Complete Guide to PCI DSS Compliance for Mobile Apps

A mobile application that processes payments must comply with the PCI DSS standard. Acquirers demand security confirmation, and code often contains vulnerabilities: PAN in logs, missing certificate pinning, ability to take screenshots of the screen with the card. Our team helps bring the app to the current version of the standard and pass a QSA audit with guaranteed compliance. With over 5 years of experience and 50+ mobile security projects, we ensure your app meets all requirements.

Why PCI DSS is Critical for Mobile Apps

Source: PCI DSS is the standard of the Payment Card Industry Security Standards Council, mandatory for any software that transmits, processes, or stores cardholder data. For mobile apps, Section 6 (Secure Development) and Section 4 (Encryption in Transit) are especially important. Without compliance, major acquirers do not allow direct acquiring—only iFrame solutions with limited functionality.

Typical Violations and How to Fix Them

Storing PAN in Logs

A developer adds Log.d("Payment", "Card: $cardNumber") for debugging. Data ends up in logcat, readable by any app on an unsecured Android. PCI DSS requirement 3.3: PAN must not appear in logs in plaintext. The correct solution is masking PAN and logging only operations without card data.

Lack of Screen Protection

Android by default allows screenshots of any Activity. On the card entry screen, this is a critical vulnerability:

// Must be on any screen with card data
window.setFlags(
    WindowManager.LayoutParams.FLAG_SECURE,
    WindowManager.LayoutParams.FLAG_SECURE
)

On iOS similarly, you need to cover the UI when entering background:

func applicationWillResignActive(_ application: UIApplication) {
    coverSensitiveContent()
}

Certificate Pinning Not Configured

Traffic to the payment server is intercepted by Charles Proxy or mitmproxy with no obstacles. PCI DSS 6.5.4 requires protection against man-in-the-middle attacks. Implementation on iOS:

class PinnedURLSessionDelegate: NSObject, URLSessionDelegate {
    func urlSession(
        _ session: URLSession,
        didReceive challenge: URLAuthenticationChallenge,
        completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void
    ) {
        guard
            let serverTrust = challenge.protectionSpace.serverTrust,
            let certificate = SecTrustGetCertificateAtIndex(serverTrust, 0)
        else {
            completionHandler(.cancelAuthenticationChallenge, nil)
            return
        }

        let pinnedHash = "sha256/AbCdEfGhIjKlMnOpQrStUvWxYz123456789="
        let serverHash = certificateHash(certificate)

        if serverHash == pinnedHash {
            completionHandler(.useCredential, URLCredential(trust: serverTrust))
        } else {
            completionHandler(.cancelAuthenticationChallenge, nil)
        }
    }
}

Root/Jailbreak Detection

PCI DSS 6.4.3 recommends detecting compromised devices. We use a combination: check for /bin/bash, Cydia, su command, process signature mismatch. Major acquirers require this via SDK.

Why Tokenization Is the Key Tool for PCI DSS?

The main principle is to never store PAN at all. The app works with a token from the payment provider: Stripe PaymentMethod, CloudPayments Token, YooKassa payment_method_id. Tokenization reduces PCI DSS scope from SAQ D to SAQ A—that's 10 times simpler and 20 times less audit effort. Fines for PAN leakage can reach $500,000 per quarter, and savings on audit due to correct scoping can be up to $3,000 (or more).

import StripePaymentSheet

var configuration = PaymentSheet.Configuration()
configuration.merchantDisplayName = "YourShop"

PaymentSheet.FlowController.create(
    paymentIntentClientSecret: clientSecret,
    configuration: configuration
) { [weak self] result in
    switch result {
    case .success(let flowController):
        self?.paymentSheetFlowController = flowController
    case .failure(let error):
        // handle
    }
}

Card data goes directly to the Stripe SDK; the app receives paymentMethodId. PAN never touches your server.

Audit Trail and Logging

PCI DSS requirement 10: log access to the cardholder data environment. For mobile apps:

• Log every successful/unsuccessful payment with timestamp, userId, masked PAN (first 6 + last 4 digits), status.
• Store logs for at least 12 months, with 3 months immediately accessible.
• Protect logs from modification (append-only storage).

Masking PAN in logs:

fun maskPan(pan: String): String {
    return pan.take(6) + "*".repeat(pan.length - 10) + pan.takeLast(4)
}
// "4111111111111111" → "411111******1111"

What Is Scoping and Why Is It Needed?

The choice of SAQ type directly affects the audit volume. Comparison of SAQ A and SAQ D:

Proper tokenization and outsourcing card processing (Stripe, CloudPayments) allow you to qualify for SAQ A. The savings on audit can exceed the cost of modifications.

Our Process: 5 Steps to Compliance

Step-by-Step Certificate Pinning on iOS

1. Obtain the server certificate (DER).
2. Compute SHA-256 hash of the certificate.
3. Create URLSessionDelegate with hash check.
4. Embed the hash as a constant in code.
5. For each request, compare server hash with the embedded one.
6. On mismatch, terminate the connection.

This sequence guarantees protection against MITM attacks. On Android, certificate pinning is easier via NetworkSecurityConfig. Just add XML config in res/xml/network_security_config.xml with a list of pin certificates. However, for more flexibility we use OkHttp with CertificatePinner.

What's Included

• Full gap analysis of codebase and infrastructure (identify all non-conformities)
• Implement certificate pinning on iOS and Android with version and config handling
• Protect card entry screens (FLAG_SECURE, overlay prevention)
• Set up tokenization via Stripe/CloudPayments
• Implement root/jailbreak detection with multiple checks
• Audit logs and implement PAN masking
• Consultation on SAQ and passing QSA audit

Estimated Timeline

Audit and basic fixes: from 2 to 4 weeks. Full cycle with penetration testing and QSA preparation: up to 6 weeks. Cost is calculated individually after analyzing the current state.

Order a preliminary audit—we will assess the scope and timeline in 2 days. Contact us for a consultation, and we will help prepare your app for certification. We guarantee compliance with the standard and successful external audit.

Get your app evaluated in 2 days—reach out to us.

Payments in Mobile Apps: In-App Purchase, StoreKit 2, Google Billing, Stripe, RevenueCat

In every monetization project, we balance App Store and Google Play policies, PCI DSS requirements, and purchase verification logic on the backend. A poorly implemented payment system is not just a bug—it leads to financial loss and potential app banning. Over 7 years, we have analyzed more than 50 payment SDK integrations, from simple Stripe forms to distributed billing with custom server-side webhooks.

In-App Purchase: Two Platforms, Two Different APIs

If your app sells digital content or subscriptions, Apple and Google require you to use their payment systems. This is non-negotiable: violating App Store rule 3.1.1 or Google Play Developer Policy results in app removal. Physical goods and offline services are a different story.

StoreKit 2 (iOS 15+)

StoreKit 2 is a complete overhaul of the original StoreKit with async/await API. Product.products(for:), product.purchase(), Transaction.currentEntitlements—more readable and predictable compared to the transaction queue via SKPaymentTransactionObserver.

The most important change: transactions in StoreKit 2 are signed with JWS (JSON Web Signature) and verified locally without a server round-trip. Transaction.verificationResult returns .verified(Transaction) or .unverified(Transaction, VerificationError). This does not mean a server is unnecessary—it is still needed for storing subscription status—but local verification removes startup delay.

StoreKit.AppTransaction verifies the actual app download from the App Store. Required for paid downloads or non-renewing purchases.

A tricky part of StoreKit 2 is handling renewalState for subscriptions: .subscribed, .expired, .inBillingRetryPeriod, .inGracePeriod, .revoked. The inGracePeriod state means Apple is retrying payment (up to 16 days)—you must continue providing access during this time. Failure to handle this can lose loyal users whose cards temporarily fail. Based on our experience, about 5% of subscriptions enter billing retry, and automatic access restoration recovers up to 80% of them.

Google Play Billing Library (v6+)

Google Billing is more complex than StoreKit in terms of scenario handling. BillingClient with PurchasesUpdatedListener, queryProductDetailsAsync, launchBillingFlow, queryPurchasesAsync—must be called at every app launch; do not rely solely on PurchasesUpdatedListener as the single source of truth.

Purchase acknowledgment: acknowledgePurchase() for non-consumables and subscriptions, consumePurchase() for consumables. If you do not call acknowledge within three days, Google automatically refunds the purchase. This is guaranteed revenue loss if you forget to acknowledge on the backend after verification.

ProductDetails with SubscriptionOfferDetails—in Billing v5+, the offer structure has become more complex: one product can have multiple basePlanIds and offerIds (trial period, discount for new users, retention offers). BillingFlowParams.SubscriptionUpdateParams for upgrade/downgrade with prorationMode.

Why Is Server-Side Verification Mandatory?

Never trust only client-side code when unlocking paid content. Client-side verification can be bypassed by modifying the app.

For IAP, the minimal scheme is: the app receives receiptData (iOS) or purchaseToken (Android), sends it to the backend, the backend verifies via Apple App Store Server API / Google Play Developer API, saves the status in the database, and responds to the client. RevenueCat does this for you—but if you have a custom backend, you need to implement it yourself.

Webhooks are more important than they seem. Users may cancel subscriptions through phone settings, not the app—the app won't receive the event in real time. Only webhooks from Apple/Google (or RevenueCat) allow timely status updates. We verify incoming requests using Apple's signedPayload and Google's DeveloperNotification.

How Does RevenueCat Simplify Integration?

Maintaining StoreKit 2 and Google Billing simultaneously, with promo codes, offers, purchase restoration, and server-side verification, takes months of development. RevenueCat handles most of this layer.

RevenueCat is not just a payment SDK. It offers:

• A unified API for iOS and Android (and Stripe for web)
• Server-side verification and subscription status storage
• Webhooks for events (purchase, renewal, cancellation, billing issue)
• Analytics for cohorts, MRR, churn
• A/B testing of offers via Experiments

Purchases.configure(withAPIKey:) at startup, Purchases.shared.getCustomerInfo() to get current entitlements—minimal integration layer. Purchases.shared.purchase(package:) instead of directly calling StoreKit/Billing.

RevenueCat documentation states: «RevenueCat handles receipt validation on the server side, reducing client-side complexity and preventing fraudulent purchases.»

Limitations of RevenueCat: it is paid (free up to $2.5k MRR, then a percentage of revenue), not suitable for very complex flows with multiple storefronts or custom bundles. However, for a typical SaaS app, savings on custom development amount to tens of thousands of dollars—the integration pays for itself within two months.

Stripe in Mobile Apps

Stripe is used for physical goods, services, and B2B payments where IAP is not required by platform policy.

Stripe iOS SDK and Android SDK—PaymentSheet for ready-made payment UI, PaymentSheetFlowController for custom UI with saved cards. Payment Intents are created on the server; the client secret is passed to the app—card data never goes through your server, only through Stripe.

Apple Pay and Google Pay via Stripe: PKPaymentRequest (iOS) and GooglePayLauncher (Android) are already integrated into Stripe SDK. Apple Pay conversion rates are 1.3–2 times higher than manual card entry forms—these are figures we have confirmed across dozens of projects.

Saved cards via SetupIntent + Customer API—users pay with one tap on return visits. Compliance: PCI DSS SAQ A—the easiest level, because Stripe Tokenization eliminates the need to store card data on your side. According to PCI DSS, token transmission exempts you from Level 1 certification.

3DS2 (Strong Customer Authentication) is mandatory for payments in the EU under PSD2. Stripe handles it automatically via PaymentIntent.confirmPayment, but you need to correctly handle the .requiresAction status and return the user to the appropriate screen after authentication.

What Is Included in the Work (Deliverables)

Process and Timeline

We start by clarifying the business model: subscriptions, one-time purchases, consumables, freemium. The architecture depends on this. Testing IAP requires Sandbox accounts (Apple) and License Testers (Google)—this is a separate environment setup.

Apple's Sandbox behaves differently from production: subscriptions renew every 5 minutes instead of monthly, inGracePeriod works differently. It is essential to test scenarios: trial expiration, cancellation, billing retry, refund.

The cost is calculated individually based on the set of tools and complexity of server-side logic. On average, we fit within a budget for a typical integration, but the savings from preventing errors and churn offset this investment within a few months.

Get a consultation for your project—contact us. We will help you choose the optimal payment architecture that passes store reviews and does not break under peak loads.