; Mint new carbon credits (verifiers only)
(mint-carbon-credits (recipient principal) (amount uint) (project-id (string-ascii 64)) 
                     (vintage uint) (methodology (string-ascii 32)) (verification-body (string-ascii 32)))

;; Retire credits permanently
(retire-credits (amount uint))

;; Batch transfer multiple recipients
(batch-transfer (transfers (list 10 {recipient: principal, amount: uint})))

Administrative Functions

;; Add/remove authorized verifiers (owner only)
(add-verifier (verifier principal))
(remove-verifier (verifier principal))

;; Pause/unpause contract (owner only)
(set-contract-paused (paused bool))

Read-Only Functions

• get-balance: Check token balance for an address
• get-token-metadata: Retrieve detailed credit information
• get-project-total: Total credits issued for a project
• get-retired-credits: Credits retired by a user
• is-contract-paused: Check if contract is paused

Error Codes

Code	Error	Description
100	ERR_UNAUTHORIZED	Caller lacks required permissions
101	ERR_INSUFFICIENT_BALANCE	Insufficient token balance
102	ERR_INVALID_AMOUNT	Invalid amount (must be > 0)
103	ERR_TOKEN_NOT_FOUND	Token ID does not exist
104	ERR_ALREADY_RETIRED	Credit already retired
105	ERR_INVALID_RECIPIENT	Invalid recipient address
106	ERR_TRANSFER_FAILED	Transfer operation failed
107	ERR_INVALID_PRINCIPAL	Invalid principal address
108	ERR_INVALID_STRING	Invalid string parameter

Usage Examples

Minting Carbon Credits

Only authorized verifiers can mint new credits:

(contract-call? .carbon-credit-token mint-carbon-credits 
  'SP1234567890... ;; recipient
  u1000000        ;; amount (1 tonne CO2 with 6 decimals)
  "PROJ-001"      ;; project ID
  u2024           ;; vintage year
  "VCS"           ;; methodology
  "VERIFIER-A"    ;; verification body
)

Transferring Credits

(contract-call? .carbon-credit-token transfer 
  u500000         ;; amount (0.5 tonnes)
  tx-sender       ;; sender
  'SP9876543210... ;; recipient
  none            ;; memo
)

Retiring Credits

(contract-call? .carbon-credit-token retire-credits u1000000)

Security Considerations

1. Authorized Verifiers: Only trusted entities should be granted verifier status
2. Project Validation: Verify project IDs correspond to real carbon offset projects
3. Double Counting: Ensure credits aren't double-counted across different systems
4. Retirement Permanence: Retired credits cannot be recovered or transferred