yin Solutions Blog

What is SSL pinning?

SSL pinning (also called certificate pinning or public-key pinning) is a defensive technique apps use to ensure they are talking to an expected server by validating the server certificate or public key against a known, hard-coded value. This reduces the effectiveness of man-in-the-middle (MITM) attacks and helps protect user data in mobile environments.

Why app publishers use pinning (Instagram, Facebook, TikTok, Snapchat, etc.)

• Prevents interception of sensitive API traffic and tokens.
• Reduces risk of traffic tampering and content injection.
• Helps meet compliance and data-protection requirements.

Common pinning modes (high-level)

• Certificate pinning: the app keeps a copy of the server certificate and compares it at runtime.
• Public-key pinning: the app stores and compares a hash of the server public key instead of the full certificate — this can be more robust across certificate renewals.

iOS developer best practices (implementing pinning safely)

• Prefer public-key pinning with multiple backup pins to allow certificate rotation without breaking clients.
• Integrate pinning checks into your network layer and fail safely with helpful telemetry for debugging.
• Provide clear staging modes so internal testing can use test certificates without weakening production checks.
• Monitor pin validation failures in production and have a rollback/rotation plan for pinned keys.
• Use platform APIs (TrustKit, built-in URLSession callbacks) and follow OWASP mobile guidance for secure implementations.

Testing pinning — ethical & legal guidelines (must-read)

Security researchers and internal teams commonly test pinning to verify it behaves as expected. Safe testing guidelines:

• Obtain explicit written permission for the target application and infrastructure.
• Use separate test/staging environments and test accounts; never test on production user data.
• Document the scope, methods, and findings; coordinate disclosure with the app owner if you find issues.
• Prefer using vendor-recommended tooling and follow accepted disclosure practices.

How to bypass SSL Pinning on iOS? (Jailbroken)

• SSLKillSwitch: A tool for iOS/macOS that disables SSL certificate validation, mainly used for testing and security research. It bypasses SSL pinning, allowing apps to accept all certificates—even self-signed or invalid ones.
  Install: Usually on jailbroken devices via Cydia or by injecting the library during development.
  More info & GitHub: SSLKillSwitch2, Original SSLKillSwitch


• Frida SSL Pinning Bypass Scripts: Frida is a dynamic instrumentation toolkit that lets you inject scripts into iOS, Android, or macOS apps at runtime. Using Frida scripts, developers and security testers can hook SSL/TLS functions and bypass certificate validation without modifying the app itself.
  How it works: Hooks SSL functions (like NSURLSession, OkHttp, SecTrustEvaluate) and forces them to accept all certificates.
  Resources & Scripts: iOS SSL Pinning Bypass, OWASP Frida Scripts


• Binary Patching with IDA Pro: IDA Pro is a disassembler and reverse engineering tool that allows security testers to analyze compiled iOS, Android, or macOS binaries. By inspecting SSL/TLS functions, you can identify and patch certificate validation checks directly in the binary.
  How it works: Locate functions like SecTrustEvaluate, SSL_CTX_set_verify, or OkHttpClient validation calls and modify the instructions to always succeed, effectively bypassing SSL pinning.
  Resources: IDA Pro Official

Developer checklist: make your iOS app pinning-ready

• Use public-key pinning + multiple keys for rotation.
• Enable verbose logging in staging and safe telemetry in production.
• Document pin rotation procedures and embed backups in the app.
• Offer opt-in debugging builds that trust internal test certificates only.
• Run automated tests that simulate certificate renewal and failover.

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