SSH Key Generation and Upload

To connect to Komondor, you need an SSH key pair. This page explains how to generate one and how to register your public key via the HPC Portal.

If you already have an appropriate SSH key pair, you may skip directly to registering your public key.

Generating an SSH key pair

KOMONDOR accepts SSH keys based on the ed25519 or RSA (4096-bit) algorithms. We recommend using ed25519 if possible.

Linux, macOS and Windows PowerShell

Windows 10 and 11 include a built-in OpenSSH client. You can open PowerShell and use the exact same commands as on Linux/macOS below.

Open a terminal and use one of the following commands.

Recommended: ed25519

ssh-keygen -t ed25519

Alternative: RSA 4096-bit

ssh-keygen -t rsa -b 4096

You will be prompted for a file name and location. Accept the defaults by pressing Enter, or specify a custom path, e.g.:

ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519_komondor

Next, you will be asked for a passphrase. Please choose a strong passphrase — at least 8 characters (preferably 12+), containing a mix of letters, numbers and special characters. Do not leave the passphrase empty.

After generation, two files are created, for example:

  • ~/.ssh/id_ed25519_komondor — your private key (keep this safe!)

  • ~/.ssh/id_ed25519_komondor.pub — your public key (this is what you upload)

Warning

Never share your private key. Do not send it to anyone, including KOMONDOR support staff. Store it only on your local machine and protect it with a strong passphrase.

Windows — PuTTYgen / MobaKeyGen

If you prefer a graphical tool, you can generate an SSH key pair using PuTTYgen (bundled with PuTTY) or MobaKeyGen (bundled with MobaXTerm). Both tools are identical in functionality.

  1. Open PuTTYgen or MobaKeyGen (in MobaXTerm: Tools → MobaKeyGen).

  2. Select RSA and set the number of bits to 4096. Newer versions of PuTTY also support EdDSA (ed25519), which is the preferred option if available.

  3. Click Generate and move your mouse in the key area until the progress bar is full.

  4. Enter a comment in the Key comment field (e.g. your email address).

  5. Enter a strong passphrase in the Key passphrase and Confirm passphrase fields. Do not leave it empty.

  6. Click Save public key and save the file (e.g. as id_rsa_komondor.pub).

  7. Click Save private key and save the file (e.g. as id_rsa_komondor.ppk).

Warning

Never share your private key. Do not send it to anyone, including KOMONDOR support staff. Store it only on your local machine and protect it with a strong passphrase.

Via the HPC Portal

The HPC Portal can generate an RSA key pair for you directly, without any local tools:

  1. Log in to the HPC Portal and go to Profile.

  2. Scroll to the bottom and click + Generate RSA key.

  3. Save the private key immediately (e.g. as id_rsa_dkf). This is the only time it will be available — if you close the page without saving it, you will need to generate a new one.

  4. Place the private key in your ~/.ssh/ folder and set the correct permissions:

chmod 600 ~/.ssh/id_rsa_dkf

For Windows users, save the private key file and convert it to PPK format if needed (see Key formats: PPK vs OpenSSH).

Note

The public key is automatically registered in the portal when generated this way — no separate upload step is needed.

Registering your SSH public key

If you generated your key locally, you need to upload the public key to the HPC Portal.

  1. Log in to the HPC Portal and go to Profile.

  2. Click + Upload SSH key.

  3. Paste the contents of your public key file (e.g. ~/.ssh/id_ed25519_komondor.pub) and click Upload.

Note

Only OpenSSH format public keys are accepted. If you generated your key with PuTTYgen, copy the public key text directly from the PuTTYgen window (the text starting with ssh-rsa or ssh-ed25519), rather than using a file saved in PPK format.

After uploading, it may take a few minutes before the key becomes active.

Key formats: PPK vs OpenSSH

PuTTYgen/MobaKeyGen saves the private key in PPK format by default. Depending on how you connect to KOMONDOR, you may need a different format:

  • PPK format — required by PuTTY and MobaXTerm GUI sessions

  • OpenSSH format — required when using the ssh command in a MobaXTerm terminal or Windows PowerShell

You can convert between formats at any time in PuTTYgen/MobaKeyGen:

  • OpenSSH → PPK: Load the key via Conversions → Import key, then click Save private key.

  • PPK → OpenSSH: Load the key via Conversions → Import key, then save via Conversions → Export OpenSSH key.