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Building Secure Cross-Platform SSH Clients: Security Best Practices from GoShell's Development

Developing a cross-platform SSH terminal application like GoShell presents unique security challenges that extend beyond typical application development. As we built GoShell—a free, modern SSH client for Windows, macOS, Linux, and Android—we learned valuable lessons about implementing robust security measures across diverse ecosystems. Here are the key security best practices we embraced throughout our development journey.

Secure Authentication Handling

One of our primary concerns was ensuring secure authentication management. SSH clients handle sensitive credentials, including passwords, private keys, and host information. We implemented several safeguards:

  • Memory protection: All credentials are stored in encrypted memory segments and wiped immediately after use
  • Secure storage: Platform-specific secure storage APIs (Keychain on macOS, Credential Manager on Windows, KeyStore on Android) protect saved connections
  • Certificate validation: Strict host key verification prevents man-in-the-middle attacks

Cross-Platform Cryptographic Consistency

Maintaining consistent cryptographic implementations across different platforms proved challenging. We addressed this by:

  • Using well-audited libraries like OpenSSL for core cryptographic operations
  • Implementing comprehensive test suites that verify encryption/decryption behavior across all platforms
  • Ensuring TLS/SSL implementations meet modern security standards on every supported OS

Secure Network Communication

As an SSH client, GoShell's entire purpose revolves around secure communications. Beyond the SSH protocol itself, we implemented:

  • Certificate pinning for update servers and ancillary services
  • Strict validation of all network responses
  • Secure fallback mechanisms when primary security features encounter compatibility issues

Sandboxing and Process Isolation

Modern operating systems provide robust sandboxing capabilities, but implementing them consistently across platforms requires careful planning:

  • We utilized platform-specific sandboxing technologies (AppContainer on Windows, App Sandbox on macOS)
  • Critical components like ZMODEM file transfer operate in isolated processes
  • Network operations run with minimal necessary permissions

Secure Default Configuration

We established security-first defaults throughout GoShell:

  • Connection security: Default to most secure supported algorithms
  • Privacy protections: Enable features like session recording protection automatically
  • Update mechanism: Secure automatic update system with cryptographic verification

Addressing Platform-Specific Vulnerabilities

Each platform presented unique security considerations:

  • Windows: Protected against DLL hijacking and injection attacks
  • macOS: Implemented proper entitlement management and hardened runtime
  • Linux: Ensured compatibility with various security modules (SELinux, AppArmor)
  • Android: Followed Android security best practices for network applications

Continuous Security Testing

We integrated security testing throughout our development process:

  • Automated vulnerability scanning of dependencies
  • Regular penetration testing by security researchers
  • Platform-specific security review for each major release

Lessons Learned

Building GoShell taught us that cross-platform security requires both universal principles and platform-specific adaptations. The most important lesson: security cannot be an afterthought—it must be integrated into every development phase, from initial design to final deployment.

Best Practices Summary

  1. Use established cryptographic libraries rather than custom implementations
  2. Leverage platform-specific security features instead of fighting against them
  3. Implement defense in depth with multiple security layers
  4. Assume network hostility and validate all inputs rigorously
  5. Maintain transparency about security practices to build trust with users

Developing GoShell reinforced that security is a continuous process, not a one-time achievement. By sharing these insights, we hope to contribute to more secure cross-platform applications across the development community.

GoShell remains completely free and open source, allowing security researchers to audit our implementation and contribute to making it more secure for everyone.

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