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Create an SSH key

Prerequisites

To use SSH to communicate with the SSH gateway ci-ssh.inria.fr, you need an OpenSSH client (which comes pre-installed on GNU/Linux, macOS, and Windows 10), with an SSH version 6.5 or later (earlier versions used an MD5 signature, which is not secure).

To view the version of SSH installed on your system, run ssh -V.

ED25519 SSH keys:

  • more secure and performant than RSA keys.
  • OpenSSH 6.5 introduced ED25519 SSH keys in 2014 and they should be available on most operating systems.

RSA SSH keys:

  • RSA key generated with the Windows 10 SSH native client are not supported by the SSH gateway because of a bug in key generation (fixed but requires your system to be up-to-date)
  • Since 2015, NIST recommends a minimum of 2048 bits keys for RSA (Source).
  • The default key size depends on your version of ssh-keygen. Review the man page for your installed ssh-keygen command for details.

SSH key pair generation

If you do not have an existing SSH key pair, generate a new one.

  1. Open a terminal.

  2. Type ssh-keygen -t followed by the key type and an optional comment. This comment is included in the .pub file that’s created. It is a good practice to use your email address for the comment.

    For example, for ED25519:

    ssh-keygen -t ed25519 -C "<comment>"

    For 2048-bit RSA:

    ssh-keygen -t rsa -b 2048 -C "<comment>"

  3. Press Enter. Output similar to the following is displayed:

    Generating public/private ed25519 key pair.
Enter file in which to save the key (/home/user/.ssh/id_ed25519):

  4. Accept the suggested filename and directory, unless you are generating a deploy key or want to save in a specific directory where you store other keys.

  5. Specify a passphrase:

    Enter passphrase (empty for no passphrase):
Enter same passphrase again:

  6. A confirmation is displayed, including information about where your files are stored.

Your private SSH key (not to be shared) is available in your home directory at .ssh/id_ed25519 or .ssh/id_rsa if you did not specify any directory.

Your public SSH key (to be uploaded on the portal) is available in your home directory at .ssh/id_ed25519.pub or .ssh/id_rsa.pub if you did not specify any directory.