SSH client on Windows
Significant changes to authentication coming in April 2025
Starting April 14 2025, SSH login to Puhti and Mahti will only work using
SSH keys added in MyCSC. Password authentication and public keys stored in
users' personal ~/.ssh/authorized_keys file on the supercomputer will no
longer work. This authentication method is already in use on LUMI.
Read the detailed instructions on setting up and using SSH keys.
There are various programs that can be used for creating a remote SSH connection on a Windows system. This page provides instructions for three popular alternatives: MobaXterm, PuTTY and PowerShell.
MobaXterm
MobaXterm is an SSH client with an embedded X server, which means that it can be used to display graphics.
Generating SSH keys (MobaXterm)
Connecting to CSC supercomputers using an SSH client requires setting up SSH keys. You can generate SSH keys using the utility tool MobaKeyGen (see tutorial), or in a local terminal by running:
Supported key types are Ed25519 and RSA 4096 through 16384. We strongly recommend Ed25519.
If you want your generated keys to persist through MobaXterm restarts,
set a persistent home directory for MobaXterm in the program settings
(Settings --> Configuration --> General). Note, this is only required if
you have generated your keys via the terminal, not MobaKeyGen.
After you have generated an SSH key pair, you need to add the public key to the MyCSC portal. Read the instructions here.
You may also wish to configure authentication agent to make using SSH keys more convenient.
Using SSH keys
See the page on setting up SSH keys for general information about using SSH keys for authentication. Please note that it is mandatory to add your public key to MyCSC – copying it directly to a CSC supercomputer does not work!
Basic usage (MobaXterm)
After setting up SSH keys and adding your public key to MyCSC, you can connect to a CSC supercomputer using MobaXterm. To connect using MobaXterm, open the terminal and run:
# Replace <username> with the name of your CSC user account and
# <host> with "puhti" or "mahti"
ssh <username>@<host>.csc.fi
If you have stored your SSH key file with a non-default name or in a
non-default location, you must tell the ssh command where to look for the
key. Use option -i as follows:
# Replace <username> with the name of your CSC user account,
# <host> with "puhti" or "mahti" and <path-to-private-key>
# with the path to your SSH private key
ssh <username>@<host>.csc.fi -i <path-to-private-key>
Alternatively, you may connect using the GUI following this tutorial.
Graphical connection (MobaXterm)
To enable displaying graphics over SSH, use the -X (X11 forwarding) or -Y
(trusted X11 forwarding) option when creating the connection:
Authentication agent (MobaXterm)
To avoid having to type your passphrase every time you connect, enable the
MobAgent authentication agent in the program settings (Settings -->
Configuration --> SSH).
PuTTY
The PuTTY SSH client is an alternative to using OpenSSH.
Generating SSH keys (PuTTY)
Connecting to CSC supercomputers using an SSH client requires setting up SSH keys. To generate SSH keys for connecting with PuTTY, use the PuTTYgen key generator. The PuTTY documentation provides instructions for using PuTTYgen.
Supported key types are Ed25519 and RSA 4096 through 16384. We strongly recommend Ed25519.
After you have generated an SSH key pair, you need to add the public key to the MyCSC portal. Read the instructions here.
You may also wish to configure authentication agent to make using SSH keys more convenient.
Using SSH keys
See the page on setting up SSH keys for general information about using SSH keys for authentication. Please note that it is mandatory to add your public key to MyCSC – copying it directly to a CSC supercomputer does not work!
Basic usage (PuTTY)
After setting up SSH keys and adding your public key to MyCSC, you can connect to a CSC supercomputer using PuTTY. When you launch PuTTY, you are asked to configure your SSH session. Do so according to the table below:
| Option | Value |
|---|---|
| Host Name | puhti.csc.fi or mahti.csc.fi |
| Port | 22 |
| Connection type | SSH |
When creating a remote connection using PuTTY, select the private key file
under Connection --> SSH --> Auth --> Credentials. If you want the private
key to be used each time you connect, save your session to store your choice.
Finally, click Open and enter your CSC username and SSH key passphrase.
If you are connecting for the first time, PuTTY will ask if you trust the host.
Click Accept.
Graphical connection (PuTTY)
If you want to create a connection with graphical support,
you can use, for example, the
Xming X server. To enable displaying
graphics remotely, select Enable X11 forwarding in the PuTTY program settings
(Connection --> SSH --> X11).
Authentication agent (PuTTY)
To avoid having to type your passphrase every time you connect, you can use the Pageant authentication agent to store your private keys in memory.
PowerShell
You can use the Windows PowerShell command-line shell to connect to a CSC supercomputer using the Win32 OpenSSH client. To install OpenSSH on a Windows device, follow these installation instructions.
Generating SSH keys (PowerShell)
Connecting to CSC supercomputers using an SSH client requires setting up SSH keys. After installing OpenSSH, you can generate SSH keys using PowerShell by running:
Supported key types are Ed25519 and RSA 4096 through 16384. We strongly recommend Ed25519.
After you have generated an SSH key pair, you need to add the public key to the MyCSC portal. Read the instructions here.
You may also wish to configure authentication agent to make using SSH keys more convenient.
Using SSH keys
See the page on setting up SSH keys for general information about using SSH keys for authentication. Please note that it is mandatory to add your public key to MyCSC – copying it directly to a CSC supercomputer does not work!
Basic usage (PowerShell)
After setting up SSH keys and adding your public key to MyCSC, you can connect to a CSC supercomputer by opening PowerShell and running:
# Replace <username> with the name of your CSC user account and
# <host> with "puhti" or "mahti"
ssh <username>@<host>.csc.fi
If you have stored your SSH key file with a non-default name or in a
non-default location, you must tell the ssh command where to look for the
key. Use option -i as follows:
# Replace <username> with the name of your CSC user account,
# <host> with "puhti" or "mahti" and <path-to-private-key>
# with the path to your SSH private key
ssh <username>@<host>.csc.fi -i <path-to-private-key>
Graphical connection (PowerShell)
If you want to create a connection with graphical support, you can use, for example, the Xming X server. To enable displaying graphics remotely, run:
Then, use the -X (X11 forwarding) or -Y (trusted X11 forwarding) option when
creating the connection:
Authentication agent (PowerShell)
To avoid having to type your passphrase every time you connect, you can configure the Windows SSH agent to store your keys in memory for the duration of your local login session.
Corrupted MAC on input
When connecting using the OpenSSH client software on Windows, you might encounter an error stating "Corrupted MAC on input". This is a known issue, and can be avoided by explicitly choosing a different MAC algorithm. For details, please see our FAQ page on the topic.