13.6 OpenSSL s_client

OpenSSL is an open source project implementing the OpenSSL software, a commercial-grade, feature-rich toolkit for cryptography and TLS [137]. OpenSSL’s technical decision making is governed by the OpenSSL Technical Committee (OTC) and the software is published under an Apache-style license, making it suitable for both non-commercial and commercial purposes.

At the time of this writing, the latest stable OpenSSL version is the 3.1 series, which the OpenSSL project will support until March 14, 2025. In addition, OpenSSL 3.0 series is available as a Long-Term Support (LTS) version, which will be supported until September 7, 2026.

The OpenSSL source code is hosted at https://github.com/openssl/openssl. The software includes the following:

• libssl, the implementation of TLS protocol versions up to TLS 1.3

• libcrypto, a feature-rich cryptography library that is the basis for libssl, but can also be used as a standalone library

• The openssl command-line tool,...