Secure Mobile Coding

Secure coding means writing apps that resist attack by default.

For mobile, it combines safe data handling, careful networking, and defensive design from the very start.

Never trust data coming from the user or the network.

Validate and sanitize every input before using it, to prevent injection and crashes.

All network traffic should travel over HTTPS with TLS.

This protects data from being read or altered on untrusted networks like public Wi-Fi.

Certificate pinning tells the app to trust only specific server certificates.

This blocks man-in-the-middle attacks where an attacker presents a fake but valid-looking certificate.

Keep tokens and keys in the Keystore or Keychain, never in plain files.

Encrypt any sensitive data you must store yourself.

Only ask for the permissions your app truly needs.

Fewer permissions mean less data at risk if the app is compromised, and more trust from users.

Critical checks, like price, balance, or access rights, must run on the server.

Client-side checks can be bypassed by anyone who reverses the app.

Error messages should not reveal internal details.

Log details privately, but show users only generic, safe messages.

Third-party libraries can contain vulnerabilities.

Track your dependencies, update them regularly, and remove any you no longer use.

Use short-lived tokens and refresh them safely.

Log users out after inactivity and revoke tokens on logout so a stolen session does not last forever.

Security is not done at release. Run security testing: static scans, dependency checks, and penetration tests.

Fix findings before users ever install the app.

Why must critical checks like price or access rights run on the server, not the client?

Secure mobile coding means validating input, using TLS with certificate pinning, storing secrets safely, minimizing permissions, enforcing logic on the server, handling errors carefully, updating dependencies, securing sessions, and testing before release.