Audit Scope

github.com/t402-io/t402/
├── typescript/              # TypeScript SDK (36 npm packages)
│   └── packages/
│       ├── core/           # Protocol types
│       ├── mechanisms/
│       │   ├── evm/        # EVM signing (IN SCOPE)
│       │   ├── svm/        # Solana signing (IN SCOPE)
│       │   ├── ton/        # TON signing (IN SCOPE)
│       │   ├── tron/       # TRON signing (IN SCOPE)
│       │   ├── near/       # NEAR signing (IN SCOPE)
│       │   ├── aptos/      # Aptos signing (IN SCOPE)
│       │   ├── tezos/      # Tezos signing (IN SCOPE)
│       │   ├── polkadot/   # Polkadot signing (IN SCOPE)
│       │   ├── stacks/     # Stacks signing (IN SCOPE)
│       │   └── cosmos/     # Cosmos signing (IN SCOPE)
│       └── ...
├── go/                      # Go SDK
│   ├── signers/            # Signer implementations (IN SCOPE)
│   │   ├── evm/
│   │   └── svm/
│   ├── mechanisms/         # Chain-specific logic (IN SCOPE)
│   │   ├── evm/
│   │   ├── svm/
│   │   ├── ton/
│   │   ├── tron/
│   │   ├── near/
│   │   ├── aptos/
│   │   ├── tezos/
│   │   ├── polkadot/
│   │   ├── stacks/
│   │   └── cosmos/
│   └── ...
├── python/                  # Python SDK
│   └── t402/src/t402/
│       ├── schemes/        # Scheme implementations (IN SCOPE)
│       ├── wdk/            # Wallet signing (IN SCOPE)
│       └── erc4337/        # Account abstraction (IN SCOPE)
├── java/                    # Java SDK
│   └── src/main/java/io/t402/
│       └── crypto/         # Crypto signers (IN SCOPE)
├── services/
│   └── facilitator/        # Facilitator service (IN SCOPE)
└── specs/                   # Protocol specifications (REFERENCE)

File: go/mechanisms/evm/exact/facilitator/scheme.go

Function: Verify(ctx, payload, requirements)
├─ 1. Validate scheme = "exact"
├─ 2. Parse EVM payload from bytes
├─ 3. Extract authorization from payload
├─ 4. Get network configuration
├─ 5. Validate recipient matches payTo
├─ 6. Validate amount ≥ required
├─ 7. Check nonce not already used          ← CRITICAL: Replay prevention
├─ 8. Query payer balance                    ← CRITICAL: Sufficient funds
├─ 9. Get token metadata (name, version)
├─ 10. Compute EIP-712 hash                  ← CRITICAL: Correct hashing
├─ 11. Recover signer from signature         ← CRITICAL: Signature validation
├─ 12. Compare recovered address with from   ← CRITICAL: Authorization match
└─ 13. Return VerifyResponse

File: go/mechanisms/evm/exact/facilitator/scheme.go

Function: Settle(ctx, payload, requirements)
├─ 1. All verification steps (above)
├─ 2. Build transferWithAuthorization call
├─ 3. Estimate gas
├─ 4. Submit transaction                     ← CRITICAL: Correct parameters
├─ 5. Wait for confirmation
├─ 6. Mark nonce as used                     ← CRITICAL: Prevent double-spend
└─ 7. Return SettlementResponse

File: go/mechanisms/svm/exact/facilitator/scheme.go

Function: ValidateTransaction(tx, feePayer, requirements)
├─ 1. Verify exactly 3 instructions
│   ├─ [0] ComputeBudget.SetLimit
│   ├─ [1] ComputeBudget.SetPrice
│   └─ [2] SPL Token TransferChecked
├─ 2. Verify compute price ≤ 5 lamports     ← CRITICAL: Fee limit
├─ 3. For each instruction:
│   └─ Verify feePayer NOT in accounts      ← CRITICAL: Fee payer safety
├─ 4. Verify transfer authority ≠ feePayer  ← CRITICAL: Fee payer safety
├─ 5. Verify token source ≠ feePayer        ← CRITICAL: Fee payer safety
├─ 6. Verify transfer amount = required     ← CRITICAL: Exact amount
└─ 7. Verify destination = payTo ATA        ← CRITICAL: Correct recipient

File: go/mechanisms/evm/eip712.go

Function: HashEIP3009Authorization(domain, authorization)
├─ 1. Encode domain separator
│   ├─ Hash type string
│   ├─ Hash name
│   ├─ Hash version
│   ├─ Encode chainId
│   └─ Encode verifyingContract
├─ 2. Encode struct hash
│   ├─ Hash type string
│   ├─ Encode from
│   ├─ Encode to
│   ├─ Encode value
│   ├─ Encode validAfter
│   ├─ Encode validBefore
│   └─ Encode nonce
├─ 3. Compute final hash
│   └─ keccak256(0x19 || 0x01 || domainSeparator || structHash)
└─ 4. Return hash                           ← CRITICAL: Must match contract

// Signature edge cases
func TestVerifySignature_InvalidLength(t *testing.T) {
    // Signatures shorter than 65 bytes
    // Signatures longer than 65 bytes
}
 
func TestVerifySignature_InvalidV(t *testing.T) {
    // v = 0, 1, 26, 29, 30, 255
}
 
func TestVerifySignature_MalleableS(t *testing.T) {
    // s > n/2 (signature malleability)
}

// Nonce tests
func TestNonceUniqueness(t *testing.T) {
    // Same nonce, same payer
    // Same nonce, different payer
    // Concurrent nonce usage
}

// Time window tests
func TestTimeWindow_BoundaryConditions(t *testing.T) {
    // validAfter = now (exact boundary)
    // validBefore = now (exact boundary)
    // validAfter = validBefore
    // validAfter > validBefore
}

// Full payment flow on testnet
func TestFullPaymentFlow_EVM(t *testing.T) {
    // 1. Generate valid payment
    // 2. Verify payment
    // 3. Settle payment
    // 4. Verify nonce marked as used
    // 5. Attempt replay (should fail)
}

# Check for known vulnerabilities
go list -m all | nancy sleuth
 
# Key dependencies to review:
# - github.com/ethereum/go-ethereum (crypto)
# - github.com/gagliardetto/solana-go (Ed25519)
# - golang.org/x/crypto (Ed25519)

# Check for known vulnerabilities
pip audit
 
# Key dependencies:
# - eth-account (EIP-712 signing)
# - web3 (RPC client)
# - pynacl (Ed25519)

# Check for known vulnerabilities
npm audit
 
# Key dependencies:
# - viem (EVM signing)
# - @solana/web3.js (Solana)

# Maven dependency check
mvn dependency-check:check
 
# Key dependencies:
# - web3j (EVM)
# - bouncycastle (Ed25519)

# Clone repository
git clone https://github.com/t402-io/t402
cd t402
 
# Go SDK
cd go && go test ./...
 
# Python SDK
cd python && pip install -e ".[dev]" && pytest
 
# TypeScript SDK
cd typescript && pnpm install && pnpm test
 
# Java SDK
cd java && mvn test