I receive a post-quantum key algorithm warning when connecting via SSH, what should I do?

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When connecting to a server, you may receive a warning in your terminal such as the following:

** WARNING: connection is not using a post-quantum key exchange algorithm.
** This session may be vulnerable to "store now, decrypt later" attacks.
** The server may need to be upgraded. See https://openssh.com/pq.html

The warning occurs because the server is running an OpenSSH version that does not support the post-quantum algorithms recommended by OpenSSH. Support for these algorithms is available in newer versions of OpenSSH, which in turn are not yet supported by the server’s operating system. A future upgrade of the operating system will provide support for the version of OpenSSH required for this type of algorithm.

This does not mean that we are running insecure OpenSSH versions on our servers; we discuss this in more detail here.

The absence of post-quantum algorithms is, however, not a problem at present, as quantum computers do not yet exist on any significant scale. In practice, this means that before quantum computers become commonplace, we will have migrated to newer versions of OpenSSH that support these more secure algorithms.