This is an example of a library. You may see a list of other libraries used on Rosetta Code at Category:Solutions by Library.
From the OpenSSL site: The OpenSSL Project is a collaborative effort to develop a robust, commercial-grade, full-featured, and Open Source toolkit implementing the Secure Sockets Layer (SSL v2/v3) and Transport Layer Security (TLS v1) protocols as well as a full-strength general purpose cryptography library.
OpenSSL has two libraries:
crypto(3)implements cryptographic algorithms, such as ciphers, message digests, and X.509 certificates.
crypto(3)also exposes features, including arbitrary-precision integers called BIGNUMs, and a secure random number generator.
ssl(3)implements SSL and TLS.
To link OpenSSL to a C program, a typical Unix command is
cc -o program program.c -lcrypto -lssl