Security & Code Quality Review

Document Version: 1.0 Review Date: October 13, 2025 Mercuryo API Version: 1.6.0 Platforms: iOS, Android

Executive Summary

This document provides a formal security and code quality assessment of the Tokeo/Mercuryo Spend Card integration implemented on iOS and Android platforms. The integration leverages Mercuryo's On- and Off-Ramp iFrame solution with virtual payment card capabilities.

Overall Risk Rating: MEDIUM Implementation Complexity: HIGH Compliance Requirements: CRITICAL (KYC/AML)

1. Architecture Review

1.1 Integration Components

Core Components Implemented:

Mercuryo Widget iFrame (via native wrappers)
Silent Authentication System
Spend Card Management
Transaction Callback Handler
Signature Verification System
KYC/AML Integration (SumSub)

Platform-Specific Implementation:

iOS: WebView-based wrapper with Custom Tabs support
Android: Custom Tabs integration for Google Pay compatibility

1.2 Data Flow Analysis

User Action → Mobile App → Mercuryo Widget (iFrame) 
           ↓
Mercuryo Backend → Transaction Processing → Blockchain
           ↓
Callback → Tokeo Backend → Signature Verification → Database Update
           ↓
User Notification/UI Update

Critical Path Identified:

User authentication (silent auth or standard)
Widget initialization with signature v2
Transaction execution
Callback reception and verification
State synchronization

2. Security Assessment

2.1 CRITICAL SECURITY FINDINGS

🔴 HIGH PRIORITY

FINDING #1: Signature v2 Implementation (CRITICAL)

Status: ✅ MUST BE IMPLEMENTED

Details:

v2 signature mechanism is mandatory for production
Signature format: v2:HMAC-SHA256(address + secret + IP + merchantTransactionId)
Verified before 3D Secure processing
Invalid signatures block transactions

Implementation Checklist:

Secret key stored in secure keychain/keystore (iOS/Android)
Signature generation happens on secure backend (NOT client-side)
IP address captured server-side to prevent spoofing
Merchant transaction ID follows secure generation pattern
Signature prefix "v2:" included in all requests

Code Review Requirements:

// INCORRECT - Never generate signatures client-side
const signature = generateSignature(address, secret, ip, txId); // ❌

// CORRECT - Backend generates signature
const signature = await fetchSignatureFromBackend(address, ip, txId); // ✅

Risk if Not Implemented: Transaction hijacking, unauthorized access, financial loss

FINDING #2: Callback Signature Verification (CRITICAL)

Status: ✅ REQUIRED

Details:

All callbacks MUST verify X-Signature header
Use HMAC-SHA256 with sign key from dashboard
Validate against full callback body payload
No partial payload verification allowed

Implementation Requirements:

// Callback verification pseudocode
function verifyCallback(body, receivedSignature, signKey) {
  const calculatedSignature = hmacSha256(body, signKey);
  if (calculatedSignature !== receivedSignature) {
    // REJECT callback, log security event
    return false;
  }
  return true;
}

Checklist:

X-Signature header validation implemented
Full body used for signature calculation (not parsed JSON)
Sign key stored securely (environment variable/secrets manager)
Failed verification logged and alerted
Replay attack prevention (event_id tracking)

Risk if Not Implemented: Fraudulent callbacks, phantom transactions, data manipulation

FINDING #3: Secret Management

Current State: REQUIRES VERIFICATION

Critical Secrets:

Widget Secret Key (for v2 signatures)
Callback Sign Key
SDK-Partner-Token header
Init tokens (short-lived)

Security Requirements:

No secrets in source code or version control
iOS: Keychain Services for secret storage
Android: EncryptedSharedPreferences or Keystore
Backend secrets in environment variables/vault
Regular secret rotation schedule defined
Access logs for secret retrieval

Recommended Approach:

Secrets Flow:
Backend Secure Storage → Encrypted API → Mobile App Secure Storage → Runtime Memory Only

🟡 MEDIUM PRIORITY

FINDING #4: WebView Security (iOS/Android)

iOS WebView Concerns:

WKWebView used (NOT deprecated UIWebView)
JavaScript evaluation restricted to trusted sources
allowsInlineMediaPlayback configured appropriately
SSL pinning considered for Mercuryo domains

Android Custom Tabs Concerns:

CustomTabsIntent properly configured
Chrome Custom Tabs version compatibility checked
Deep link handling secured
Intent filtering prevents malicious app intercepts

Apple Pay/Google Pay Integration:

Apple Pay: Safari WebView required (Fully Compatible)
Google Pay: Custom Tabs required (WebView incompatible)
Mixed implementation strategy needed for optimal coverage

FINDING #5: IP Whitelisting & Sandbox Security

Status: REQUIRES CONFIGURATION

Production Requirements:

Production IP addresses whitelisted with Mercuryo
Sandbox IPs documented and whitelisted separately
Dynamic IP handling strategy defined
CDN/proxy IPs accounted for in whitelist

Testing Considerations:

Sandbox credentials separate from production
Test cards documented (4444 4444 4444 3333, etc.)
Environment switching mechanism secure and clear

2.2 Data Privacy & Compliance

GDPR/PCI-DSS Compliance:

User Data Handled:

Email addresses
Phone numbers (required for Spend Card)
Payment card data (PCI scope - handled by Mercuryo)
KYC documents (identity verification)
Transaction history
IP addresses

Compliance Checklist:

Terms of Service acceptance captured before silent auth
Data sharing consent explicit (required for Mercuryo registration)
User data retention policy defined
Right to deletion implemented
Data encryption at rest and in transit
PCI-DSS scope minimized (no card data storage)

KYC Requirements:

SumSub integration for identity verification
Document requirements vary by country
Valid mobile phone required for Spend Card
Only one Spend Card per user per partner

2.3 Authentication Security

Silent Authentication Flow:

Positive Security Measures:

Token-based authentication (init_token)
Short token expiry (1 hour or first use)
UUID-based user identification
SDK-Partner-Token header authentication

Security Concerns to Address:

Init token stored securely (not in UserDefaults/SharedPreferences)
Token expiry handling graceful
Re-authentication flow secure
Session management prevents token reuse

Authentication Scenarios:

New User: Email + accept → init_token
Verified User with Share Token: Email + accept + share_token → init_token
Existing User: Email/phone/UUID → init_token

3. Code Quality Assessment

3.1 Error Handling

Error Codes Documented:

400001: Validation error
401000: Authorization failed
403007: Transaction lock
403020: IP blacklisted
403026: Resource unavailable
403031: Login/signup failed
405000: Method not allowed
500001: Server error

Implementation Requirements:

All error codes handled explicitly
User-friendly error messages (not raw codes)
Error logging with context
Retry logic for transient errors
Fallback UX for critical failures

Recommended Error Handling Pattern:

// iOS example
func handleMercuryoError(_ errorCode: String) {
    switch errorCode {
    case "403020":
        // IP blacklisted - serious issue
        showCriticalError()
        logSecurityEvent()
    case "500001":
        // Transient error - retry with backoff
        scheduleRetry()
    default:
        showGenericError()
    }
}

3.2 Transaction State Management

Transaction Types & Statuses:

Buy Transaction (External Card):

new → pending → paid → order_verified_not_complete → completed
Failure paths: cancelled, order_failed, failed_exchange

Buy Transaction (Spend Card):

Fiat balance option
Zero balance card auto-created if needed

Sell Transaction:

6-hour crypto receipt window
Refund to user wallet after timeout
EUR/USD only supported

Spend Card Transactions:

type: "sell" + payment_method: "spend_card_open"
Card opening in off-ramp scenario
Top-up: payment_method: "spend_card_topup"

State Management Checklist:

Finite state machine implemented for each transaction type
Invalid state transitions prevented
Callback-driven state updates only
Local state reconciliation with backend state
Timeout handling for stuck transactions
User notification for state changes

3.3 Callback Handling

Callback System Design:

Transaction Callbacks:

{
  "data": {
    "id": "transaction_id",
    "type": "buy|sell|deposit|withdraw|fiat_deposit",
    "payment_method": "card|spend|spend_card_open|spend_card_topup",
    "status": "new|pending|paid|succeeded|failed|...",
    "merchant_transaction_id": "your_id"
  }
}

Spend Card Event Callbacks:

card_status: Card state changes
crypto_top_up: Spend card top-up events
card_transaction: POS/e-commerce transactions

Implementation Requirements:

Idempotent callback processing (event_id tracking)
Exponential backoff retry logic (up to 10 attempts)
HTTP 200 response for successful processing
500 errors trigger automatic retry
Callback queue/job system for reliability
Dead letter queue for failed callbacks

Retry Strategy:

Attempt 1: Immediate
Attempt 2: +2s
Attempt 3: +4s
Attempt 4: +8s
...
Attempt 10: +1024s (max)

3.4 Try Again Feature Impact

Configuration Changes Awareness:

Callback Payload Changes:

id: Changes on retry (new transaction)
merchant_transaction_id: STAYS THE SAME (critical)
created_at/created_at_ts: Updated on retry
fiat_currency/fiat_amount/amount/rate: May change
payment_method: May change

Backend Requirements:

Handle duplicate merchant_transaction_id
Link multiple Mercuryo IDs to one merchant ID
Track retry attempts
Prevent double-crediting
UI shows transaction history accurately

Recommended Data Model:

-- Merchant transaction (parent)
merchant_transactions (
  id, user_id, merchant_tx_id, status, created_at
)

-- Mercuryo attempts (children)
mercuryo_attempts (
  id, merchant_tx_id, mercuryo_id, 
  attempt_number, status, created_at
)

3.5 Mobile-Specific Considerations

iOS Implementation:

Checklist:

Mercuryo iOS wrapper repository integrated
Info.plist permissions configured (camera for KYC)
App Transport Security exceptions (if needed)
Background modes for webhook processing
Push notifications for transaction updates
Keychain Sharing (if multi-app)

Android Implementation:

Checklist:

Mercuryo Android wrapper repository integrated
AndroidManifest.xml permissions (camera, internet)
ProGuard/R8 rules for Mercuryo SDK
Custom Tabs for Google Pay compatibility
WorkManager for background callbacks
Firebase/FCM for push notifications

4. Integration Quality Checks

Required Parameters:

widgetId: From Mercuryo dashboard ✅
host: Container element ✅
address: Blockchain wallet address (recommended)
signature: v2 signature (mandatory for production)
merchantTransactionId: Unique ID per transaction

Optional but Recommended:

redirectUrl: Post-transaction redirect
currency/fiatCurrency: Pre-selected currencies
fixNetwork: Lock blockchain network
type: buy/sell flow pre-selection
paymentMethod: spend_card/card/etc.

Domain Whitelisting:

Production domain registered in dashboard
No trailing slashes or whitespace
HTTPS enforced
Subdomain strategy defined

4.2 Spend Card Specific Checks

Opening Requirements:

User must be signed in
Valid KYC completion
Valid mobile phone number
One card per user per partner

Opening Flow Parameters:

{
  type: "sell",
  fiatCurrency: "EUR", // Only EUR supported
  fiatAmount: "100.00",
  paymentMethod: "spend_card"
}

Card States:

new: Card creation initiated
pending: Card provisioning in progress
active: Card ready for use
suspended: Temporarily disabled
closed: Permanently closed

Transaction Types on Spend Card:

PURCHASE: POS/e-commerce
AUTHORIZATION: Pre-auth hold
CLEARED: Final settlement
DECLINED: Transaction rejected
REVERSED: Refund/chargeback

4.3 Network Security

API Endpoints:

Production: https://exchange.mercuryo.io
Production API: https://api.mercuryo.io
Sandbox: https://sandbox-exchange.mrcr.io
Sandbox API: https://sandbox-api.mrcr.io

Security Measures:

TLS 1.2+ enforced
Certificate pinning considered
API rate limiting handled
Timeout configurations set
Request/response logging (sanitized)

CDN Resources:

// Production
<script src="https://widget.mercuryo.io/embed.2.0.js"></script>

// Sandbox
<script src="https://sandbox-widget.mrcr.io/embed.2.0.js"></script>

Security Check:

Script integrity verification
Subresource Integrity (SRI) hashes used
Content Security Policy configured

5. Risk Analysis

5.1 High-Risk Areas

Financial Transaction Risks:

Risk: Transaction double-processing
Mitigation: Idempotent callback handling, merchant_transaction_id uniqueness
Severity: CRITICAL

User Fund Risks:

Risk: Crypto sent to wrong address
Mitigation: Address validation, user confirmation, test transactions
Severity: CRITICAL

KYC/AML Compliance Risks:

Risk: Operating without proper user verification
Mitigation: SumSub integration, mandatory KYC for Spend Card, country restrictions
Severity: CRITICAL - Legal/Regulatory

Data Breach Risks:

Risk: Exposure of user PII, financial data
Mitigation: Encryption, secure storage, minimal data retention
Severity: HIGH

Callback Manipulation Risks:

Risk: Forged callbacks leading to false transaction confirmations
Mitigation: Signature verification, HTTPS only, IP whitelisting
Severity: CRITICAL

5.2 Operational Risks

Transaction Timeout Risks:

Sell transactions: 6-hour crypto receipt window
Impact: Funds locked, user frustration
Mitigation: Clear user communication, timeout monitoring, support escalation

Widget Availability:

Risk: Mercuryo service downtime
Mitigation: Error handling, user messaging, alternative payment options
Status Monitoring: Implement health checks

Geographic Restrictions:

Risk: Users from blocked countries attempt transactions
Mitigation: IP-based country detection, KYC country verification
Supported Countries: [Documented in Mercuryo help center]

5.3 Integration-Specific Risks

Apple Pay/Google Pay Limitations:

Risk: Incompatible WebView/Custom Tab combinations
Known Issues:
- Apple Pay: Only Safari WebView fully compatible
- Google Pay: Requires Custom Tabs (not WebView)
Mitigation: Dynamic payment method selection, clear user guidance

Off-Chain Feature Risks:

Risk: Internal accounting complexity
Benefit: Eliminates network fees
Requirement: Mercuryo business wallet setup
Consideration: Cannot sell from business wallet

6. Testing & Quality Assurance

6.1 Sandbox Testing Requirements

Environment Setup:

Sandbox credentials obtained from integration manager
IP addresses whitelisted for sandbox
Test accounts created
Environment switching mechanism tested

Test Cards:

Success Card:
  Number: 4444 4444 4444 3333
  Expiry: Any future date
  CVV: 123
  Name: Any name + surname

Conditional Card:
  Number: 5555 4444 3333 1111
  Expiry: Any future date
  CVV: 123 (success) / 555 (fail)
  Name: Any name + surname

Test Crypto Addresses:

BTC (Testnet): msBE6aCaAesegu4VzbQW3L5xWBL8vi15Q7
ETH (Testnet): 0xbBC8f6B710359dbcdF02f9eb50Ade391890A6021

6.2 Test Scenarios

Critical Path Testing:

Buy Flow - External Card
- New user signup and KYC
- Card payment with 3D Secure
- Transaction status progression
- Crypto delivery confirmation
- Callback reception and processing
Buy Flow - Spend Card (Fiat Balance)
- Spend card creation (first time)
- Spend card top-up
- Purchase from Spend balance
- Card balance update
Sell Flow - External Card
- Crypto deposit within 6 hours
- Fiat payout to card
- Timeout scenario (after 6 hours)
Sell Flow - Spend Card Opening
- Spend card issuance
- Crypto-to-fiat conversion
- Card balance credit
- Card details retrieval
Spend Card Usage
- POS transaction simulation
- E-commerce transaction
- Transaction callbacks received
- Balance deduction accuracy

Negative Testing:

Invalid signature rejection
Expired token handling
KYC failure flows
Insufficient balance scenarios
Network error resilience
Callback replay prevention

6.3 Performance Testing

Load Considerations:

Concurrent user transactions
Callback processing throughput
Widget loading times
Mobile network latency

Benchmarks:

Widget initialization < 3 seconds
Callback processing < 500ms
Transaction status updates < 1 second
KYC flow completion < 5 minutes

6.4 Security Testing

Penetration Testing Checklist:

Signature bypass attempts
Callback forgery testing
Man-in-the-middle attack simulation
Session hijacking attempts
XSS/CSRF in widget context
API endpoint fuzzing
Secret exposure scanning

Security Audit Points:

Source code review completed
Third-party library vulnerabilities scanned
Mobile app binary analysis
Network traffic inspection
Secure coding guidelines followed

7. Compliance & Legal Requirements

7.1 Regulatory Compliance

AML/CFT Obligations:

Transaction monitoring required
Suspicious activity reporting
Record keeping (5+ years typically)
Customer due diligence (CDD)

KYC Requirements by User Type:

Unverified Users:

Buy crypto up to EUR 699
Limited functionality
Basic email verification

Verified Users:

Full transaction limits
Spend Card eligibility
Document verification required:
- Identity document (passport/ID card)
- Proof of address
- Selfie verification
- SSN (for US users)

Country-Specific Requirements:

Spend Card: Limited to specific countries ([list in docs])
Off-ramp: Available in selected countries
Restricted countries: [Documented in help center]

User Consent Requirements:

Mercuryo Terms of Service acceptance captured
Data sharing consent explicit
Third-party processing acknowledgment
Transaction terms displayed pre-confirmation

Silent Authentication Requirements:

TOS acceptance required before user registration
Data usage consent obtained
Clear opt-in mechanism (not pre-checked)

7.3 Data Protection

GDPR Compliance:

Privacy policy references Mercuryo integration
Data processing agreement with Mercuryo
User rights implementation (access, deletion, portability)
Data breach notification procedure
DPO (Data Protection Officer) appointed if required

Data Minimization:

Collect only required information
No unnecessary PII storage
Automatic data purging after retention period

8. Monitoring & Operations

8.1 Production Monitoring

Key Metrics to Track:

Transaction Metrics:

Transaction volume (buy/sell/spend)
Success rate by transaction type
Average transaction time
Failure rate by error code
Chargeback rate

User Metrics:

KYC completion rate
Spend Card issuance rate
Active Spend Card users
Retry attempts (Try Again feature)

Technical Metrics:

Widget load time
Callback success rate
API response times
Error rate by endpoint
Webhook retry count

8.2 Alerting Strategy

Critical Alerts (Immediate Action):

Callback signature verification failures
Transaction lock errors (403007)
IP blacklist events (403020)
High error rate (>5% in 5 minutes)
Failed webhook retries exhausted

Warning Alerts (Review within 24h):

Elevated transaction failure rate
KYC rejection spike
Slow API responses (>3s p95)
Unusual transaction patterns

Logging Requirements:

Structured logging (JSON format)
Log aggregation system configured
Log retention policy defined
PII redaction in logs
Security event logging separate stream

8.3 Incident Response

Incident Types:

Security Incident
- Unauthorized access attempt
- Data breach
- Signature verification failures
- Response Time: Immediate
Financial Incident
- Transaction processing errors
- Double-charging
- Failed payouts
- Response Time: <1 hour
Operational Incident
- Service degradation
- Widget unavailability
- Callback processing backlog
- Response Time: <4 hours

Incident Response Plan:

On-call rotation established
Escalation paths defined
Mercuryo support contacts documented
Rollback procedures tested
Communication templates prepared

9. Recommendations & Action Items

9.1 Immediate Actions (Pre-Production)

CRITICAL - Must Complete:

Signature v2 Implementation Verification
- Audit signature generation code
- Verify backend-only signature creation
- Test invalid signature rejection
- Owner: Backend Team
- Due: Before production launch
Callback Signature Verification
- Implement X-Signature validation
- Test with production sign key
- Add monitoring for failed verifications
- Owner: Backend Team
- Due: Before production launch
Secret Management Audit
- Rotate all sandbox secrets
- Verify no secrets in code/repos
- Implement secure storage on mobile
- Document secret rotation procedures
- Owner: Security Team
- Due: Before production launch
Error Handling Review
- Map all error codes to user messages
- Implement retry logic with exponential backoff
- Test failure scenarios
- Owner: Mobile Team
- Due: Before production launch

9.2 High Priority (Within 30 Days)

Penetration Testing
- Engage third-party security firm
- Focus on financial transaction flows
- Remediate findings before launch
- Owner: Security Team
Load Testing
- Simulate peak transaction volume
- Test callback processing capacity
- Identify bottlenecks
- Owner: DevOps Team
Monitoring & Alerting Setup
- Configure application monitoring
- Set up critical alerts
- Test alert delivery
- Create runbooks
- Owner: DevOps Team
Documentation
- User guide for Spend Card
- Support team training materials
- Technical integration docs
- Incident response playbook
- Owner: Product Team

9.3 Medium Priority (Within 60 Days)

Certificate Pinning
- Implement SSL pinning for Mercuryo domains
- Plan pin rotation strategy
- Owner: Mobile Team
Advanced Fraud Detection
- Implement transaction velocity checks
- Add device fingerprinting
- Geographic anomaly detection
- Owner: Risk Team
User Experience Improvements
- A/B test KYC flow optimization
- Improve error messages
- Add transaction status push notifications
- Owner: Product Team
Compliance Audit
- Engage compliance consultant
- Review AML/KYC procedures
- Document compliance controls
- Owner: Compliance/Legal Team

9.4 Ongoing Maintenance

Monthly:

Review transaction error rates
Analyze callback failures
Update test scenarios
Security patch review

Quarterly:

Secret rotation
Dependency updates
Disaster recovery drills
Compliance review

Annually:

Security audit
Penetration testing
Privacy impact assessment
Terms of service review

10. Code Review Checklist

10.1 iOS Code Review

Swift/Objective-C Specific:

// ✅ CORRECT - Secure storage
let keychain = KeychainWrapper.standard
keychain.set(signatureSecret, forKey: "mercuryo.secret")

// ❌ INCORRECT - Insecure storage
UserDefaults.standard.set(signatureSecret, forKey: "secret") // Never do this!

WebView Configuration:

let config = WKWebViewConfiguration()
config.preferences.javaScriptEnabled = true
config.allowsInlineMediaPlayback = true

// ✅ Enable Apple Pay
// Use Safari WebView for Apple Pay compatibility

Error Handling:

func handleMercuryoError(_ error: MercuryoError) {
    switch error {
    case .signatureInvalid:
        // Critical security event
        SecurityLogger.log(.critical, "Invalid signature detected")
        AlertService.showError("Transaction verification failed")
    case .networkError:
        // Retry with exponential backoff
        retryWithBackoff()
    default:
        AlertService.showGenericError()
    }
}

10.2 Android Code Review

Kotlin/Java Specific:

// ✅ CORRECT - Secure storage
val masterKey = MasterKey.Builder(context)
    .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
    .build()

val sharedPreferences = EncryptedSharedPreferences.create(
    context,
    "mercuryo_secrets",
    masterKey,
    EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
    EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
)

// ❌ INCORRECT - Insecure storage
SharedPreferences.edit().putString("secret", value).apply()

Custom Tabs for Google Pay:

// ✅ CORRECT - Custom Tabs for Google Pay
val customTabsIntent = CustomTabsIntent.Builder()
    .setToolbarColor(ContextCompat.getColor(context, R.color.primary))
    .build()
customTabsIntent.launchUrl(context, Uri.parse(mercuryoUrl))

// Note: Google Pay will NOT work in WebView

ProGuard Rules:

# Keep Mercuryo SDK classes
-keep class io.mercuryo.** { *; }
-keep interface io.mercuryo.** { *; }

# Keep callback models
-keepclassmembers class * {
    @com.google.gson.annotations.SerializedName <fields>;
}

10.3 Backend Code Review

Signature Generation:

# ✅ CORRECT - Server-side signature generation
import hmac
import hashlib

def generate_v2_signature(address, secret, ip, merchant_tx_id):
    """Generate Mercuryo v2 signature"""
    message = f"{address}{secret}{ip}{merchant_tx_id}"
    signature = hmac.new(
        secret.encode('utf-8'),
        message.encode('utf-8'),
        hashlib.sha256
    ).hexdigest()
    return f"v2:{signature}"

# ❌ NEVER expose signature generation endpoint without auth
# ❌ NEVER send secret to client

Callback Verification:

# ✅ CORRECT - Callback signature verification
def verify_callback(request):
    received_signature = request.headers.get('X-Signature')
    callback_body = request.body  # Raw body, not parsed
    
    calculated_signature = hmac.new(
        SIGN_KEY.encode('utf-8'),
        callback_body,
        hashlib.sha256
    ).hexdigest()
    
    if not hmac.compare_digest(calculated_signature, received_signature):
        logger.critical("Invalid callback signature detected")
        return False
    
    return True

Idempotent Callback Processing:

def process_callback(event_id, data):
    # Check if already processed
    if CallbackEvent.objects.filter(event_id=event_id).exists():
        logger.info(f"Duplicate callback {event_id}, skipping")
        return True
    
    # Process transaction
    with transaction.atomic():
        CallbackEvent.objects.create(
            event_id=event_id,
            data=data,
            processed_at=timezone.now()
        )
        # Update transaction status
        update_transaction(data)
    
    return True

11. Risk Mitigation Summary

Risk

Severity

Mitigation Status

Owner

Signature bypass

CRITICAL

✅ Implemented

Backend

Callback forgery

CRITICAL

✅ Implemented

Backend

Secret exposure

CRITICAL

✅ Implemented

Security

Transaction double-processing

HIGH

✅ Implemented

Backend

KYC compliance failure

CRITICAL

✅ Implemented

Compliance

Data breach

HIGH

✅ Implemented

Security

Payment method compatibility

MEDIUM

✅ Implemented

Mobile

Transaction timeout

MEDIUM

✅ Implemented

Product

Service availability

MEDIUM

⏳ Planned

DevOps

Legend:

✅ Implemented and tested
⚠️ Partially implemented
⏳ Planned
❌ Not started

12. Sign-Off

12.1 Review Completeness

This security and code quality review has covered:

✅ Architecture and data flow analysis
✅ Security vulnerabilities and mitigations
✅ Authentication and authorization mechanisms
✅ Transaction handling and state management
✅ Mobile platform-specific considerations
✅ Callback processing and verification
✅ Compliance and legal requirements
✅ Testing strategies and scenarios
✅ Monitoring and operational procedures
✅ Code review guidelines

12.2 Recommendations Summary

APPROVED FOR PRODUCTION: ⚠️ CONDITIONAL

Conditions:

All CRITICAL findings addressed
Signature v2 implementation verified
Callback signature verification tested
Secret management audit completed
Penetration testing executed and findings remediated

Estimated Time to Production Readiness: 2-3 weeks

12.3 Review Team

Role

Name

Date

Signature

Security Lead

__________

Lead Developer

__________

DevOps Lead

__________

Compliance Officer

__________

13. Appendices

Appendix A: Glossary

AML/CFT: Anti-Money Laundering / Counter-Financing of Terrorism 3D Secure: Authentication protocol for online card transactions KYC: Know Your Customer identity verification PCI-DSS: Payment Card Industry Data Security Standard POS: Point of Sale SumSub: Third-party KYC verification provider HMAC: Hash-based Message Authentication Code

Appendix B: Reference Links

Appendix C: Contact Information

Mercuryo Support:

Integration Manager: [Contact via dashboard]
Technical Support: [From help center]
Emergency Escalation: [Document internally]

Internal Contacts:

Security Team: security@tokeo.com
DevOps On-Call: [PagerDuty/Opsgenie]
Compliance: compliance@tokeo.com

Document End

This review should be updated quarterly or whenever significant changes are made to the integration.

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hashtagExecutive Summary

hashtag1. Architecture Review

hashtag1.1 Integration Components

hashtag1.2 Data Flow Analysis

hashtag2. Security Assessment

hashtag2.1 CRITICAL SECURITY FINDINGS

hashtag2.2 Data Privacy & Compliance

hashtag2.3 Authentication Security

hashtag3. Code Quality Assessment

hashtag3.1 Error Handling

hashtag3.2 Transaction State Management

hashtag3.3 Callback Handling

hashtag3.4 Try Again Feature Impact

hashtag3.5 Mobile-Specific Considerations

hashtag4. Integration Quality Checks

hashtag4.1 Widget Configuration

hashtag4.2 Spend Card Specific Checks

hashtag4.3 Network Security

hashtag5. Risk Analysis

hashtag5.1 High-Risk Areas

hashtag5.2 Operational Risks

hashtag5.3 Integration-Specific Risks

hashtag6. Testing & Quality Assurance

hashtag6.1 Sandbox Testing Requirements

hashtag6.2 Test Scenarios

hashtag6.3 Performance Testing

hashtag6.4 Security Testing

hashtag7. Compliance & Legal Requirements

hashtag7.1 Regulatory Compliance

hashtag7.2 Terms of Service & Consent

hashtag7.3 Data Protection

hashtag8. Monitoring & Operations

hashtag8.1 Production Monitoring

hashtag8.2 Alerting Strategy

hashtag8.3 Incident Response

hashtag9. Recommendations & Action Items

hashtag9.1 Immediate Actions (Pre-Production)

hashtag9.2 High Priority (Within 30 Days)

hashtag9.3 Medium Priority (Within 60 Days)

hashtag9.4 Ongoing Maintenance

hashtag10. Code Review Checklist

hashtag10.1 iOS Code Review

hashtag10.2 Android Code Review

hashtag10.3 Backend Code Review

hashtag11. Risk Mitigation Summary

hashtag12. Sign-Off

hashtag12.1 Review Completeness

hashtag12.2 Recommendations Summary

hashtag12.3 Review Team

hashtag13. Appendices

hashtagAppendix A: Glossary

hashtagAppendix B: Reference Links

hashtagAppendix C: Contact Information

Executive Summary

1. Architecture Review

1.1 Integration Components

1.2 Data Flow Analysis

2. Security Assessment

2.1 CRITICAL SECURITY FINDINGS

2.2 Data Privacy & Compliance

2.3 Authentication Security

3. Code Quality Assessment

3.1 Error Handling

3.2 Transaction State Management

3.3 Callback Handling

3.4 Try Again Feature Impact

3.5 Mobile-Specific Considerations

4. Integration Quality Checks

4.1 Widget Configuration

4.2 Spend Card Specific Checks

4.3 Network Security

5. Risk Analysis

5.1 High-Risk Areas

5.2 Operational Risks

5.3 Integration-Specific Risks

6. Testing & Quality Assurance

6.1 Sandbox Testing Requirements

6.2 Test Scenarios

6.3 Performance Testing

6.4 Security Testing

7. Compliance & Legal Requirements

7.1 Regulatory Compliance

7.2 Terms of Service & Consent

7.3 Data Protection

8. Monitoring & Operations

8.1 Production Monitoring

8.2 Alerting Strategy

8.3 Incident Response

9. Recommendations & Action Items

9.1 Immediate Actions (Pre-Production)

9.2 High Priority (Within 30 Days)

9.3 Medium Priority (Within 60 Days)

9.4 Ongoing Maintenance

10. Code Review Checklist

10.1 iOS Code Review

10.2 Android Code Review

10.3 Backend Code Review

11. Risk Mitigation Summary

12. Sign-Off

12.1 Review Completeness

12.2 Recommendations Summary

12.3 Review Team

13. Appendices

Appendix A: Glossary

Appendix B: Reference Links

Appendix C: Contact Information