OpenSSL is a cryptographic library that enables an open source implementation of Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols. It provides functions to generate private keys, manage certificates, and equip client applications with encryption and decryption.

OpenSSL is widely used by software developers and system administrators to implement secure communication and encryption in various applications, such as web servers (like NGINX), email servers, VPNs, and more. It’s available as a library that can be integrated into software applications or used as standalone command-line tools for various cryptographic operations.

OpenSSL Use Cases for Secure Application Delivery

OpenSSL can play a crucial role in a secure application delivery strategy, particularly when it comes to ensuring the confidentiality, integrity, and authenticity of data transmitted over networks.

It is commonly used for these use cases:

  • Secure communication between clients and servers
  • Data encryption
  • Certificate management
  • Data integrity and authentication
  • Random number generation
  • Secure protocols and algorithms
  • Secure web server deployment
Advantages of OpenSSL

OpenSSL has been a widely used and established cryptographic library for many years. While there are alternatives available, OpenSSL has several advantages that have contributed to its popularity.

These advantages include:

  • Maturity and wide adoption – OpenSSL has been in use for a long time and has been battle-tested in a wide range of applications. Its maturity and widespread adoption contribute to its reliability and stability. OpenSSL’s implementation of SSL/TLS has been extensively used and reviewed, and it has been instrumental in securing internet communications.
  • Community and documentation – OpenSSL has a large, active user and developer community, which results in better support, bug fixes, and security updates. Additionally, there are plenty of resources and documentation available for learning and troubleshooting.
  • Feature rich – OpenSSL provides a comprehensive set of cryptographic functions, protocols, and tools, making it suitable for a wide variety of applications and use cases. In addition to SSL/TLS it also supports various encryption algorithms, key management, and certificate-related operations.
  • Flexible – OpenSSL provides a wide range of options and configurations, allowing developers to tailor the library to their specific needs. It also provides bindings for various programming languages (including C, C++, Python, Java) and is available on many platforms and operating systems, making it versatile for cross-platform development.
OpenSSL with NGINX

NGINX and OpenSSL are a natural pairing for TLS-based solutions. NGINX’s high performance and flexibility seamlessly integrate with OpenSSL’s encryption capabilities, ensuring secure and efficient TLS-encrypted connections for web applications and data.

NGINX uses OpenSSL to:

  • Handle TLS connections for HTTPS – When acting as a web server or reverse proxy for client and upstream connections.
  • Handle TLS connections over TCP – When acting as an L4 proxy for client and upstream connections.
  • Handle TLS connections for mail – When acting as a mail server for IMAP, SMTP, and POP3. This includes support for STARTTLS and STLS protocols.
  • Work with standard TLS extensions – This includes the integration of TLS features like Service Name Identification (SNI), Application Layer Protocol Negotiation (ALPN), and Online Certificate Status Protocol (OCSP).