OpenSSH, developed as part of the OpenBSD project, is a free implementation of SSH. SSH, developed as a replacement for rsh, implements a "secure" method of communication between two machines. As of version 2.0, OpenSSH supports both SSH Protocol 1.5 (used by ssh1) and SSH Protocol 2.0 (used by ssh2): something that not even the "real" SSH produced by SSH Communications Security can claim.

See also Blowfish and OpenSSL.