OpenSSL is a robust, commercial-grade open source toolkit implementing the Transport Layer Security protocol family, including TLS up to version 1.3, DTLS up to version 1.2, and QUIC version 1. Written in C, the project provides both protocol implementations and a standalone cryptographic library suitable for independent use. The toolkit includes a FIPS-validated cryptographic module for standards compliance. OpenSSL descends from the SSLeay library originally developed by Eric A. Young and Tim J. Hudson and has evolved into a foundational component of secure internet communications infrastructure.
The project is organized around three primary components. libssl implements all TLS protocol versions, DTLS protocol versions, and QUIC, serving as the protocol layer. libcrypto provides the underlying full-strength general purpose cryptographic library that forms the basis of the TLS implementation but can be deployed independently for cryptographic operations. The openssl command-line tool functions as a comprehensive utility for cryptographic tasks, supporting key parameter creation, X.509 certificate and CSR generation, message digest calculation, encryption and decryption operations, protocol testing, and S/MIME mail handling.
Development activity on the repository is substantial and ongoing.
GitGenius identifies shared contributors with microsoft/vscode, rust-lang/rust, and microsoft/typescript, indicating that OpenSSL's cryptographic infrastructure serves as a dependency or reference point across diverse technology ecosystems. This cross-project involvement underscores OpenSSL's role as foundational security infrastructure.
Documentation is comprehensive and version-specific. The project maintains manual pages for the master branch and multiple stable releases including versions 3.6, 3.5, 3.4, 3.3, 3.2, and 3.0. Specialized documentation covers QUIC protocol implementation, the provider architecture, and FIPS module usage. Platform-specific build instructions are provided for UNIX-like systems, Android, Windows, DOS with DJGPP, OpenVMS, and include notes on Perl and Valgrind integration. The repository is licensed under Apache License 2.0, permitting both commercial and non-commercial use subject to license conditions. Development occurs exclusively through GitHub pull requests against the public mirror, with the primary repository maintained privately and automatically synchronized to the GitHub mirror on each commit.
