Following the provided instructions, you are able to securely login to RWTH HPC from Windows to Linux using FastX Client or X-Win32.
A secure and convenient method to authenticate using an SSH public key along with pageant.exe.

Detailed instructions can be found on StarNet Communications website.

However, we would kindly ask you to refrain from using RSA (especially RSA keys < 4096 bit!) and to generate Ed25519 keys instead, as these are (provably) more secure and efficient than RSA keys in several respects.
Ed25519 keys can also be generated by Puttygen. Unfortunately, the even more secure Ed448 keys are not yet supported in the available OpenSSH versions on our cluster.
Since Ed25519 has been an established procedure for some time and is actually supported everywhere, clients that do not (or no longer) support this procedure should no longer be used on the cluster in general. It can be assumed that these clients are too old and/or insecure.