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keys. When signing messages in ssh-agent using a FIDO key that has an application string that does not start with "ssh:", ensure that the message being signed is one of the forms expected for the SSH protocol (currently pubkey authentication and sshsig signatures). This prevents ssh-agent forwarding on a host that has FIDO keys attached granting the ability for the remote side to sign challenges for web authentication using those keys too. Note that the converse case of web browsers signing SSH challenges is already precluded because no web RP can have the "ssh:" prefix in the application string that we require. ok markus@ OpenBSD-Commit-ID: 9ab6012574ed0352d2f097d307f4a988222d1b19
Portable OpenSSH
OpenSSH is a complete implementation of the SSH protocol (version 2) for secure remote login, command execution and file transfer. It includes a client ssh and server sshd, file transfer utilities scp and sftp as well as tools for key generation (ssh-keygen), run-time key storage (ssh-agent) and a number of supporting programs.
This is a port of OpenBSD's OpenSSH to most Unix-like operating systems, including Linux, OS X and Cygwin. Portable OpenSSH polyfills OpenBSD APIs that are not available elsewhere, adds sshd sandboxing for more operating systems and includes support for OS-native authentication and auditing (e.g. using PAM).
Documentation
The official documentation for OpenSSH are the man pages for each tool:
Stable Releases
Stable release tarballs are available from a number of download mirrors. We recommend the use of a stable release for most users. Please read the release notes for details of recent changes and potential incompatibilities.
Building Portable OpenSSH
Dependencies
Portable OpenSSH is built using autoconf and make. It requires a working C compiler, standard library and headers, and zlib. libcrypto from either LibreSSL or OpenSSL may also be used, but OpenSSH may be built without it supporting a subset of crypto algorithms.
FIDO security token support need libfido2 and its dependencies. Also, certain platforms and build-time options may require additional dependencies, see README.platform for details.
Building a release
Releases include a pre-built copy of the configure script and may be built using:
tar zxvf openssh-X.YpZ.tar.gz
cd openssh
./configure # [options]
make && make tests
See the Build-time Customisation section below for configure options. If you plan on installing OpenSSH to your system, then you will usually want to specify destination paths.
Building from git
If building from git, you'll need autoconf installed to build the configure script. The following commands will check out and build portable OpenSSH from git:
git clone https://github.com/openssh/openssh-portable # or https://anongit.mindrot.org/openssh.git
cd openssh-portable
autoreconf
./configure
make && make tests
Build-time Customisation
There are many build-time customisation options available. All Autoconf destination path flags (e.g. --prefix) are supported (and are usually required if you want to install OpenSSH).
For a full list of available flags, run configure --help but a few of the more frequently-used ones are described below. Some of these flags will require additional libraries and/or headers be installed.
| Flag | Meaning |
|---|---|
--with-pam |
Enable PAM support. OpenPAM, Linux PAM and Solaris PAM are supported. |
--with-libedit |
Enable libedit support for sftp. |
--with-kerberos5 |
Enable Kerberos/GSSAPI support. Both Heimdal and MIT Kerberos implementations are supported. |
--with-selinux |
Enable SELinux support. |
--with-security-key-builtin |
Include built-in support for U2F/FIDO2 security keys. This requires libfido2 be installed. |
Development
Portable OpenSSH development is discussed on the openssh-unix-dev mailing list (archive mirror). Bugs and feature requests are tracked on our Bugzilla.
Reporting bugs
Non-security bugs may be reported to the developers via Bugzilla or via the mailing list above. Security bugs should be reported to openssh@openssh.com.