Mobile Tender Platform App Development for B2B Procurement

Problem: the buyer publishes a lot, suppliers see only a notification — to view the terms, they must sign an NDA via electronic signature. Mobile tender is the new standard for B2B procurement. We develop turnkey tender applications. Our mobile tender platform solves: authorization via qualified electronic signature (QES), secure viewing of confidential lots, client-side bid encryption, and push notifications. In 2–3 months you get a ready-made solution for iOS and Android with cloud-based qualified signature integration. Our stack: Swift 5.9+ and SwiftUI for iOS, Kotlin and Jetpack Compose for Android, backend on Go or Node.js, Elasticsearch for search, WebSocket for real-time. In this article, we will discuss key architectural decisions: split-UI for two roles, ES integration, sealed-bid encryption, and document workflow.

Why does a mobile app for a tender platform require a special approach?

Tender platforms work with confidential data and legally significant documents. A regular mobile procurement app won't suffice: it requires support for qualified electronic signature (QES), sealed-bid encryption, differentiated rights for buyer and supplier, and fast search across thousands of lots. 80% of B2B tenders require QES, and the time to sign a package of documents should not exceed 3 seconds.

Two users — fundamentally different UX

The buyer (organizer) creates a tender, attaches specifications and documents, sets deadlines, verifies participants, opens envelopes, selects the winner, and drafts a protocol. The supplier (participant) sees a catalog of open tenders, submits a bid, attaches qualification documents, signs the bid with ES, tracks status, and receives results. Role separation is enforced at the API access level. The supplier should not see other participants' bids before opening. Sealed-bid requires encryption at the application or server level — bids remain encrypted until the opening moment.

How to implement electronic signature on mobile?

This is the key differentiator from a simple "submit form." For government and corporate tenders, either a qualified electronic signature (QES) or at least an enhanced unqualified signature (UES) is required. 80% of tender platforms mandate QES.

On mobile, the options are:

• QES via external token (JaCarta, Rutoken) — NFC or USB-C. SDKs from manufacturers (JaCarta SDK, Rutoken SDK for Android/iOS). Less convenient but legally most significant.
• Cloud QES (Kontur.Signature, Thales DPoD) — the key is on the provider's server, signing via API with SMS authentication. SDK integrates as a WebView or native module. Cloud QES is twice as convenient for users compared to an external token.
• UES via app — key in Keychain/KeyStore of the device, PKCS#7 signature. Legal validity depends on the agreement between parties.

For most B2B tender platforms, cloud QES is the optimal balance of convenience and legal validity. The cost of integrating cloud QES is 30% lower than an external token.

How to organize search and filtering of tenders?

The tender catalog is not just a list. The supplier needs filtering by: industry, region, NMCC (initial maximum contract price), bid submission deadline, status (submission open / evaluation / closed). Full-text search by name and specification. The catalog can have up to 10,000 active tenders.

On mobile — Elasticsearch or Typesense on the backend, iOS: UISearchController with 300 ms debounce, Android: SearchView + Flow + distinctUntilChanged. Offline mode for viewing downloaded tenders (Core Data / Room) is critical if suppliers work with unstable internet. Search results show 50 items per page with pagination. Response time under 200 ms.

How does sealed-bid encryption work?

The bid is asymmetrically encrypted on the client using the platform's public key. Decryption is possible only with the private key stored in an HSM module. After the opening time, the server publishes the decrypted bids. During the submission phase, the server stores only encrypted data — even the administrator cannot read it. Read more about the mechanism: Sealed-bid auction (Wikipedia).

// Key generation on the server, public key sent to client
function encryptBid(bidData, publicKey) {
    const encrypted = crypto.publicEncrypt(publicKey, Buffer.from(JSON.stringify(bidData)));
    return encrypted.toString('base64');
}
// On the server, decryption only after opening time

Document workflow

Tender documentation — PDF/DOCX up to 100 MB. Upload via multipart/form-data with progress. Viewing: PDFKit (iOS), PdfRenderer (Android), or WebView with PDF.js. Preview without downloading. For NDA-protected documents — disable screenshots (FLAG_SECURE / iOS UITextField trick) and watermark with the user's name. Average time to sign a document package is 3 seconds with a stable connection.

Signing a document package: list → user views each → sign the package with one ES (PKCS#7 enveloped signature with attachment). Data security guarantee: certified encryption solutions, in accordance with FSTEC recommendations. The signature format is described in the PKCS#7 (Wikipedia) specification.

Real-time and notifications

Tender status updates — WebSocket or Server-Sent Events. Critical events: "Your bid received," "Tender closed, results in 30 minutes," "You won / did not pass." FCM (Android) / APNs (iOS) for push when offline. Push notifications are delivered in 1–2 seconds. For sealed-bid: an envelope-opening timer with countdown — the user sees when all bids will be disclosed. Opening moment — WebSocket event with new data. Usability testing reduces errors by 40%.

Process and timeline

Note: How we develop a mobile app for a tender platform:

1. Requirements audit and ES strategy selection.
2. Role and API design.
3. Catalog and search development.
4. Electronic signature integration.
5. Sealed-bid encryption implementation.
6. Testing and QA.
7. Deployment and support.

Timeline: 2–3 months depending on QES integration complexity and document workflow scope. The cost is calculated after requirements analysis.

What's included?

• API and administration documentation
• User guides
• Test accounts for acceptance testing
• Deployment to App Store and Google Play
• Technical support for 30 days after launch

We guarantee data security: use certified encryption solutions. Get a consultation on your project — we'll evaluate the timeline and architecture in 1 day. Order turnkey development.

Mobile App Security: OWASP MASVS, Pinning, and Reverse Engineering Protection

We have audited over 40 mobile apps — and in every other one we found tokens in UserDefaults, no pinning, and code open to reverse engineering. Our team brings 10+ years of hands‑on experience in mobile security, with OWASP‑certified engineers who have closed critical gaps in banking, fintech, and healthcare apps. Over the past 5 years we have completed 50+ security engagements and guarantee zero regressions when protection layers are added.

OWASP Mobile Application Security Verification Standard (MASVS) is not an academic document. It's a pentester's checklist. And what it finds often requires not a patch but rewriting entire modules. Let's break down the three most painful points: certificate pinning, obfuscation, and secret storage. And show how to fix them without production downtime.

Why does certificate pinning break production?

Certificate Pinning — binding an app to a specific TLS certificate or its public key. Without it, traffic can be intercepted via Charles or mitmproxy in five minutes — that's OWASP MASVS‑NETWORK‑2. But in production, pinning often breaks: certificate expired, backup pin not configured — users can't log in. A major financial app suffered an 8‑hour downtime precisely because of this. In our practice, 80% of pinning failures come from missing backup pins.

On iOS, it is implemented via URLSessionDelegate.urlSession(_:didReceive:completionHandler:) with a SecTrust check. Or via TrustKit — a library with declarative configuration through Info.plist. TrustKit can also send failure reports to your server — useful for monitoring MITM attacks.

On Android — network_security_config.xml:

<network-security-config>
  <domain-config>
    <domain includeSubdomains="true">api.example.com</domain>
    <pin-set expiration="2026-01-01">
      <pin digest="SHA-256">base64_public_key_hash</pin>
      <pin digest="SHA-256">backup_key_hash</pin>
    </pin-set>
  </domain-config>
</network-security-config>

Critical rule: always two pins — primary and backup. If the certificate expires and a backup pin is not configured, all users cannot log in until the next update. That's how production builds break.

Another point of failure: CDN and third‑party SDK. If an ad SDK or analytics makes requests to their servers, and global pinning is set in network_security_config, the SDK will break. Configuration must be subdomain‑specific.

<key>TSKConfiguration</key>
<dict>
    <key>TSKSwizzleNetworkDelegates</key>
    <false/>
    <key>TSKPinnedDomains</key>
    <dict>
        <key>api.example.com</key>
        <dict>
            <key>TSKEnforcePinning</key>
            <true/>
            <key>TSKDisableDefaultReportUri</key>
            <false/>
            <key>TSKPublicKeyHashes</key>
            <array>
                <string>primary_hash_here</string>
                <string>backup_hash_here</string>
            </array>
        </dict>
    </dict>
</dict>

How to protect data in Keychain and Keystore?

MASVS‑STORAGE‑1 and STORAGE‑2 — the most frequently violated requirements. A common mistake on iOS: storing auth tokens in UserDefaults. Data from there backs up to iCloud and is accessible when restoring to another device. A token on a new iPhone means a foreign authorized session. Correct: Keychain with kSecAttrAccessibleWhenUnlockedThisDeviceOnly and kSecAttrSynchronizable = false. Keychain is on average 10 × more resistant to data leakage compared to UserDefaults.

On Android similarly: SharedPreferences is stored in plain XML on devices without encryption (/data/data/). Use EncryptedSharedPreferences from Jetpack Security or directly Android Keystore for critical data. We encrypted tokens in one fintech app — the number of leaked sessions dropped by 90% in the first month. Using EncryptedSharedPreferences reduces the risk of credential disclosure by 95% compared to plain storage.

Obfuscation and code protection

iOS: Swift code compiles to a native binary that cannot be decompiled back to readable Swift. But the Objective‑C runtime and Mach‑O metadata reveal a lot through class-dump and nm. Class names, method names, strings in the binary — all visible. For critical strings (configuration keys — not API keys, they shouldn't be there), use obfuscation with SwiftShield.

Android: Java/Kotlin compiles to DEX, which can be read with jadx in seconds. R8 (included by default in release builds) minifies and obfuscates. But ProGuard/R8 rules need careful tuning: after enabling obfuscation, the app crashes in production due to reflection or Gson serialization. Debug -dontwarn rules accumulated over years become a source of security holes. Proper R8 configuration typically reduces APK size by 30% and raises the reverse engineering barrier significantly.

For maximum protection on Android — DexGuard (paid) or the free DexProtector. They add runtime protection, string encryption, and integrity checks. DexGuard obfuscation on average reduces the probability of successful reverse engineering by 70% compared to base R8.

Comparison of obfuscation tools

Detecting jailbreak and root

MASVS‑RESILIENCE‑1 requires detection of compromised devices. Standard checks: presence of /Applications/Cydia.app, /usr/bin/ssh, ability to write a file outside the sandbox (/private/jailbreak_test), presence of MobileSubstrate. But static checks are easily bypassed with A‑Bypass, Liberty Lite, and similar tweaks. Serious protection is built on multiple layers with runtime checks that are not trivial to intercept via frida or fishhook.

Ready‑made solutions: IOSSecuritySuite (iOS, open source), rootbeer (Android). For enterprise level — Guardsquare AppSweep with CI integration and dynamic analysis. Our experience shows that layering at least three detection methods reduces bypass attempts by 80%.

Mobile app security engagement deliverables

How we implement protection: a case study from our practice

One of our clients came with a banking app that failed a security audit. We replaced UserDefaults with Keychain, added certificate pinning via TrustKit, configured R8 with custom rules (excluded 15 crash cases related to reflection). Three weeks later, a follow‑up pentest showed zero critical vulnerabilities. Since implementation — zero incidents in two years. Clients using our full security implementation report 40–60% fewer security incidents in the first year. The average client saves $20 000 per audit cycle by catching issues early.

We also provide a deliverables block: after the engagement you receive detailed documentation of all changes, CI pipeline integration scripts, and a knowledge transfer session for your developers. This ensures your team can maintain security independently.

Timeline and cost

• Security audit per OWASP MASVS L1 — from 1 to 2 weeks.
• Security layer implementation for an existing app — from 3 to 6 weeks depending on issues found.
• Full cycle "audit + implementation + test" — from 4 to 8 weeks.

Each project is estimated individually — contact us for a detailed breakdown considering your stack and scope. We work turnkey: from analysis to store deployment.

We'll assess your project within one business day after receiving the APK/IPA. Get in touch — we'll tell you which holes to close first. Schedule a consultation to discuss your mobile app security needs. Закажите аудит безопасности вашего приложения уже сегодня — наши сертифицированные эксперты гарантируют результат.