OpenSSL
OpenSSL is an open-source cryptography library and a toolkit that provides implementations for internet communication protocols like Secure Sockets Layer (SSL) and Transport Layer Security (TLS).
OpenSSL includes a set of encryption/decryption tools for securing and safeguarding the sensitive data sent between systems. OpenSSL is written in C and implemented by all the Web servers to generate private keys, create CSRs, and identify certificate information.