Best Practices for Securing API Keys in Mobile Applications

Beyond the basic DeviceCheck implementation, there are several critical practices you should follow to ensure your API keys remain secure. Let's explore these essential security measures.

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Never Embed Plain API Keys in the App

This is rule #1 of mobile app security:

• Don't hardcode API keys in your app's binary
• Attackers can easily decompile apps and extract keys
• If you need a client-side identifier, use:
  • A less-privileged token
  • A project ID that maps to the real key on your server
  • Time-limited tokens generated by your backend

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Use a Secure Backend Proxy

Your mobile app should be a thin client:

• Route all API calls through your secure server
• Keep real API keys on the server
• Never let keys leave your control
• Let your server handle sensitive operations
• Enforce rate limits and authorization checks

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Employ Device Attestation

Use platform-specific verification services:

• iOS: DeviceCheck or App Attest
• Android: Play Integrity API or SafetyNet
• These provide cryptographic proof of app authenticity
• Ensure API keys are only used by genuine app instances
• Verify the environment is trusted

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Secure Communications

Protect data in transit:

• Always use HTTPS for network calls
• Implement certificate pinning:
  • App only trusts your server's certificate
  • Prevents MITM attacks with fake certificates
  • Be careful with cert updates to avoid breaking the app
• Validate all server responses
• Use secure protocols and current best practices

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Limit API Key Scope and Permissions

Minimize potential damage:

• Use restrictive API keys when possible
• Limit access to specific endpoints
• Set usage caps and rate limits
• Restrict to specific origins/IPs
• Create separate keys for different functions
• Follow the principle of least privilege

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Monitor Usage and Rotate Keys

Stay vigilant:

• Track API usage patterns
• Set up alerts for:
  • Sudden usage spikes
  • Abnormal patterns
  • Geographic anomalies
  • Rate limit violations
• Rotate keys periodically
• Have a plan for emergency key rotation
• Keep logs for forensic analysis

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Store Keys Securely Server-Side

Don't forget server security:

• Use environment variables or secure vaults
• Never store keys in code or version control
• Limit access to keys based on roles
• Protect server endpoints:
  • Require proper authentication
  • Validate all inputs
  • Rate limit requests
  • Log access attempts

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Defense in Depth

Remember, security is about layers:

• Each measure adds protection
• Multiple barriers slow attackers
• Monitoring catches breaches early
• Quick response limits damage
• Regular audits find weaknesses

At Proxed, we implement all these best practices in our proxy service. Our infrastructure is designed with security-first principles, handling the complexity of key management, monitoring, and rotation so you don't have to. Stay tuned for our next post where we'll dive into real-world security incident case studies and lessons learned.