OpenSSH

OpenSSH (also known as OpenBSD Secure Shell) is a suite of secure networking utilities based on the Secure Shell (SSH) protocol, which provides a secure channel over an unsecured network in a client–server architecture. OpenSSH started as a fork of the free SSH program developed by Tatu Ylönen; later versions of Ylönen's SSH were proprietary software offered by SSH Communications Security. OpenSSH was first released in 1999 and is currently developed as part of the OpenBSD operating system. OpenSSH is not a single computer program, but rather a suite of programs that serve as alternatives to unencrypted protocols like Telnet and FTP. OpenSSH is integrated into several operating systems, namely Microsoft Windows, macOS and most Linux operating systems, while the portable version is available as a package in other systems. OpenBSD Secure Shell was created by OpenBSD developers as an alternative to the original SSH software by Tatu Ylönen, which is now proprietary software. Although source code is available for the original SSH, various restrictions are imposed on its use and distribution. OpenSSH was created as a fork of Björn Grönvall's OSSH that itself was a fork of Tatu Ylönen's original free SSH 1.2.12 release, which was the last one having a license suitable for forking. The OpenSSH developers claim that their application is more secure than the original, due to their policy of producing clean and audited code and because it is released under the BSD license, the open-source license to which the word open in the name refers. OpenSSH first appeared in OpenBSD 2.6. The first portable release was made in October 1999. Developments since then have included the addition of ciphers (e.g., ChaCha20-Poly1305 in 6.5 of January 2014), cutting the dependency on OpenSSL (6.7, October 2014) and an extension to facilitate public-key discovery and rotation for trusted hosts (for transition from DSA to Ed25519 public host keys, version 6.8 of March 2015).